Lightning Detection and Ranging (LDAR) Dataset
Table of Contents
Summary
This document provides basic information on the Lightning Detection and Ranging (LDAR) instrument, the data file format, and the software that is used to extract the lightning data from the files.
NOTE: This dataset is now static, with a starting date of February 28, 1997, and a stopping date of June 11, 2008.
Lightning Detection and Ranging (LDAR)
The Lightning Detection and Ranging (LDAR) system is located at the Kennedy Space Center. The center lat/long of the LDAR network is 28.5387 and -80.6428. All x, y, and z values represent distance (in meters) from this location. LDAR is a volumetric lightning mapping system providing near real-time location of lightning in support of Space Shuttle operations. It consists of seven antennas, microwave and land line communication between the outlying antennas and the central station, and a central processing facility located at the central station. Data are collected by Lincoln Labs and pushed to GHRC on a daily basis.
The LDAR central station located at antenna #1 is surrounded by six additional antennas arranged in a hexagonal pattern from 6 to 10 km away. Each site is comprised of an antenna to detect the 66 MHz VHF pulse of an intracloud event, and an electric field detector which monitors the electric field change (K change) associated with a cloud to ground strike. Data arrives at the central site from the six outlying antennas on a continual basis via either microwave or land line transmission at a rate of 6 MHz. With a time resolution of 10 nanoseconds, the time and amplitude of the peak signal are input to the central workstation from each antenna for event calculation.
Determination of the event location is found in the following manner. Only four of the seven sites are required to obtain a location for each source. With seven sites receiving the signal and requiring that the central site participate in all solutions, there are 20 possible combinations of 4 sites. Two of the 20 combinations are optimal for minimizing location errors for all x,y, and z values. If each coordinate (x,y,z) from two site combinations agree within 5 percent or 350 meters, whichever is greater, the average x,y and z are used. Otherwise the solution as derived from all 20 combinations are used in determining the event location. In this case, an x,y,z solution is calculated for each of the 20 site combinations. The solutions are inter-compared for consistency and weighted appropriately. If x, y, and z of a given combination agrees within 50r 350 meters, whichever is greater, of another combination, the weight of that solution is incremented by one. The event is located if the weight of any of the solutions exceeds seven, otherwise the location is the solution with the largest weight.
Data Format
Data archived at the GHRC are Raw (Source) data. The GHRC produces daily GIF imagery from the raw data.
Raw Data
Raw data consists of level 1 processed data and is the output of an individual event (K change) location in both time and space. The data are contained in daily tar compressed files named:
ldarraw_yyyy.ddd_daily.tar.gz
Where yyyy is the four digit year and ddd is the day of the year. Hourly data is collected and contained in hourly Packet files. Once uncompressed and untarred the individual files have the form:
LDAR_Packets_yymmdd_hhmmss.asc
Where yy is the last two digits of the year, mm is the month, dd is the calendar date, and hhmmss is the time on a 24 hour clock of hours, minutes and seconds in UTC. The file output is in ASCII form with each line representing the temporal and spatial location of a K change event. An example of actual data appears as follows:
...
23 16 53 32 591358 -26757 -69148 9898
23 16 53 32 600120 -28619 -74354 10628
23 16 53 32 603596 -30781 -80679 12180
23 16 53 32 603728 -27895 -73060 10700
23 16 53 32 642798 -26039 -68447 9894
23 16 53 32 650965 -27387 -71243 9814
23 16 53 32 801970 82929 -60508 10098
23 16 53 32 877638 83748 -61107 8776
23 16 53 33 60986 -807 -55698 4170
23 16 53 33 67516 725 -53679 3151
23 16 53 33 68209 -1758 -54675 3695
23 16 53 33 69511 857 -57520 3730
23 16 53 33 71210 -1984 -56410 4863
23 16 53 33 75900 625 -55021 3413
23 16 53 33 76303 580 -55764 4193
23 16 53 33 80922 -497 -57109 4349
...
Data format is:
dd hh mm ss llllll xxxxxxx yyyyyyy zzzzzz
where
dd = day of the month
hh = hour of day UTC (24 hour clock)
mm = minute
ss = second
llllll = microsecond
xxxxxxx = distance in meters from site #1 in the X (+ to the east) direction
yyyyyyy = distance in meters from site #1 in the Y (+ to the north) direction
zzzzzz = distance in meters above the surface of the Earth
Images
A daily .gif image is produced from raw data. This image is a plot in the xy plane of the location of each flash recorded in a 24 hour period. In addition, above the xy plot is an xz plot which graphically depicts all flashes. Similarly, to the right of the plan view is a yz plot showing distribution of all flash data projected onto that plane. LDAR gif images are available on line at http://lightning.nsstc.nasa.gov/cgi-bin/ldar/ldar_cal.pl.
References
Maier L., Lennon C. L., Britt T., and Schaefer S., 1995: Lightning Detection and Ranging (LDAR) System Performance Analysis. Proceedings of the 6th Conference on Aviation Weather and Systems, Paper 8.9.
Poeher, H.A. and Lennon, C.L,1979: Lightning Detection and Ranging System, LDAR, System Description and Performance Objectives, NASA Technical Memorandum 74105.
Contact Information
To order this data or for further information, please contact:
Global Hydrology Resource Center
User Services
320 Sparkman Drive
Huntsville, AL 35805
Phone: 256-961-7932
E-mail: ghrcdaac@itsc.uah.edu
Web: http://ghrc.nsstc.nasa.gov/
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