MIAVHRR creates a text segment which contains all ephemeris orbital elements for the satellite image. The extracted data are also called the Keplerian elements. If the ephemeris data values are in the tape header, MIAVHRR will extract them and write them into the text segment. If no ephemeris data can be found in the header, MIAVHRR will write default (invalid) values into the text segment.
A GCP segment is created, using Earth location data recorded with the image, for Level 1b LAC/HRPT and GAC formats only. In addition, the single GCP which is reported in the text segment is available only for Level 1b LAC/HRPT and GAC formats.
CEOS imagery is typically rotated to be in a north-up orientation. When the NOAA satellite is in an ascending orbit, the CEOS image on tape will already have been rotated. This an important point to consider, especially since there are certain programs which require raw AVHRR imagery as input (e.g., imagery which has not been rotated north-up). For example, AVHRCOR is such a program. To resolve this problem, it may be necessary to check the value of the ASCEND/DESCEND flag in the AVHRR text segment and then decide whether to rotate the image back to its raw orientation or not. Rotation of 180 degrees can be accomplished using the ROT program. In addition to rotating the image back to its raw orientation, it is also necessary to rotate (flip) the value of the pixel Y-coordinate of the single GCP in the AVHRR text segment. Editing the AVHRR text segment can be accomplished using the TEXWRIT and TEXREAD programs.
Level1b tapes may contain only a subset of the 5 AVHRR channels. This is known as the "channel selection" option. Channel selection configurations of 1, 2, and 3 channels are supported for Level1b data only.