GLM INR and Instrument Performance Evaluation

Transcription

1 GLM INR and Instrument Performance Evaluation Presented by Dennis Buechler University of Alabama in Huntsville Joint MTG LI Mission Advisory Group & GOES-R GLM Science Team Workshop, Rome Italy May 2015 Page No. 1

2 GLM INR / MSFC GLM Team Post Launch Product Tests (PLPTs) have been developed to assess the geolocation accuracy of GLM L1b and L2+ products (events, groups, and flashes) Develop validation tools VaLiD (Validate Lightning Detection) Various reference datasets will be used to evaluate GLM event, group, and flash geolocation accuracy Page No. 2

3 GLM INR - Comparison with Satellite and Radar Observations Initial quick look to verify GLM lightning is located in areas of convective activity Visible and IR satellite images Radar observations (e.g., NEXRAD) Page No. 3 LIS lightning flashes (magenta) and Precipitation Radar (PR) reflectivity LIS group events (cyan) on VIRS (Visible and InfraRed Scanner) visible image.

4 GLM INR GLM Considerations: Parallax Flash extent (not a point location) Optical output at cloud top Page No. 4

5 GLM INR - Ground based Observations Long Range Networks (e.g., GLD360, ENTLN, WWLLN) Mainly cloud-to-ground flashes and/or strokes Point data Local Networks (e.g., LMA, HAMMA) Total lightning (cloud-to-ground and in-cloud) Show flash extent Laser Beacons Known fixed locations No parallax Page No. 5

6 GLM INR - Above Cloud Observations Satellite (ISS-LIS, TARANIS): ISS-LIS will be directly comparable to GLM observations Same detection methodology as GLM Different resolution Parallax Airborne (FEGS Fly s Eye GLM Simulator): GLM simulator Higher resolution Page No. 6

7 GLM Performance Assessment Trend various GLM parameters Detection Efficiency Flash, group, and event energy Flash, group footprint size Events per group and flash, groups per flash Number of flashes Number of flashes detected by LIS per year. Values post-orbit boost exhibit little change. Page No. 7

8 Deep Convective Cloud (DCC) Method Deep Convective Cloud (DCC) Method A vicarious calibration method using radiance of DCCs Visible and other satellite channels are routinely calibrated and intercalibrated using DCCs (Global Satellite InterCalibration System - GSICS) GLM background data is used to obtain DCC radiance values The GLM has no onboard calibration The DCC method can be used to analyze and trend GLM optical performance Page No. 8

9 DCC Methodology DCCs are cold and bright clouds near the tropopause in the tropics ( 30 S to 30 N) DCCs provide stable radiance observations in the solar reflective bands Little scattering or attenuation Nearly constant albedo Seasonality No other information necessary to calibrate with DCCs No atmospheric profile adjustments needed No surface information required Use LIS data as proxy for GLM since designs are similar Look at observed LIS radiances from Page No. 9

10 DCC Methodology (Cont d) Criteria for LIS BG pixels: 1) Between ±30 Latitude 2) 10.8 µm Tb < 205K 3) Solar Zenith Angel (SZA) < 40 4) Viewing Zenith Angle (VZA) < 40 5) Relative Azimuth Angle (RAA) > 10 and < 170 6) Ratio of standard deviation of pixel radiance and its 8 surrounding pixel radiances divided by the pixel radiance (σ BG ) < ) Standard deviation of VIRS pixel Tb and 8 surrounding pixels (σ TB ) < 1 K 8) No lightning within 50 km 9) Need large number of DCCs for adequate analysis (>200,000) Solar and viewing angles. P 1 P 2 P 3 P 4 P i P 5 P 6 P 7 P 8 Pixels used for σ BG and σ TB. Page No. 10

11 LIS DCC Methodology (cont d) LIS used as example Each July-August Use VIRS (colocated onboard TRMM with LIS) 11 µm to identify DCCs ( < 205K) Identify colocated LIS Background (BG) pixels Get adjusted LIS radiance (ρ) adjust to SZA of 0 (divide by cosine of SZA) assume Lambertian surface LIS background images every 35 s Page No. 11

12 LIS DCC Locations Page No. 12

13 LIS DCC Results LIS DCC radiance distributions very similar from Page No. 13

14 LIS DCC Results Mean yearly July August LIS DCC radiance values vary little over the period Page No. 14

15 DCC Conclusions The DCC method is successfully applied to TRMM LIS and VIRS observations for the period The maximum yearly deviation is ~2% The maximum deviation occurs in 2000 No discernible trend Instrument operation is stable over its lifetime no evident degradation The DCC method is applicable to monitor GOES-R GLM radiance measurement precision using ABI and GLM The DCC method may be in conjunction with ISS-LIS to intercalibrate GLM and LI Buechler et al, 2014: Atmospheric Research Page No. 15

16 GLM Performance Assessment Other vicarious targets could be used Deserts Fewer observations Limited number of deserts Intervening atmosphere Solar glint Clouds, aerosols, moisture Seasonality Intervening atmosphere Also need to wind data LIS background image of the Sonoran desert. Page No. 16

17 Questions? Page No. 17

18 LIS DCC BRDF Page No. 18

19 LIS DCC Page No. 19

20 GLM Performance Assessment Trend various GLM parameters Detection Efficiency Flash, group, event energy Flash, group footprint size Events per group and flash, groups per flash Trend number of flashes Number of flashes detected by LIS per year. Values post-orbit boost exhibit little change. Yearly mean LIS group radiance. Page No. 20

21 Using DCC with GLM Deep Convective Cloud (DCC) Method A vicarious calibration method using DCCs Visible and other satellite observations are routinely calibrated and intercalibrated using DCCs (Global Satellite InterCalibration System - GSICS) The GLM has no onboard calibration The DCC method can be used to analyze and trend GLM optical performance Page No. 21 Complications in comparing GLM with other systems as their characteristics change Improvements or declines in system performance Systems added or taken offline

22 LIS DCC Locations AM AFR IND WPAC 91.5% of LIS DCCs occur over oceans Western Pacific (WPAC) Bay of Bengal and Indian Ocean (IND) near central America (AM) 8.5% of LIS DCCs occur over land Africa (AFR) Near the Himalayas (IND) 31% of LIS DCCs associated with lightning occur over land Mostly over Africa (AFR) Page No. 22