Evaluation of hand-held lightning strike detectors

Evaluation of hand-held lightning
strike detectors
Jeff Wimer , Ph.D., ATC
Alex DeCaria, Ph.D.
Hank Fijalkowski, MS, ATC
Questionnaire: administered fall 2008
n = 338 (37% return rate)
1. Do you use handheld lightning detection
devices in your work setting?
Yes = 58%
No = 41%
2. Is the use of handheld lightning detection
devices cited in your Emergency Action Plan
or other policy documents.
Yes = 38%
No = 61%
3. Have you ever used a handheld lightning
detection device by itself to convince a
coach, referee, parent or administrator to
suspend play or practice?
Yes = 40%
No = 60%
4. If you use a handheld lightning detection
device is it your sole source of
information in determining lightning
danger?
Yes = 40%
No = 60%
5 On a scale from 1-4 with 1 being the lowest
and 4 the highest, how much trust (i.e. faith)
do you have in handheld lightning detection
devices?
No trust the device works as directed =
Little trust the device works as directed =
Some trust the device works as directed =
Full trust the device works as directed =
2%
17%
71%
9%
Types of Lightning
• Intracloud
– Never touches ground
– Most frequent
– Not dangerous to persons on ground
• Cloud-to-ground
– Dangerous to persons on ground
– Main focus of commercial lighting detectors
Lightning Detection
• Lightning emits radio-frequency (RF)
radiation.
• AM radio very good at detecting
lightning.
Lightning Location
• The most accurate methods use
multiple stations and direction and/or
time-of-arrival (TOA) information.
Direction Finding
Time-of-Arrival
Lightning Detection Networks
• National Lightning Detection Network
(NLDN).
– Since the 1990’s
– Owned by Vaisala, Inc.
• U.S. Precision Lightning Network
(USPLN)
– Recent competitor
– Owned by WSI, Inc.
National Lightning Detection Network (NLDN)
Images courtesy of Vaisala, Inc.
National Lightning Detection Network (NLDN)
• Self-reported mean position error of
less than 1 km.
• Self-reported, negligible false alarm
rate.
– 1 of 10,000 strikes have significant position
error that can be categorized as ‘falsealarm’
• Reports cloud-to-ground strikes only
Single-station Techniques
• Use direction finding along with
technique to determine distance.
• Distance techniques
– Strength-of-signal technique
– Signal-shape technique
Strength-of-Signal Technique
• Closer strikes have stronger signal
• Assumes all strikes have same initial
signal strength
• Not very accurate, since strength of
initial signal varies widely
Shape-of-Signal Technique
• Ratio of signal at different frequencies
changes with distance
Shape-of-Signal Technique
• Ratio of S1/S2 correlated with distance.
Single-station Techniques
• Known to be less reliable than multiple
station techniques.
• Higher false-alarm rate.
– No independent sensors to cross-check.
Single-station Techniques
• Used by portable, hand-held lighting
detectors.
• Marketed primarily to hikers, athletes,
construction workers, etc.
• Not used by airports, military, National
Weather Service, etc.
Lightning Detection Business Model
• Make money by selling information
• Information is highly proprietary.
– Even NWS buys lightning information.
– Techniques are proprietary
– NLDN and USLPN more transparent than
marketers of hand-held devices, since data
also used by researchers.
Portable, Hand-held Lightning Detectors
• Specific techniques are highly guarded.
• No independent verification allowed.
• Must rely on word of manufacturer.
Method
• Videotape portable lightning detectors
during lightning activity
• Compare results with NLDN
Detectors Used
SkyScan
StrikeAlert
Thunderbolt
Detectors
• SkyScan (purchased)
• StrikeAlert (supplied by manufacturer)
• Thunderbolt by Spectrum Electronics
(supplied by manufacturer)
• No agreements with made with
manufacturers for review of results
Difficulties
• Detectors do not have data ports for
data logging.
• Had to videotape detectors and
manually transcribe data to
spreadsheet.
• Needed accurate time stamp (within 1
second)
• Had to shelter detectors from rain,
strong wind
Data Analysis
• Created spreadsheet to show status of
detectors at 1 second interval.
• Created separate spreadsheet showing
NLDN lightning activity occurring within
40 miles of detectors.
Data Analysis (SkyScan/StrikeAlert)
• For every NLDN strike within 40 miles,
recorded if detector had a “hit” or a
“miss” for detection only.
• For every NLDN strike within 40 miles,
recorded if detector placed strike within
proper range bin.
Data Analysis (SkyScan/StrikeAlert)
• Used data at t, t  1, and t + 1 to
account for possible clock error.
• Allowed 1 mile range-bin overlap to
account for possible NLDN position
error.
Results (SkyScan/StrikeAlert)
Date
SkyScan
Range Efficiency
5/16/2007
126
96
65
7/11/2007
55
100
76
Date
StrikeAlert
NLDN Strikes Detection Efficiency
NLDN Strikes Detection Efficiency
Range Efficiency
5/16/2007
96
100
42
7/11/2007
55
98
36
Results (Thunderbolt)
• Difficult to quantify, since display is text
rather than LED’s.
• Handout shows tables for Thunderbolt,
with highlighted cells showing data that
are not consistent with NLDN data.
Thunderbolt Example Results
t (sec.) Miles
t 1
t
t+1
63280
18
local activity possible
local activity possible
local activity possible
63288
17
local activity possible
closest strike 1 mile
closest strike 1 mile
63294
20
closest strike 1 mile
closest strike 1 mile
closest strike 1 mile
63321
17
closest strike 1 mile
closest strike 1 mile
closest strike 1 mile
63333
27
closest strike 1 mile
closest strike 1 mile
closest strike 1 mile
63335
20
closest strike 1 mile
closest strike 1 mile
closest strike 1 mile
63340
18
closest strike 1 mile
closest strike 1 mile
closest strike 1 mile
63357
20
local activity possible
local activity possible
local activity possible
63377
18
warning strikes detected
warning strikes detected
warning strikes detected
Summary
• Devices Used
(results from
questionnaire)
– Skyscan 37%
– Strike Alert 6%
– Thunderbolt 1%
Summary
• Handhelds - 99% detection efficiency
• Handhelds at most 70% efficient at
determining distance
• More than 50% of AT’s polled use a handheld
lightning detection device.
• More than 1/3 of AT’s polled site them in
their EAP’s
Summary
• 40% of AT’s polled use them as sole source
of information
• 70% of AT’s polled have “Some trust the
device works as directed”
Conclusion
• Handheld Lightning Detectors are not
accurate at determining lightning strike range
• The AT using a handheld device needs to
account for this when determining suspension
of play and resumption of activities.
• Handhelds should be used as an adjunctive
source of information along with internet
radar maps and “Flash-to-Bang” measures
Other Options – Weather Service
•
DTN/Meteorlogix
– Lightning Manager
• Real time, actual Lightning strike information
• alerts you when lightning is in an advisory zone
from your address
• alert when lightning is in your warning zone
• alert when it is All CLEAR and you can resume
play
• Up to 18 persons can be set-up to receive TEXT
ALERTS or email alerts per subscriber.
• Lightning strikes can be visualized on web
radar or mobile access
Other Options – Weather Service
•
Subscription Cost
– $1060 / month for minimum one year
– Option to bundle with up to 5 other
institutions with significant discount
– Discount can range from $70.00 - $90.00
per month
– Great idea for conferences
Thank You!
Questions?