global soil spectral library, a global reference, spectral library and conversion database for...
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Global Soil Spectral Library
World Agroforestry Centre (ICRAF) & ISRIC
A global reference, spectral library and conversion database for harmonization of legacy soil data for the
GlobalSoilMap.net project
Towards Global Soil Information: activities within the GEO Task Global Soil Data, FAO, Rome, 19 – 23 March 2012
Rationale
• GlobalSoilMap.net largely based on making effective use of legacy soils data.
• Legacy soil data consists of field observations, laboratory analyses and conventional soil maps collected over the last 60-80 years as part of numerous national, regional and institutional soil survey programs.
• Much of this legacy soils data is fragmented, non-standard between countries and often even within countries.
• Difficult to share or exchange data across national, state or even project borders because of significant differences in standards, methods of analysis, definitions and legends.
• Need for soil data to be harmonized to a single consistent reference method in order to be comparable globally and suitable for use in producing global maps and databases.
• In addition soil infrared spectroscopy and proximal sensing methods increasingly used for estimating soil properties, but as yet no comprehensive global calibration libraries exists (Viscarra Rossel, 2009; Terhoeven et al.,
Project Objectives
1. Design and populate a global soil property and spectral reference library Full range of soil types & environmental settings
on each continent or node (500 profiles per node) Sample from each horizon analysed using
commonly used methods for each soil property
2. Provide inter-method calibrations 1. Provide infrared spectral calibrations 1. Maintain and further build the reference library
Infrared Spectroscopy for rapid soil characterization
• Rapid
• Low cost
• Reproducible
•Predicts many soil functional properties
What soil properties affect spectral shape?
These are the key determinants of soil functional properties: nutrient supply & retention; carbon sequestration; hydraulic properties; erodibility; tillage & engineering properties
www.africasoils.net
Randomization of Sentinel Site locations stratified by climate zone
African Soil Information Service
AfricaSoils Sentinel Site based on the Land Degradation Surveillance
Framework a spatially stratified, hierarchical, randomized sampling framework
Sentinel site (100 km2)
16 Clusters (1 km2)
10 Plots (1000 m2)
4 Sub-Plots (100 m2)
?
Cost surfaces, etc.
Covariates Remote Sensing (RS) and Spatial Data
Elevation
Vegetation
Hydrology
Topographical properties
Climate
Landsat
Legacy data
ASTER
Quickbird
MODIS 500 m
250 m
28.5 m
15 m
2.4 m
0.6 m
Loca
l (si
te-le
vel)
Cre
f
High resolution digital mapping
10 km
Reg
iona
l Cre
f
160 km
Regional mapping
Instrumentation Dispersive VNIR FT-NIR FT-MIR Handheld NIR/MIR
• Portable • Repeatability? • External service • No validation
• Benchtop • Repeatability *** • Self serviceable • Validation in-built • ISO compliant • Industry proven • Multipurpose
• Benchtop • Repeatability*** • No gas purging • Some servicing • Robotic • Validation in-built • ISO compliant • Outperforms NIR
• Handheld • Sample
homogeneity? • Variable
moisture? • Repeatability? • Still expensive • Rapidly
developing • Need to prepare
by developing soil reference libraries
Current global spectral library initiatives
• Soil Spectroscopy Group
(Geophysical Research Abstracts, Vol. 11, EGU2009-14021, 2009; NIR News 2009 doi: 10.1255/nirn.1131)
• global soil spectral library (VNIR) • community of practice for soil spectroscopy
BEN DOR, Eyal - Tel Aviv University; BROWN, David - Washington State University; DEMATTE, Alexandre - Sao Paolo University; SHEPHERD, Keith – ICRAF; STENBERG, Bosse - Swedish Agricultural University; VISCARRA ROSSEL*, Raphael – CSIRO Land & Water
• Brown et al 2006: VNIR spectra from NSSC archives: 3768 samples from all 50 U.S. states and two tropical territories and an additional 416 samples from 36 different countries in Africa (125), Asia (104), the Americas (75) and Europe (112)
• Terhoeven-Urselmans et al 2010: MIR spectra from ISRIC archives: 4438 soil samples from 754 soil profiles (56 countries) but only 971 samples from 18 countries with complete data
ISRIC global spectral library
Terhoeven-Urselmans T, Vagen T-G, Spaargaren O, Shepherd KD. 2010. Prediction of soil fertility properties from a globally distributed soil mid-infrared spectral library. Soil Sci. Soc. Am. J. 74:1792–1799
Results for 30%
independent validation set
Spectral prediction of TOC, POC, Charcoal-C Australian and Kenya
soils
Janik LJ, Skjemstad JO, Shepherd KD and Spouncer LR (2007) The prediction of soil carbon fractions using mid-infrared-partial least square analysis. Journal of Australian Soil Research 45(2): 73–81.
TOC: alkyl–CH2 stretching modes; carbohydrate overtones of the –COH stretch; carboxylic acid–COOH; amide I and II bands; alkyl–CH2 deformation; aromatic–CH in plane deformation; carbohydrate–COH stretch. CHAR: C=C skeletal vibrations; phenolic, or COO stretching vibrations; ring C–H in plane deformations
Africa Soil Information Service Spectral library
Prediction performance for soil physical properties and total carbon and nitrogen using mid-infrared spectroscopy for sentinel sites analysed to date. Validation results are for a 50% random hold-out sample using boosted regression trees.
Spectral calibration transfer
Robotoic high throughput MIR (Shepherd & Walsh, 2007)
Current global spectral library limitations • Soil spectral calibrations limited by quality and
consistency of the reference data
• Large libraries needed to cover the global range in soil conditions
• Need to include a number spectral instrument types (VNIR, NIR, MIR)
A viable library will be based on conducting new reference measures in one laboratory with excellent quality control
Proposed plan • Phase 1 (6 months): Scoping, evaluation, feasibility
assessment • Survey available profiles; additional sampling? • Export/import procedures; shipping • Suite of methods to be used • Analytical lab for spectral and reference methods • Cost analysis • Full proposal development
• Phase 2 (3 years): Sampling and analysis
• Full implementation • Global database made available