On-orbit Validation Of The Geolocation Accuracy Of GOES-16 .

On-orbit validation of the geolocation accuracy ofGOES-16 Geostationary Lightning Mapper (GLM)flashes using ground-based laser beaconsDennis Buechler, University of Alabama Huntsville (USA); Tom Varghese,Cybioms Corp. (USA); Peter Armstrong, MIT Lincoln Lab. (USA); JamesBremer, ASRC Federal Holding Co. (USA); Rivers Lamb, NASA GoddardSpace Flight Ctr. (USA); Jon Fulbright, Arctic Slope Tech Services (USA);Steven Goodman, Thunderbolt Global Analytics (USA) [10764-18]August 21, 2018

Geostationary Lightning Mapper (GLM)The GLM data shown in this presentation

Geostationary Lightning Mapper (GLM)New Instrument on GOES-R Series SatellitesNatural Hazards and Lightning Tornadoes Hailstorms Wind Thunderstorms Floods Hurricanes Volcanoes Forest Fires Air Quality/NOx

GLM OverviewSpaceborne Instrument parametersStaring sensor with truncated 8o radius circular FOVAt nadir 30x30 mm pixel has 8x8 km footprintPixel pitch decreases with increasing field angleto minimize footprint growth1372x1300 pixel array, single spectral band: l 777.4 nm Dl 1 nm503 Hz frame rateOnboard processing (Real Time Event Processor [RTEP])Signal in each pixel compared to background (average of previoussignals in same pixel)Event detected when Pixel Signal Threshold BackgroundBackground saved every 2.5 minutes and used for image navigationGround processingLightning flash declared when 2 spatially overlapping groups are detected within 1/3 secFlashes at same frame time & adjacent pixels groupedSW filters eliminate cosmic ray streaks, contrast leakage, sun glints, etc.Can detect lightning against 100x brighter cloud background

GLM’s Coverage from GEO @ 89.5o W(intersection of 2 curves)Mon. Pk.116.4o W32.8o NGLM fieldangleqx 3.72o W,qy 5.26o NGSFC76.5o W39.0o NGLM Fieldangleqx 1.67o E,qy 6.11o N8oMax field angleUsing MOBLAS sites within the USA minimizes cost & requirements (e.g. ITAR)

Optical Lightning Detection: How it worksLightning from Space: Lightning appears like a pool of light on the top of the cloud as thedischarge lights up the cloud.Daytime Challenge: During day, sunlight reflected from cloud top dominates the lightningsignal. Daytime lightning detection drove the design.Solution: Special techniques are applied to extract the weak, transient lightning signal fromthe bright, background signal.SpatialSpectralTemporalOptimal samplingof lightning scenerelative to background scene.Optimal samplingof lightning signalrelative to background signal.Optimal samplingof lightning pulserelative to background signal .Pixel field-of-view4-10 km.LIS uses 1nm filterat 777.4 nm.LIS uses 2 msframe rate. Even with spatial, spectral and temporal filters,background can exceed lightning signal by 100 to 1 atthe focal plane. The final step is a frame-by-frame backgroundsubtraction to produce a lightning only signal Filtering results in 105 reduction in data raterequirements while maintaining high detectionefficiency for lightning .BackgroundSubtractionOptimal subtractionof background signallevels at each pixel.Transient eventsselected forprocessing.ISS ImageApril 30, 2012

Events Clustered to FlashesGroups - Eventsthat occur at sameframe time inadjacent pixelsFlashes – Groupsthat occur closetogether in spaceand time

Events Clustered to Flashes (cont’d)A flash is ended when nonearby groups occur for 1/3 s.GLM products – Geolocated (latitude, longitude), calibrated (i.e., radiant energy) events,groups , and flashesEvent geolocation – pixel latitude, longitude adjusted to specified cloud top heightGroup geolocation – Radiance weighted mean event locationFlash geolocation – Radiance weighted mean group location

Why are Laser Beacons Beneficial? The GLM’s lightning detections must be navigated to 140 mrad (3s) to providegeographically accurate severe weather warnings. The GLM’s error budget allocation is 112 mrad (3s). The primary image navigation with respect to land features in the background Earthimagery is only useable from 1000-1400 hours satellite time Navigation is extrapolated for entire day assuming GLM’s FOV is fixed with respect toGOES-16’s attitude reference from startrackers Thermal gradients can change the boresight between the GLM & the startrackers. Theyare most severe at night when the satellite’s nadir surface is sunlit. The GLM’s wide-FOV lens assembly contains a large number of refractive elements.Misalignments among them can change boresight, focus & plate scale. Radiation canchange indices of refraction over the lifetime of the mission. Ground and space based observations of lightning are not necessarily co-located The beacon measurements provide unambiguous control points throughout the diurnalcycle that can be used to verify the image navigation algorithm and the GLM opticalmodel or, if necessary, modify them.

Laser h (l)777.2 0.3 nmGLM’s central l at 6.4o field anglePulse RepetitionFrequency (PRF)50 HzMin PRF 3 Hz Coherency filterMax 100-200 Hz for threshold relaxationPulse Duration (t)1.5 msecMaximize power from CW laser & minimize framesplitting (1.8 msec exposures)Receivedenergy/pulse 50,000 photo-e’s 1,500,000 photo-e’sExceed threshold by 10x to permit centroidingPrevent saturationMode/polarizationMostly TEM00Polarization not criticalMaximize received energy

GLM Beacons use MOBLAS Satellite Laser Ranging (SRL) FacilitiesBeacons share existing MOBLAS pointing &tracking systems, and co-boresighted radar withshutter (Facilitates GSFC Code 350, FAA & LCHsafety approval)MOBLAS sites at Greenbelt, MD & MonumentPeak, CA provide a long baseline within theGLM’s FOV for GOES-16 & 17 during PLT (89.5oW) & for GOES-16 operating as GOES-E (75.2o W)Laser beacon pulses transmits 1.5 ms pulses @50 Hz & 777.2 nm (optimized for field angles)Identical detection & processing for naturallightning & beacon pulsesNo operational accommodation required forsatellite nor interference with other instrumentsMOBLAS Station (above)Laser located inside station laser room &fiber coupled to telescope (important forsafety, T & l control)

GLM Beacons use MOBLAS Satellite Laser Ranging (SRL) Facilities Advantages of MOBLAS Laser Facilities: The piggybacked beacon telescope-fiberoptics assembly on top of the NASA SLRtelescope at the MOBLAS facility.Already staffedStaff trained in satellite pointing usingephemeris dataAbility to perform GLM beacon operationsalong with normal SLR operationsCost effectiveGreenbelt, MD (MOBLAS 7)Monument Peak, CA (MOBLAS 4)

Laser Beacon Web Page GLM Laser Beacon Operations Need ability to monitor GLMactivity at laser beacon sites Near Real time web display wasdeveloped GLM L2 data obtained viaNOAA PDA (ProductDistribution and Access) Display latency of 1-2 minutesThese GOES-16 data are preliminary, non-operational data and are undergoing testing. Users bearall responsibility for inspecting the data prior to use and for the manner in which the data are utilized.

Laser Beacon Web Page: Real Lightning ExampleThese GOES-16 data are preliminary, non-operational data and are undergoing testing. Users bearall responsibility for inspecting the data prior to use and for the manner in which the data are utilized.

Laser Beacon Test Procedure The satellite ephemeris was obtained weekly from NOAA Used to determine pointing angles Schedule dates 1-2 weeks in advance Notify NOAA so user notifications can be sent out Monitor weather conditions at sites Morning of test confirm go/no go based on: Weather (clouds or high winds) Personnel Data availability Start web tool for monitoring test Hosted on the GOES-R Field campaign web site15

Laser ment PkApril 19, 20170152-0352GBApril 29, 20170055-0200GBMay 3, 20171720-1850GBMay 8, 20171730-1840GBJune 9, 20171645-1710GBJune 11, 20170300-0340GBJune 13, 20171700-1712GBJune 24, 20170420-0510MPJune 28, 20171750-1754GBJuly 13, 20170339-0715GB & MPAug 10, 20170225-03231440-1552GB & MPGB & MPSep 5, 20171405-1455GB & MPNotesditherditherVery few eventsNightDay16

Laser Operations ument PkSep 21, 20171450-16551850-1830GB & MPGB & MPOct 2-3, 20171020/2-1409/3GB & MPNov 28, 20170340-0425GBNov 29, 20170250-03202149-2215GB & MPGB & MPNov 30, 20170350-0415GB & MPDec 19, 20172115-21302200-2240MPGB & MPDec 20 , 20170010-00450155-0225GB & MPGB & MPJan 5, 20180018-00402250-2328GBGB & MPJan 6, 20180210-0240GB & MPJan 17, 20182225-2255MPJan 18, 20180150-02100445-0515GB & MPGB & MPNotes24 hr test (hourly obs)At 75.2 W17

Results: Time SeriesThese GOES-16 data are preliminary, non-operational data and are undergoing testing. Users bearall responsibility for inspecting the data prior to use and for the manner in which the data are utilized.

Results: EventsThese GOES-16 data are preliminary, non-operational data and are undergoing testing. Users bearall responsibility for inspecting the data prior to use and for the manner in which the data are utilized.

Results: GroupsThese GOES-16 data are preliminary, non-operational data and are undergoing testing. Users bearall responsibility for inspecting the data prior to use and for the manner in which the data are utilized.

Results: FlashesThese GOES-16 data are preliminary, non-operational data and are undergoing testing. Users bearall responsibility for inspecting the data prior to use and for the manner in which the data are utilized.

Summary and Conclusions Demonstrated laser signal can be detected by GLM The laser signal detected by GLM passes through the GPA as lightning Developed a methodology for real time monitoring of GLM laserlightning Verified that the GLM “lightning” flashes were within 5 km The offset was also less than 5 km at 0500 UTC 01/18/2018 laserbeacon period Laser operations now underway for GOES-17 Further analysis of GOES-16 and GOES-17 datasets

GLM backgrounds and lightning with laser beacon signalhttps://www.youtube.com/watch?v Uf9C-yr9iaAThese GOES-16 data are preliminary, non-operational data and are undergoing testing. Users bearall responsibility for inspecting the data prior to use and for the manner in which the data are utilized.

Thanks

Back-up Charts

No Plausible Damage to the GLM or the ABIBoth GLM and ABI required to survive direct Sun in the FOV for 2 minWorst-case laser illumination of GOES-R (requiring major errors by beaconoperators) won’t damage the GLM or the ABI1. GLM laser beacon operated in CW mode:890x weaker than direct sunlight in a single pixel2. Wrong laser: Nd:YAGx2 @ 532 nm:Not focused on ABI’s FPA (Blocked by spectral filters)ABI Band 1:450-490 nmNd:YAGx2532 nmABI Band 2:600-680 nmGLM & Beacons777 nmABI Band 3:850-880 nml

Beacon parameters for GOES-EParameterBeacon AzimuthBeacon ElevationRangeGLM E/W field angleGLM N/S field angleGLM E/W pixel pitchGLM N/S pixel pitchGSFC to GOES-E177.09o44.81o37,422 km0.24o W6.13o N30 mm22 mmMon. Pk. To GOES-E121.58o31.64o38,466 km5.31o W5.16o N24 mm24 mm

Beacon Parameters for GOES-W @ 137oW(GSFC lies outside the GLM’s FOV)ParameterBeacon AzimuthMon. Pk./GOES-W214.68oTahiti/GOES-W36.55oMt. Haleakala/GOES-W135.31oBeacon Elevation45.79o64.81o57.34oRangeGLM E/W field angle37,355 km2.90o E36,307 km2.10o W36,652 km3.09o WGLM N/S field angle5.30o N3.02o S3.51o NGLM E/W pixel pitch30 mm30 mm30 mmGLM N/S pixel pitch24 mm30 mm30 mm

Beacon Telescope MountMOBLAS transmitters,optimized for Nd:YAGx2,transmit poorly @ 777.4 nmBeacon telescopes“piggybacked” on MOBLAStelescopes uses theirpointing system,co-boresighted radar,power, & enclosureInexpensive COTS telescopeshave good transmission@ 777.4 nm

Dither Events30

Results: Time Series

GLM products –Geolocated (latitude, longitude), calibrated (i.e., radiant energy) events, groups , and flashes Event geolocation –pixel latitude, longitude adjusted to specified cloud top height Group geolocation –Radiance weighted mean event location Flash geolocation –Radia