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:

  1. Move the satellite to the start time (Ts) of the image (orbital model)
  2. Calculate time into image using the number of lines, T = Ts + (nlines * delta_time) (sensor model)
  3. Move satellite to the new location for T (orbital model)
  4. Calculate bore sight vector using attitude information (platform/sensor model)
  5. Calculate bore sight angle using the relationship between sample location and bore sight angle (sensor model)
  6. Calculate line of sight vector and its intersection with the ellipsoid (earth model)
  7. 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:

  1. Move satellite to start time (Ts) of the image (orbital model)
  2. Calculate bore sight vector and image line plane using attitude information. (platform model)
  3. Calculate angle between target and image plane (earth/platform models)
  4. Calculate time of target to image plane (orbital model)
  5. if time is << 1 line break out of loop
  6. Move satellite through time
  7. goto step 2
  8. (break point) Relate total time from start of image to line number in image (sensor model)
  9. Calculate line of sight vector from current satellite position to target (earth model)
  10. Relate bore sight angle to sample number in image (sensor model)