Ms. Shuyan Lang Profile

Shuyan Lang

at National Satellite Ocean Application Service

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Proceedings Article | 4 November 2010 Paper

Accuracy and spatial resolution analysis of spaceborne pencil beam microwave scatterometers for ocean observation

Shuyan Lang, Xiaolong Dong

Proceedings Volume 7841, 78410C (2010) https://doi.org/10.1117/12.873205

KEYWORDS: Backscatter, Signal to noise ratio, Spatial resolution, Microwave radiation, Radar, Computer simulations, Satellites, Optical simulations, Doppler effect, Antennas

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For ocean observation, the wind velocity over water is one major concern. Spaceborne microwave scatterometers can provide global, all-day, all-time, high-accuracy, high-resolution and short cycle wind velocity observations over the earth's bodies of water. For a microwave scatterometer system, backscattering coefficient accuracy and spatial resolution are two important parameters. And they are used to evaluate the performance of a scatterometer. High quality scatterometer data intends to have both high accuracy measurement of backscattering coefficient and high resolution. However, these two important parameters are restricted by each other, and cannot reach optimal level at the same time. Therefore, a compromise between the two variables is necessary for the system design of a scatterometer. In this paper, simulation results of conically scanned pencil beam scatterometers are presented. Analysis of backscattering coefficient measurement accuracy under different spatial resolution conditions is also presented. With the same instrument parameters, larger spatial resolution will increase the number of independent samples of backscattering measurement. It is well known that the backscattering coefficient accuracy of scatterometers is decided by the SNR of returned signal and number of independent samples. And simulation results show that the number of independent samples plays a more important role in backscattering coefficient accuracy than SNR of the returned signal. As a result, backscattering measurement accuracy and accuracy of retrieved wind velocity can be improved. The simulation results and analysis can be of benefit to the system design of next generation spaceborne pencil beam scatterometers.

Proceedings Article | 30 October 2009 Paper

A comparison of SAR image speckle filters

Shuyan Lang, Colin Yu Lin, Jianqiang Liu, Ngai Wong, Hayden Kwok-Hay So

Proceedings Volume 7498, 749804 (2009) https://doi.org/10.1117/12.830946

KEYWORDS: Image filtering, Speckle, Synthetic aperture radar, Gaussian filters, Image processing, Image quality, Linear filtering, Electronic filtering, Reflectivity, Copper

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High quality images of Earth produced by synthetic aperture radar (SAR) systems have become increasingly available, however, SAR images are difficult to interpret. Speckle reduction remains one of the major issues in SAR imaging process, although speckle has been extensively studied for decades. Many reconstruction filters have been proposed and they can be classified into two categories: multilook and/or minimum mean-square error (MMSE) despeckling using the speckle model; and maximum a posteriori (MAP) or maximum likihood (ML) despeckling using the product model. The most well known Lee, Kuan, and Frost filters belong to first category. These filters are based on conventional techniques that were originally derived for stationary signals, such as MMSE. In the second category, filters are based on the product model, such as the MAP Gaussian filter and the Gamma filter, and require knowledge of the a priori probability density function. These filters force speckle to have nonstationary Gaussian or gamma distributed intensity mean. The speckle filtering is mainly Bayesian model fitting that optimizes the MAP criteria. Scene reconstruction is performed using an inversion of the ascending chain. An objective measure is required to compare the technical merits of these filters, and Shi et al. presented a comparison 15 years ago. In this paper, a brief introduction of speckle, product, and filter models is summarized. A review of some most widely used SAR image speckle filters is given. And stationary speckle filters, like Lee, Kuan, and Frost filters, and nonstationary speckle filters like Gamma MAP filter are studied. Despeckling results on stationary and nonstationary SAR image of these speckle filters are presented.

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