RapidScat is a Ku-band radar that measures the normalized backscatter coefficient σ0 of the Earth's surface. Launched in 2015, it currently operates on the International Space Station. Nearly one year into its mission, RapidScat measurements began exhibiting strange behavior that is believed to be caused by a change in receiver gain. Changes in gain are compensated for during post-processing, but the measurements have a lower signal-to-noise ratio (SNR). Calibration and validation of σ0 measurements from this low SNR state are performed using extended land targets with various signal strengths. Study areas include the Amazon rainforest, Congo rainforest, Argentina pampas, two regions in the Sahara desert, and a desert region in Australia. The effects of seasonal, azimuthal, incidence angle and local-time-of-day variations on σ0 are studied using data from two Ku-band sensors, QuikSCAT and RapidScat, for each study area. Calibration is performed comparing RapidScat data from all SNR states to QuikSCAT data as well as comparing RapidScat low SNR state data to the nominal (high SNR) state data. Results from both calibrations are consistent with each other. Results suggest that σ0 is unbiased by noise for the ranges of σ0 covered in this study (-7 dB to -27 dB). However, the second low SNR state vertically polarized σ0 appears to be biased lower than would be expected from year-to-year seasonal variation. The third low SNR state σ0 appears unbiased compared to the nominal RapidScat SNR σ0.



College and Department

Ira A. Fulton College of Engineering and Technology; Electrical and Computer Engineering



Date Submitted


Document Type





scatterometry, calibration, validation, land