Current Technology of the New Mexico Tech Lightning Mapping Array

Substantial advances have recently been made in the technology of the Lightning Mapping Array (LMA), both in the construction of individual stations and in the ease of setting up and operating networks. The use of solid state disk drives has eliminated the need to cool the station electronics and allows the electronics to be placed in an RF-tight enclosure. In turn this has allowed a) the stations to be operated reliably from solar power, b) the VHF receiving antenna to be placed in the immediately vicinity of the electronics without RF feedback or interference, and c) the station to have a compact modular construction, typically with a 4' x 4' square footprint on the ground and self-supporting 10' masts for the VHF and communications antennas. Communications with the stations are achieved by use of broadband cellular modems, rather than dedicated wireless and/or hardwire links. The stations thus operate on a completely standalone basis, enabling them to be easily deployed and placed in remote or other RF-quiet environments for excellent sensitivity.

In typical operation, an LMA station determines and records (on the local hard drive) the time of the peak VHF signal every 80 microseconds. Overall timing accuracy is typically 30 ns rms, and recording thresholds as low as -85 to -90 dBm are readily achieved in RF-quiet locations. For real time processing the data are decimated to the peak arrival time every 400 microseconds. The resulting low rate (~4 kB/sec) decimated data are transfered at one minute intervals over the cellular network to a remote central processing computer, where they are processed to determine source locations and a variety of image files are generated. Images are generated both of the individual source locations (useful for storms with low lightning rates) and of the log density of source locations. Images are posted on the web of the most recent 10- or 2-minutes of lightning activity, automatically refreshed every minute with a latency of about two minutes. For an example see http://lighting.nmt.edu/colma/current.

In addition to the stand-alone image files (which have state and county borders for reference), geo-referenced images with transparent backgrounds are also generated. These geo-referenced images can be loaded with a KML file as a layer to overlay on Google Earth. This allows comparison with other Google Earth layers, such as NEXRAD radar data or research instrument tracks. In addition to generating images, the one-minute source-location ascii text files can be sent to other users for ingest in such things as nowcasting systems. Archival web pages are also produced (e.g., see http://lightning.nmt.edu/colma), containing processed data files and images for successive one-hour and ten-minute time intervals.

The above approaches have been utilized in establishing the North Colorado and Houston LMAs. Data from the CO LMA was utilized to help guide research aircraft during the recent DC3 study. A similar network is currently being setup in Southern France for operation during HyMeX in September and October.