CEOS/IVOS Libya_4 Workshop Summary Patrice Henry - CNES GSICS – GRWG Web. Meeting – Nov 2012 – Patrice Henry / CNES
Libya_4 Workshop ■ October 4 -5, CNES Paris ■ 24 participants w Mainly European + US w Space agencies, science laboratories, industry ■ 25 presentations + 2 round tables w First day : site characterization w Second day : intercalibration methods and results w Presentation slides available on the ESA Cal/Val Portal http: //calvalportal. ceos. org/cvp/web/guest/home GSICS – GRWG Web. Meeting – Nov 2012 – Patrice Henry / CNES
Workshop objectives ■ Special workshop fully dedicated to the use of the Libya-4 site for calibration purpose w Libya-4 as an example for more general desert calibration w Technical presentations of existing studies w Exchange experience w Paving the way for international cooperation and data/results exchange GSICS – GRWG Web. Meeting – Nov 2012 – Patrice Henry / CNES
Why Libya_4 ? ■ Not the best but the most used desert site by the on-orbit sensor calibration community w But not exactly the same site for everybody… ■ Historically used for AVHRR calibration monitoring ■ One of the 5 CEOS selected calibration sites (PICS = Pseudo Invariant Calibration Site) ■ Several recent studies presented at CEOS WGCV meeting w Calibration monitoring w Cross calibration of sensors w Site characterization and modelling GSICS – GRWG Web. Meeting – Nov 2012 – Patrice Henry / CNES
What are the main areas of concern ? ■ Spectral behaviour w Spectral adjustements are to be applied w Error : systematic bias (several %) w Need to be improved using Sciamachy or hyperspectral sensor (? ) ■ BRDF w Most important error source w 2 models : CNES (based on POLDER/Parasol data) Y. Govaerts (more analytical) w Simple modelling can be sufficient for calibration trending or for sensors on the same orbit (ETM+/MODIS_Terra, VGT 1/VGT 2…) ■ Atmosphere w Can be considered as ‘noise’ → statistical approach ■ Site modelling is mandatory w At To. A or Bo. A level ? GSICS – GRWG Web. Meeting – Nov 2012 – Patrice Henry / CNES
Impact of the site spectral behaviour (1) Simulation of a Landsat 7/ETM+ and Terra/MODIS cross calibration (simulated spectra using Hyperion data) Direct To. A reflectance comparison GSICS – GRWG Web. Meeting – Nov 2012 – Patrice Henry / CNES Spectral adjustement (spline interpolation)
Impact of the site spectral behaviour (2) Simulation of MODIS/MERIS cross calibration (using Hyperion data) GSICS – GRWG Web. Meeting – Nov 2012 – Patrice Henry / CNES
Impact of the site spectral behaviour (3) __ __ MERIS calibration vs MODIS calibration vs MERIS Results of MODIS/MERIS cross calibration (20 desert sites) GSICS – GRWG Web. Meeting – Nov 2012 – Patrice Henry / CNES
Impact of the site BRDF (1) MERIS MODIS VGT 2 Applying the POLDER/PARASOL model on Libya-4 timeseries (green and PIR surface reflectance) GSICS – GRWG Web. Meeting – Nov 2012 – Patrice Henry / CNES
Impact of the site BRDF (2) 865 nm channel 555 nm channel MERIS surface reflectance time series over Libya-4 - green and PIR channels GSICS – GRWG Web. Meeting – Nov 2012 – Patrice Henry / CNES
Impact of the site BRDF (3) 865 nm channel 555 nm channel MERIS surface reflectance over Libya-4 normalized by the BRDF model GSICS – GRWG Web. Meeting – Nov 2012 – Patrice Henry / CNES
What are the expected accuracies ? ■ More difficult in the ‘blue’ range (atmosphere) ■ For ‘close spectrally’ channels w Cross calibration : 2 to 3% w Multi-date calibration : better than 2% for long trend w Absolute calibration : 5% (? ) ■ Need for climate studies : better than 0. 5% !!! GSICS – GRWG Web. Meeting – Nov 2012 – Patrice Henry / CNES
Main conclusions ■ Improve the BRDF characterization w CNES to provide BRDF model to other teams To be applied in their studies (Univ. of South Dakota, DMCii, RAL…) Results to be presented at next IVOS meeting w CNES to provide POLDER/Parasol for new models fitting After the complete reprocessing of Parasol data (end of 2013) ■ Improve the spectral characterization w Identify and assess hyperspectral data and/or spectral laboratory measurements w Propose model fitting ■ International cooperation : a key issue to improve the calibration sites properties and cross calibration methods GSICS – GRWG Web. Meeting – Nov 2012 – Patrice Henry / CNES
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