The HIRS/3 is an atmospheric sounding instrument with one visible channel, seven shortwave IR channels, and 12 longwave IR channels. The IFOV for each channel is approximately 1.4° in the visible and shortwave IR channels, and 1.3° in the longwave IR band which, from an altitude of 833 km (517.6 mi), provides a nominal spatial resolution at nadir of 20.3 km (12.6 mi) and 18.9 km (11.7 mi), respectively. The scan mirror provides a cross-track scan of 56 steps of 1.8° each. Each Earth scan takes 6.4 seconds and covers ±49.5° from nadir. IR calibration of the HIRS/3 is provided by views of space and the internal warm target, each viewed once per 38 Earth scans.

The instrument measures scene radiance in the infrared spectrum. Data from the instrument is used, in conjunction with the Advanced Microwave Sounding Unit (AMSU) instruments, to calculate the atmosphere’s vertical temperature profile from the Earth’s surface to about 40 km (24.9 mi) altitude. The data is also used to determine ocean surface temperatures, total atmospheric ozone levels, precipitable water, cloud height and coverage, and surface radiance.