Abstract
The microwave scatterometer onboard the China-France Oceanography Satellite (CFOSAT Scatterometer, CSCAT) is the first rotating fan-beam scatterometer (RFSCAT) in operation. It is used to obtain the ocean surface wind field by measuring the backscattering coefficient over a large observation swath. To estimate the backscattering coefficient, the scatterometer needs to measure the scattered signal accurately. The process of removing noise from the echo signal (scattered signal plus noise) is called noise subtraction. Noise subtraction has a great influence on the measurement of the backscattering coefficient and subsequent wind field retrieval. Therefore, accurate noise subtraction is necessary and important. In this article, an improved noise subtraction method for CSCAT is proposed. According to the distribution characteristics of backscattering coefficients, noise correction factors are introduced to improve the noise subtraction of CSCAT. The ocean surface wind fields are obtained using the improved backscattering coefficient data, and the deviation of wind speed and direction are calculated by comparison with the European Centre for Medium Range Weather Forecasts wind fields. The results show that the improved noise subtraction method can lead to improvement of the quality of wind field effectively. In addition, based on the improved method of noise subtraction, a method of estimating the noise correction factor is proposed at a large incidence angle, furtherly improving the noise subtraction method. The results show that the proposed method is effective.
Highlights
T HE spaceborne microwave scatterometer is an active microwave remote sensor, which measures the backscatter coefficient of a target and obtains the global ocean surface wind field
With the rotation of the antenna, an observation swath with a width of 1000km is formed on the ground, which is determined by the incidence angle along the outer edge of the beam
Where N is the number of views with different incidence and azimuth angles, σm0 i is the average backscatter coefficient of the ith view, σs0i is the backscatter coefficient simulated by the NSCAT-4 geophysical model function (GMF) [12], and Kpi is the normalized standard deviation (SD) of the backscatter coefficient
Summary
T HE spaceborne microwave scatterometer is an active microwave remote sensor, which measures the backscatter coefficient of a target and obtains the global ocean surface wind field. It is required to minimize the measurement error caused by instrument deviation and improve the measurement accuracy of the microwave scatterometer in the design and in-orbit operation of the microwave scatterometer system, so as to realize the accurate measurement of global backscatter coefficient and provide real-time, highprecision ocean wind field measurements. Misra [7] used deep space detection data to analyze the backscatter coefficient measured by the rotating scanning pen beam microwave scatterometer carried by Oceansat-II. It includes the improvement of noise subtraction, deviation estimation of signal bandwidth and correction of attitude angle.
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