A NASA instrument that will measure ocean winds from space was integrated this week into Japan's host spacecraft, the Advanced Earth Observation Satellite, in preparation for the spacecraft's launch and three-year mission beginning in February 1996.

The instrument was delivered to Japan's National Space Development Agency last December for reassmbly and extensive testing before full integration work began this week.

James Graf, project manager of the NASA Scatterometer at the Jet Propulsion Laboratory, said the collaborative effort to put a NASA instrument aboard a Japanese satellite represents one of the first times the United States and Japan have carried out a joint Earth-observing mission. The agreement, signed in 1989, calls for launch of the instrument-laden satellite on an H-11 rocket from Tanegshima Space Center, located about 1,000 kilometers (625 miles) southwest of Tokyo.

The measurements of the winds over the oceans by radar will be used by JPL for climate research, helping scientists better understand ocean circulation and the role of air-sea interactions in the global ecosystem. Data from the scatterometer will be transmitted to JPL in real time and be incorporated by the National Oceanic and Atmospheric Administration into their weather models to improve weather forecasting.

The NASA Scatterometer will complement the measurements of two other instruments onboard the spacecraft: a Japanese instrument, called the Ocean Color and Temperature Scanner, which will look at the biomass of the oceans, and another NASA instrument, the Total Ozone Mapping Spectrometer, which will provide daily maps of global ozone levels.

The scatterometer will be capable of taking 190,000 wind measurements per day, mapping more than 90 percent of the world's ice-free oceans every two days. The instrument looks at the small waves on the ocean surface which are caused by wind, and can read wind direction by using two or more radar antennas pointed at different angles.

After early tests on aircraft and on NASA's Skylab mission in the 1970s, a scatterometer was launched in 1978 on NASA's experimental ocean monitoring satellite known as Seasat. The NASA Scatterometer is based broadly on the concepts of the Seasat scatterometer but makes improvements in many areas.

The NASA Scatterometer uses an array of stick-like antennas that radiate microwave pulses at a frequency of 14 gigahertz (14 billion cycles per second) across broad regions of the Earth's surface. A small percentage of the radar pulses are reflected back and the scatterometer's antennas capture the returned pulses as it orbits about 800 kilometers (500 miles) high in space. The data are processed by onboard computers and this processed information is then transmitted to receiving stations on Earth.

The scatterometer's array of six antennas -- each measuring 3 meters by 20 centimeters by 20 centimeters (10 feet by 6 inches by 6 inches) -- will scan two bands of ocean on either side of the satellite's near-polar, sun-synchronous orbit around the Earth. Each band is 600 kilometers (375 miles) wide to provide wind data over 90 percent of the oceans every two days.

As the NASA Scatterometer adds information to that of other Earth-observing satellites, the data will be put on compact discs (CD-ROMs) and sent to schools, along with a science curriculum on global change that is being prepared by the NASA Scatterometer project's Educational Outreach Office.

The Jet Propulsion Laboratory built the NASA Scatterometer under contract to NASA's Office of Mission to Planet Earth.

NASA's Mission to Planet Earth (MTPE) program is studying how the global environment is changing. From the unique vantage point of space, NASA will observe, monitor and assess large-scale environmental processes with a focus on climate change.

The MTPE spaceborne data, complemented by aircraft and ground studies, will give scientists highly detailed information which will help them distinguish natural environmental changes from those that are the result of human activity. NASA will distribute MTPE data to the international scientific community so that this essential research is available to people everywhere who are trying to make informed decisions about protecting the environment.

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