Abstract
Since the 2000s, bioenergy land use has been rapidly expanded in U.S. agricultural lands. Monitoring this change with limited acquisition of remote sensing imagery is difficult because of the similar spectral properties of crops. While phenology-assisted crop mapping is promising, relying on frequently observed images, the accuracies are often low, with mixed pixels in coarse-resolution imagery. In this paper, we used the eight-day, 500 m MODIS products (MOD09A1) to test the feasibility of crop unmixing in the U.S. Midwest, an important bioenergy land use region. With all MODIS images acquired in 2007, the 46-point Normalized Difference Vegetation Index (NDVI) time series was extracted in the study region. Assuming the phenological pattern at a pixel is a linear mixture of all crops in this pixel, a spatially constrained phenological mixture analysis (SPMA) was performed to extract crop percent covers with endmembers selected in a dynamic local neighborhood. The SPMA results matched well with the USDA crop data layers (CDL) at pixel level and the Crop Census records at county level. This study revealed more spatial details of energy crops that could better assist bioenergy decision-making in the Midwest.
Highlights
The Midwest is one of the major agricultural regions in the United States
This study developed a spatially constrained phenology-assisted unmixing (SPMA) approach to extracting crop percent covers in the U.S Midwest using Moderate Resolution Imaging Spectroradiometer (MODIS) time series in 2007
The Normalized Difference Vegetation Index (NDVI) time series of a pixel was assumed to be a linear combination of phenological curves from multiple crops in the pixel, and endmembers in a dynamic local neighborhood were selected in the unmixing process
Summary
The Midwest is one of the major agricultural regions in the United States. In 2007, the Midwestern states had a market value of over $76 billion for crops (corn, soybean, wheat, and forage grass) and livestock [1]. Corn grain is still the most commonly utilized feedstock for ethanol [2]. Food security and environmental contamination from intensified corn cropping become major concerns in this region [3]. Perennial native prairie grasses are recognized as promising alternative energy crops for cellulosic feedstock [4].
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