Pergamon Phys. Chem. Earth, Vol. 22, No. 3--4, pp. 275-278, 1997

© 1997 Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain

0079-1946/97 $17.00 + 0.00

PII: S0079-1946(97)00143-2

Applications of Snow Cover Mapping in High Mountain Regions

H. Haefner t, K. Seidel 2 and H. Ehrler 2

IRemote Sensing Laboratories, Department of Geography, University of Ziirich-Irchel, Winterthurestrasse 190, 8057 Zurich, Switzerland 2Institute for Communication Technology, Swiss Federal Institute of Technology, 8092 Zurich, Switzerland

Received 10 May 1996; accepted 2 October 1996

Abstract. Periodical and precise mapping of the snow cover is the essential basis for snow hydrological applications. Today, it is carried out operationally by means of optical satellite imagery. Snow cover information systems of different basins are set up with reference to elevation, slope, aspect, and bio- physical parameters using GIS techniques. The newly developed management system, the SRM- ETH, combines remote sensing, runoff modelling, GIS, DEM, and computer graphics. It is being tested in three basins in the Swiss Alps, and is well suited to analyse snow hydrological processes, in particular runoff, to improve day-to-day water management practices, and to simulate future trends based on various climate scenarios. But all applications depend on a careful snow cover mapping. © 1997 Published by Elsevier Science Ltd

1 Introduction

Snow is a most important component of the hydrological cycle. It is a vital resource in many parts of the world. Variations in the cryosphere have significant geoecological effects and consequen- ces. Hence, snow hydrology is not only a key factor for various practical applications in the field of runoff prediction, reservoir management, electric power production, irrigation practices, flood control etc., snow is at the same time a crucial variable in modell ing and simulating alterations of global change on the water resources, the ecological conditions, the albedo, and ultimately on the radia- tion budget.

The basis for all these activities related to snow hydrology is a precise, periodical and continuous mapping of the snow cover area in its seasonal fluctuations, to document the yearly accumulation and ablation processes in its time-spatial dimen- sions. It is essential to set up snow cover information systems (SIS) for individual basins or other hydro- logical units, planning regions or even entire moun- tain ranges on a long-term perspective.

Only satellite remote sensing enables such a proce-

dure, and many fundamental research activities have been carried out in this respect. Today, these methods are operational for optical data of various scales. For large areas like the Northern Hemi- sphere, the information is obtained from NOAA data creating average weekly and monthly snow cover frequency maps (Wiesnet et al., 1987; Matson, 1991). For very small watersheds in combination with the demand for very accurate results, as is usually the case in Europe, in particular in the Alps, operationalization has also been reached, but the technical and financial input is very high. High resolution and quite often even multisensoral data is needed. Irrevocable prerequisites are a high preci- sion geocoding also for rough mountainous topo- graphy, and illumination corrections. For an accurate classification, GIS techniques have to be included, providing information on the relief (elevation, slope, aspect) from a high resolution DEM, on bio- physical parameters of the ground (land cover, land use, water, glacier, permafrost etc.), and on the boundaries of the various hydrological units under consideration. The methods have been tested and described (Steinmeir, 1995); (Brtasch, 1996). But the acquisition of 5 - 10 (or more) satellite scenes for a single melting season is rather costly, which seve- rely hampers practical applications in runoff fore- casting. Consequently, it is only fair to conclude that regional snow cover monitoring is operational from a technical, but not from an economical point of view.

The aim of this paper is not to add another contri- bution to the methodology and techniques of snow cover mapping and monitoring, but rather to demon- strate the widespread possibilities for consequtive research and applications in relation to the sensor system, the dimensions of the spatial process invol- ved, and the accuracy required.

2 Study Areas, Time Frame and Satellite Data

Snow cover mapping with satellite data in the

Correspondence to: "Prof. Dr. H. Haefner, Remote Sensing Laboratories, Department of Geography, University Zurich-Irchel, Winterthurerstr. 190, 8057 Zurich, Switzerland".

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Swiss AIps started in the late sixties (Itten, 1969), and has systematically been investigated since the start of Landsat in 1972. These first studies are summarized in Haefner (1980). Main additional steps are documented in Keller (1987), Baumgartner (1987), Burkart (1991), Steinmeier (1995), and reviewed best in Seidel et al. (1989 & 1995).

First test sites were located in Grisons, in Eastern Switzerland, with the Dischma Valley near Davos as the core area (Martinec, 1985). Today, a carefully selected network of representative basins has been set up, with three major test areas, the first one on the northern side, one in the central part, and the third one on the southern side of the Alps. All areas represent hydrological units with a water gauge at the lowest end, and are divisible into smaller basins or subbasins.

Various types of optical satellite data such as Landsat, SPOT, and NOAA were tested, but Landsat-TM and SPOT-XS are the most heavily used systems. This results from the fact that the accuracy demands in Europe are generally very high, and the hydrological units to be investigated relatively small and heterogenous. Therefore preference has to be given to a high-resolution satellite system. These long and continuous research activities led to the compilation of snow cover information systems (SIS).

From the Dischma Valley 28 Landsat-MSS scenes, recorded between 1976 and 1982, e.g. all more or less classifiable images registered during this period, were analysed, using the same digital processing technique (Keller, 1987). From the Rhein-Felsberg test site, in which Dischma Valley is integrated as a subunit , the SIS today contains a complete documentation of the variations of the snow cover over a period of seven years.

3 Scope of Applications

Systematic, periodical and precise snow cover mapping supported by GIS technology, and the organisat ion of the results in a snow cover information system forms the basis for a wide range of applications. On the practical side, these appli- cations are related to the monitoring of seasonal and yearly alterations of the snow cover under the presently existing climatic conditions, to simulate and forecast runoff, to map the regional distribution of the water equivalent, and to document the recession process of the snow cover during the melting period in its relation to geoecological features. The other more scientifically oriented aspects deal with the effects and consequences of the changing climate on the time-spatial variations of the snow pack, be it regionally or globally.

H. Haefner et al.

All these aspects have been investigated carefully for regional and subregional basins in the Alps, and the classification, s imulat ion and forecasting procedures have been operationalized. These methodological and technical achievements have been reported in previous papers (Seidel et al., 1995), together with the achieved results. The newly developed management system, the SRM-ETH, combines remote sensing, runoff modelling, GIS, DEM, and computer graphics. It is well suited to analyse snow hydrological processes, in particular runoff, to improve day-to-day water management practices, and to simulate future trends based on various climate scenarios (Br~isch, 1996). But all applica- tions depend on a careful snow cover mapping.

The SRM-ETH Data Acquisition and Management System is outlined for operational runoff simulations and forecasts in Fig. 1. The core of the menue system is a Relational Data Base Management System which integrates the results of the snow cover mapping and the online collection of meteorological data inputs such as temperature and precipitation. Furthermore, a link to a GIS has been installed to allow easy data access related to different regions for comparative studies. The GIS incorporates also a powerful visualization tool to display input data and results.

4 Outlook

Setting up snow information systems will contribute substantially to a better understanding of high mountain geoecological entities, and its variations under a changing climate. It also improves modelling and simulation of the hydrological cycle, or at least part of it. Again such an approach will lead to many applications in the field of water resources management, realistic planning of traffic and touristic infrastructure in mountainous areas etc. This concludes, that based on an accurate snow cover

mapping over longer time periods, snow information systems should be set up in all mountain ranges of the World in a basinwise approach, and updated regularly. Only then real applications may be executed successfully, and scientific studies towards global change will provide substantial, meaningful and worldwide comparable results.

From the remote sensing point of view, a continuous snow classification over regular time intervals has to be guaranteed. This cannot be achieved with optical sensors alone, especially not in high mountain areas, because of the cloud problem. Therefore the potentials of active microwaves have to be exploited as best as possible, and combined with the optical data, using data fusion techniques. Corresponding studies are under progress (Piesbergen et al., 1996).

Applications of Snow Cover Mapping 277

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278 H. Haefner et al.

5 R e f e r e n c e s

Baumgartner, M., Schneeschmelz-Abflusssimulation basierend auf Schneefl/ichenbestimmungen mit digitalen Landsat-MSS und NOAA-AVHRR-Daten, Remote Sensing Series, 11, Dept. of Geography, University of Zurich, 201 pp, 1987.

Br~isch, W., Das Snowmelt Runoff Model ETH (SRM-ETH) als universel les Simulations- und Prognosesystem von Schneeschmelz-Abflussmengen, Remote Sensing Series, 27, Dept. of Geography, University of Zurich, 166 pp, 1996.

Burkhar t , U.J., S imu la t i on und P r o g n o s e des Schmelzwasserabflusses sowie Bestimmung des regionalen Schneewasser / iquivalents un te r Zuhi l fenahme von Satellitenbilddaten - dargestellt am Beispiel des Einzugsgebietes Rhein-Felsberg und Teilgebieten, Remote Sensing Series, 20, Dept. of Geography, University of Zurich, 126 pp, 1992.

Haefner, H., Snow Surveys from Earth Resources Satellites in the Swiss Alps, A Review on Six Years' Research, Remote Sensing Series, I, Dept. of Geography, University of Zurich, 65 pp, 1980.

Haefner, H, Schumann, A.H., Remote Sensing Applications in Hydrology and Water Resources Management, Remote Sensing Series, 21, Dept. of Geography, University of Zurich, 39 pp, 1992.

I t t en , K.I., G e o g r a p h i s c h e I n t e r p r e t a t i o n von Wettersatellitenbildern, M.S. Thesis, Department of Geography, University of Zurich, 1969 (unpublished).

Keller, M., Ausaperungskartierung mit Landsat-MSS Daten zur Erfassung 6kologischer Einflussgr6ssen im Gebirge, Remote Sensing Series, 10, Dept. of Geography, University of Zurich, 111 pp, 1987.

Martinec, J., Snowmelt runoff models for operational forecasts, Nordic Hydrology, 16, 129-136, 1985.

Matson, M., NOAA satellite snow cover data, Palaeogeography, Palaeoclimatology, Palaeoecology, 90, 1-3, Elsevier Science Publishers, Amsterdam, 213 -218,1991.

Piesbergen, J., Holecz F. and Haefner H., Snow Cover Monitoring Using Multitemporal ERS-1 SAR Data., Proc. IGARSS'95, Firenze, II, 1750-1752, 1995.

Seidel, K. Burkhart, U. Baumann, R. Martinec, J. Haefner, H., Itten, K.I., Satellite Data for Evaluation of Snow Reserves and Runoff Forecasts, Proc. Hydrology and Water Resources Symposium, Christchurch, N.Z., 28-30, 1989.

Seidel, K., Briisch W., Steinmeier Ch., Martinec J., Real time runoff forecasts for two hydroelectric stations based on satellite snow cover monitoring, Proc. of EARSeL Symp., Basel, 253-261,1995.

Seidel, K., Brtisch W., Steinmeier Ch., Martinec J., Real time runoff forecasts for two hydroelectric stations based on satellite snow cover monitoring, Proc. EARSeL Symposium, Gothenburg, 253-261, 1995.

Steinmeier, Ch.A.M., Model-based snow cover mapping from remote sensing data for operational snowmelt runoff forecasts, Dissertation No. 11248, Swiss Federal Institute of Technology, Zurich, Switzerland, 146 pp, 1995.

Wiesnet, D.R., A discussion of the accuracy of NOAA satellite- derived global seasonal snow cover measurements, Proc. Vancouver Symposium, IAHS Publ. No. 166, 291-304,1987.