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Winds - Measuring ocean winds from space
MISSIONS
NSCAT
NSCAT Spacecraft

NSCAT, a microwave radar scatterometer, measured near-surface wind vectors (both speed and direction) over the global oceans. This information is critical in determining regional weather patterns and global climate. NSCAT had two major systems - the spaceborne instrument system and the ground data processing system.




Mission

NSCAT was launched at 6:54 p.m. U.S. PDT, Friday, August 16, 1996, aboard the Advanced Earth Observing Satellite (ADEOS), a mission of the National Space Development Agency of Japan. ADEOS was launched into a near-polar Sun-synchronous orbit, by an H-II launch vehicle from Japan's Tanegashima Space Center. The largest satellite ever developed by Japan, ADEOS had a mass of approximately 3500 kilograms and a power-generation capability of approximately 4500 watts; its overall dimensions at launch were 4 x 4 x 5 meters. When the NSCAT antenna and the solar array paddle were deployed, the satellite was an impressive 11 meters in height and the solar array extends outward 29 meters.




Science Objectives

On-orbit satellite overview of ADEOS Details
  • Acquire all-weather high-resolution measurements of near-surface winds over the global oceans.
  • Determine atmospheric influences, ocean response and air-sea interactions on various spatial and temporal scales.
  • Develop improved methods of assimilating wind data into numerical weather and wave prediction models.
  • Combine wind data with measurements from various scientific disciplines to understand processes of global climatic change and weather.




Measurements

Deployed NSCAT Antenna
  • The instrument was operated continuously at a frequency of 13.995 GHz.
  • Six dual-polarized, 3-meter long, stick-like antennas collected backscatter data with a resolution of 50 km for nine months before loss.
  • Backscatter data was combined and processed to yield 268,000 globally distributed wind vectors per day.




Instrument Description

  • Mass: 280 kg
  • Power: 240 W
  • Data rate: 3.2 Kbps
Tracking of Adeos NSCAT Instrument
Every two days, under all weather and cloud conditions, NSCAT measured wind speeds and directions over at least 90% of the Earth's ice-free oceans. Since oceans cover approximately 70% of Earth's surface, NSCAT played a key role in scientists' efforts to understand and predict complex global weather patterns and climate systems. NSCAT used eight antenna beams to scan two wide bands of ocean, one on each side of the instrument's orbital path. NSCAT transmited short pulses of microwave energy to probe ocean surfaces and then measured the reflected or backscattered power. Variations in the magnitude of this backscattered power are caused by changes in small (centimeter-sized), wind-driven waves. Using a method called Doppler processing (a change in the observed frequency of the radio waves due to relative motion of source and observer), the measured backscattered power was separated into cells at specific locations on Earth's surface; these were then transmitted to the ground for processing. During ground processing, wind direction and speed was determined from these variations. Within two weeks of receiving the raw data, the ground system processed wind measurements.

NASA sponsors a team of scientific investigators who served as project advisors during the development of the NSCAT instrument and ground data processing system. These investigators conduct research based on NSCAT data. Their studies are expected to lead to improved methods of global weather forecasting and modeling - and possibly to a better understanding of environment phenomena (i.e. El NiƱo).




ADEOS Launch

 
Important locations in Japan

Important locations in Japan

H-II Launch vehicle at Tanegashima Space Center

H-II Launch vehicle at Tanegashima Space Center

Earth Observation Center (EOC)

Earth Observation Center (EOC)


After this separation, ADEOS started turning slowly. Then, ADEOS spun down and deployed the Solar Array Paddle, and automatically established a three axis stabilized attitude. ADEOS deployed an IOCS unit, the NSCAT antennae, and OCTS's radiant cooler cover by commands sent from the ground station. Next, all sensors and units were checked, and then ADEOS was maneuvered into its proper orbit. ADEOS was placed into a sun synchronous, subrecurrent orbit.
 

H-II Launch Vehicle at night

H-II Launch Vehicle at night

Image of ADEOS launch

Image of launch

Image of ADEOS launch

Image of launch


In its operational phase, ADEOS was operated by an observation plan made at the ground station. The command plans for operations was sent from the ground station once or twice a week. The On-Board Computer carried out the commands of the plans. The data gathered by the sensors were transferred to the ground stations directly or recorded by the Misson Data Recorder and reproduced later. ADEOS had an IOCS unit, which allowed data to also be transmitted through a relay satellite.
 



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