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Remote Sens. 2016, 8(8), 660; doi:10.3390/rs8080660

Spectral Indices to Improve Crop Residue Cover Estimation under Varying Moisture Conditions

1
School of Agricultural Engineering and CEIGRAM, Technical University of Madrid, Madrid 28040, Spain
2
USDA-ARS Hydrology and Remote Sensing Laboratory, 10300 Baltimore Ave., Beltsville, MD 20705, USA
*
Author to whom correspondence should be addressed.
Academic Editors: Clement Atzberger and Prasad S. Thenkabail
Received: 23 June 2016 / Revised: 8 August 2016 / Accepted: 10 August 2016 / Published: 17 August 2016
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Abstract

Crop residues on the soil surface protect the soil against erosion, increase water infiltration and reduce agrochemicals in runoff water. Crop residues and soils are spectrally different in the absorption features associated with cellulose and lignin. Our objectives were to: (1) assess the impact of water on the spectral indices for estimating crop residue cover (fR); (2) evaluate spectral water indices for estimating the relative water content (RWC) of crop residues and soils; and (3) propose methods that mitigate the uncertainty caused by variable moisture conditions on estimates of fR. Reflectance spectra of diverse crops and soils were acquired in the laboratory over the 400–2400-nm wavelength region. Using the laboratory data, a linear mixture model simulated the reflectance of scenes with various fR and levels of RWC. Additional reflectance spectra were acquired over agricultural fields with a wide range of crop residue covers and scene moisture conditions. Spectral indices for estimating crop residue cover that were evaluated in this study included the Normalized Difference Tillage Index (NDTI), the Shortwave Infrared Normalized Difference Residue Index (SINDRI) and the Cellulose Absorption Index (CAI). Multivariate linear models that used pairs of spectral indices—one for RWC and one for fR—significantly improved estimates of fR using CAI and SINDRI. For NDTI to reliably assess fR, scene RWC should be relatively dry (RWC < 0.25). These techniques provide the tools needed to monitor the spatial and temporal changes in crop residue cover and help determine where additional conservation practices may be required. View Full-Text
Keywords: cellulose absorption index; shortwave infrared normalized difference residue index; normalized difference tillage index; spectral moisture index; water content indices cellulose absorption index; shortwave infrared normalized difference residue index; normalized difference tillage index; spectral moisture index; water content indices
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Quemada, M.; Daughtry, C.S.T. Spectral Indices to Improve Crop Residue Cover Estimation under Varying Moisture Conditions. Remote Sens. 2016, 8, 660.

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