evaluation of hand-held lightning strike...

Evaluation of hand-held lightning strike detectors

Jeff Wimer , Ph.D., ATC Alex DeCaria, Ph.D.

Hank Fijalkowski, MS, ATC

http://www.millersville.edu/index.php

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 = 2%

Little trust the device works as directed = 17%

Some trust the device works as directed = 71%

Full trust the device works as directed = 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 ‘false-alarm’

• 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.


• Known to be less reliable than multiple station techniques.

• Higher false-alarm rate.

– No independent sensors to cross-check.


• 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 NLDN Strikes Detection Efficiency Range Efficiency

5/16/2007 126 96 65

7/11/2007 55 100 76

Date NLDN Strikes Detection Efficiency Range Efficiency

5/16/2007 96 100 42

7/11/2007 55 98 36

SkyScan

StrikeAlert

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





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?

evaluation of hand-held lightning strike...

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