Scaling Chlorophyll Content in Corn From Leaf Reflectances to Airborne Imaging Spectrometers.

Chlorophyll content is an important variable for agricultural remote sensing because of its close relationship to leaf nitrogen content and nitrogen fertilizer recommendations.  In 1999, Dr. Paul Doraiswamy and investigators funded by NASA's Earth Observations Commercialization and Applications Program collaborated on a nitrogen fertilization experiment with irrigated corn in Nebraska.  Twenty plots (75 m × 90 m) with different levels of applied nitrogen were established along the center of the field in a randomized complete block design with four replications. On 5 June 1999, sidedress fertilizer of 0, 50, 100, 150 or 200 kg/ha N (as anhydrous ammonia) was applied to one plot in each block.  Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data and Landsat 5 Thematic Mapper (TM) data were acquired along with leaf chlorophyll meter and field-portable spectrometer data.  On 6 July 1999 when the corn was at stage V14, only the plots with 0 kg/ha sidedress nitrogen were detectable with either high-altitude AVIRIS imagery or chlorophyll meter data. On 22 July 1999 when the corn was at stage R1, all of the treatments could be distinguished on the ground or from low-altitude AVIRIS imagery. Estimates of chlorophyll content were generally better using narrow bands based on the red edge of the chlorophyll absorption feature.