Evaluation of Soil Erosion Protective Cover by Crop Residues Using Vegetation Indices and Spectral Mixture Analysis of Multispectral and Hyperspectral Data

摘要

Crop residues are efficient in reducing erosion and surface water runoff on agricultural soils. Evaluating the crop residue cover fraction and its spatial distribution is important to scientists involved in the modelling of soil erosion and surface runoff, and also authorities wishing to assess soil conservation adoption by farmers. Four techniques were evaluated for estimating the crop residue cover fraction. These are the Soil Adjusted Corn Residue Index (SACRI), the Crop Residue Index Multiband (CRIM), the Normalized Difference Index (NDI) and the spectral mixture analysis technique (SMA). Field campaigns that were carried out by the FLOODGEN project in Sainte-Angele-de-Monnoir, Quebec, Canada and in the Pays-de-Caux located in the Normandy region of France, allowed to gather digital photographs, spectra and other measurements to determine the actual ground cover fraction. A linear regression analysis between results obtained from a TM satellite image of Ste-Angele-de-Monnoir acquired in May 1998 and the actual ground cover fractions showed best results for the CRIM with a R~2 value of 0.91, while the SMA gave an R~2 value of 0.63. A hyperspectral simulation using field spectra from a GER-2100 instrument improved results for both the CRIM and SMA. Results obtained with the field spectra and the CRIM correspond to a R~2 of 0.96 for the Ste-Angele-de-Monnoir study site, and 0.94 for the Pays-de-Caux site. When the SMA was applied to the field spectra, an R~2 value of 0.92 and 0.89 were obtained for both sites respectively. Results obtained with the NDI and SACRI from both TM and field spectra were not conclusive.