review of eu-dem and eu-hydro upgrade requirements ......hydro draft 1.0 28 february 2017 first...

EEA/IDM/15/026/LOT2

Review of EU-DEM and EU-HYDRO Upgrade Requirements and Options

Doc. ID: EG-RPT-EEA-SC1-0020 Issue: 1.0 Date: 28/03/2017

Framework Service Contract EEA/IDM/15/026/LOT 2 for Services supporting the European Environment Agency’s (EEA)

implementation of cross-cutting activities for coordination of the in situ component of the Copernicus Programme Services

Call for tenders No EEA/IDM/15/026

Lot 2 Spatial data themes


Document Code: EG-RPT-EEA-SC1-0020 Issue: 1.0

Date: 28/03/2017

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Table of Contents 1. Introduction ............................................................................................................................... 5

2. Service Requirements and Product Specifications ..................................................................... 8

3. Review of Specifications vs. Requirements; Improvement Options ........................................ 13

4. Availability of relevant Datasets............................................................................................... 17

5. Review of EU-DEM and EU-HYDRO use by current/future Copernicus projects ..................... 21

6. Conclusions and Outlook .......................................................................................................... 25

List of Tables Table 1: EU-DEM mandatory and optional requirements (taken from [RD10, Appendix] as

compiled from [RD8], vertical accuracy corrected) ................................................................... 9

Table 2: Summary of EU-DEM specifications as accepted in response to Call for Tender ENTR/ 2009/27 (taken from [RD10, APPENDIX] as compiled from accepted Technical Proposal) ....... 9

Table 3: EU-HYDRO mandatory and optional requirements (compiled from [RD8])....................... 11

Table 4: Freely available national DEMs in European northern countries (status: Feb. 2017) ........ 17

Legal Notice:

The contents of this report were compiled by GAF AG under EEA contract 3436/R0-COPERNICUS/EEA.56569 implementing Framework Service Contract EEA/IDM/15/026/Lot 2. Neither the European Environment Agency nor any person or company acting on its behalf is responsible for the use that may be made of the information that is contained in this report.

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[DOCUMENT RELEASE]

Name(s) Affiliation

Prepared by: Markus Probeck GAF

Contributions: Andreas Uttenthaler, Alexander Klaus, Arnd Berns, David Herrmann, Elisabeth Weis, Inés Ruiz Gómez, Birgit Wunschheim

GAF

Review: Sebastian Carl GAF

Endorsement: Sergio Proietti e-GEOS

Approval: Henrik Steen Andersen European Environment Agency

Prepared for: European Environment Agency (EEA)

Represented by: (Project Manager)

Henrik Steen Andersen

Contract No. 3436/R0-Copernicus/EEA.56569 Implementing Framework Service Contract No EEA/IDM/15/026/Lot 2

[Change Record] Version Date Changes

Draft 0.1 25 January 2017 First commented outline of the report on EU-DEM and EU-HYDRO

Draft 1.0 28 February 2017 First complete draft version of report ‘Review of EU-DEM and EU-HYDRO Upgrade Requirements and Options’

Draft 1.1 09 March 2017 Minor changes. Henrik Steen Andersen

Issue 1.0 28 March 2017 First Issue of report ‘Review of EU-DEM and EU-HYDRO Upgrade Requirements and Options’. Updates to sections 4 and 6.

[Applicable Documents] ID Document

AD1 Framework Service Contract EEA/IDM/15/026/Lot 2

AD2 Specific Contract No. 3436/R0-COPERNICUS/EEA.565659

[Reference Documents] ID Document

RD1 Regulation (EU) No 377/2014 of the European Parliament and of the Council of 3 April 2014 establishing the Copernicus Programme and repealing Regulation (EU) No 911/2010 Text with EEA relevance. Official Journal of the European Union L122/44, Vol. 57, 24 April 2014

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ID Document

RD2 Regulation (EU) No 911/2010 of the European Parliament and of the Council of 22 September 2010 on the European Earth monitoring programme (GMES) and its initial operations (2011 to 2013) (Text with EEA relevance). Official Journal of the European Union L 276/1, 20 October 2010

RD3 Directive 2007/2/EC of the European Parliament and of the Council of 14 March 2007 establishing an Infrastructure for Spatial Information in the European Community (INSPIRE). Official Journal of the European Union L108/1-14, 25 April 2007

RD4 Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy. Official Journal of the European Union, L 327/1, 22 December 2000

RD5 Note on “Copernicus Reference Data: Proposal for Coordinated Actions with Member States” dated 3rd May 2016, submitted by the French and Spanish representatives to the 10th Copernicus User Forum on 27 May 2016 (CUF-2016-44), 5 pp.

RD6 European Commission’s “Answer to the Note (ES-FR) ‘Copernicus Reference Data: Proposal for Coordinated Actions with Member States’ ” (CUF 2016-53), 5 pp.

RD7 Presentation on “Copernicus Reference Data: Proposal for Coordinated Actions with Member States”, presented at the 11th Copernicus User Forum on 6 September 2016, 10 pp.

RD8 EC Call for Tenders No ENTR/2009/27: Implementation of an Initial GMES Service for Geospatial Reference Data Access (Lot 1: Implementation of an initial GMES service for geospatial reference data access covering Europe; Lot 2: Implementation of an initial GMES service for geospatial reference data access covering areas outside Europe). Tender Specifications Document – Corrigendum, published June 2009

RD9 EEA Call for Tenders EEA/MDI/14/005: Framework service contract for the provision of IT and GIS consultancy services on implementation of Copernicus Reference Data Access (RDA) Component and on supporting EEA in other Copernicus related activities (2 lots)- Tender Specifications Document, published May 2014

RD10 Report on “EU-DEM Statistical Validation”, prepared by DHI-GRAS, August 2014, 27 pp.

RD11 Report “EU-DEM Upgrade – Documentation EEA User Manual”, Issue 1.2, prepared by INDRA, 14 October 2015, 12 pp.

RD12 Report “EU-Hydro Upgrade – User Guide”, Issue 3.0, prepared by INDRA, 30 October 2015, 29 pp.

RD13 Flyer “Copernicus Monitoring Service – Reference Data: EU-DEM”, EEA, October 2015

RD14 Flyer “Copernicus Monitoring Service – Reference Data: EU-Hydro”, EEA, Oct. 2015

RD15 Copernicus Space Component Data Access Portfolio: Data Warehouse 2014 – 2020. Issue 2.1 of 1 August 2016 prepared by B. Hoersch & V. Amans, ESA, 84 p.

RD16 Download statistics of the Copernicus Land portal (01.01.2015 - 31.12.2016), made available by the EEA, February 2017

RD17 Weissteiner, C., Ickerott, M., Ott, H., Probeck, M., Ramminger, G., Clerici, N., Durfour-mont, H., Ribeiro De Sousa, A. (2016): Europe’s Green Arteries – A Continental Dataset of Riparian Zones. In: Remote Sensing, Vol. 8, Issue 11, Article 925: p. 1-27; doi: 10.3390/rs8110925

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1. INTRODUCTION The EU-DEM and the EU-HYDRO are pan-European reference datasets, which are publically accessible via the Copernicus Land portal (http://land.copernicus.eu/) under the Copernicus full, free and open data access policy. Produced from satellite observations and other ancillary data sources, the two datasets provide spatially explicit digital information on the land surface elevation and the hydrographic network across Europe. Both datasets were initially developed in the frame of the GMES 1 Reference Data Access (RDA) Preparatory Action in 2009-2012, and have been undergoing several improvement steps since.

The EU-DEM is a hybrid Digital Elevation Model (DEM) based on SRTM (Shuttle Radar Topography Mission) and ASTER-GDEM (Advanced Space-borne Thermal Emission and Reflection Radiometer - Global Digital Elevation Model) data, fused by a weighted averaging approach. For areas north of 60° northern latitude, also publically available Russian topographic maps were incorporated. It is predominantly a raster-based Digital Surface Model (DSM) of the EEA-39 countries2, representing the first surface as “seen” by satellite sensors, i.e. including the aboveground height of objects such as built-up areas and forests. 3 It provides elevations at one arc second (approximately 30m) postings. The EU-DEM is currently available as updated version 1.1.4

The EU-HYDRO provides an EEA-39 wide cartographic representation of hydrographic vector datasets of surface water bodies, i.e. lakes and the river network. This information had initially been photo-interpreted from High-Resolution (HR) optical satellite imagery of the reference year 2006 and in a 2nd step been updated from Very High Resolution (VHR) optical satellite imagery of the reference year 2012. Beyond the upstream limits of interpretability of the imagery, the dataset was complemented with parts of a modelled drainage network with catchments, drainage lines and nodes, as derived from EU-DEM v1.0. The product is currently available as public beta version 0.9, with validation currently ongoing.

Main targeted users of the EU-DEM and EU-HYDRO products are the operational Copernicus services, particularly the Land Monitoring Service that typically is in need of freely available, continent-wide consistent information layers. Both datasets intend to address a need for “gap filling in those areas for which no national or geospatial regional reference data can be accessed (because they don’t exist at the required scale or quality, or available only commercially), or in cases where homogeneous data specifications are required over the full geographic coverage in EEA39 countries.” 5 Digital Elevation Models (DEMs) provide information required for a broad range of applications with different technical requirements and use cases in the various fields of earth observation, whereas the hydrographic network is typically associated with use in hydrology (such as assessment of water resources on a European level, run-off modelling and flood forecasting) and ecological applications.

In September 2016, the French and Spanish representatives to the Copernicus User Forum presented a note on “Copernicus Reference Data: Proposal for Coordinated Actions with Member States” [RD5] to the 11th Copernicus User Forum meeting of 6th September 2016, addressing

1 GMES (Global Monitoring for Environment and Security) was the previous name of Copernicus 2 Comprising the 33 member countries of the European Environment Agency (i.e. the 28 European Union member states together with

Norway, Switzerland, Liechtenstein, Iceland and Turkey) and the six cooperating countries Albania, Bosnia and Herzegovina, the Former Yugoslav Republic of Macedonia, Montenegro, Serbia as well as Kosovo under the UN Security Council Resolution 1244/99. More information at the EEA website: http://www.eea.europa.eu/about-us/countries-and-eionet

3 in contrast to a Digital Terrain Model (DTM), which would provide information on the height of the real earth’s surface 4 The previous version 1.0 had been validated and found to overall conform to the requested specifications, see [RD10] 5 Taken from product description at the Copernicus Land portal: http://land.copernicus.eu/pan-european/satellite-derived-

products/view

http://land.copernicus.eu/

http://www.eea.europa.eu/about-us/countries-and-eionet

http://land.copernicus.eu/pan-european/satellite-derived-products/view

http://land.copernicus.eu/pan-european/satellite-derived-products/view

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primarily the two Copernicus in-situ component’s pan-European reference data products EU-DEM and EU-HYDRO. The document raises concerns about duplication of efforts between Copernicus and national reference data sets as well as over inconsistencies especially in terms of geometry, creating difficulties for national use of Copernicus services and products and the setting-up of related downstream applications. The note specifically makes reference to Article 5 in the Copernicus Regulation [RD1], and asks for a change in the current practise of producing Copernicus reference data (i.e. EU-DEM and EU-HYDRO datasets); moving away from a currently centralised generation of services to a mix of (i) bottom-up provision and re-use of (appropriately generalised and harmonised) existing national data towards defined technical specifications, and (ii) maintaining the current centralised approach for those “Member States which […] do not express the will to collaborate in generating Copernicus reference data”.

In their presentation to the 11th Copernicus User Forum meeting on 6th September 2016 [RD7], the French and Spanish representatives further underlined that the EU-DEM and EU-HYDRO datasets exhibit lower data quality than some national level datasets as well as inconsistencies therewith, and that separate maintenance efforts for national and Copernicus reference data are needed. The presentation acknowledged that in case of a bottom-up approach, the data sharing provisions of INSPIRE6 [RD3] only would not be sufficient to ensure that data can be shared under the Copernicus data and information policy. Furthermore, an example of ES-FR cross-border selection of river-segments intends to highlight that INSPIRE provisions would be insufficient for ensuring pan-European data homogeneity (in terms of geometry and attribution) and consistency with national-level data as well as meeting the Copernicus services’ needs7. In conclusion, the French and Spanish representatives proposed to establish a “convergence mechanism towards consistency between European and national” reference data at least for voluntary Member States (MS), and a “coordinated bottom-up production process” as a second step.

In response to the note by France and Spain and subsequent interventions by Member States, the European Commission (EC) provided a reply [RD6], welcoming the note as a valuable “source of recommendations for the entity that is entrusted with the cross-cutting in situ coordination”, i.e. the European Environment Agency (EEA). Amongst others, the document confirms the importance of the delivery and sharing of INSPIRE compliant national reference data and information, encouraging Member States to further increase efforts for speeding up the process, rather than going “beyond the INSPIRE level of ambition on specifications at a stage where Member States are still far from reaching the baseline”. Such improved sharing of data “would then naturally ease and facilitate the necessary consistency between the national reference data and the Copernicus reference data”, reducing the need to make use of other sources. The EC further recommended “that the EEA analyses the note and its recommendations to enhance Copernicus’ access to and application of existing European and national assets including the INSPIRE compliant data and services.” This investigation should be “taking into account the main criteria for the Copernicus reference data sets:

1) full open and free access;

2) full EU28 coverage (extended coverage: EEA39);

3) harmonised specifications, fit for spatial analysis;

4) timely delivery.

6 Infrastructure for Spatial Information in the European Community 7 The example requires further analysis, as it may be the consequence of applying different thresholds in the hierarchy of river systems,

rather than flaw in the INSPIRE provisions..

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The EC concluded that in case fulfilment of these four criteria would be recognised by EEA at a certain time, national reference data “could then feed into the improvement of EU-DEM and EU-Hydro”.

To prepare this report, the EEA has been supported by a dedicated expert consortium contracted in June 2016 for various issues related to spatial reference data, producing, amongst others, in-situ newsletters, fact sheets, “State of Play” reports and further analyses on Copernicus service component level.8 It is important to state that neither the author nor part of the expert consortium have been involved in the production process of the EU-DEM or EU-HYDRO datasets.

The mandate and objective of this report is to provide a comprehensive, independent and objective analysis of the EU-DEM and EU-HYDRO requirements, specifications and further upgrade options, for enabling an informed discussion between involved stakeholders. Since there is a considerable legacy of reviews and validations for both datasets, the present report focuses mainly on synoptically evaluating the publically available information from the various reports, documentations and previous analyses9. This is complemented by further own analyses where required, as well as by information gathered through interviews with relevant stakeholders, Copernicus projects, etc. In essence, this report aims to contribute to answering the question to which extent the current versions of the EU-DEM and EU-HYDRO products could benefit from further upgrade, and whether for such purpose an integration of “existing space, in situ and reference data and capacities in Member States” would (at least partially) be “technically feasible, cost-effective or possible in a timely manner” in the sense of the Copernicus Regulation [RD1]. For that purpose, this report focuses on analysing:

the service requirements specified for the EU-DEM and EU-HYDRO products, the undertaken product upgrades, as well as the products’ resulting actual technical and quality specifications (section 2);

the level of matching between requirements and specifications, identifying existing issues and improvement options (section 3);

the availability of relevant national-level and EEA-39 wide datasets and their specifications as well as their suitability for further product upgrade (section 4);

the actual and expected future use of the EU-DEM and EU-HYDRO products by Copernicus services and the broader public (section 5);

resulting conclusions and an outlook to the future (section 6).

This first complete draft version of the ‘Review of EU-DEM and EU-HYDRO Upgrade Requirements and Options’ report is provided as basis for further discussion between main stakeholders.

8 More information at the Copernicus in-situ portal: http://insitu.copernicus.eu/news/newsletter-1-editorial 9 All direct quotations in this report are marked by “text in italics”. All reference documents are indicated as [RD..] as listed on p.3/4.

Other reference documents except the indicated have not been used for this report.

http://insitu.copernicus.eu/news/newsletter-1-editorial

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2. SERVICE REQUIREMENTS AND PRODUCT SPECIFICATIONS This section provides a comprehensive inventory of the service requirements specified for the EU-DEM and the EU-HYDRO products, the measures undertaken to upgrade them further, and the resulting actual technical and quality specifications.

The EU-DEM and EU-HYDRO datasets were initially created between 2009 and 2012 under an EC contract following the open Call for Tender ENTR/2009/27 on “Implementation of an Initial GMES Service for Geospatial Reference Data Access” [RD8] as part of the GMES Preparatory Actions phase. The general objective of that phase was “to support the uptake of GMES services and to prepare the ground for a future legislative proposal on a GMES Programme and associated budget”,10 with a particular view to implement a European “initial GMES service for a geospatial reference data service element cross-cutting the different GMES services (Land, Emergency, Security in particular)”. This had been identified as necessary for taking “a step up of the R&D results and GMES precursor activities towards fully operational services”, under an “open and free access” scheme [RD8].

The two datasets, which had been identified as most crucial, were “hydrological networks and elevation data for which there is a need to improve both access and quality at European level” [RD8]. According to the EC, this need was “based on clearly identified gaps: (i) areas for which no national or geospatial regional reference data could be accessed because they were not existing at the required scale or quality or available only commercially; (ii) cases where homogeneous data specifications are required over the full geographic coverage in EEA39 countries” [RD6].

In this context, it is worth noting that specifically the INSPIRE Directive [RD3] aims at overcoming such gaps by establishing common specifications, enabling data interoperability and allowing, amongst others, bottom-up data sharing approaches by European Member States. Since the Call for Tender had however been “launched in an early stage of the implementation phase of the INSPIRE Directive, and exactly because of the gaps identified, a mitigating approach had to be applied”. In essence, this meant the creation of “top down reference datasets, in combination with decentralised access to national/regional data where possible taking into account the main criteria for the Copernicus reference data sets: 1. full open and free access, 2. full EU28 coverage (extended coverage: EEA39), 3. harmonised specifications, fit for spatial analysis, 4. timely delivery.” [RD6].

EU-DEM

The initial Call for Tender [RD8] identified the “urgent need for an EU-DEM” with continent-wide consistent elevation data, since it was realised in previous consultations that at that time, and following the conclusions from the workshop on European Elevation Data11, “no single data source can provide a fully consistent and complete pan-European coverage”, which was “considered a sufficient reason to consider the possibility of setting up a GMES DEM service as part of the GMES core Land Monitoring services portfolio.” The related tender specifications had therefore requested production of the EU-DEM as a “mid-scale digital elevation model” along a set of mandatory and optional requirements as summarised in Table 1. Additionally, the tender specifications asked for “the elevation data are focussing on the actual bare ground height, meaning, excluding object heights as typically included in a Digital Surface Model (DSM).” [RD8].

10 as was subsequently realised through the establishment of the GMES Initial Operations (GIO) in October 2010 [RD2], succeeded by

the establishment of the operational Copernicus Programme in April 2014 [RD1] 11 EU-DEM workshop, Stresa, May 2009 (back to back w. ISRSE-33)

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Table 1: EU-DEM mandatory and optional requirements (taken from [RD10, Appendix] as compiled from [RD8], vertical accuracy corrected)

Mandatory requirements Optional requirements

Coverage EU27 Extended coverage of EEA38, EEA38 + international river basin districts according to the requirements as set out by the Water Framework Directive, or full wall to wall pan-European coverage

Consistency / homogeneity

Cross border consistency (countries, different data sources etc.)

Consistency both with the geometry of the hydrographical pattern and Consistency with the hydrological modelling of (continuity of water flow)

Water surfaces burnt in the DEM

Resolution Horizontal: 1 arc sec (+/-30 m) posting (consistent with 1:100.000 scale for other (topographic) data themes);

Vertical units: integer meters

Minimum variation in Z between 2 adjacent posting values should be properly described in DEM values according to following differentiation (95% confidence):

lowland plains: 2m (<10% slopes) ;

midlands: 5m (10 – 30 % slopes);

mountains: 10m (> 30% slopes).

Accuracies Horizontal: better than 5 m

Vertical: overall accuracy of 5 m RMSE 12

Vertical differentiated accuracies, corresponding with the differential resolution categories:

lowlands: 1 m absolute RMSE;

midlands: 2,5 m absolute RMSE;

mountains: 5 m absolute RMSE

Projections WGS84, ETRS 89 and EVRF2000; geographic coordinates (Lat/Long)

the INSPIRE compliant European projection systems(LCC, LAEA, UTM)

national projections/datums

Access conditions

Full, open and free access.

As outcome of the tendering process, alternative specifications were accepted by the EC, as summarised in Table 2 below. Specifically the dataset’s character, being composed of predomi-nantly DSM data sources, and the lower vertical accuracy, are noticeable modifications compared to the initial tender requirements.

Table 2: Summary of EU-DEM specifications as accepted in response to Call for Tender ENTR/2009/27 (taken from [RD10, APPENDIX] as compiled from accepted Technical Proposal)

Product Coverage Data Sources Resolution Vertical Accuracy Access

EU-DEM EEA38 SRTM & ASTER GDEM (+ topomaps north of 60°N)

1 arc-second (~30 m)

+/- 7.0 m RMSE Unrestricted

The EU-DEM was produced by the selected commercial service provider as a hybrid DEM, composed through a weighted averaging approach of SRTM 3 arc sec and ASTER-GDEM in combination with Russian topographic maps. The EU-DEM has been additionally edited to ensure that water features are adequately represented. Version 1.0 was released to public upon completion of the GMES Preparatory Action on Reference Data Access (RDA), together with the ‘EU-DEM Statistical Validation Report’ [RD10].

12 The EU-DEM Statistical Validation Report [RD10] erroneously lists in the text and in the Appendix, Table A.1 „2m RMSE“ as overall

vertical accuracy requested by the Call for Tender ENTR/2009/27, whereas the final (corrigendum) version of the Call [RD8] had actually requested 5m overall vertical accuracy. It had been updated from 2m to 5m during the tendering phase, following a respective Request for Clarification.

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The latter provides the results of an independent validation, undertaken by a GIS consultancy service provider on request of the EEA. The report was published in August 2014, basically confirming the EU-DEM’s “overall values within specifications”, with only a small vertical bias of -0.56 m and a measured overall vertical accuracy of 2.9 m RMSE, which was in compliance with the agreed specifications (cf. Table 2). More detailed and in-depth findings were obtained under regional, terrain- and LC/LU-related aspects. Due to the relevance for the assessment of the product’s current improvement potential, these detailed validation results are discussed more extensively in section 3.

The validation report determined improvement potential for the dataset, such as an “observed difference in EU-DEM accuracies between the regions north and south of 60°N” as the main issue that “need to be a target for the planned upgrade of EU-DEM.” [RD10]. This has however not yet been implemented and may thus be subject to future upgrade approaches (as further discussed in section 3). Some further upgrade recommendations were subsequently provided by experts from EEA, the EC’s Joint Research Centre (JRC), Eurostat and an EEA contractor DHI-Gras, such as for “correcting geo-positioning issues, reducing the number of artefacts, improving the vertical accuracy using ICESat as reference and ensuring consistency with EU-HYDRO 2015” [RD11].

Due to these recommendations, the EEA issued a follow-up open Call for Tender during the GMES/Copernicus Initial Operations (GIO) phase as part of the Copernicus RDA activities 2013-2015 [RD9], addressing a number of short- to medium-term measures for enhancing the EU-DEM’s quality. Several measures were implemented to correct the previously detected issues. A more detailed analysis of the respective improvements of the dataset is given in section 3.

The resulting, most recent EU-DEM version 1.1 is publicly available as online viewing service, Web Map Service (WMS) and for download via the Copernicus Land portal.13 It is provided as contiguous 32-bit (zipped, LZW-compressed) GeoTIFF raster dataset with 25m pixel size and elevation as the only attribute. The dataset is provided for download in tiles of 1000 km x 1000 km size. The EU-DEM version 1.1. has not been separately validated yet. Further improvements, particularly in areas north of 60° northern latitude, are planned to be addressed during the current operational phase of the Copernicus Land Monitoring service [RD13].

Overall, the main areas of use recommended for the EU-DEM by the EEA are [RD13]:

“Digital Elevation Model of reference in a contiguous dataset for the entire European region. Drainage network generation, river basin, tributary rivers analysis. Flood modelling and flood risk management. Thematic mapping applications for different purposes. Visibility and coverage studies: radio and network coverage, visibility, etc.”

EU-HYDRO

For the EU-HYDRO, the initial Call for Tender [RD8] had requested production of a pan-European hydrographic network, fit to serve as a pan-European reference dataset, along detailed mandatory and optional requirements. It should be composed of line, polygon and node types, constituting a “hierarchy of watercourses as a connected and routed network, and including name and key hydrological attribute information (slope, depth, segment length…)”, at a 1:100,000 (or better) scale resolution for all linear objects and a minimum of 1:250,000 scale resolution for derived polygons such as lakes, catchments, etc. It should encompass “rivers, confluences, water surfaces […], lagoons and estuaries, dams, cascades, locks, canals and aqueducts, coastlines and shorelines of inland water bodies.” In terms of lakes and surface water bodies, “virtual centre lines shall connect

13 available at: http://land.copernicus.eu/pan-european/satellite-derived-products/eu-dem/eu-dem-v1.1/view

http://land.copernicus.eu/pan-european/satellite-derived-products/eu-dem/eu-dem-v1.1/view

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river inlets and outlets”. The nodes should consistently indicate river sources, confluences, mouths and endorheic river system ends. Furthermore, [RD8] specified: “rivers and canals should be, where relevant, topologically consistent with coastlines, i.e. rivers should end at coastlines.” The more detailed specifications for the EU-HYDRO product are summarised in Table 3.

Table 3: EU-HYDRO mandatory and optional requirements (compiled from [RD8])


Coverage EU27 The EFTA countries (IL, LI, NO, CH)

The remaining EEA member state (TR)

The 6 EEA cooperating countries (Albania, Bosnia and Herzegovina, Croatia, the former Yugoslav Republic of Macedonia, Montenegro, Serbia )

The other European countries: Andorra, Ukraine, Moldavia, Belarus and the European part of Russia

Consistency / homogeneity

The continuity of the hydrographic system must be respected in cross –border situations (regions, countries…)

Underground segments, covered segments or any crossing by artificial constructions shall not provoke in any circumstance an interruption in the network, and shall at least be represented by its virtual centre line, such as to provide the ability of generating a flow network.

Resolution Typically between 1:100.000 and 1:250.000, i.e. a respective spatial accuracy level Between 20 and 50 m.

Categorisation of spatial objects may be according to a smaller scale level; however, the geometrical generalisation should rather fit the 1:100.000 scale, in order to better fit overlays with ortho -rectified satellite imagery and LC/LU datasets.

Smaller scales may be added on top

access to national/regional reference data at a higher scale range, in view of ad hoc access for emergency services.

Projections

Usage of ETRS 89 as geodetic datum

Usage of spatial data according to following projection systems: o Lambert Azimuthal Equal Area coordinate reference system of

2001 [ETRS-LAEA], for statistical analysis and display. o Lambert Conic Conformal coordinate reference system of

2001 [ETRS-LCC] for conformal pan -European mapping at scales smaller or equal to 1:500,000.

o Transverse Mercator coordinate reference systems [ETRSTMzn], for conformal pan-European mapping at scales larger than 1:500,000.

the INSPIRE compliant European projection systems(LCC, LAEA, UTM)

national projections/datums

Attributes

Feature Type: River, lake, canal, ditch, coastline, shoreline, spring, confluence, mouth…

Navigability: Is the hydrographical feature navigable?

Origin/creation: Official name( s) in national language(s)

Area of length: Area in km2; Length in km

Drainage type: Perennial, intermittent, episodic

Hierarchy: Place in the hierarchy of drainage

network (1st, 2nd, 3rd, 4th order)

Operational status: In use, planned, abandoned

Shore-, coastline construction type

Languages: Language of name(s) in ISO 639 code

Country Code: ISO 3166 country code of feature

Metadata

The related metadata will be available for distribution via a data catalogue service which will be part of the INSPIRE geo -portal within the Commission, and which will be hosted by JRC/ESTAT.

Metadata shall at least fulfil the requirements as defined by the regulation 1205/2008/EC implementing Directive 2007/2/EC of the European Parliament and of the Council as regards metadata

Topology

The geographic data has polygon, line or point topology, depending on the reference data theme. Data themes that have polygon, line or point topology have an attribute record for each single or multipart polygon, line or point.

Topological rules for lines:

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o Lines must not self intersect or self overlap (exceptions might be allowed for certain feature classes, e.g. roads)

o Nodes must be covered by lines, i.e. the position of nodes must be identical with the position of endpoints of lines.

Topological rules for polygons: o Polygons may not overlap, i.e. their boundaries may not

intersect with boundaries of the same and with other polygons.

o Boundaries of neighbouring polygons have the same set of coordinates, within the specified resolution.

o Lines must not have pseudo -nodes, the boundaries should not be unnecessarily subdivided.

Access conditions

Full open and free access.

The EU-HYDRO dataset was produced by the same commercial contractor as the EU-DEM product, through computer-assisted photo-interpretation of HR optical satellite imagery of the reference year 2006, complemented by parts of a modelled drainage network with catchments and drainage lines, as derived from the EU-DEM v1.0. Upon completion of the GMES Preparatory Action on Reference Data Access, a beta version of EU-HYDRO was created, which remained however available only internally at the EEA.14

In order to address both, remaining technical issues and new user demands, the EEA subsequently asked in a follow-up RDA Call for Tender [RD9] during the GIO phase for upgrade of the EU-HYDRO product alongside the upgrade of the EU-DEM. The purpose of this upgrade was “enhancement in quality and enriching of the datasets with new features, within the main objective of providing these reference datasets fit for use by the Copernicus services” [RD9]. The upgrade was produced on the basis of VHR optical satellite imagery of the reference year 2012, and upstream, beyond the interpretability of hydrography on satellite imagery, complemented with parts of a modelled drainage network as derived from EU-DEM v1.0.

These updates resulted in the most recent EU-HYDRO public beta version 0.9, replacing the previous (non-public) EU-HYDRO beta version. It is made available on a full, free and open basis to the public as online viewing service, Web Map Service (WMS) and for download via the Copernicus Land portal. 15 Data are provided in ESRI File Geodatabase format with 12 feature classes, compatible to shapefile format, with the coordinate reference system ETRS89-LAEA [RD12]. The EU-HYDRO public beta version is currently under validation.

The improved river network is recommended to be used at a “1:30,000 scale resolution for linear objects and a minimum 1:50,000 scale resolution for derived polygons” [RD14], such as catchments and lakes. The Minimum Mapping Unit (MMU) is one ha (10,000 m²).

14 More information is given at the Copernicus Land portal: http://land.copernicus.eu/pan-european/satellite-derived-products 15 available at: http://land.copernicus.eu/pan-european/satellite-derived-products/eu-hydro/eu-hydro-public-beta

http://land.copernicus.eu/pan-european/satellite-derived-products

http://land.copernicus.eu/pan-european/satellite-derived-products/eu-hydro/eu-hydro-public-beta

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3. REVIEW OF SPECIFICATIONS VS. REQUIREMENTS; IMPROVEMENT

OPTIONS This section provides a review of the level of matching between requirements and actual specifications (including the upgrade improvements implemented) for the most recent versions of the EU-DEM and EU-HYDRO products, as well as an inventory of identified remaining issues and possible improvement options. This assessment is presented for EU-DEM and EU-HYDRO separately:

EU-DEM

As an outcome of the tendering process, some alternative specifications as compared to the initial requirements formulated in the open Call for Tender [RD8] were accepted by the EC in 2009, specifically for the EU-DEM. Most noticeably, the specifications of vertical accuracy and DTM vs. DSM character were relaxed, with resulting certain limitations in the usability of the EU-DEM for specific land surface modelling and hydrological applications until today, as found e.g. by Weissteiner et al. 2016 [RD17].

A systematic review of the matching between actual specifications of the EU-DEM (version 1.0) versus the requirements was undertaken by the report on ‘EU-DEM Statistical Validation’ [RD10] in August 2014, using ICESat measurements as continental-scale reference elevation data. It documented a relatively low bias of -0.56 m and an overall ‘fundamental’ vertical accuracy of 2.9 m RMSE (corresponding to an LE9516 of 5.69 m) in short- or non-vegetated areas with low relief intensity, which meets the accepted general specification of 7m RMSE (cf. Table 2). Particularly high deviations were found for northern countries such as Iceland (9.41 m RMSE), Sweden (7.41 m RMSE) and Norway (5.75m RMSE), which was explained by “the lack of SRTM data and hence the heavier reliance on ASTER GDEM and Russian topographic maps“ in the composition of the EU-DEM north of 60°N. Accordingly, the measured mean vertical accuracy was 2.23 m RMSE (4.37 m LE95) south of 60° N, and 5.19 m RMSE (10.18 m LE95) north of 60°N, confirming the systematic nature of the issue in all areas north of 60°N.

The report also investigated the influence of land cover (specifically forest) and slope on the vertical accuracy, observing that the “EU-DEM becomes a less reliable measure of ground topography as the terrain slope becomes steeper and the density of the tree cover increases.” [RD10]. Specifically slopes were shown to cause significant imprecisions in the vertical accuracy. North of 60°N, samples with slopes < 10% showed a vertical accuracy of 5.53 m RMSE (10.83 m LE95), samples with 10-30% slope 8.45 m RMSE (16.56 m LE95) and samples with > 30% slope 10.80 m RMSE (21.16 m LE95). The report concluded suggesting, “that the observed difference in EU-DEM accuracies between the regions north and south of 60°N is the dominating issue that need to be targeted for the planned upgrade of EU-DEM” [RD10].

Subsequent additional investigations of EU-DEM upgrade requirements by experts from, EEA, the EC’s Joint Research Centre (JRC), Eurostat and a specialised EEA contractor DHI-Gras identified a need to address also the following issues [RD11]:

“Ensure proper fixing/alignment of coastline/islands delineation. Fixing river step downs (ensure correct hydro-enforcing). […] obtain, use and merge DEM for Scandinavian countries.

16 Linear Error at 95% confidence level

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[…] rework EU-DEM such that a reasonable match between catchments […] and EU-Hydro is achieved. […]”

Additionally, measures for compensating the abovementioned vertical accuracy bias using ICESat, and for generally reducing the number of artefacts were suggested [RD11], since a low number of contained artefacts is commonly considered an important quality factor of DEMs. Artefacts can regularly occur in DSMs due to the sensors’ physical properties and the related processing techniques, typically in rugged terrain or lowland flat areas, unless specifically corrected. Typical artefacts are so-called pits, spikes, mole runs or step anomalies.

The subsequent EU-DEM upgrade to version 1.1 has addressed several of these enhancement recommendations, as summarised in the ‘EU-DEM Upgrade Documentation EEA User Manual’ [RD11]. More specifically, the following corrections and improvements were made in the frame of that upgrade by the awarded contractor:17

“systematic correction of geo-positioning issues (found and corrected for Malta and Lampedusa islands);”

elevation “bias adjustment with ICESat;” 18 “screening and removal of artefacts, including the presence of blunders (i.e. negative or

positive anomalies); more than 75.000 artefacts have been detected and corrected; consistency with the upgraded version of EU-Hydro, in order to produce a better river network

topology.”

Ensuring consistency with the upgraded EU-HYDRO product included several further individual aspects [RD11]:

“Consistency of the coastline with the EU-HYDRO coastline, including the removal of DEM values outside the EU-HYDRO coastline.

Use of the EU-HYDRO coastline to smooth the gradient to the coast in flat regions. Burning of EU-HYDRO water bodies to set EU-DEM to the minimum height inside the water

body, smoothing the boundaries.”

Additional to the above corrections, the awarded contractor had actually offered an option for “inclusion of national datasets over the Spanish territory and possibly other countries willing to provide access to national datasets” [RD6], which would actually have been in line with the more recent suggestions by France and Spain to the Copernicus User Forum [RD5]. However, according to [RD6], “this option had to be abandoned for budgetary reasons, and priority had to be given first to a correct fulfilment of the requested core improvement tasks” on both, EU-DEM and EU-HYDRO products.

Hence, some known issues had to remain un-addressed in the version 1.1 upgrade of the EU-DEM, and should thus be regarded priority for any next upgrade endeavour. Considering the respective impact and effort, a two-stage approach is suggested, fully respecting the principles requested by [RD6]19, and taking care to maintain and further improve consistency with the EU-HYDRO product and avoid introducing new artefacts:

17 As summarised at the Copernicus Land portal: http://land.copernicus.eu/pan-european/satellite-derived-products/eu-dem/view 18 The ICESat (Ice, Cloud, and land Elevation Satellite) was a NASA satellite mission launched in 2003, for measuring ice sheet mass

balance, cloud and aerosol heights, land topography and vegetation characteristics. 19 1) full open and free access; 2) full EU28 coverage (extended coverage: EEA39); 3) harmonised specifications, fit for spatial analysis; 4)

timely delivery”.

http://land.copernicus.eu/pan-european/satellite-derived-products/eu-dem/view

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Mid-term: Integration of meanwhile freely available, better-quality national DEMs (converted to EU-DEM specifications), with first priority given to Scandinavian and northern countries (not precluding further ones if feasible);

Long-term: Careful incorporation of further, newly available and European-wide consistent DEM data sources with adequate spatial resolution, in areas south of 60°N.

The available respective DEM datasets and their specifications are discussed in section 4. EU-HYDRO

Upon completion of the GMES Preparatory Action on Reference Data Access, a beta version of EU-HYDRO was created. Due to unresolved technical issues, this remained however available only

internally at the EEA.20

In order to properly address these technical issues, as well as further, newly emerged user demands, the EEA subsequently asked in the GIO-phase follow-up RDA Call for Tender [RD9] for further upgrade of the EU-HYDRO product, alongside the EU-DEM upgrade. The overall aim was to arrive at a “fully consistent database on surface hydrography […], fit to serve as a European reference dataset in terms of completeness, consistency, coherence, semantics, topology and metadata” [RD9], before issue of the dataset to the public. A detailed list of upgrade requirements was provided in the respective Call for Tender’s Technical Specifications document [RD9], which is not reported here at full length. It should be highlighted though that specific emphasis was laid on preserving consistency between the EU-DEM and the EU-HYDRO products through final “transfer of the adjustments into the Digital Elevation Model (DEM) and maintaining consistency between river network and corresponding catchment areas” [RD9].

The Copernicus Land portal summarises the quality enhancement and thematic enrichment steps that have actually been implemented in this EU-HYDRO upgrade:21

“integration of the relevant information from the drainage network into the river network with the result of one river network containing common properties of both source networks;

improvement of the coastline; correction of geometry and topology errors; correction of Strahler codes in certain upstream parts”.

According to [RD14], significant geometry corrections have been achieved for coastlines, transitional waters, inland waters, dams, culverts, and the general river network. Additionally, the number of river courses, inland water bodies, culverts and islands was increased. Improvements were also reported for topological relationships and consistency. In addition to the initial river network retrieval from 20m spatial resolution satellite imagery and the drainage network modelling from the 25m spatial resolution EU-DEM, the feature data extraction was upgraded through photo-interpretation of 2.5m spatial resolution VHR optical satellite imagery, primarily from the reference year 2012 (± 1 year)22 at scales between 1:30,000 and 1:50,000 [RD14].

Furthermore, codes of the national surface water bodies as reported by Member States under the Water Framework Directive [RD4] were integrated, allowing “linkages between EU-Hydro public beta version and the respective national datasets, thus ensuring compliance between the Pan-European and the national datasets, as required by countries.”

23 This inclusion of national-level

20 More information is given at the Copernicus Land portal: http://land.copernicus.eu/pan-european/satellite-derived-products 21 see http://land.copernicus.eu/pan-european/satellite-derived-products/eu-hydro/view. 22 ESA Data Warehouse (https://spacedata.copernicus.eu/) „CORE_03“ dataset, see [RD15]

23 see http://land.copernicus.eu/pan-european/satellite-derived-products/eu-hydro/view

http://land.copernicus.eu/pan-european/satellite-derived-products

http://land.copernicus.eu/pan-european/satellite-derived-products/eu-hydro/view

https://spacedata.copernicus.eu/

http://land.copernicus.eu/pan-european/satellite-derived-products/eu-hydro/view

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codes of hydrographic bodies is deemed to technically enable a “bridging between the spatial data held by or on behalf of the public authorities in the MS for the performance of their public tasks and EU-hydro” [RD6], as well as providing a good basis for enabling a future consistent updating of the EU-HYDRO product in that respect, maintaining compatibility with Member States’ data and avoiding duplication of efforts.

At the time of this report’s preparation, the quantitative validation of the EU-HYDRO public beta v0.9 dataset was still ongoing. It is currently undertaken by a team of service providers contracted by the EEA under a contract for validation of the GIO/Copernicus Land Monitoring and RDA products.24 The EU-HYDRO river network and a set of its associated features are validated in a pan-European sampling approach, addressing nearly 2000 sample cells of 1km x 1km size. A visual interpretation and assessment of the EU-HYDRO river network in the sampling cells is performed using Very High Resolution (VHR) satellite imagery from the reference year 2012 (± 1 year) with 2.5m spatial resolution, as provided by the ESA Data Warehouse. Additional topological checks are applied. The validation specifically checks for omission, commission and attribution errors of dataset features, and the assigned Strahler level and attributes of river segments (such as flow direction). Final results are scheduled for end of the first quarter 2017. Preliminary partial validation results do however exhibit some trends already: only few feature and attribution errors were found in the river network of this updated dataset, and the positional accuracy, although not explicitly part of the validation, appears to be adequate as compared to the image data basis. However, these findings are to be consolidated and confirmed by the respective final report.

Without conducting a detailed assessment (which is beyond the scope of this report), it appears from random visual checks that due to the use of 2.5m VHR imagery indeed an improvement of the feature data extraction and an increase of the number of hydrographic objects has been achieved. Geometric and topological issues seem to have been generally reduced; specifically the coastline issues appear improved. More detailed checks would be needed for assessing e.g. the overall improvement of the river network through incorporation of the modelled drainage network, etc.

Except corrections of possible remnant issues and future continuous updating of the established linkage with national-level hydrographic data (as described above), further evolution of the EU-HYDRO dataset appears primarily meaningful in combination with a further upgrade of the EU-DEM, through either:

incorporation of better-quality national and/or other, meanwhile freely available consistent DEMs of better spatial resolution (as already stated for the EU-DEM), and/or

taking steps for evolving the EU-DEM more towards a DTM (however, this would entail a major reconsideration and reorientation of the EU-DEM nature and specifications).

Both options would directly allow improving the spatial accuracy and feature density of derived drainage networks, small river basin delineations, etc., specifically in low-relief regions. The related possible options are discussed in sections 4 and 6.

24 EEA contract no. 3436/R0-COPERNICUS/56601

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4. AVAILABILITY OF RELEVANT DATASETS This section provides the results of a detailed investigation of the current availability, specifications and suitability of both, relevant national-level datasets, and other European-wide datasets, for further enhancing the quality of the EU-DEM and EU-HYDRO products.

As discussed in section 3, the conducted review of currently available feasible options for further upgrading the two products points actually into the same direction: enhancing the spatial precision and quality of the EU-DEM first, with highest priority. Therefore, this section focusses on reviewing suitable options offered by national-level DEMs and other, European-wide DEMs that have newly entered into the public domain since the creation of the EU-DEM. Suitability in that sense is defined by the previously given overarching conditions of [RD6], interpreted as follows:

1. “full, open and free access”, including the necessity to pass this access level on to a future (to-be) upgraded EU-DEM;

2. “full EU28 coverage (extended coverage: EEA39)”, understood as being achievable in principle also through consistent combination of some individual suitable data sets towards common specifications (cf. 3.);

3. “harmonised specifications, fit for spatial analysis”, i.e. fulfilling all the technical specifications of EU-DEM and EU-HYDRO in a consistent and spatially explicit manner, maintaining the products’ character and preserving the linkage and consistency between the two datasets;

4. “timely delivery”, basically meaning datasets which are available “now”. National-level DEMs

Substantial quality issues of the EU-DEM are recognised in European areas north of 60°N, i.e. Iceland, Norway, Sweden and Finland. Therefore, an integration of freely available, better-quality national DEMs appears first priority there. Since the first creation of the EU-DEM, these four countries have all made suitable national DEMs freely available. The following Table 4 provides a comprehensive overview of the respective national DEMs’ characteristics and specifications.

Table 4: Freely available national DEMs in European northern countries (status: Feb. 2017)

Country Dataset Description Spatial resolution

Vertical accuracy

Character Coverage CRS25 License

Iceland IS 50V Based on topogra-phic map contour lines

20m DTM whole Iceland

ISN93/ ISN2004

Open Data

Norway Digital terrengmodel

Provided by Statens Kartverk

10 m ± 2.3m - ± 6.4m

DTM whole Norway

EUREF89, NN1954

Open Data

Sweden GSD-Höjddata, grid 50+ 26

High quality, since aggregated from original 1m DSM (from LIDAR & aerial imagery)

50m Standard error 1m (in hilly terrain)

DTM whole Sweden

SWREF99TM, RH2000

Open Data

Finland Korkeusmalli Based on topogra-phic maps contour lines; partially on 2m DEM

10m 1.4m on average

DTM whole Finland

ETRS-TM35FIN

Open Data

License conditions of all four datasets consistently allow full, free and open use of the data. Due to their uniformly better (original) spatial resolution27 than the EU-DEM, a conversion towards EU-

25 Coordinate Reference System (CRS) 26 Also a 2m-resolution DSM based on laser-scanning data is available, however only under commercial conditions 27 The 50m Swedish DEM exhibits actually much better performance (in terms of characteristics and spatial representation of details)

than the 50m aggregated spatial resolution suggest, since the data are derived from an originally 1m-resolution DEM

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DEM specifications appears technically feasible in a harmonised manner, if done with the necessary caution to avoid introducing artefacts. The vertical accuracies of the DEMs (as far as known) would constitute tangible improvements compared to the current situation in the EU-DEM. Keeping (or improving) consistency between EU-DEM and EU-HYDRO is another paramount consideration. In that respect, it needs to be taken into account that in contrast to the EU-DEM, all four datasets are DTMs. Although disadvantageous in terms of reducing the overall EU-DEM consistency (which is DSM-dominated), it would be at the same time an asset in terms of consistency with the EU-HYDRO, allowing much better drainage system modelling and any other hydrographic/hydrological applications without the disturbing influence of surface objects (i.e. built-up areas, forests). There is actually already a certain proof of the meaningfulness of this ‘integration’ approach, since those four national DEMs have already been used in the frame of some key Copernicus Land Monitoring tasks, in a complementary manner to the EU-DEM (cf. section 5). Thus, a “true” dataset incorporation seems the logical next step.

In theory, national-level DEMs could likewise contribute to improving the EU-DEM for the spatial extent of the 35 other European EEA-39 countries south of 60°N if possible in a likewise consistent fashion. Therefore, a further investigation has been undertaken to inventory the situation with respect to national-level availability of further high-quality DEMs with appropriate specifications, licensing scheme, etc. For this purpose, national INSPIRE and other geoportals as well as the Copernicus Reference Data Access Platform (CORDA)28 have been checked. This review is to be considered a “snapshot” of a continuous development. The differences and communalities between the datasets on the portals are not always evident, and the datasets often lack clear documentation and/or English translation. The results of this investigation are given in the following:

As a first step, national INSPIRE and other geoportals have been reviewed for the level, extent and status of free DEM provision.

Beyond the four abovementioned northern countries, only 10 other countries seem to provide freely available countrywide DEMs with potentially adequate specifications.

(Horizontal) spatial resolution typically varies from ± 1m to 25m, up to 50m The national DEMs comprise both DSMs and DTMs, of various origin. Dataset documentation varies from extensive to marginal and is often only available in

national languages. Specifically, information on vertical accuracy is mostly missing. Most DEMs are made available only with specific national projections, ellipsoids and geodetic

datums.

Furthermore, CORDA has been reviewed for further elevation data sources. The following observations were made:

In total, CORDA currently lists 258 individual datasets and services related to the INSPIRE theme “Elevation”. Many of those data sources do however cover only parts of countries, from sub-national (federal state) down to (sub-) regional levels.

Various DEM sources are listed, for which service is however currently or regularly unavailable. Other datasets lack information on spatial resolution, metadata, etc., and can thus not be properly assessed.

A count indicates at least 11 country-wide, currently regularly accessible DEMs (beyond the four northern countries), with spatial resolutions between < 1m and 25m.

28 Access via https://corda.eea.europa.eu/. Note that access to CORDA is only enabled for providers of operational Copernicus services,

in order to support the creation of Copernicus core products.

https://corda.eea.europa.eu/

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Most of those DEMs are also available via national portals (as counted above), but some seem to be made available only via CORDA for the Copernicus Services and appear to be unavailable to the public (which raises questions about their availability for an EU-DEM upgrade in terms of license). The access mechanisms to some DEMs listed on CORDA appear not sufficiently clear.

Few of the DEMs go together with other explicit use restrictions, e.g. availability only for the Copernicus EMS service, only for national users, or only for non-commercial use. Some other data require separate license agreements.

The data origin of the DEMs is quite mixed, with some having been derived from LIDAR, others from satellite or aerial imagery, or from topographic maps.

Some DEMs have DTM character, others are provided as DSMs, or as shaded reliefs only. At least one DEM seems to be a national copy of the EU-DEM. Most DEMs are available only in specific national projections, ellipsoids and geodetic datums. Typically, information on vertical accuracy is mostly not published with the data.

Altogether, the review displayed quite a heterogeneous situation in terms of availability and specifications of national DEMs. While some countries appear to be generally forerunners in the free and open provision of national INSPIRE compliant geodata, either to the general public or at least to the Copernicus services, the status is less advanced for other countries. The available datasets’ specifications vary considerably, hampering a consistent and homogeneous integration. In view of these findings and the previously discussed overarching conditions, it appears at least questionable whether the currently available national DEMs (except Scandinavia) could collectively sufficiently contribute to an operationally feasible and timely, pan-European (and inter-product) consistent next upgrade of the EU-DEM in a cost-efficient manner. Any such consideration would need to take into account also additional efforts for associated post-processing, harmonisation and artefact removal to ensure a consistent and uniform dataset. Specifically a comparison should be made with alternative approaches using other available DEMs, as described below. In any case, the progress of DEM availability from Member States should be closely monitored. Other available DEMs

As discussed in section 3, a complementary upgrade (or even partial replacement) of the current SRTM/ALOS GDEM based EU-DEM south of 60°N may be considered on the longer term. This may entail careful and considerate incorporation of further, newly available and European-wide consistent DEM data sources with adequate spatial resolution, accuracy and overall quality.

Among the technically best solutions may be commercially available datasets, since these can typically offer the highest degrees of spatial precision and accuracy, as well as dedicated gap filling, hydrological consistency and correction of various other artefacts, thus allowing to minimise post-processing effort. Currently available suitable DEMs that are offered on the open market are Elevation 30 SPOTDEM 29 , WorldDEM 30 , ALOS World 3D 31 and Euro-Maps 3D 32 . Due to the associated questions with respect to commercial procurement and licensing conditions for full, free and open use in an EU-DEM upgrade (if possible at all), this may turn out to be not a straightforward option though.

Beyond commercially available data sources, also other freely available DEMs have been made accessible in recent years, each with better individual specifications than the original input data to

29 See http://www.intelligence-airbusds.com/en/6073-elevation30-products 30 See http://www.intelligence-airbusds.com/worlddem/ 31 See http://aw3d.jp/en/ 32 See http://www.euromap.de/products/prod_008.html

http://www.intelligence-airbusds.com/en/6073-elevation30-products

http://www.intelligence-airbusds.com/worlddem/

http://aw3d.jp/en/

http://www.euromap.de/products/prod_008.html

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the EU-DEM. These comprise the SRTM 1 arc sec (30m) DEM, the ALOS 3DW30 (30m) and the improved ASTER GDEM-V2 (30m). The three datasets are briefly presented below:

In addition to the previous 3 arc sec (90m) DEM of the Shuttle Radar Topography Mission (SRTM), which had been used for the first version of the EU-DEM, there is meanwhile also the 1 arc sec version freely available since mid-201533, providing significantly better quality. It is a void-filled DSM with 30m posting and an absolute vertical accuracy of 7.86m LE95. Due to the mission characteristics, it is available only between 60°N and 56°S.

ALOS3DW3034 is a 1 arc sec (30m) DSM, derived through resampling of the commercially available 5m ALOS World 3D product (see above), based on ALOS PRISM35 data with originally 2.5m spatial resolution. The global dataset has been released by JAXA in May 2016 for free and open use. It is available between 82°N and 82°S, and has a vertical accuracy of 5m (standard deviation).

The first version of ASTER GDEM (used as input for the EU-DEM v1.0) had been generated from optical stereo-pair images of the ASTER instrument on-board the Terra satellite and was released in mid-2009. The significantly improved GDEM V2 was released in late 201136. It used additional 260,000 stereo image pairs, thus improving spatial coverage, horizontal and vertical accuracy, and significantly reducing the occurrence of artefacts. The GDEM V2 is freely and openly available with 30m posting and an absolute vertical accuracy of 17m LE95.

Comparing these three openly available DEMs, all have their pros and cons. For example, SRTM and ALOS show the best spatial precision and vertical accuracy. Specifically the ALOS data (since derived from 2.5m original data) shows also many additional surface feature details. In addition, the ALOS3DW30 coverage pattern over Europe shows some significant acquisition gaps (Eastern Europe, Scandinavia, Iceland and British Isles). The ASTER GDEM V2 still contains a certain number of anomalies and artefacts in combination with a distinct DSM character, which could compromise effectiveness for hydrological applications. In summary, it appears fully feasible to use a sophisticated integration and prioritisation approach of the three datasets, making use of the individual strengths of these three publically available DEMs for the sake of a meaningful, harmonised and consistent incorporation into a next-generation upgrade of the EU-DEM. National hydrographic datasets

National hydrographic data, as reported by Member States under the Water Framework Directive, have already been incorporated into the upgraded EU-HYDRO public beta version 0.9. Specifically codes of the national surface water bodies and river networks have entered, thus providing a meaningful linkage between national and European-level hydrographic datasets. Future updates of national datasets should also be transferred into the next update of the EU-HYDRO in order to keep the datasets consistent in a sustainable and cost-efficient manner.

33 Further information at: https://lta.cr.usgs.gov/SRTM1Arc 34 See http://www.eorc.jaxa.jp/ALOS/en/aw3d30/ 35 Advanced Land Observing Satellite - Panchromatic Remote-sensing Instrument for Stereo Mapping 36 More information at: https://asterweb.jpl.nasa.gov/gdem.asp

https://lta.cr.usgs.gov/SRTM1Arc

http://www.eorc.jaxa.jp/ALOS/en/aw3d30/

https://asterweb.jpl.nasa.gov/gdem.asp

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5. REVIEW OF EU-DEM AND EU-HYDRO USE BY CURRENT/FUTURE

COPERNICUS PROJECTS Additional to the analysis of the EU-DEM and EU-HYDRO specifications, issues and improvement potentials in the previous sections, this section 5 provides a non-exhaustive inventory of the actual current use and expected future use of both products, in order to complement the picture. It analyses the situation in the various domains of Copernicus and beyond, as far as is currently known and reasonably foreseeable.

Copernicus Land Monitoring Service

Little surprising, both datasets have so far predominantly been used in the Copernicus Land Monitoring Service (CLMS) domain. In the CLMS’s continental component, first use of the EU-DEM was made in the GMES Initial Operations (GIO) phase by the different industrial consortia producing the five High-Resolution Layers (HRLs) of land cover/land use (LC/LU) characteristics (Impervious-ness, Forest, Grassland, Wetlands and Water) for the reference year 201237, under contract of the EEA. The use of the EU-DEM has significantly increased for the currently ongoing production of four of the five updated and extended High-Resolution Layers for the reference year 2015 (Imperviousness, Forest, Grassland and Water/Wetness)38. This is being implemented since 2016 by an industrial consortium of earth observation service providers, addressing all five HRLs in a more consistent and synergistic manner. Specifically, a common pre-processing chain of HR optical satellite imagery (from the ESA Data Warehouse; Sentinel-2; Landsat) is applied, in order to enable geometrically and radiometrically consistent time series analyses. The approach makes use of the EU-DEM for image geometry validation and geometric correction where needed, as well as for consistent topographic normalisation of terrain-dependent illumination effects in the imagery. For this task, a mixed approach has been implemented, much like suggested already by [RD11]. Imagery of the Scandinavian countries plus Iceland, as well as of the Azores and the Canary Islands are pre-processed with (aggregated) freely available national DEMs of higher initial quality, complementing the pan-European EU-DEM. Additionally the HR Water/Wetness Layer 2015 uses the EU-DEM operationally for calculation of intermediate wetness indices.

In the CLMS’s local component, it has primarily been the GIO-phase Riparian Zones39 initiative (2014-2015) making extensive use of both, the EU-DEM and the EU-HYDRO products. Specifically the delineation of Riparian Zones by means of a GIS-based modelling approach made use of the EU-HYDRO dataset’s delineation and characterisation of European river courses and surface water bodies for identifying and localising the relevant riparian zone areas and associated lakes of all large and medium-sized European river systems and their floodplains. Complementary, the EU-DEM was used for calculating topography-dependent wetness indices and for terrain-dependent modelling of the spatial extent of the potential, observable and actual Riparian Zone.40 The EU-DEM has further been used as ancillary dataset supporting the discrimination of specific LC/LU classes by means of topographic criteria in the mapping of 556,658 km² of Riparian LC/LU from very-high resolution (VHR) satellite imagery, within the spatial extent of the Riparian Zones for the reference year 2012. 41 Since the Riparian Zones’ LC/LU product discriminates 79 different LC/LU classes, the use of such ancillary data and information is indispensable. Since early 2017, the Riparian-Zones

37 More information at the Copernicus Land portal: http://land.copernicus.eu/pan-european/high-resolution-layers/ 38 The fifth HR Layer 2015 on ‘Small Woody Features‘ uses VHR imagery as basis for classification and is therefore out of scope 39 More information at the Copernicus Land portal: http://land.copernicus.eu/local/riparian-zones 40 Available via the Copernicus Land portal: http://land.copernicus.eu/local/riparian-zones/riparian-zones-delineation/view 41 Available via the Copernicus Land portal: http://land.copernicus.eu/local/riparian-zones/land-cover-land-use-lclu-image/view

http://land.copernicus.eu/pan-european/high-resolution-layers/

http://land.copernicus.eu/local/riparian-zones

http://land.copernicus.eu/local/riparian-zones/riparian-zones-delineation/view

http://land.copernicus.eu/local/riparian-zones/land-cover-land-use-lclu-image/view

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LC/LU product is spatially being extended also to riparian zones of small-sized European rivers for the reference year 2012, and will be consistently updated in the near future for the reference year 2018. This activity is directly dependent on the EU-HYDRO product, e.g. enhancements introduced to the river network and associated Strahler level attribution through the EU-HYDRO upgrade (to public beta version) will have to be properly reflected also in the spatial extension and update of the Riparian Zones product. Thus, the EU-HYDRO and EU-DEM will remain important, directly linked inputs to this monitoring activity.

Similar to the Riparian Zones LC/LU product, also the local component’s GIO Natura2000 product42 provides a VHR LC/LU delineation for selected European biodiversity hotspots of the reference years 2006 and 2012. More than 160,000 km² of (buffered) Natura2000 areas were mapped as part of the Copernicus/GMES Initial Operations Phase until 2015. Established under the 1992 Habitats Directive, the Natura2000 sites constitute an EU-wide network of nature protection areas, aiming to ensure the long-term survival of Europe's most valuable and threatened species and habitats. Also for this service, topographic criteria were applied to the EU-DEM for discriminating the occurrence of specific, ecologically important LC/LU classes (such as alpine grassland). Since early 2017, the investigation of the status and development of these important protected areas is significantly spatially extended, aiming to reach more than 630,000 km² of mapped area by 2018/19.

Beyond the regular service maintenance and evolution efforts undertaken by the EEA as Entrusted European Entity (EEE) in charge of the continental and local component of the LMCS, there are also several accompanying research and development activities ongoing, aiming to investigate, develop, prototypically test and suggest candidate products and services for the next generation of the Copernicus Land Monitoring Service, such as the EU-funded Horizon2020 research projects ECoLaSS (Evolution of COpernicus LAnd Services based on Sentinel data)43, SENSAGRI (SENtinels Synergy for AGRIculture)44 or MULTIPLY (MULTIscale Sentinel land surface information retrieval PLatform).45

All these developments will necessitate an excellent operational pre-processing of satellite imagery in terms of geometric, topographic and illumination effects, supported by a consistent and freely available European DEM with adequate quality. Only then, a precise multi-temporal co-registration and spectral calibration – irrespective of the different sensors’ observation geometries, terrain displacement and illumination effects – will be possible. This will be mandatory to make the related novel multi-temporal, multi-sensor, sub-pixel and/or data assimilation approaches operationally feasible with a sufficient level of accuracy and reliability at a high level of automation. At present, the EU-DEM fulfils these quality requirements only partially.

Furthermore, an improved EU-DEM could also serve the need for a uniform sole elevation data source as basis for ortho-rectification of pan-European satellite image coverages, such as of the ESA Data Warehouse or the Sentinel fleet of satellites. Such has been asked for at least since 200946, however the current situation is still that different Copernicus Contributing Mission Entities (CCMEs) process their respective satellite data with different DEMs [RD15]. For example, SPOT-5 imagery as part of the ‘Optical HR Pan European coverage’ (HR_IMAGE_2015) have been processed with support of the SPOT ‘Reference 3D DEM’ complemented by SRTM, whereas Resourcesat-2 imagery within the same HR_IMAGE_2015 data collection have been using “SRTM, DEMs of national land surveying offices of Finland, Norway, Sweden, ASTER GDEM and where required other

42 More information on the Natura2000 product at the Copernicus Land portal: http://land.copernicus.eu/local/natura/ 43 More details on the ECoLaSS project are available at: http://www.ecolass.eu 44 SENSAGRI project website: http://www.sensagri.eu/ 45 MULTIPLY project website: http://www.multiply-h2020.eu/ 46 For example [RD8], p.45

http://land.copernicus.eu/local/natura/

http://www.ecolass.eu/

http://www.sensagri.eu/

http://www.multiply-h2020.eu/

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DEMs” [RD15]. Depending on actual image acquisition angles, this causes small but avoidable deviations between the different sensors’ image data and Copernicus services, especially when multi-sensor and/or time series approaches are employed.

Beyond the core CLMS products and their envisaged evolution, a consistent European DEM of further improved quality would be also beneficial for various kinds of downstream Land applications on more regional scale, such as water storage and volume assessment, assessment of precipitation run-off and flood risk, risk assessment of landslides and soil erosion as well as various applications in urban and mountainous areas. The EU-HYDRO dataset is expected to be increasingly used for various hydrological and climate change related land surface modelling approaches by research institutions and academia, specifically in synergistic combination with the Riparian Zones VHR Land Cover/Land Use product, in cases where large-scale (country or continental) coverages of consistent input data are required.

Other Copernicus Services

Within the frame of the Copernicus Emergency Management Service (EMS) Rapid Mapping activities, the EU-DEM, amongst other DEM sources, has been implemented in the internal Spatial Data Infrastructure (SDI) of the service providers for access and download of relevant data. The EU-DEM is used as the primary source of map physiography and elevation information and for the ortho-rectification and geo-referencing process of image data sets acquired, processed and classified in the frame of emergency activations. Additionally, the relevant elevation information can be used for deriving contour lines or spot heights. This information is provided to the authorised users of the emergency service activations as vector data or integrated into digital raster maps.

The Copernicus Security Service is focussing on three key components: Border Surveillance, Maritime Surveillance and Support to the EU External Actions (SEA). These activities are carried out not only within Europe, but mostly along its border areas, open seas, ports and coastal regions, or abroad in various regions around the world. Due to this global character of the service, the globally available SRTM DEM is typically used. For specific more regional-scale applications, higher-resolution commercial DEMs may be used, such as a 5m resolution DEM recently acquired by Frontex, covering the EU borders.

Due to the global-scale nature of the Copernicus Atmosphere Monitoring Service (CAMS) and the Copernicus Climate Change Service (C3S), typically Digital Elevation Models with lower spatial resolutions are currently applied, such as a 300m SRTM-derived DEM. For high-resolution small-scale models, sometimes also 30m SRTM is used.

Public Use

Beyond the use as inputs to the creation of Copernicus Services or for further value-added downstream applications, the EU-DEM and EU-HYDRO products are also available for use by research and academia, public authorities, private companies and the general public. Both datasets are fully, freely and openly available for download via the Copernicus Land portal, which allows the EEA to track the amount and origin of the downloads. In this way, download statistics have been regularly captured since 1st July 2015 by the EEA using Google Analytics [RD16].

An evaluation of these download statistics from the Copernicus Land portal shows that the EU-DEM v1.1 and EU-HYDRO public beta datasets have experienced a huge increase in public download since first availability on the portal in the first half of 2016. Already in the second half of 2016, both datasets have been downloaded 783 times and 652 times, respectively, making them the third most and fourth most downloaded products of all 28 ranked products. Both ranked among the biggest

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download increases captured so far. Only the long-established CORINE Land Cover (2012) and the Urban Atlas (2012) products showed higher overall download numbers in the second half of 2016. The top-5 countries from which users downloaded the EU-DEM were France, Germany, the Netherlands, Bulgaria and the United Kingdom, whereas main downloads of the EU-HYDRO product came from the Netherlands, Germany, Switzerland, the United Kingdom and France.

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6. CONCLUSIONS AND OUTLOOK Finally, this section provides a synthesis of the above findings and conclusions as well as an outlook to possible next steps of development and action. First of all, the high importance of reference and in-situ data for any kind of operational thematic Copernicus Services needs to be stressed.

The conducted review of the Copernicus Services’ requirements and increasing use of the EU-DEM and EU-HYDRO (cf. section 5) gives clear evidence of the obvious need and generally growing importance of these pan-European reference data products. Specifically the need for an intermediate-resolution, quality-controlled and consistent pan-European DEM, ranging between low resolution existing free DEMs and commercial very high quality DEMs, has been highlighted by the Copernicus services, and is underpinned by the remarkable data access and download figures (cf. section 5). From a Copernicus Service perspective, a consistent EU-DEM is considered important for various kinds of applications at pan-European level, such as consistent satellite image processing, future higher-frequency HRL updates or other Copernicus and EU initiatives employing extensive time series analyses. Services generally emphasised the need to maintain and further improve the EU-DEM.

The EU-HYDRO dataset is expected to be increasingly used for various hydrological and climate change related land surface modelling approaches, specifically in synergistic combination with VHR Land Cover/Land Use products. Furthermore, complementary national reference and in-situ data as provided by Member States in the frame of INSPIRE and CORDA play an indispensable role in the Copernicus service implementation.

Altogether, this report has presented a number of reasons for considering further upgrades to the EU-DEM as well as several related options and possible priorities. The analysis has further shown that such upgrade would be also allowing further improvement of the EU-HYDRO product, specifically in terms of better representation of the drainage network in lowland areas. Paramount considerations for such upgrade approaches will be the principles of full, open and free access, timely availability and full EU-28 (extended: EEA-39) coverage, at harmonised specifications and consistent quality. Furthermore, an upgrade should maintain the overall products’ characteristics and preserve or improve the strong inter-product connection and consistency between EU-DEM and EU-HYDRO.

A review of the situation with respect to the EU-HYDRO has shown that improvements to the drainage network and a stronger hydrologic conditioning appear possible. Reductions of surface object effects in lowland terrain seem also desirable. The analysis of available options supports the need for a respective upgrade of the EU-DEM in the first instance.

Any update of the EU-DEM should primarily take into account the unresolved quality issues in the areas north of 60°N, and address general upgrade requirements in the remaining parts as a second priority. An associated two-stage approach has been suggested (cf. section 3) and the suitability of various possible input datasets has been evaluated (cf. section 4). Whilst for the northern countries an incorporation of national, high-quality DEMs appears rather straightforward, at least two upgrade options exist for the remaining part.

A review of available national DEMs displayed a significantly heterogeneous situation in terms of current availability and dataset specifications. Respective improvement potential was found in terms of national DEM documentation, service availability, license conditions, etc. (cf. section 4). Alternatively, freely available non-commercial DEMs with suitable specifications have been assessed, giving evidence of feasibility of use for EU-DEM upgrade, even more so if used in a combined manner.

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In view of the different possible integration strategies and input data options as well as the resulting consequences for derived products and applications, one shall be aware that this choice of strategy could affect the fundamental specifications of EU-DEM (DSM vs. DTM).

In view of all findings from the available information sources, and taking into account the overarching requirements, it appears doubtful whether for an EU-DEM upgrade south of 60°N the currently available national DEMs could collectively provide a sufficiently cost-efficient and operationally feasible (i.e. timely, harmonised, spatially explicit) alternative at the moment.

Efforts could be taken also by Member States proactively (e.g. in the frame of EuroGeographics and the European Location Framework (ELF), as suggested by [RD5]) to discuss and agree on common specifications and standards, at least in terms of licensing conditions, product documentation and coordinate reference systems, and preferably also in terms of spatial posting and vertical accuracy.

Nevertheless, the initiative of France and Spain [RD5] reflects a considerable interest of Member States in this matter. Consequently, the further progress of free and open DEM availability from Member States should be closely monitored.