The Spin-Scan Camera Idea

In the mid-1960s, Dr. Verner E. Suomi, founder of the Space Science and Engineering Center, University of Wisconsin-Madison and “Father of Satellite Meteorology,” invented the Spin-Scan Camera. This instrument was the payload of the Applications Technology Satellites –I and –III (ATS-I and ATS-III) launched in 1966 and 1967, respectively. The launching of the ATS-I into geosynchronous Earth orbit pioneered continuous viewing of weather from space. The ability to obtain continuous satellite imagery of a fixed point on the earth, at 20-minute intervals, allowed scientists to study a synoptic picture of existing meteorological conditions for the first time. Having this period in our weather history (1966-1972) accessible increases the time base available for climate study and modeling.

Before the age of remote sensing, Suomi understood the benefits that could be gained by observing a single weather phenomenon at frequent intervals. But these kinds of observations weren’t possible using the early, low polar-orbiting satellites. NASA’s new geostationary Advanced Technology Satellite (ATS), 22,000 miles out in space, would move in an orbit above the equator at the same speed as the Earth rotates on its axis. This is called geostationary orbit. For Suomi, the spin-scan idea was suddenly simple: “the weather moves, not the satellite.” Suomi used the spin of the satellite to scan the earth — 2400 revolutions of the satellite (spinning at about two revolutions per second) were needed to produce one complete image of Earth. Mounted aboard the spin-stabilized satellite, the camera scanned a small strip of the Earth with each rotation. By tilting the camera slightly for the next rotation (the next line of the picture), an image of Earth could be created in about 20 minutes. Suomi saw his Spin-Scan Camera launched on the ATS-1 in 1966.

The camera allowed scientists to observe weather systems as they developed. Satellite sensing technology was suddenly transformed from the production of interesting snapshots into the gathering of meaningful, quantitative data. This concept revolutionized satellite meteorology. The weather satellite images and “movies” of weather in motion seen on the evening news are a direct result of Suomi’s invention.

Using these images, it was possible to measure and track air motion, cloud heights, rainfall, even pollution and natural disasters. This technology soon became operational. It helped to improve the accuracy of forecasting, improved models and has saved many thousands of lives over the years. While the original spin-scan design is no longer in use in the United States, Suomi’s basic concept has been adopted for many satellites and space probes built for NASA, the National Oceanic and Atmospheric Administration, as well as the European Space Agency, the Japanese Meteorological Agency and the Chinese National Satellite Meteorological Center.

By 1967 the spin-scan pictures were in color — the ATS-III was the only geostationary satellite with a blue channel which was, and still is, a unique feature. By 1971 work had begun on an instrument that would profile the atmosphere’s temperature and water vapor from geostationary satellites. The Visible-Infrared Spin-Scan Radiometric Atmospheric Sounder (VAS) was a modification of the original spin-scan design with additional detectors for the various spectral bands. By observing temperature and moisture structures, Suomi hoped to improve the prediction of severe weather with increased understanding of how the atmosphere works.

When the VAS was launched in 1980 aboard the GOES-4 satellite, it performed with the accuracy Suomi had predicted in his original 1971 proposal. Suomi’s work established the need for sounders and demonstrated their feasibility; profoundly affecting the field of atmospheric science.

With the advent of these new instruments, the flow of meteorological data quickly became an overwhelming flood. Experiments conducted under the Global Atmospheric Research Program (GARP) added to the already vast amount of data. To make sense of all this, or as he put it, to try “to get a sip from a fire hydrant,” Suomi became the driving force behind the development of a computer system that could gather and handle the vast amount of imagery and data.

The study of the atmosphere and its dynamics quickly moved into the electronic age but the ATS photographs, until now, have not been part of this electronic data set. The ATS digitization project was undertaken to preserve the hard copy originals and make available a digital version of this unique, historically significant data set.

Exerpted from: Verner E. Suomi, 1916-1995: A man for all seasons. Madison, WI, Space Science and Engineering Center, (1996).

Spin-Scan Camera on ATS-I and ATS-III

The Applications Technology Satellite-I was the first of a series of ATS scientific satellites built for NASA. Dr. Vernor Suomi of the University of Wisconsin-Madison, Space Science and Engineering Center, was the Principal Investigator for the ATS-I Spin-Scan Cloudcover Camera (SSCC) Experiment. The ATS-I was launched 7 December 1966 and was designed for the purpose of (1) testing new concepts in spacecraft design, propulsion, and stabilization, (2) collecting high-quality cloudcover pictures and relaying processed meteorological data via an earth-synchronous satellite, (3) providing in situ measurements of the aerospace environment, and (4) testing improved communication systems. (NSSDC). The basic ATS-I spacecraft was a cylinder 54 inches long and 57.6 inches in diameter with a solar cell array mounted around its periphery. The satellite weighed 775 pounds in orbit. (From: The Applications Technology Satellite Meteorological Data Catalog: Volume I)

The ATS-III was the third in this series of scientific satellites built for NASA. The Multicolor Spin-Scan Cloudcover Camera (MSSCC) experiment, one of eleven payloads of ATS-III was again led by Dr. Verner Suomi. The satellite was launched on 5 November 1967 and provided color pictures for approximately three months at which time the red and blue channels failed. The system continued to provide black-and-white pictures until 11 December 1974. (NSSDC). The basic ATS-III spacecraft was a cylinder 54 inches long and 57.6 inches in diameter. Two solar arrays containing 24230 silicon solar cells provided 175 watts for the 11 experiments and two 6 amp-hour nickel-cadmium batteries provided reserve power for transient loads and during periods of solar eclipse. (From: The Applications Technology Satellite Meteorological Data Catalog: Volume II)

The view of the earth from the ATS-III satellite at earth synchronous height is similar, in many respects, to that of the moon viewed from the earth. The earth goes through “phases” on a 24 hour cycle similar to the phases of the moon, with some differences (From: The Applications Technology Satellite Meteorological Data Catalog: Volume II)