INFRARED CONTINENTAL SURFACE EMISSIVITY SPECTRA AND SKIN TEMPERATURE RETRIEVED FROM IASI OBSERVATIONS

Transcription

1 INFRARED CONINENAL SURFACE EMISSIVIY SPECRA AND SKIN EMPERAURE RERIEVED FROM IASI OSERVAIONS V. Capelle E. Péquignot 2 A. Chédin N. A. Scott. LMD CNRS/IPSL Ecole Polytechnique Palaieau France 2. CNES - Centre Spatial de ouloue ouloue France

2 Spectral variation of emiivity in IR are oil: quartz ε µm Quartz Rettrahlen band from MODIS/UCS and ASER/JPL emiivity librarie are oil: calcite Snow and Ice Vegetation are oil: gypum Spectral variation impact on IR emiivity: up to 5% particularly over bare oil in quartz Rettrahlen band

3 Infrared RE lambertian urface clear ky night Surface Emiion Upwelling Atmophere Emiion ' z z ' S = Reflected Downwelling Atmophere Emiion for a Lambertian urface z OA urf lnp d + = ] I ε d + ' ] ε

4 Multi Spectral Method MSM = ' ] ' ] ] I ε In order to calculate ε one need: identifying clear ky radiance 2 knowing the thermodynamic tate of the atmophere H2O O3 profile Proximity recognition of radiance in the IGR * climatological dataet 3 etimating the urface kin temperature For channel preenting the double property of being atmopheric window and having an almot contant emiivity whatever the urface i remain the only unknown of the radiative tranfer equation Péquignot et al. 28 Infrared continental urface emiivity pectra retrieved from hyperpectral enor. Application to AIRS. JAMC. For window channel ε can be computed by : with * Chédin et al. 85; Chevallier et al. 98 Scott et al. 99

5 Surface kin temperature : emi-tranparent pectral band - 2 µm] = ' ] ' ] ε ε at d d I right hand ide calculated with retrieved atmopheric profile uing a Fat Radiative ranfer Model baed on 4A line-by-line code 4A : Scott and Chédin 98] Emiivity variability µ±σ of the 846 IASI channel calculated from oil and vegetation emiivity pectra of MODIS/UCS and ASER/JPL librarie 3 channel elected for their good tranmittance tau tau tau tau~.6 and a mall variability of the emiivity σ ~.: =.429 µm 2 =.6 µm 3 =2.µm ε~.97 i no more an unknown for thee channel

6 Infrared Emiivity Spectrum from 3.7 to 4 µm = ' ] ' ] ] I ε εcalculated for IASI channel elected for their high enitivity to urface parameter and low enitivity to other contribution. hee channel are ditributed along the pectrum and are particularly located where the emiivity variability i highly dependant on the type of oil or vegetation in order to allow an accurate recontruction of the entire pectrum. Dicontinuou pectrum with an expected accuracy on the retrieved emiivity of ~3% at 4 µm and le than % at 2 µm. MSM Emiivity databae : - 65 pectra for variou oil and vegetation type extracted from MODIS/UCS and ASER/JPL emiivity librarie. - ampling : ] µm at.5 µm reolution. Leat quare minimization + hape adjutment Emiivity continuou pectrum between 3.7 and 4. µm at.5 µm reolution

7 Etimation of S : comparion with MODIS and ECMWF ECMWF forecat MODIS4 MODIS5 For nighttime June 28 2 verion of MODIS data: v5 and v4 globally in agreement for the different product he larget dicrepancie are located mainly on Sahara: -Δ ~ 2.5K iai modi4 -Δ ~ 5.5K iai modi5 -Δ ~ K iai ECMWFfc v4 more conitent with IASI reult which lie between ERA-4 and MODIS

8 Etimation of S : comparion with MODIS and ECMWF For nighttime Dec. 28 ECMWF forecat MODIS4 In general the two verion of MODIS colder than or ECMWF-fc. See Autralia or South America On Sahara ECMWF-fc i the warmet MODIS5 the coldet. IASI-MSM and MODIS4 imilar. MODIS5

9 Etimation of S: comparion with MODIS June 28 Dec. 28 =.74 ± 2.2 K =-.69 ± 2. K Value conitent with reported error on found in the literature. ia : keep in mind the hour time hift between IASI and ERRA 2h3.v. 22h3.

10 Emiivity pectra :Comparion with MODIS datapoint and continuou pectra /2 Deert June 28 Savanna UW F4 MODIS v4 Emiivity trongly depend on the type of urface and it value increae with the vegetation. he Quartz Rettrahlen band are well oberved and dominate the pectra Good agreement between and MODIS emiivity UW F4 MODIS v4

11 Emiivity pectra :Comparion with MODIS datapoint and continuou pectra 2/2 ropical foret Semi-Deert UW F4 MODIS v4 June 28 For tropical region the emiivity pectra i flat with a value cloe to. In emi-deert region the quartz rettrahlen band i alo important UW F4 F4 MODIS v4 MODIS v4

12 Map of emiivity at 4.5 micron for IASI and MODIS4 for June 28 MODIS4

13 Map of emiivity at 8.55 micron for IASI and MODIS4 for June 28 MODIS4

14 Seaonal variation of the emiivity March 28 June 28 September 28 December 28 Deert Northern hemiphere March 28 June 28 September 28 December 28 Savanna March 28 June 28 September 28 December 28 ropical foret March 28 June 28 September 28 December 28 Semi-Deert Southern hemiphere Seaonal variation are almot negligible in mot region except Savanna where the vegetation i more influenced by eaonal precipitation.

15 Seaonal variation of the emiivity : Cae of Savanna IASI MODIS F4 AIRS time-erie for emiivity at and 2.2 micron he eaonal variation are quite urpriing: Emiivity in the rettrahlen band i higher in December uppoed to be the dry eaon than in June wet eaon. Diagree with previou reult on AIRS for the period In agreement with MODIS F reult even if the MODIS amplitude i maller than the IASI one. ut the 2 period differ : El Nino/La Nina epiode work in progre Multivariate ENSO index E. Péquignot 26 thei Standardized Departure AIRS time-erie Year 28 NOAA/ESRL/Phyical Science Diviion Univerity of Colorado a oulder/cires/cdc

16 Concluion Relatively good agreement between and MODIS continental emiivity and urface temperature for the region conidered IASI-MSM in between MODIS and ECMWF fct. Some dicrepancie can be partly explained by the diurnal cycle. 2 We will oon tart to build a climatology of monthly continental urface emiivity a well a temperature retrieved from IASI. hi climatology will be freely available through our webite a i currently available the climatology of emiivity retrieved from AIRS. 3 Preliminary reult on eaonal variation ak the quetion of the validity of a climatology by month averaged over year ince it appear that the emiivity could be enitive to non-cyclic phenomena uch a El Nino/La Nina. 4 Such high reolution emiivity pectra and urface kin temperature hould help improving model of the earth urface-atmophere interaction and the retrieval of meteorological profile from infrared vertical ounder.