Postlaunch sensor verification and calibration of the NASA Scatterometer



W. Tsai; J. E. Graf; C. Winn; J. N. Huddleston; S. Dunbar; M. H. Freilich; F. J. Wentz; D. G. Long;W. L. Jones


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Abbreviated Journal Title

IEEE Trans. Geosci. Remote Sensing


calibration; NSCAT; scatterometer; sea; winds; OCEAN; Geochemistry & Geophysics; Engineering, Electrical & Electronic; Remote; Sensing; Imaging Science & Photographic Technology


Scatterometer instruments are active microwave sensors that transmit a series of microwave pulses and measure the returned echo power to determine the normalized radar backscattering cross section (sigma-0) of the ocean surface from which the speed and direction of near-surface ocean winds are derived, The NASA Scatterometer (NSCAT) was launched on board the ADEOS spacecraft in August 1996 and returned ten months of high-quality data before the failure of the ADEOS spacecraft terminated the data stream in June 1997, The purpose of this paper is to provide an overview of the NSCAT instrument and sigma-0 computation and to describe the process and the results of an intensive postlaunch verification, calibration, and validation effort, This process encompassed the functional and performance verification of the flight instrument, the sigma-0 computation algorithms, the science data processing system, and the analysis of the sigma-0 and wind products, The calibration process included the radiometric calibration of NSCAT using both engineering telemetry and science data and the radiometric beam balance of all eight antenna beams using both open ocean and uniform land targets, Finally, brief summaries of the construction of the NSCAT geophysical model function and the verification and validation of the wind products will be presented. The key results of this paper are as follows: The NSCAT instrument was shown to function properly and all functional parameters were within their predicted ranges. The instrument electronics subsystems were very stable and all of the key parameters, such as transmit power, receiver gain, and bandpass filter responses, were shown to be stable to within 0.1 dB. The science data processing system was thoroughly verified and the sigma-0 computation error was shown to be less than 0.1 dB, All eight antenna beams were radiometrically balanced, using natural targets, to an estimated accuracy of about 0.3 dB. Finally, a new model function, called NSCAT-1, was constructed and used to produce wind products. The wind products were statistically verified using ECMWF wind fields and were validated using NDBC buoy measurements. Overall, we believe that NSCAT generated high-quality wind products with wind speed and direction accuracies that met the science requirements.

Journal Title

Ieee Transactions on Geoscience and Remote Sensing





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