|
Description:
|
The Houston LDAR II network is an array of twelve VHF time -of -arrival (TOA )
sensors operated by Texas A &M University . The goals of the network are to conduct indepth
studies of thunderstorm electrification and provide timely lightning threats to the
Houston area . Before analyses are conducted using data from the Houston LDAR
network , it is necessary to understand the LDAR networkâ s performance and limitations ,
such as the LDAR source detection efficiency , network range , and location accuracy .
Initial results from the 31 October 2005 Mesoscale Convective System (MCS )
timing error analysis revealed an RMS timing error for the Houston LDAR network of
90 ns for 6 sensor solutions . This gives a three -dimensional location accuracy of 1 km at
a distance of 150 km and 100 m over the center of the network . Reanalysis with updated
sensor positions decreased the RMS timing error to 75 ns . This decrease in RMS timing
error increased the median three -dimensional location accuracy by ~100 m at a 100 km
range . The network has been operated at both 70 MHz and 40 MHz . Model results of
detection efficiency suggest that the change to 40 MHz yields an increase of 9 - 10 dB in
network sensitivity . Analysis of VHF source power distributions shows a similar shift
from that expected from the model . These results show that the 40 MHz LDAR network
detects ~3 .3 times more VHF sources than the 70 MHz network .
The analysis of the usable network range for research purposes is currently set by
rough guidelines of location accuracy and detection efficiency . For location accuracy , a
1 km limit allows storm analysis out to a range of more than 150 km . For the detection
efficiency analysis , results based on source power distributions suggest a gradual fall off
with range . Examining the change in VHF source density by range reveals different
results . VHF source density remained fairly constant out to a range of 100 km at which
point a significant fall off was observed . Based on these results the usable network
range for the Houston network is 100 km . |