L1A级影像产品是中国高分三号SAR卫星产品发布的初级产品形式。为实现后续科学研究、增值应用，提出一套完整的L1A级产品处理流程，用以生成辐射纠正产品、几何纠正产品等高级产品形式。在辐射纠正过程中，为剔除L1A级产品量化过程中存在空值和零值像素对辐射纠正结果造成的统计偏差，基于高分三号等效噪声系数提出改进的辐射纠正方法。在几何纠正中，提出RPC参数反算算法确定影像角点坐标，基于xml元数据文件中提供的轨道方向、视向以及采样间隔参数保证反算方法的稳健性，在几何校正重采样部分引入SAR滤波算子实现等效视数的提升。对使用Envi5.5软件无法完成几何校正的部分高分三号影像，使用本文提出的处理流程可以顺利完成，其处理结果通过与同为C波段的Sentinel-1影像辐射精度，以及Sentinel-2光学影像几何精度的对比，表明本方法对L1A产品进行处理的精确性和可靠性。
Level one A (L1A) product of Gaofen-3 SAR satellite is the primary image set delivering for customer. This paper presents a complete workflow to facilitate the post-process of GF-3 L1A images for follow-up scientific research or value-added applications, where robust and precise processing is essential to generate the advanced high-level product concerning radiometric correction and geometric correction. Firstly, to eliminate the statistical bias caused by the null and zero pixel values induced in the quantization of the L1A product, an improved radiometric correction formula is derived based on the equivalent noise coefficient of Gaofen-3 images. Then, to determine the coordinates of image corners, an inverse algorithm supported by RPC parameters is proposed for geometric correction. This algorithm is robust by counting on the orbit direction, look direction, and sampling interval provided in an XML metadata file. Finally, a SAR filter operator is introduced into the resampling step of output results to improve the equivalent look number. Experimental results comparing with the radiometric values of a sentinel-1 image and the geometric accuracy of a sentinel-2 optical image, respectively, validate the accuracy and reliability of this method for L1A product processing.
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