Effective use of the GOES I-M imager and sounder data is accomplished by rigorous quality control procedures. I-M series was to develop a navigation system that would improve earth location and registration accuracy. That involved maintaining a stable imaging platform in a three-axes satellite environment and predicting image shifts due to orbital motion as well as instrument motion and thermal distortion. This requires precise knowledge of the spacecraft's position in the orbit and attitude within that orbit at the time of image acquisition.
Separate star sensing capability exists in the imager and the sounder.
It is anticipated that three star measurements with good geometric separation will be obtained every half-hour without any significant impact on imaging operations. This should provide sufficient input data to determine daily attitude profiles. While imager visible data is the primary source for landmarks, they can also be obtained from imager IR and sounder visible data. Landmarks are obtained in an off-line manner and therefore have little impact on operations. Range is estimated in the SPS by measuring the elapsed time between the uplink and downlink signal of the retransmitted data.