标称网格计算将地球给定区域投影变换成标称图像,是静止轨道卫星图像定位与配准的关键技术。分析了以风云四号(FY-4A)、Himawari-8、MTG、Electro-L等卫星为代表的气象卫星协调组(CGMS)规范和以GOES-R为代表的两种标称网格定义,对两种标称网格的计算过程进行了详细推导,并总结了CGMS规范和GOES-R标称网格的异同。结果表明,CGMS规范沿用了自旋卫星扫描成像方式,GOES-R标称网格基于“先南北后东西”双扫描镜高级基线成像仪(ABI)真实入射光路设计。两种标称网格都是在卫星空间直角坐标系中定义的,尽管计算方法不同,但可相互转换。进一步以FY-4A卫星观测数据为例,给出了由CGMS规范标称图像计算GOES-R标称图像的详细过程,变换后的图像与由GOES-R方式计算的海岸线套合得很好。FY-4A先进静止轨道成像仪的扫描角和步进角与GOES-R的相比,两者差分别为10 ^-16 μrad和10 ^-17 μrad数量级,表明GOES-R标称网格是从ABI的光机结构出发定义的。为方便用户使用,并保证与全球规范的一致性,FY-4A L1产品目前采用国际上普遍接受的CGMS LRIT/HRIT全球规范中定义的标准投影。

Calculation of nominal fixed grid, aimed to project a given area of the earth to the nominal image, is a key technique for navigation and registration of geostationary satellites. In view of the existing nominal fixed grid definitions from coordination group for meteorological satellites (CGMS) specification and geostationary operational environmental satellite-R series (GOES-R) user's guide, whose representatives are FY-4A, Himawari-8, MTG, Electro-L satellites and GOES-R satellite, respectively, the formulas of CGMS and GOES-R nominal fixed grid calculation are deduced in detail, and the difference and relationship between CGMS and GOES-R nominal grids are summarized. Both nominal fixed grids are defined in satellite body Cartesian coordinate system. Furthermore, the detailed transforming process from nominal image of CGMS specification to the corresponding nominal image of GOES-R definition is presented using FY-4A observations. The results demonstrate that the nominal images defined by the two aforementioned methods can be converted to each other. Besides, by comparing the scanning and stepping angles of FY-4A advanced geosynchronous radiation imager to the responding angles of GOES-R fixed grid, the differences are 10 -16 μrad and 10 -17 μrad magnitude, respectively, which reveals that GOES-R fixed grid is defined from the point view of opto-mechanical design of advanced base imager. Considering that the foreign satellites, except GOES-R, all use CGMS fixed grid to calculate the nominal image, for end-user's convenience, FY-4A nominal fixed grid will adopt the internationally accepted standard projection defined in CGMS LRIT/HRIT global specification.