Wildfires are a recurring natural hazard faced by Californians. In Santa
Barbara County, a wildfire, called the Jesusita fire, ignited on May 5,
2009 in the Cathedral Peak area northwest of Mission Canyon. As of midday
May 8, the fire, which was 10-percent contained, had scorched 3,500 acres,
damaged or destroyed 75 structures, and had forced the evacuation of tens
of thousands of residents.
This image shows soil moisture change in the top soil layer (2-inches deep) on
2 and 3 May 2009, as measured by the NASA QuikSCAT satellite scatterometer
(radar). Rainwater increased the amount of moisture in the soil by a moderate
4 percent (represented by the green color) on May 2, which rapidly dried up on
the next day (0 percent, as depicted by the grey color on May 3). Son Nghiem of
JPL is leading a science team to develop wildfire applications using QuikScat data.
“Information critical to assessing the conditions leading to wildfires can be
obtained from NASA’s SeaWinds scatterometer, a stable and accurate radar
aboard the QuikScat satellite,” says Dr. Son Nghiem, a JPL scientist in remote
sensing. This is accomplished by using QuikScat data to map moisture changes
in the topsoil. As such, QuikScat can detect rainwater that actually reaches the
land surface and accumulates on it, rather than raindrops in the air. While rain r
adars may detect a significant rain rate, rainwater may evaporate in part before
reaching the surface. For example, in the case of dry thunderstorm (known as
virga), raindrops disappear on the way down, leaving the land dry, while the
associated lightning ignites fires.
For the case of the current fire in Santa Barbara, QuikScat detected a
moderate increase of 4 percent in soil moisture on May 2, while rain radar
data seemed to indicate a significant and extensive rain. The next day,
QuikScat revealed that whatever rainwater that had accumulated earlier
quickly dried up over the whole area. The maximum temperature in Santa
Barbara approached 90 degrees Fahrenheit and broke the record set in
1984. An important characteristic of QuikScat measurements is that they
represent the average conditions over the whole area, rather than some
disparate data collected at a few localized points. The rapid dry-up in
Santa Barbara together with high temperatures and high winds led to the
devastating Jesusita fire.
Soil moisture information is critical to enhance the capability for Red
Flag Warning and to improve the National Fire Danger Rating System.
QuikSCAT can provide such data.
QuikSCAT, managed by JPL, measures ocean surface wind/stress by sending
radar pulses to the surface and measuring the strength of the signals
returned.
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/missions/quikscat/.
QuikScat is managed for NASA's Science Mission Directorate, Washington,
DC, by NASA's Jet Propulsion Laboratory, Pasadena, CA.