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For Release: November 5, 1997
|NASA Takes Step Toward Improved
Severe Weather Analyses and Forecasts
The launch of NASA's Lightning Imaging Sensor aboard the Tropical Rainfall Measuring Mission set for Nov. 18 will be an important step toward a day when weather forecasters will be able to use real-time lightning data from space-based instruments for their routine forecasts and severe storm warnings.
The lightning sensor will help to pave the way for a future space-based lightning mapper that could deliver day and night lightning information to a forecaster's workstation within 30 seconds of occurrence -- providing an invaluable tool for storm "nowcasting" and giving people more advance warning of severe storms.
The Lightning Imaging Sensor was developed by the Global Hydrology and Climate Center at NASA's Marshall Space Flight Center in Huntsville, AL., with contributions from Lockheed Martin in Palo Alto, Calif., and Kaiser Electro-Optics Inc., in Carlsbad, Calif.
The small, sophisticated instrument will provide information on cloud characteristics, seasonal and yearly variability of thunderstorms, precipitation, the Earth's water cycle, storm dynamics, and the release of latent heat.
This lightning detector is three times more sensitive than its predecessor, the Optical Transient Detector -- a lightning detector launched in April 1995. "Lessons learned from the currently orbiting detector have provided valuable input for the development and future use of the new detector," said Dr. Hugh Christian, the project's principal investigator and Marshall Center scientist.
"The Lightning Imaging Sensor will study both day and night cloud-to-ground, cloud-to-cloud and intra-cloud lightning as well as its distribution around the globe," said Christian.
The lightning detector is a compact combination of optical and electronic elements that includes a unique form of an electronic eye known as a staring imager, capable of locating and detecting lightning within individual storms. The imager's field of view from its low-Earth orbit allows the sensor to observe a point on the Earth or a cloud for 80 seconds. "This allows sufficient time to estimate the flashing rate, and may often be sufficient to indicate whether a storm is growing or decaying," said Christian.
The staring imager is comprised of an expanded optics lens system which provides a wide field of view, and a narrow-band filter which minimizes background light. A device within the imager -- behaving similarly to the retina of the human eye -- creates an image of the lightning and the background scene. After the image is created, a real-time event processor extracts the signal, determining when a lightning flash occurs.
This event processor allows the detection of lightning even in the presence of bright sunlit clouds. Weak lightning signals that occur during the day are hard to detect because of the strong background illumination.
"It is designed to detect 90 percent of all lightning strikes. It records the time of a lightning event, its radiant energy -- how bright the lightning flash is -- and an estimate of the lightning's location," said Christian.
As part of the Tropical Rainfall Measuring Mission, the Lightning Imaging Sensor will contribute to NASA's Mission to Planet Earth program, aimed at gaining a better understanding of how the Earth functions as a system, and how this system is being influenced by the rapid growth of the human population.
The mission is the first Earth science satellite dedicated to studying the properties of tropical and subtropical rainfall. Tropical rainfall -- all rain that falls within the zone 35 degrees above and 35 degrees below the equator -- comprises more than two-thirds of global rainfall. More precise information about this rainfall and its variability is crucial to understanding and predicting global climate change.
The joint NASA and Japanese Space Agency mission is scheduled to be launched on an H-II rocket from the Tanegashima Space Center in Tanegashima, Japan on Nov. 18, at 3:40 p.m. EST (Nov. 19, 5:40 a.m., JST).
Prepared by Kelly McFalls