19QB073_PWS-MERLIN_Low_DE_[13Feb19].pdf

PERFORMANCE WORK STATEMENT

FOR

LOW DETECTION EFFICIENCY OF MERLIN FOR LIGHTNIGN STRIKES TO TALL STRUCTURES AND/OR

LARGE CATENARY WIRE LIGHTNIGN PROTECTION SYSTEMS

(13 Feb 2019)

1. Title: Low Detection Efficiency of MERLIN for lightning Strikes to Tall Structures and/or Large Catenary Wire Lightning Protection Systems

2. Definition/Acronyms:

a. MERLIN – Mesoscale Eastern Range Lightning Information Network; the local lightning locating system used by the 45th Weather Squadron.

b. Detection Efficiency – the frequency of lightning events that is detected and reported by lightning locating systems.

c. Catenary Wire Lightning Protection System – Overhead hanging wires that protect the area beneath them from lightning by intercepting lightning about to strike and diverting the current into an electrical grounding system.

d. CG – Cloud-to-ground, as in cloud-to-ground lightning

3. Background: In general, MERLIN provides excellent cloud-to-ground lightning performance with CG flash detection efficiency over 99% and median location accuracy of about 60 m. However, there has been anecdotal evidence that CG strikes to tall structures and/or large catenary wire lightning protection systems have lower detection efficiency, perhaps as low as 75%.

This apparent low detection efficiency may be due to the strikes being detected but not reported due to the MERLIN quality control algorithms due to the waveforms differing for normal CG strikes, or being wrongly classified as lightning aloft, or being reported with locations far away from the true location relative to the location error ellipses. These large structures and/or large catenary wire systems include launch pads and other important facilities for which detecting and reporting CG lightning strikes is critical. Therefore, the purpose of this project is to determine if the detection efficiency for tall structures/large catenary wire systems is significantly lower than the detection efficiency for MERLIN CG strikes to nearby normal ground. If the detection efficiency for tall structures/large catenary wire systems is significantly lower, make the data on these events available to Vaisala, the MERLIN vendor, to try to tune MERLIN to improve detection efficiency for tall structures/large catenary wire systems without degrading the overall performance of MERLIN. This effort by Vaisala would be done separately from this project.

4. Description: Install a network of high-performance lightning detection and locating system to provide virtually 100% detection efficiency and location accuracy of at least 20 meters of the launch pads. This will be the ground truth for measuring the detection efficiency to these tall structures/large catenary wire systems. We assume this system would require short-range optical detection of the CG lightning strikes and supplemented by short-range electromagnetic CG lightning sensors. This data will be collected for 1-year with the possibility of additional funding for a second and a third year. The U.S. Air Force will provide the MERLIN lightning solutions corresponding to the lightning events for comparison.

The detection efficiency of CG-MERLIN will be calculated against this near-absolute ground truth for strikes to tall structures/catenary wire systems and for nearby strikes to normal ground. A Bayesian statistical method may help supplement this analysis in case MERLIN reports CG strikes to tall structures/catenary wire systems that are not reported by the other system.

Finally, the differences in these two detection efficiencies will be tested to see if the differences are statistically significant to include p-value for the statistical test. If the differences are statistically significant, then the data from the additional lightning system will be provided to Vaisala, the MERLIN vendor, to try to improve the MERLIN detection efficiency for tall structures/catenary wire systems without degrading MERLIN’s performance too much elsewhere.

5. Deliverables:

a. Installation and maintenance of an extremely high-performance lightning locating system to serve as near absolute ground truth for CG strikes to tall structures/large catenary wire systems

b. Collection and analysis of the data from the new lightning locating system and calculation of the MERLIN CG detection efficiencies for tall structures/catenary wire systems and nearby CG strikes to normal ground to include determination if those detection efficiencies are statistically significantly different.

c. Written report documenting the development process and results.

d. Briefing of the development process and results to the 45 WS.

e. Make the lightning case data available to other vendors, if needed, for possible use in improving the MERLIN performance for CG strikes to tall structures and large catenary wire lightning protection systems.

6. Point of Contact: William Roeder, 45 WS/SYS, william.roeder@us.af.mil, (321) 853-8410

7. References: None mailto:illiam.roeder@us.af.mil