ISS-RapidScat (ISS-RapidScat) - 09.17.14
ISS Science for Everyone
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ISS-RapidScat is a space-based scatterometer that replaces the inoperable SeaWinds payload aboard the QuickSCAT satellite. Scatterometers are radar instruments that measure wind speed and direction over the ocean, and are useful for weather forecasting, hurricane monitoring, and observations of large-scale climate phenomena such as El Niño. The ISS RapidScat instrument enhances measurements from other international scatterometers by cross-checking their data, and demonstrates a unique way to replace an instrument aboard an aging satellite.
Science Results for Everyone
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Human Exploration and Operations Mission Directorate (HEOMD)
ISS Expedition Duration
September 2014 - Ongoing
Previous ISS Missions
A scatterometer is a remote sensing instrument that uses radar pulses reflected from the ocean surface from different angles to calculate surface wind speed and direction. Small ocean waves can reflect radar energy, and how much is reflected or scattered depends directly on the size of these small waves. This effect is called Bragg scattering. and was put in practice by the 1999-2009 NASA QuikSCAT mission, which produced high quality wind data the National Oceanic and Atmospheric Administration (NOAA) and other operational weather agencies used to improve weather forecasting. TOceanography and climate scientists also gained a better understanding of the way the ocean interacts with the atmosphere to transfer heat, gases, and mechanical energy.
The ISS-RapidScat instrument is a spare of the QuikSCAT scatterometer modified for operation on the ISS to provide a low-cost way to make up for the loss of QuikSCAT in 2009. The resulting instrument package measures ocean winds with accuracy similar to QuikSCAT, but with a measurement swath on the ground smaller by a factor of two due to the lower ISS orbit. This swath width is similar to the EUMETSAT ASCAT scatterometer, and the two data sets complement each other to achieve coverage similar to QuikSCAT. Using existing hardware, like on ISS-RapidSCAT, represents a low cost approach to acquiring valuable wind vector data. It does come with technical and programmatic risks. The hardware was not directly fabricated for space and requires rework in order to prepare for the rigors of space travel and operation. Meeting the cost commitment requires new and innovative approaches to development.
The specific objectives of the ISS-RapidScat Mission are:
To provide ocean vector wind data for a period of two years to mitigate the loss of QuikSCAT to scientists and weather forecasters.
To serve as a calibration standard to the international scatterometer constellation, enabling the continuation of the QuikSCAT data record, and enabling monitoring of climate variability and change over multiple decades.
ISS-RapidSCAT studies the systematic variation of ocean winds as a function of time of day. These variations are important in understanding the dynamics and interactions of the ocean and atmosphere in the tropics, where current climate models still exhibit shortcomings.
After ten years of successful operations, in late 2009 the NASA SeaWinds instrument on the QuikScat satellite suffered a degradation that significantly decreased the amount of wind data it could collect over the oceans, leaving a hole in the global collection of wind scatterometers. The QuikSCAT instrument is still able to operate collecting a small swath, and has been used successfully by NASA to provide a calibration standard for the international scatterometer group of ISRO’s OSCAT and EUMETSAT’s ASCAT. Although next-generation replacements to this satellite have been under study by NASA and NOAA, these instruments are not available to mitigate the degradation of QuikScat in the near term.
To meet the QuikScat data loss challenge, the Jet Propulsion Laboratory (JPL), in partnership with NASA’s International Space Station Program Office, deploys the QuikScat spare engineering unit, which was used previously to test the functions and performance of the instrument to the ISS to continue and improve QuikSCAT’s calibration standard across the present global scatterometer collection. This investigation also demonstrates NASA’s fast response capability to meet science challenges in a costeffective way.
ISS-RapidScat exploits the special characteristics of the ISS orbit to advance the understanding of the Earth’s winds. Current scatterometers are in polar sun-synchronous orbits, visiting each point on the Earth at approximately the same local time.Therefore, satellites in the scatterometer array have different local observation times, and present significant challenges in stitching the data from different satellites into a data record appropriate for monitoring subtle changes in the wind field across satellite records and over long periods. The ISS orbit, on the other hand, is not synchronized with the Earth’s rotation and has a lower inclination than polar sun-synchronous satellites. ISS orbit intersects the orbits of every one of these sun-synchronous satellites approximately every hour, allowing winds to be estimated simultaneously by ISS-RapidScat and the other scatterometers around the globe. These simultaneous views allow ISS-RapidScat to serve as the calibration golden standard that enables improved calibration of the international scatterometer constellation.
In addition, ISS-RapidScat makes measurements of the wind field at all hours of the day. Winds over the ocean are influenced by the Sun’s radiation, and, therefore are expected to vary systematically with the time of day depending on the location. These so-called diurnal (daily) variations are especially noticeable over the tropics, and near land-sea boundaries. They can also play a significant role in the formation of clouds, including the energetic mesoscale tropical systems, which play a dominant role in the Earth’s water and energy cycle along with Earth’s climate. The ISS-RapidScat observations provide a unique data set to help scientists understand these phenomena and incorporate improved physics into weather and climate prediction models.
ISS RapidScat compiles scatterometer wind measurements to fill the gap left by the QuikSCAT satellite, enabling continuous contributions to the international Earth observation satellite community. Improved understanding of the variability of sea surface winds between day and night could improve climate models and may affect future observation strategies, which in turn may lead to new mission designs. Placing the RapidScat instrument aboard station demonstrates faster space instrument deployment using existing infrastructure, rather than a dedicated satellite.
RapidScat improves observations of wind processes that drive ocean circulation, waves, swell, distribution of nutrients, and severe weather. Data from RapidScat enhances climate and weather models used to forecast short-term and long-term climatic changes. In addition, its position aboard the station will allow the first observations of the changes in ocean winds between day and night, which can also improve climate models. Although the International Space Station is not ideal for this type of instrument, its view will cross the orbital paths of other scatterometers every hour, allowing scientists to cross-check instrument readings.
One month of post-installment checkout and two years of operations.
NASA's RapidScat: Watching the Winds from Space