ISS RapidScat (ISS RapidScat) - 03.04.14
ISS Science for Everyone
Science Objectives for Everyone
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
OpNom ISS RapidScat
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
March 2014 - September 2014
Previous ISS Missions
A radar scatterometer is a remote sensing instrument that uses the strength of radar pulses reflected from the ocean surface from different angles to infer surface wind speed and direction. The radar pulses interact with small waves in the ocean through a resonant mechanism called Bragg scattering, which will cause the amount of radiation reflected from the ocean surface back to the radar to increase as the amplitude of the ocean waves increases. This technique was demonstrated by the 1999-2009 NASA QuikSCAT mission, which produced high quality wind data that was used by NOAA and other operational weather agencies to improve weather forecasting and the oceanography and meteorology communities to gain improved understanding of the way the ocean interacts with the atmosphere to transfer heat, gases, and mechanical energy between the two fluids/systems.
The ISS-RapidScat instrument will utilize the spare engineering model used to test the QuikSCAT scatterometer, modified to operate from the ISS to provide a low-cost mission to mitigate the significant loss of measurement capability by QuikSCAT in 2009. The resulting instrument package will produce ocean vector winds similar in accuracy 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 will be similar to the EUMETSAT ASCAT scatterometer, and the two data sets will complement each other to achieve coverage similar to QuikSCAT. Using engineering models in space, 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 will require rework in order to prepare for the rigors of space travel and operation. Meeting the cost commitment will require 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.
To study 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, and which play a significant role in governing the Earth’s energy and water budgets.
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 constellation 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 constellation 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 will not be readily available to mitigate the degradation of QuikScat in the near term.
To meet this challenge, the Jet Propulsion Laboratory (JPL), in partnership with NASA’s International Space Station Program Office, will deploy the QuikScat engineering model, which had been used to test the basic functionality and performance of the instrument, on the ISS to continue and improve QuikSCAT’s calibration standard across the present scatterometer constellation and demonstrate NASA’s capability for fast response to science challenges in a cost constrained environment.
ISS-RapidScat will also exploit the special characteristics of the ISS orbit to advance our 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. Consequently, satellites in the scatterometer constellation have different local observation times, and products 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. This will cause the ISS orbit to intersect 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. These simultaneous views will allow ISS-RapidScat to serve as the calibration golden standard that will enable improved calibration of the international scatterometer constellation.
In addition, over time, ISS-RapidScat will make 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 variations are especially noticeable over the tropics, and near land-sea boundaries, where they can 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, key drivers in the Earth’s climate. The ISS-RapidScat observations will provide a unique data set to help scientists to 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.