QWG7 icor atmospheric correction evaluation

Transcription

1 QWG7 icor atmospheric correction evaluation E. Wolters, S. Sterckx, S. Adriaensen 03/05/2018 VITO Remote sensing

2 Contents icor atmospheric correction icor processing PROBA-V L2A Evaluation setup Results Summary & recommendation

3 icor atmospheric correction MODTRAN-5 based LUTs AOT retrieval based on Guanter et al. (2008) Superpixels of 30 x 30 km 2 atmosphere invariant within area Dark target retrieval (max. AOT boundary), refinement by endmember inversion Implementation for PROBA-V: AOT LUTs computed for all cameras altitude dependent LUTs Rural aerosol model Application to Level 2A segments (TOA reflectance)

4 icor processing 18 AERONET stations selected Time period icor LUTs for all cameras ~3,500 1 km segments processed Workflow adapted for MEP processing Parallel processing, ~300 executors Run time < 4 h

5 icor data processing No icor AOT fall-back implemented yet Outside of scope current research Spectrally homogeneous areas: AOT retrieval extrapolated from distant macropixels

6 AERONET stations AERONET station Coordinates [ o lon, o lat] Altitude [m] Site information Category West Africa Banizoumbou (Niger) E, N 250 Cultivated sandy area. Bare soil IER Cinzana (Mali) W, N 285 Cultivated area. Bare soil Zinder Airport (Niger) E, N 456 Semi-arid cultivated area (from June October) just south of Zinder. Bare soil vegetated East Asia Beijing (China) E, N 92 Urban area; instruments located at research institute s rooftop. Western Europe Aubière LAMP (France) E, N 423 Located near Clermond Ferrand, urban area. Bure OPE (France) E, N 393 Open grassland area near Hourdelaincourt. Carpentras (France) E, N 100 Cultivated area about 5 km north of Carpentras. Mainz (Germany) E, N 150 Mixture of urban and rural area, within 1 km from the Main River, moderate to highly polluted region. Urban Urban Vegetated Vegetated Urban urban Murcia (Spain) W, N 69 Located in rural and dry area, few km west of the city. Vegetated Toulouse Météo France (France) E, N 150 Located in rural/urban area southwest of Toulouse. Urban Davos (Switzerland) E, N 1596 Located at the northern edge of Davos, Vegetated close to Davosersee. Clean air. Hohenpeißenberg DWD (Germany) E, N 990 Located at a mountain top just outside Vegetated the village. South America Alta Floresta (Brazil) W, S 277 Located near an airport, west of Alta Vegetated Floresta. Ji Parana SE (Brazil) W, S 218 In pasture, surrounded by trees. Vegetated Bare soil La Paz (Bolivia) W, S 3439 Located at the edge of La Paz, air contains mixture of urban and biomass burning. Bare soil North America Bonanza Creek (AK, USA) W, N 150 Field site surrounded by conifer trees. Vegetated Goldstone (NV, USA) W, N 1100 Location in Mojave desert, within Deep Space Network Telescope area. Bare soil Monterey (CA, USA) W, N 50 Located near Monterey Airport, ~2 km from a bay. Urban

7 Performance metrics Accuracy (A): Precision (P): A = 1 n n ε i i=1 Uncertainty (U): P = 1 n 1 n i=1 (ε i A) 2 U = 1 n n ε 2 i i=1

8 icor AOT evaluation AERONET Level 2.0 data AOT 0.55 = AOT 0.44 AERONET median over +/- 30 min from overpass Cloud cover < 60% over pixels around station icor median over 9 9 pixels λ λ o α

9 icor TOC reflectance evaluation Rayference reference dataset (single-pixel) icor single pixel values Cloud cover < 60% over pixels Current operational ( OP ) TOC from S1 TOC data Temporal collocation using S1 TIME grid

10 Results: icor AOT

11 Results: current AOT retrieval AOT retrieval AOT latitudinal fall-back

12 Results: icor TOC BLUE icor OP S1

13 Results: icor TOC RED icor OP S1

14 Results: icor TOC NIR icor OP S1

15 Results: icor TOC SWIR icor OP S1

16 Results: time series examples Aubière (France, urban) Cinzana (Mali, BS)

17 Results: time series examples Monterey (USA, urban) Carpentras (France, veg)

18 Summary AOT icor compares well against AERONET over vegetated and urban areas Low agreement over bare soils lack of spectral variability, fall-back necessary Results conform ACIX evaluation (LS 8 & S-2A)

19 Summary TOC reflectance Performance differences icor vs OP S1 TOC small Slight improvement for BLUE, RED over vegetation icor performance slightly lower than OP S1 for NIR and SWIR Performance icor AOT icor TOC, aerosol models MODTRAN?

20 icor vs SMAC aerosol models Aerosol type relative contribution Water soluble Dust-like Soot ω 0.55 µm [-] icor (MODTRAN5) 70% 30% 0% SMAC (6S) 29% 70% 1% Different contributions of water soluble and dust-like aerosols Small soot contribution in 6S more absorption

21 Options for C2 AC baseline 1. Maintain SMAC with BLUE/SWIR AOT retrieval Provide additional SMAC accuracy information to users (e.g. good, acceptable, unreliable, bad) Replace latitudinal fall-back with CAMS NRT/climatology Effort WD 2. Implement icor (given the good AOT retrievals) Additional research for NIR and SWIR TOC required Impact of different aerosol microphysical properties 6S and MODTRAN? Larger effort: WD

22 SMAC: accuracy vs SZA+VZA, WV Proud et al. (2010), SMAC on SEVIRI RED SWIR, Africa: SMAC accuracy decreases for a.o. joint SZA+VZA > ~100 o, WV > 2.0 g cm -2 Joint SZA+VZA SZA AOT WV

23 THANK YOU Sentinel-2 image Copernicus Sentinel data (2016)