All 1C products have a common L1C data structure, simple and generic. Each L1C swath includes scan time, latitude and longitude, scan status, quality, incidence angle, Sun glint angle, and the intercalibrated brightness temperature (Tc). One or more swaths are included in a product. The radiometer data are recalibrated to a common basis so that precipitation products derived from them are consistent. 1CSSMIS contains common calibrated brightness temperature from the SSMIS passive microwave instruments flown on the DMSP satellites. Swath S1 has 3 low frequency channels (19V 19H 22V). Swath S2 has 2 low frequency channels (37V 37H). Swath S3 has 4 high frequency channels (150H 183+/-1H 183+/-3H 183+/-7H). S4 has 2 high frequency channels (91V 91H). All the above frequencies are in GHz. Earth observations for all four swaths are taken during a 144o segment of the instrument rotation when SSMIS scans in the direction of foreward satellite motion. We define the spacecraft vector (v) at the center of this segment.
SSMI geometric footprints are: 69 x 43 km (19.35 GHz), 50 x 40 km (22.235 GHz), 37 x 28 km (37 GHz), 15 x 13 (85.5 GHz). GPM Project cross-calibrates channels at spatial sampling: 19.35-37 GHz at (25x25 km) and channel 85 GHz at (12x12 km).