OVER SEA
Scatterometry
Satellites
Research Programs

OVER LAND
Doppler Radar
U.S. Radar Coverage
Research Programs

ON SITE
Mini- SODAR
Research Programs

WIND POWER
Growth in Wind Energy
Finding Strong Winds
Wind Atlases
Site Studies

Web site created by
Paul Kelly
Graduate Student
Geo Information Science
Department of Geography
Salem State College
Salem, Massachusetts, USA.

E-mail comments and suggestions to pmkelly@prodigy.net.

Last updated 4/24/2002.

OVER SEA
The following discussion focuses on scatterometry.  However, other space-based remote sensing systems have been used to track winds over the ocean with varying success.  These include detection of passive microwave emissions and infra-red tracking of cloud and water vapor movements.  A brief, excellent discussion of these various remote sensing techniques, along with scatterometry, was presented by David Kilham in a 1999 workshop, "Wind Measurement from  Space" .  (See sec. 4.4, p. 19, of the workshop report.)

Scatterometry
[MERS at Brigham Young University has a good introduction to scatterometery.]

Traditionally, data on winds over the open ocean has had wide gaps, relying upon reports from ships at sea, bouys, and coastal stations.  Space-based remote sensing of winds has greatly increased the available data over the 70 percent of earth’s surface that is covered by water.  The results have dramatically improved early detection of severe storms.  They are also being incorporated into climate models.  Relevant to wind energy generation, this satellite data is now being integrated into wind atlases prepared for coastal and island areas.

Satellites use radar scatterometry to estimate wind speed and direction over open water.  The actual reflecting (or “backscattering”) surface is ripples on the ocean surface.  Small, centimeter-sized waves, caused by wind, give back stronger backscatter as the ocean surface roughens.  Analysis of the data is complex because, for individual ground resolution cells, there is no unique solution for wind speed and direction.  In one procedure, called point-wise wind retrieval, possible solutions (based on multliple measurements made at differing angles) are correlated, ranked in probability, and selected based on best-fit with adjacent cells. The development of algorithms for point-wise and field-wise wind retrieval is a subject of ongoing research. 

Illustration of possible wind vectors,
ranked as most probable: blue=1st, red=2nd, green=3rd, aqua=4th
MERS, Brigham Young University

Satellite Missions
The first space-based scatterometry experiments were performed in 1973 and 1974 aboard Skylab.  In 1978, SASS operated successfully for 3 months onboard NASA’s Seasat satellite.  The European Space Agency launched a single-swath scatterometer on ERS-1, and on ERS-2 in 1995.  In 1995 NASA’s dual-swath NSCAT operated for 9 months on Japan’s ADEOS satellite.  When the ADEOS power system failed, NSCAT data had proven so useful that plans for a follow-on mission were sped up, and SeaWinds (with dual pencil-beams rather than earlier fan-beams) has now been operating on the QuikSCAT satellite since 1999.  QuikSCAT was only designed for an operating life of 2 years.  A similar SeaWinds scatterometer will fly on ADEOS-II, which was originally scheduled to launch in February, but will now not fly before November 2002.

NOAA publishes a daily global image of wind estimates from SeaWinds on QuikSCAT.

The SeaWinds systems have 25 to 50 km resolution and cover 90 percent of the earth’s surface each day.  They estimate wind speed within 2 meters/second accuracy over a range of 3 to 20 m/sec and wind direction within 20 degrees.  Data from QuickSCAT are processed and distributed for weather forecasting within 3 hours.  Data for scientific analysis are available within two weeks.

Research Programs
The Microwave Earth Remote Sensing (MERS) Laboratory at Brigham Young University is conducting research on wind field models, point-wise quality assurance algorithms, and field-wise wind retrieval.

The College of Oceanic and Atmospheric Sciences at Oregon State University analyzes near-surface wind speeds and directions measured by satellite-borne radar scatterometers to provide essential insight into atmospheric forcing of upper ocean processes and climatically important air-sea interactions on many scales.  Relevant research reports to include "Orthographically Modified Winds," "Satellite Observations of Wind Jets off Central American," and "Sampling Errors in Wind Fields Constructed from Single and Multiple Scatterometer Datasets."

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