qwg7 icor atmospheric correction evaluation qwg7...آ icor atmospheric correction modtran-5 based...
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QWG7 – iCOR atmospheric correction evaluation
E. Wolters, S. Sterckx, S. Adriaensen
03/05/2018 VITO Remote sensing
• iCOR atmospheric correction
• iCOR processing PROBA-V L2A
• Evaluation setup
• Summary & recommendation
iCOR atmospheric correction MODTRAN-5 based LUTs
AOT retrieval based on Guanter et al. (2008)
Superpixels of 30 x 30 km2 atmosphere invariant within area
Dark target retrieval (max. AOT boundary), refinement by end- member inversion
Implementation for PROBA-V:
AOT LUTs computed for all cameras
altitude dependent LUTs
Rural aerosol model
Application to Level 2A segments (TOA reflectance)
• 18 AERONET stations selected
• Time period 2014 – 2015
• iCOR LUTs for all cameras
• ~3,500 1 km segments processed
• Workflow adapted for MEP processing
• Parallel processing, ~300 executors
• Run time < 4 h
iCOR data processing
• No iCOR AOT fall-back implemented yet
• Outside of scope current research
• Spectrally homogeneous areas: AOT retrieval extrapolated from distant macro- pixels
AERONET station Coordinates [olon, olat] Altitude [m] Site information Category
West Africa Banizoumbou (Niger) 2.665 E, 13.541 N 250 Cultivated sandy area. Bare soil
IER Cinzana (Mali) 5.934 W, 13.278 N 285 Cultivated area. Bare soil
Zinder Airport (Niger) 8.990 E, 13.777 N 456 Semi-arid cultivated area (from June – October) just south of Zinder.
East Asia Beijing (China) 116.381 E, 39.977 N 92 Urban area; instruments located at
research institute’s rooftop. Urban
Aubière LAMP (France) 3.111 E, 45.761 N 423 Located near Clermond Ferrand, urban area.
Bure OPE (France) 5.505 E, 48.562 N 393 Open grassland area near Hourdelaincourt.
Carpentras (France) 5.058 E, 44.083 N 100 Cultivated area about 5 km north of Carpentras.
Mainz (Germany) 8.300 E, 49.999 N 150 Mixture of urban and rural area, within 1 km from the Main River, moderate to
highly polluted region.
Murcia (Spain) 1.171 W, 38.001 N 69 Located in rural and dry area, few km west of the city.
Toulouse Météo France (France) 1.374 E, 43.575 N 150 Located in rural/urban area southwest of Toulouse.
Davos (Switzerland) 9.844 E, 46.813 N 1596 Located at the northern edge of Davos, close to Davosersee. Clean air.
Hohenpeißenberg DWD (Germany) 11.012 E, 47.802 N 990 Located at a mountain top just outside the village.
Alta Floresta (Brazil) 56.104 W, 9.871 S 277 Located near an airport, west of Alta Floresta.
Ji Parana SE (Brazil) 61.852 W, 10.934 S 218 In pasture, surrounded by trees. Vegetated
La Paz (Bolivia) 68.066 W, 16.539 S 3439 Located at the edge of La Paz, air contains mixture of urban and biomass
Bonanza Creek (AK, USA) 148.316 W, 64.743 N 150 Field site surrounded by conifer trees. Vegetated
Goldstone (NV, USA) 116.972 W, 35.233 N 1100 Location in Mojave desert, within Deep Space Network Telescope area.
Monterey (CA, USA) 121.855 W, 36.593 N 50 Located near Monterey Airport, ~2 km from a bay.
Performance metrics • Accuracy (A):
𝐴 = 1
• Precision (P):
𝑃 = 1
𝑛 − 1 (𝜀𝑖 − 𝐴)
• Uncertainty (U):
𝑈 = 1
iCOR AOT evaluation • AERONET Level 2.0 data
𝐴𝑂𝑇0.55 = 𝐴𝑂𝑇0.44 𝜆
• AERONET median over +/- 30 min from overpass
• Cloud cover < 60% over 50 × 50 pixels around station
• iCOR median over 9 × 9 pixels
iCOR TOC reflectance evaluation • Rayference reference dataset (single-pixel)
• iCOR single pixel values
• Cloud cover < 60% over 50 × 50 pixels
• Current operational (‘OP’) TOC from S1 TOC data
• Temporal collocation using S1 TIME grid
Results: iCOR AOT
Results: current AOT retrieval AOT retrieval AOT latitudinal fall-back
Results: iCOR TOC BLUE
Results: iCOR TOC RED
Results: iCOR TOC NIR
Results: iCOR TOC SWIR
Results: time series examples Aubière (France, urban) Cinzana (Mali, BS)
Results: time series examples Monterey (USA, urban) Carpentras (France, veg)
• 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)
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?
iCOR vs SMAC aerosol models
Aerosol type relative contribution
Water soluble Dust-like Soot ωo @ 0.55 µm [-]
iCOR (MODTRAN5) 70% 30% 0% 0.943
SMAC (6S) 29% 70% 1% 0.893
• Different contributions of water soluble and dust-like aerosols • Small soot contribution in 6S more absorption
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 30 – 50 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: 70 – 80 WD
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 > ~100o, WV > 2.0 g cm-2
Joint SZA+VZA SZA
Sentinel-2 image Copernicus Sentinel data (2016)