Douglas Isbell
Headquarters, Washington, DC                    April 12, 1996
(202/358-1753)

Steve Roy
Marshall Space Flight Center, Huntsville, AL
(205/544-0034)


RELEASE: 96-72

TANTALIZING DISCOVERIES MARK FAST-TRACK 
LIGHTNING DETECTOR'S FIRST YEAR OF OPERATION

    During its first year in orbit, a NASA lightning monitoring 
instrument called the Optical Transient Detector has uncovered 
tantalizing links between space-based lightning measurements 
and the intensity of severe storms.

    Launched into Earth orbit on April 3, 1995, by an Orbital 
Sciences Corp. Pegasus rocket, the orbiting detector has 
produced the first high-quality images of lightning on a global 
scale, according to principal investigator Dr. Hugh Christian 
of the Global Hydrology and Climate Center, Huntsville, AL.

    "Using the instrument we have determined that, in some 
cases, there are up to 20 times more lightning flashes within 
clouds than observed by the ground-based network," Christian 
said.  "This is significant because lightning flash rates offer 
the intriguing possibility of assisting predictions of tornado 
formation." 

    Data from the instrument shows that severe thunderstorms 
tend to produce lightning within clouds while the storms are 
building, and then more of a mixture of cloud and ground 
lightning as the storms dissipate.  The quanity of cloud-to-
ground lightning strikes, which can be detected by the present 
ground-based network, increase only after the storm has 
matured.  "This case study indicates that space-based 
observations may provide a more advanced warning of severe 
weather," said Christian.

    The instrument also has observed that more lightning is 
produced during the northern hemisphere summer than during the 
southern hemisphere summer.

    The experiment was made possible by a streamlined design 
and development approach for a new technology system.  

    "This highly compact lightning detector represents a 
sophisticated new research tool in space," said project manager 
Roger Chassay of the Science and Applications Projects Office 
at the Marshall Space Flight Center, Huntsville, AL .  "The 
Marshall team placed the lightning detector development on a 
fast track when given the opportunity to fly the instrument on 
the Orbital Sciences Corp. satellite, Microlab-1."

    The detector was built, tested, and delivered in less than 
a year.  "Our experience clearly shows that, for payloads 
involving small-to-medium size and complexity, we can 
definitely streamline the development process and provide 
flight hardware of high quality that produces valuable new 
science."

    The Optical Transient Detector is a highly compact 
combination of optical and electronic elements.  The optics and 
the electronics are a little bigger than a two-pound coffee can 
and a typewriter, respectively.  In spite of its small size, 
the detector represents a major advance over previous 
technology, given its ability to detect lightning under bright, 
daytime conditions as well as at night.  

    The Optical Transient Detector is a pathfinder for a 
follow-on lightning detector called the Lightning Imaging 
Sensor, scheduled for launch in 1997 by a Japanese rocket on 
the Tropical Rainfall Measuring Mission spacecraft.  
    
    "Looking to the future, this instrument is showing us that 
lightning observations from geostationary orbit could be very 
valuable for severe weather prediction and warnings," said 
Christian.
    
    Data from the lightning detector is analyzed by scientists 
at the Global Hydrology and Climate Center.  The center is 
operated under cooperative agreement between NASA, the 
University of Alabama in Huntsville and the Universities Space 
Research Association. 

    Images and motion sequences of Optical Transient Detector 
cloud and lightning observations are available via the World 
Wide Web at the following URL:

    http://wwwghcc.msfc.nasa.gov:5678/otd.html 

                          -end-