The scanning geometry used by a particular satellite instrument affects coverage, such as the overlap between orbits, FOV resolution, and product development. AMSU and SSM/I instruments employ very different scan strategies. Impacts on data and derived products are summarized here.

The AMSU is a cross-track scanning instrument, sweeping out a line of FOVs perpendicular to the satellite's orbital track. The schematic shows that the AMSU scans to a maximum of +/- 48.3 degrees from nadir resulting in an orbital swath approximately 2200 km wide. The composite of AMSU TPW swaths from descending NOAA-15 orbits shows that this scanning leaves narrow gaps equatorward of 30 degrees north/south latitude.

Click the SSM/I Scan Pattern button above.
In contrast, the SSM/I is a conical scanning instrument, sweeping out consecutive 102-degree arcs perpendicular to the satellite's orbital track. The schematic shows that this results in an orbital swath approximately 1400 km wide, 64 percent of the swath of the AMSU. The composite of SSM/I TPW from descending DMSP-13 orbits shows that more significant gaps in data coverage are left equatorward of 50 degrees north/south latitude.