| Two weekly and freely available remotely sensed vegetation indices, Vegetation Condition Index (VCI) and Temperature Condition Index (TCI), were assessed for state level corn yield correlation in the Corn Belt region of the United States for the years of 2007-2013. VCI and TCI were 16-km pixels which are derived from the Advanced Very High Resolution Radiometer (AVHRR). Corn pixels were identified by downloading yearly USDA Cropscape pixels for corn in each state. Irrigated corn pixels were removed by using the 2007 Irrigated Agriculture Dataset developed by Pervez and Brown (2010) as a mask. Corn pixels were then resampled to 16-km in ArcGIS 10.1, with only pixels with greater than 50% corn coverage being drawn. These corn pixels were then used to identify VCI and TCI corn pixels for each state. Weekly VCI and TCI corn pixel values were then averaged for each state and correlated with yield from the National Agriculture Statistics Service (NASS). For the Corn Belt as a whole, VCI had high positive correlation in Week 34 and TCI has high positive correlation in Week 28. The highest correlating VCI and TCI weeks for each state were then used for regression with yield. Seven of the 12 states had R2 values greater than 0.7, meaning at least 70 percent of the variation in yield for seven of the states can be explained by VCI and TCI. |
