Appendix E: AVHRR Satellite Model
The forward model converts a line, sample, and an elevation to a latitude
and longitude location within an image. The forward model consists of the
following steps:
- Move the satellite to the start time (Ts) of the
image (orbital model)
- Calculate time into image using the number of lines, T = Ts +
(nlines * delta_time) (sensor model)
- Move satellite to the new location for T (orbital model)
- Calculate bore sight vector using attitude information
(platform/sensor model)
- Calculate bore sight angle using the relationship between
sample location and bore sight angle (sensor model)
- Calculate line of sight vector and its intersection with the
ellipsoid (earth model)
- Terrain correct image (separate step)
The inverse model converts a latitude, longitude, and an elevation to a line
and sample location within an image. Calculated line and sample locations
that fall outside of the image are negative or larger than the number of lines
and samples within the image. The inverse model consists of the following
steps:
- Move satellite to start time (Ts) of the image
(orbital model)
- Calculate bore sight vector and image line plane using
attitude information. (platform model)
- Calculate angle between target and image plane (earth/platform
models)
- Calculate time of target to image plane (orbital model)
- if time is << 1 line break out of loop
- Move satellite through time
- goto step 2
- (break point) Relate total time from start of image to line number
in image (sensor model)
- Calculate line of sight vector from current satellite position to
target (earth model)
- Relate bore sight angle to sample number in image (sensor model)