Isabel Trigo, Sandra Freitas, Carla Barroso, Isabel Monteiro, Pedro Viterbo

Transcription

1 Land Surface Temperature, Emissivity and Long-Wave Downwlling Fluxes from MSG Observations: current status and way forward Isabel Trigo, Sandra Freitas, Carla Barroso, Isabel Monteiro, Pedro Viterbo 1

2 Outline Land Surface Temperature & Emissivity Algorithms & Product characteristics Validation Strengths and Weaknesses Developments for CDOP-2 Downwelling Sfc Long-wave Flux Algorithm & Product characteristics Validation against in situ observations and CERES fluxes Developments for CDOP-2 2

3 SEVIRI/Meteosat IR channels & LST Solar Conamination SEVIRI reponse function Emissivity uncertainty high

4 Land Surface Temperature - Algorithm Generalised Split-Window 10.8µm and 12.0µm Trained usingclear SKYsynthetic SEVIRI/MSG data (MODTRAN + realistic sfc parameters & atmospheric profiles) 1 ε ε T T ε ε T10.8 T12. 0 T s = ( A1 + A2 + A3 ) + ( B1 + B2 + B3 ) + C 2 2 ε ε 2 ε ε 2 GSW parameters depend on: 1. total column water ECMWF fc vapour 2. viewing angle Channel Emissivity Fraction Vegetation Cover 4

5 Emissivty Pixel MSG ε = ε veg FVC+ ε ground (1-FVC) + δε LSA SAF Product Sfc Reflectances VIS Non-accounted effects (multiple reflections at sfc) Variability of bare ground/ vega within pixel 5

6 Channel Emissivty Vega/Ground BandEmissivity for VEGETATION/ SOILclasses Emissivity at λ (Spectral Libraries) ε c-vega/soil = λ 2 f λ λ1 λ 2 λ1 f ε λ λ B B λ λ dλ dλ SEVIRI/Meteosat Channels -IR 3.9 -IR 8.7 -IR IR 12.0 Channel response function Broad Band λ1= 3 µm; λ= 14 µm (fλ=1) 6

7 Emissivty SEVIRI IR3.9 SEVIRI IR10.8 Broad-Band3 14 µm Updated Daily 7

8 Emissivty uncertainty & impact on LST 1 Desert Areas EMISSIVITY DRY IR3.9 IR8.7 IR10.8 IR12.0 BroadB EverGreen Forests IR3.9 IR8.7 IR10.8 IR12.0 BroadB SEVIRI Channels LST Error(K) MOIST 8

9 Emissivty: Next Phase CDOP-2 Improved Emissivity (EM) maps EM (& LST) combination which minimizes: f = [L obs L RTM (LST, LSE)] i 2 for i = channelsir10.8, IR12.0, 6and 12 UTC, assuming EMunchanged Limited Experience carried out using: LSA SAF LSTand current EMas 1st guess MODTRAN for L RTM ( to be replaced by RTTOV) Trigo et al (2008) in IEEE Trans. Remote Sens. Geosc. Peres et al (2010) in Int J Remote Sens. 9

10 Emissivty: Next Phase CDOP-2 EMISSIVITY IR10.8 To be explored during CDOP-2: ALBEDO Better EM constraints among channels Temporal (& spatial) filtering 1 Pixel: 10

11 Land Surface Temperature - SEVIRI LST Generation Frequency- 15 min clear sky pixels... over land... where estimated errors < 4K Available since Europe Feb2005 Full disk Jul

12 Land Surface Temperature - SEVIRI LST Error Bars And error bars estimated taking into account: Uncertainty of the GSW regressions Propagation of input uncertainties: Emissivity Sensor noise TCWV ECMWF forecasts ºC Masked out δlst > 4K Trigo et al (2008) in J. Geophys. Res. Freitas et al (2010) in IEEE Trans. Remote Sens. Geosc. 12

13 LST - Validation Validation continuous activity main source of info on product compliance with requiremets Comparison against in situ observations: LSA SAF stations: Portugal (Evora, since 2005) Namibia (Gobabeb + Kalahari farm) Field Campaigns (e.g., AMMA) Comparison with similar products derived from other satellites: MODIS AATSR 13

14 Gobabeb LST - Validation Namibia 14

15 LST - Validation LST MSG/SEVIRI versus T sup in situ at Gobabeb Obs In Situ (ºC) May 2008 Bias -0.31ºC RMSE 1.16ºC LST SEVIRI/MSG (ºC) Obs In Situ (ºC) Jul 2008 Bias -0.91ºC RMSE 1.67ºC LST SEVIRI/MSG (ºC) Obs In Situ (ºC) 60 Nov Bias +0.24ºC RMSE 1. 44ºC LST SEVIRI/MSG (ºC) Obs In Situ (ºC) 60 Mar Bias -1.20ºC RMSE 1.74ºC LST SEVIRI/MSG (ºC) 15

16 LST - Validation EVORA L1 (L1, L2, L3) average L2 L RR ( T ) + ( 1 ε ) L = ε RR _ sfc LRR sfc RR _ sfc RR _ atm L3 scene emissivity LST_InSitu downward radiation [( ) ( ) ( ) ( ) ] δ LST + δ LST + δ LST δ 1 2 δ ( LST ) = ε + RotRad InSitu InSituVarT InSituVarSp 16

17 LST - Validation EVORA ( C) SEVIRI MODIS Daytime BIAS RMSD ( C) SEVIRI MODIS Night-time BIAS RMSD

18 LST - Validation SEVIRI vs MODIS LST Iberian Peninsula Morning MODIS passage (~11 UTC): [ C] 2-8Jan06 [ C] 14-20Sep05 T_SEVIRI T_MODIS MODIS Zenith Angle Remotely sensed LST is directional variable Research towards an isotropic LST during CDOP-2 18

19 Concluding Remarks - LST LST is generated, archived & disseminated (NRT or off-line) on an operational basis using: SEVIRI/Meteosat Generalized Split-Window AVHRR/MetOp Validation exercises show that: LST accuracy depends on retrieval conditions in accordance to information provided by respective error bars. CDOP-2: Improve EMISSIVITY CDOP-2: Revise LST algofor MTG LST is directional variable CDOP-2: model of directional effects for different land covers LST uncertainty; LST correction. 19

20 Downwelling Long-wave Flux at the Sfc DSLF IRradiation(4-100 µm)emitted by whole atmosphere Bulk Parameterization: F = ε sky σt sky 4 Temperature& Water Vapour Profiles Clouds/ Cloud Type Remote Sensing NWP Trigo et al. (2010) in J Geophys Res., in press 20

21 DSLF - SEVIRI Generation Frequency 30 min over landpixels available since 2005 with revised algorithm since

22 DSLF - Validation Ground Stations (BSRN) & CERES Northern Europe Stations CERES SEVIRI DSLF Period Jan Apr 2007 clear sky cloudy Stations Cambourne, UK Lerwick, UK Toravere, Estonia Clear Sky All Sky Bias CERES RMSE SEVIRI DSLF Bias RMSE Problems: -Cloud identification at the edge of Meteosat disk -DSLF model for ice clouds -Temperature inversions 22

23 DSLF - Validation Ground Stations (BSRN) & CERES Central Europe Stations CERES SEVIRI DSLF Period Jan Apr 2007 clear sky cloudy Stations Palaiseau, France Payerne, Swtzerland Carpentras, France Clear Sky CERES Bias RMSE SEVIRI DSLF Bias RMSE Problems: -Temperature inversions All Sky

24 DSLF - Validation Ground Stations (BSRN) & CERES Semi-Arid & Desert Stations CERES SEVIRI DSLF clear sky cloudy Period Jan Apr 2007 Stations Tamanrasset, Algeria Sde Boqer, Israel Niamey, Niger Clear Sky CERES Bias RMSE SEVIRI DSLF Bias RMSE Problems: -Impact of high aerosol loads All Sky

25 Concluding Remarks - DSLF DSLFis generated, archived & disseminated (NRT or off-line) on an operational basis using: SEVIRI/Meteosat Bulk Parameterization AVHRR/MetOp Scheme DSLF validation against in situ data: 60-70%of retrievals meet the target accuracy of 10% low up to mid latitudes accuracy comparable to CERES downward long-wave fluxes. CDOP-2: Algorithm development shared within SAF Network, targeting known deficiencies Aerosol, ice clouds, Review existing dependence on NWP model output. 25

26 26