Soil spectroscopy; Soil organic carbon; Soil roughness; Soil shadow; Image segmentation; Spectrométrie de sol; Carbone organique de sol; rugosité du sol; ombrage du sol; segmentation d'image
Abstract :
[en] Visible, Near and Short Wave Infrared (VNSWIR) diffuse reflectance spectroscopy (350 nm to 2500 nm) has been proven to be an efficient tool to determine the Soil Organic Carbon (SOC) content. SOC assessment (SOCa) is usually done by using calibration samples and multivariate models. However one of the major constraints of this technique, when used in field conditions is the spatial variation in surface soil properties (soil water content, roughness, vegetation residue) which induces a spectral variability not directly related to SOC and hence reduces the SOCa accuracy. This study focuses on the impact of soil roughness on SOCa by outdoor VIS-NIR-SWIR spectroscopy and is based on the assumption that soil roughness effect can be approximated by its related shadowing effect.
A new method for identifying and correcting the effect of soil shadow on reflectance spectra measured with an Analytical Spectral Devices (ASD) spectroradiometer and an Airborne Hyperspectral Sensor (AHS-160) on freshly tilled fields in the Grand Duchy of Luxembourg was elaborated and tested. This method is based on the shooting of soil vertical photographs in the visible spectrum and the derivation of a shadow correction factor resulting from the comparison of “reflectance” of shadowed and illuminated soil areas.
Moreover, the study of laboratory ASD reflectance of shadowed soil samples showed that the influence of shadow on reflectance varies according to wavelength. Consequently a correction factor in the entire [350–2500 nm] spectral range was computed to translate this differential influence.
Our results showed that SOCa was improved by 27% for field spectral data and by 25% for airborne spectral data by correcting the effect of soil relative shadow. However, compared to simple mathematical treatment of the spectra (first derivative, etc.) able to remove variation in soil albedo due to roughness, the proposed method, leads only to slightly more accurate SOCa.
Disciplines :
Engineering, computing & technology: Multidisciplinary, general & others Life sciences: Multidisciplinary, general & others Environmental sciences & ecology Agriculture & agronomy
Author, co-author :
Denis, Antoine ; Université de Liège, Belgium > Département des Sciences et Gestion de l'environnement - Arlon Campus Environnement > Eau Environnement Développement
Stevens, Antoine; Université Catholique de Louvain - UCL, Belgium > Georges Lemaître Centre for Earth and Climate Research, Earth and Life Institute
Van Wesemael, Bas; Université Catholique de Louvain - UCL, Belgium > Georges Lemaître Centre for Earth and Climate Research, Earth and Life Institute
Udelhoven, Thomas; Centre de Recherche Public Gabriel Lippmann, Luxembourg
Tychon, Bernard ; Université de Liège, Belgium > Département des Sciences et Gestion de l'environnement - Arlon Campus Environnement > Eau Environnement Développement
Language :
English
Title :
Soil organic carbon assessment by field and airborne spectrometry in bare croplands: accounting for soil surface roughness
Alternative titles :
[fr] Evaluation de la teneur en carbone organique de sols agricoles nus par spectrométrie de terrain et aéroportée: prise en compte de la rugosité du sol
Monitoring soil organic carbon in croplands using imaging spectroscopy
Funders :
BELSPO - Politique scientifique fédérale FNR - Luxembourg National Research Fund
Funding text :
Belgian Science Policy Office in the framework of the STEREO II program – Project “Monitoring soil organic carbon in croplands using imaging spectroscopy” (SR/00/110); National Research Fund of Luxembourg in the framework of the STEREO II program – Project “Monitoring soil organic carbon in croplands using imaging spectroscopy” (SR/00/110)
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