NASA to Test Image Radiometer for Cloud Measurement

Kathleen G. Tatterson

GREENBELT, Md. -- NASA's Goddard Space Flight Center has taken delivery of an uncooled, multispectral infrared imaging system -- called the first of its kind by its builder, Space Instruments Inc. of Encinitas, Calif. The imager, called the Infrared Spectral Imaging Radiometer, will undergo testing for use in weather and remote-sensing satellites on a space shuttle mission slated for next summer.

James Spinhirne, space scientist at Goddard, said NASA needed a space-borne imager that didn't require a bulky, expensive cryogenic or radiated cooling system. "The lack of cooling requirements make the instrument much lower in cost, smaller and much easier to integrate into a spacecraft," he said.

The imaging radiometer's head, comprising the lens, detectors and filters, measures 63535 in. and weighs about 5 lb, whereas current imaging-satellite instrumentation weighs about 68 lb.

The heart of the instrument is an uncooled infrared microbolometer array that detects radiant energy by measuring the resistance of a black-coated material that changes resistance with temperature. The sensitivity of the microbolometer array eliminates the need for costly cryogenic cooling systems, permitting a lightweight, compact design, said James Hoffman, Space Instruments' technical director.

The calibrated instrument, which can operate within the infrared spectrum in four bands, will obtain images in the 11- and 12-µm bands, and in the 8.5-µm band, to determine the presence of cirrus clouds and estimate the size of cloud particles.

The mission will also evaluate the radiometer's time-delay integration by means of "push-broom" scanning, which captures the entire width of the scanned area simultaneously --as opposed to traditional mechanical side-to-side scanning. This method allows the instrument to image data with higher sensitivity while eliminating the mechanical scan mechanism.

The project is funded by a NASA Small Business Innovative Research grant. Pending the successful outcome of the shuttle experiments, the next step is the design of a thermal infrared imager that NASA can incorporate into small weather and remote-sensing satellites.