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