Detailed spatial and temporal assessment of agricultural fields is crucial in site specific management of agricultural crops. Satellite imagery is limited in its application to many site-specific applications due to its typically coarse spatial resolution. Airborne imaging systems are capable of acquiring remote sensing data with spatial resolutions that satisfy the requirements for site specific crop management. Unlike satellite imagery, the radiometric characteristics of airborne imagery are usually not known. Thus, it is difficult to perform temporal analysis using airborne imagery since it is typically not known if the radiometric characteristics of the imagery have changed between acquisitions. This document describes a procedure based on histogram matching to calibrate aerial imagery to a standard radiometric level established by satellite imagery acquired near the time of the airborne image acquisition. Normalized Landsat TM and ETM+ imagery were used as reference images. The technique was tested for two dates during the cotton growing season. Two techniques of histogram matching were compared: matching histograms by automatic histogram matching in ENVI, and matching histograms based on the ratio of the pixel distribution means. Automatic histogram matching produced better results, since it not only translated the histogram distributions but also balanced the gray values with respect to the reference image. Histogram matching of aerial photos is a promising technique for calibrating multi-temporal remote sensing.
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