Question 3

Why do pixels become noticeably larger toward the edges of an AMSU swath and not for an SSM/I swath? (Click the button for the best answer below.)

a) Pixels become larger with the AMSU because of the wider swath it needs to scan.
b) Pixels become larger with the AMSU because of the increasing field-of-view as the instrument scans farther away from the satellite subpoint.
c) Pixels become larger with the AMSU because of the increasing scan angle as the instrument scans farther away from the satellite subpoint.
d) Pixels become larger with the AMSU only because of the specific type of remapping performed on the data.
e) Choices a) and c) apply.

Discussion

c) is the correct response.

Pixels or FOV footprints in the AMSU imagery become larger toward the edges of a scan because of the increasing scan angle. The AMSU is a cross-track scanner, scanning plus/minus 48.3 degrees from nadir. The SSM/I on the other hand is a conical scanner, which means that the scan angle is a constant 45 degrees with respect to nadir throughout the scan. Answer a) is incorrect since footprint size for AMSU would change regardless of how large the limits of the scan angle. Answer b) is incorrect since the FOV is fixed for AMSU (3.3 degrees for AMSU-A, 1.1 degrees for AMSU-B). Answer d) is incorrect since pixel size is also a function of scan angle.