Typhoon Haitang is shown here churning steadily towards Taiwan and China.
This image shows the storm's swirling wind patterns as observed by NASA's
QuikScat satellite on July 14, 2005, at 19:19 UTC (14:19 Eastern Daylight
Time). At this time, the typhoon was located hundreds of kilometers from
the nearest major land masses.
The image depicts wind speed in color and wind direction with small barbs.
White barbs point to areas of heavy rain. The highest wind speeds, shown
in purple, surround the center of the storm.
Measurements of the wind strength of Typhoon Haitang show sustained winds
of around 85 knots and gusts up to 105 knots at the time of the QuickScat
observations. The images, however, reveal lower wind speeds. This is
because the power of the storm makes accurate measurements difficult. The
scatterometer sends pulses of microwave energy through the atmosphere to
the ocean surface, and measures the energy that bounces back from the
wind-roughened surface. The energy of the microwave pulses changes
depending on wind speed and direction, giving scientists a way to monitor
wind around the world.
Tropical cyclones (the generic term for hurricanes and typhoons), however,
are difficult to measure. To relate the radar energy return to actual wind
speed, scientists compare measurements taken from buoys and other ground
stations to data the satellite acquired at the same time and place.
Because the high wind speeds generated by cyclones are rare, scientists
do not have corresponding ground information to know how to translate data
from the satellite for wind speeds above 50 knots (about 93 kilometers per
hour or 58 miles per hour). Also, the unusually heavy rain found in a
cyclone distorts the microwave pulses in a number of ways, making a
conversion to accurate wind speed difficult. Instead, the scatterometer
provides a nice picture of the relative wind speeds within the storm and
shows wind direction.
QuikScat Background
NASA's Quick Scatterometer (QuikScat) spacecraft was launched from
Vandenberg Air Force Base, California on June 19, 1999. QuikScat carries
the SeaWinds scatterometer, a specialized microwave radar that measures
near-surface wind speed and direction under all weather and cloud
conditions over the Earth's oceans. More information about the QuikScat
mission and observations is available at http://winds.jpl.nasa.gov.
QuikScat is managed for NASA's Science Mission Directorate, Washington,
DC, by NASA's Jet Propulsion Laboratory, Pasadena, CA. JPL also built the
SeaWinds radar instrument and is providing ground science processing
systems. NASA's Goddard Space Flight Center, Greenbelt, MD, managed
development of the satellite, designed and built by Ball Aerospace &
Technologies Corp., Boulder, CO. The National Oceanic and Atmospheric
Administration has contributed support to ground systems processing and
related activities.