Mitigating the effects of water on remotely sensed estimates of crop residue cover

Authors: Daughtry, Craig; Hunt Jr, Earle

Submitted to: Remote Sensing of Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/31/2007
Publication Date: 4/15/2008
Citation: Daughtry, C.S., Hunt, E.R. 2008. Mitigating the effects of water on remotely sensed estimates of crop residue cover. Remote Sensing of Environment. 112:1647-1657.

Interpretive Summary: Management of crop residues is an integral part of many conservation tillage systems. Current techniques for measuring crop residue cover are time-consuming and are not suitable for surveys of many fields. Remote sensing for assessing crop residue cover and conservation tillage practices have had mixed success because crop residues may be brighter or darker than the soils depending on moisture content and age of the residues. Additional work is needed to develop a strategy to mitigate the effects of water on remotely sensed estimates of crop residue cover. Reflectance spectra of crop residues and soils were measured in the lab and scenes with various residue cover fractions and moisture contents were simulated using a linear mixture model. Additional spectra of scenes with mixtures of crop residues and soil were also acquired in corn, soybean, and wheat fields with different tillage treatments and different moisture conditions near Beltsville, MD. Crop residue cover was linearly related to the relative intensity of an absorption feature near 2100 nm, called the Cellulose Absorption Index (CAI). Moisture in the crop residue significantly attenuated CAI. A new spectral residue moisture index was proposed and tested with measured reflectance data and crop residue cover from corn, soybean, and wheat fields. Adjustments for residue moisture content improved spectral estimates of crop residue cover. Regional surveys of soil conservation practices that affect soil carbon dynamics may be feasible using advanced multispectral or hyperspectral imaging systems.

Technical Abstract: Crop residues on the soil surface decrease soil erosion and increase soil organic carbon and the management of crop residues is an integral part of many conservation tillage systems. Current methods of measuring residue cover are inadequate for characterizing the spatial variability of residue cover over large fields. Several remote sensing approaches for estimating crop residue cover have been proposed, however all are affected by variations in scene moisture conditions. The objectives of this research were to determine the effects of moisture on the remotely sensed estimates of crop residue and to propose a method to mitigate the effects moisture on remotely sensed estimates of crop residue cover. Reflectance spectra of crop residues and soils were measured in the lab over the 400-2400 nm wavelength region. Reflectance of scenes with various residue cover fractions and moisture contents were simulated using a linear mixture model. Additional spectra of scenes with mixtures of crop residues and soil were also acquired in corn, soybean, and wheat fields with different tillage treatments and different moisture conditions. Crop residue cover was linearly related to the Cellulose Absorption Index (CAI), which was defined as the relative intensity of an absorption feature near 2100 nm. Moisture in the crop residue significantly attenuated CAI. Spectral vegetation moisture indices were poorly related to changes in crop residue moisture. New spectral residue moisture indices for describing the changes in the slope of residue cover versus CAI are proposed. A limited test with measured reflectance data and crop residue cover from corn, soybean, and wheat fields confirm these results and indicate that scene to scene adjustments in the spectral estimates of crop residue cover are possible. Regional surveys of soil conservation practices that affect soil carbon dynamics may be feasible using advanced multispectral or hyperspectral imaging systems.