NOAA Satellite Information System

GOES Imager Instrument

GOES Imager instrument

The GOES I-M Imager is a five channel (one visible, four infrared) imaging radiometer designed to sense radiant and solar reflected energy from sampled areas of the earth. By means of a servo driven, two-axis gimbaled mirror scanning system in conjunction with a Cassegrain telescope, the Imager's multispectral channels can simultaneously sweep an 8-kilometer (5 statute mile) north-to-south swath along an east-to-west/west-to-east path, at a rate of 20 degrees (optical) east-west per second. This translates into being able to scan a 3000 by 3000 km (1864 by 1864 miles) "box" centered over the United States in just 41 seconds. The actual 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.

The Imager 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 module provides redundant circuitry and performs command, control, and signal processing functions; it also serves as a structure for mounting and interconnecting the electronic boards for proper heat dissipation. The power supply module contains the converters, fuses, and power control for interfacing with the spacecraft electrical power subsystem. The electronics and power supply modules are mounted inside the spacecraft on the internal equipment panel.

Imager Instrument Characteristics (GOES I-M)
Channel number: 1 (Visible) 2 (Shortwave) 3 (Moisture) 4 (IR 1) 5 (IR 2)
Wavelength range (um) 0.55 - 0.75 3.80 - 4.00 6.50 - 7.00 10.20 - 11.20 11.50 - 12.50
Instantaneous Geographic Field of View (IGFOV) at nadir 1 km 4 km 8 km 4 km 4 km
Radiometric calibration Space and 290 K infrared internal backbody
Calibration frequency Space: 2.2 sec (full disc), 9.2 or 36.6 sec (sector/area)
Infrared: 30 minutes typical
System absolute accuracy IR channels: less than or equal to 1 K
Visible channel: 5% of maximum scene irradiance
Imaging rate Full earth disc, less than or equal to 26 minutes

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