Recently I processed some data detected by AGRI, a sensor loaded on FY-4 Satellite, which was launched by China. Fourteen channels designed for AGRI observe almost half of the earth in minutes. However, because AGRI is an imager, data generated by it need positioning.
There are two ways for positioning, one is querying the lookup table given by NSMC, the other is calculating by formulas.
However, there are some errors in the files given by NSMC, I wrote this note in case others will meet the same trouble I got these days.
Querying the lookup table.
There are two errors in the files.
- The first 8 bytes denote latitude, and the next 8 bytes are reserved for longitude.
- The data are stored as little-endian data.
Calculating by formulas
The formulas are OK, but the constant variable \(\lambda_D\) should be measured in rad before being used.
