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Lightning Detection and Ranging System

This system provides relatively comprehensive indications of lightning activity in the vicinity.

John F. Kennedy Space Center, Florida

The Lightning Detection and Ranging (LDAR) system is a network of lightning-monitoring stations at Kennedy Space Center. The LDAR system contains equipment for measuring and indicating the three-dimensional locations and times of lightning flashes that have occurred within distances up to tens of kilometers. The LDAR system enables weather forecasters to give timely warnings of imminent lightning hazards that can affect local outdoor activities, and to terminate the warnings with confidence when lightning no longer poses a danger.

The LDAR system includes seven stations: a central observing/controlling/computing station and six remote observing stations in a somewhat irregular hexagonal pattern (see figure). The remote observing stations are approximately 8 km distant from the central station. Each observing station continuously detects radiation in a frequency band centered at 66 MHz and amplifies the detected signal enabling the system to handle signals with the wide dynamic range typical of those from lightning.

The position from which a signal originated (the presumed location of the lightning flash) can be computed from the speed of light, the differences among the times of arrival of the signals, and the known positions of the stations. The speed of LDAR system electronics allows timing resolution as fine as 10 ns. Measurements from the central station and three remote stations are necessary for this computation. Because the system contains six remote stations, the system consists, in effect, of two subsystems, one of which can be regarded as redundant. The resulting overdeterminacy in the data provides indications of the quality of the data: if locations of the same lightning flash computed from different nonredundant subsets of the data are acceptably close to each other, then an average of the locations is accepted and displayed; otherwise, the data from the particular lightning flash are regarded as unreliable and the location is not displayed.

The LDAR system offers numerous advantages over other lightning-monitoring systems, both governmental and commercial. One advantage is sensitivity: Whereas most other systems locate only cloud-to-ground lightning, the LDAR system detects and locates essentially all lightning, including inter- and intracloud strokes. As a result, the LDAR system detects lightning at least as early as other systems do (sometimes 10 to 20 min earlier), thereby providing greater warning lead times. Also, because the LDAR system detects more of the lightning activity, forecasters can have greater confidence in terminating warnings, sometimes as much as an hour earlier than would be necessary when using other lightning-monitoring systems.

The LDAR system also provides more comprehensive information on the evolving three-dimensional distribution of lightning activity in the vicinity. A typical commercial system locates one point per flash or return stroke, whereas for one flash, the LDAR system locates an average of about 200 points, covering an average ground area of 11.4 km2. Commercial lightning-monitoring systems generally provide only two-dimensional location data with errors of the order of 2 km, whereas the LDAR provides radarlike three-dimensional location data with errors of 150 m.

The LDAR information creates heretofore unavailable insight into storm electrification processes, yielding data on lightning core heights and their meteorological dynamics. This ability could potentially lead to such benefits as improved microburst warnings for airports and passengers, in addition to obvious research implications. On a second-by-second basis, from the displayed structure of lightning sources, a user can determine whether a lightning core is vertical or geographically dispersed. The lightning core is easy to discern, as detected lightning sources extend from the ground to a height of 16 km. The stratified regions of the lightning activity are also evident and provide valuable information about the maturity of a storm.

The LDAR System includes a central station display and 6 remote stations that monitor radiation at a frequency of 66 MHz to detect lightning flashes. The location of a flash is computed from differences among the times of arrival of signals from that flash at the various stations. This work was done by Thomas O. Britt, Carl L. Lennon, and Launa M. Maier of Kennedy Space Center. No further documentation is available. Inquiries concerning rights for the commercial use of this invention should be addressed to the Patent Counsel, Kennedy Space Center; (407) 867-2544. This technology is being developed through NASA's Dual Use Technology Development Program, where NASA and their partner Global Atmospherics, Inc., are jointly funding the developmental effort. Inquiries concerning the commercial use of this technology should be addressed to

Ken Cummins, VP Engineering Global Atmospherics, Inc. 2705 East Medina Rd. Tucson, AZ 85706-7155 Tel.: 1-520-741-2838

Refer to KSC-11785, volume and number of this NASA Tech Briefs issue, and the page number.

 

 

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