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The Optical Transient Detector (OTD) is a highly compact
combination of optical and electronic elements. It was developed
as an in-house project at NASA's Marshall Space Flight Center in
Huntsville, Alabama. The name, Optical Transient Detector,
refers to its capability to detect the momentary changes in an
optical scene which indicate the occurrence of lightning. The
OTD instrument is a major advance over previous technology in
that it can gather lightning data under daytime conditions as
well as at night. In addition, it provides much higher detection
efficiency and spatial resolution than has been attained by
earlier lightning sensors.
At the heart of the system is a solid-state optical sensor
similar in some ways to a TV camera. However, in overall design
and many specific features, OTD had to be uniquely designed for
the job of observing and measuring lightning from space. Like a
TV camera, the OTD has a lens system, a detector array (serving
a function somewhat analogous to the retina in the human eye),
and circuitry to convert the electronic output of the system's
detector array into useful data.
The sensor system (camera) is approximately 8 inches in diameter
and 15 inches high, while the supporting electronics package is
about the size of a standard typewriter. Together, the two
modules weigh approximately 18 kilograms (40 pounds). The total
weight of the satellite placed on orbit is 75 kilograms (165
pounds).
Additional information available at
"http://thunder.msfc.nasa.gov/otd/"
[Summary provided by NASA]
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