The GOES I-M Sounder is a 19-channel radiometer that senses specific data parameters for atmospheric temperature and moisture profiles, surface and cloud top temperature, and ozone distribution. The atmospheric profiles that are produced are very similar to what has been achieved for decades using balloon-borne radiosondes. But the satellite Sounder system is able to achieve a greater number of profiles, and many more locations than is possible with a ground-based, balloon system.

The Sounder has 4 sets of detectors (visible, long wave IR, medium wave IR, short wave IR). The incoming radiation passes through a set of filters before reaching the detectors. The filters are mounted on a rotating (28.2 cm) wheel containing 18 filter windows, divided into 3 concentric rings, one for each IR detector group. The outer ring contains 7 long wave filters, the middle ring 6 short wave filters, and the inner ring 5 medium wave channels. The visible wave lengths do not pass through a filter. Approximately one-fourth of the wheel has no filters. While this "dead zone" is rotating in front of the detectors, the scanning mirror is stepped to the next location then stopped while the channels are sampled. The mirror scanning sequence takes places by sweeping in an East-West direction, stepping in the North-South direction, than sweeping back in a West-East direction, stepping North-South, sweeping East-West, and so on, similar to the Imager.

The Sounder consists of electronics, power supply, and sensor modules. The sensor module containing the telescope, scan assembly, and detectors, is mounted on a baseplate outside the main structure of the spacecraft, together with shields and louvers for thermal control. The electronics and power supply modules are mounted inside the spacecraft on the internal equipment panel.