HY-1C/D卫星中国海洋水色水温扫描仪几何定位方法

海洋一号C/D（HY-1C/D）卫星中国海洋水色水温扫描仪（Chinese Ocean Color and Temperature Scanner，COCTS）主要用于探测海洋水色、水温等要素，这些要素需要经过卫星资料处理才能获取，而几何定位是预处理的核心，直接影响这些要素的质量。COCTS具有114°视场角和四元逐点摆扫的特征，据此研究出一套完整的几何定位方法。从0级数据中提取卫星星历，利用插值法从中获取采样时间对应的卫星位置和速度，进而得到轨道（ORB）坐标系到地心旋转（ECR）坐标系的转换矩阵。基于四元逐点摆扫的特征，中心视矢量分别绕X轴、Y轴旋转相应角度，获得扫描行各采样点ORB视矢量，建立视矢量与地球交叉点关系模型，从而对根据波段数据绘制的遥感图像进行地理定位。本文使用插值法替代了传统需要6个轨道根数来计算卫星位置的复杂方法，同时直接计算ORB到ECR的转换矩阵，而不采用传统的两步转换方法。经过多组数据计算及定性定量验证，HY-1C/D COCTS几何定位结果一致；采样像元尺度效应导致从星下点到两侧边缘、从赤道到两极，误差逐渐增大，约在两个像元内。该方法满足一定的定位精度要求，可以用于COCTS的几何定位。

Geometric positioning method of HY-1C/D satellite Chinese ocean color and temperature scanner

Chinese Ocean Color Temperature Scanner (COCTS) of Haiyang 1C/D (HY-1C/D) satellite is mainly used to detect ocean water color, water temperature and other elements. These elements can only be achieved by processing satellite data, and geometric positioning is the core of preprocessing, which directly affects quality of these elements. COCTS has the characteristics of 114° field of view and quaternary whisk broom point by point. A set of complete geometric positioning method has been developed based on COCTS characteristics. The satellite position and velocity corresponding to the sampling time are obtained by using the interpolation method in the satellite ephemeris extracted from 0 level data, and then the transformation matrix from orbital coordinate system (ORB) to earth-centered rotating coordinate system (ECR) will be achieved. Based on the quaternary whisk broom point by point, the ORB viewing vector of every sampling point in a sweep can be calculated by rotating center viewing vector around X and Y axis in corresponding angles. The relationship model of viewing vector and the earth intersection point can be established to carry out geolocation of remote sensing images obtained from band data. This article uses interpolation to replace the traditional complex method that requires 6 orbital elements to calculate the satellite position, and directly calculates ORB to ECR transformation matrix rather than the traditional two-step transformation method. After multiple sets of data calculation and qualitative and quantitative verification, the HY-1C/D COCTS geometric positioning results are consistent. As a result of the sampling pixel scale effect, the error increases gradually from Nadir to the edge of two sides and from the equator to two poles, all within the error of 2 pixels. This method meets certain positioning accuracy requirements and can be employed for geometric positioning of COCTS.