A routine operational backscattering coefficient regrouping algorithm for a HY-2A scatterometer
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摘要: 本文提出了一种可业务化运行的海洋二号卫星散射计面元匹配方法，该算法主要用于将按时序排列的后向散射系数及相关参数投影到相应风矢量单元。面元匹配方法主要包括地面网格划分和后向散射系数观测结果重采样两个关键步骤。为简化计算，本文采用了以星下点轨迹为中心，以顺轨向及交轨向为坐标轴的地面网格划分方式。在重采样过程中，本文提出了一种“三点标定”重采样方法，利用观测脉冲的地面足印中心，星下点轨迹的起点，以及过地面足印中心做星下点轨迹垂线的交点，三点形成的直角三角形来计算每个后向散射系数观测结果在地面网格中对应的坐标。该直角三角形的两直角边分别对应观测脉冲在顺轨向和交轨向的坐标。同时，为减少由于星下点数据空间分布不连续引起的面元匹配误差，在采用三点标定法进行重采样之前，首先对星下点时空分布不连续的区域对时间插值，然后以时间为坐标，对星下点经度、纬度分别进行内插。对风矢量面元位置分布和风矢量反演精度等分析表明，本文提出的面元匹配算法，可在满足高质量海面风场反演的要求。Abstract: The routine operational sigma0 regrouping method is proposed for a HY-2A scatterometer (HSCAT) that maps time-ordered sigma0s and related parameters into a subtrack aligned grid of wind vector cells (WVCs). The regrouping method consists of two critical steps: ground grid generation and sigma0 resampling. The HSCAT uses subtrack swath coordinates, in which the nadir track of the satellite represents the center and the designated positions are specified in terms of a pair of along-track and cross-track coordinates. To calculate the subtrack coordinates for each sigma0, a “triangle marking” resampling method is developed. Three points, including the point of intersection, the center of a pulse footprint, and the origin of the subtrack coordinate system, form a right triangle; the length of the two right-angled sides is used to represent the cross-track and the along-track coordinates in the subtrack coordinate system. In addition, a nadir point interpolation correction is used to ensure the operation of the regrouping algorithm when the nadir point positional information is missing. To illustrate the ability of the proposed regrouping algorithm, the distribution of the WVC positions and wind vector retrieval results are analyzed, which show that the proposed regrouping algorithm meets the requirements for high-quality sea surface wind field retrieval.
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Key words:
- regrouping /
- HY-2A scatterometer /
- backscattering coefficient /
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