1 / 17

WP 3 : Absorbing Aerosol Index (AAI) WP 10 : Level-1 validation

WP 3 : Absorbing Aerosol Index (AAI) WP 10 : Level-1 validation. L.G. Tilstra (1,2) , I. Aben (1) , P. Stammes (2) (1) SRON; (2) KNMI. SRON, 29-11-2007. WP3: scientific AAI (SC-AAI) and operational AAI (L2-AAI). Status SC-AAI (“advantage over L2-AAI”):

karis
Download Presentation

WP 3 : Absorbing Aerosol Index (AAI) WP 10 : Level-1 validation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. WP 3 : Absorbing Aerosol Index (AAI)WP 10 : Level-1 validation L.G. Tilstra (1,2), I. Aben (1), P. Stammes (2) (1)SRON; (2)KNMI SRON, 29-11-2007

  2. WP3: scientific AAI (SC-AAI) and operational AAI (L2-AAI) Status SC-AAI (“advantage over L2-AAI”): correction for calibration offset at t=0 correction for instrument degradation (still being improved) look-up tables calculated by RTM taking polarisation into account algorithm more accurate + allows negative albedos proper sunglint filter To improve the operational L2-AAI, we worked together with DLR to solve issues (3) and (4)

  3. Improving L2-AAI: progress of work • Work on new LUTs was finished at the end of February 2007; • LUTs delivered to DLR • Format description of files and contents written and delivered to DLR • ATBD for SC-AAI written and delivered to DLR • DLR has since changed the operational algorithm to use the new LUTs, and to implement the main part of our SC-AAI algorithm. • During verification efforts, we found out that the surface height database used by DLR for their L2 products has a resolution of only 1 by 1 degrees, leading to huge errors in the AAI for pixels over land. • We provided DLR with our ETOPO-4 based surface height database, along with reading software and an algorithm description of fast and accurate surface height determination. DLR has included everything into their code. • Intensive verification and testing between DLR and KNMI/SRON was necessary to get a 100% agreement between the new L2-AAI algorithm and our SC-AAI.

  4. Remaining issues of the improved operational L2-AAI: • correction for calibration offset at t=0 • correction for instrument degradation • no proper sunglint filter Until issue (2) gets fixed, the improved operational L2-AAI would only be useful for data between 2002 and the end of 2004 Further work on the AAI within WP 3: • Improve degradation correction even further • Further study (and correct for) scan-angle dependent degradation • (for the AAI, and eventually, for the reflectance)

  5. WP10: Level-1 validation: polarisation Validation methods for SCIAMACHY polarisation are scarce: • comparison with single scattering calculations • comparison with POLDER (PMD 2, 3, 4) POLDER is really the only instrument that at the same time • measures the state of polarisation reliably, • can be collocated properly with SCIAMACHY, • can mimic the scattering geometry of SCIAMACHY observations We compared SCIA/5.01 and SCIA/6.03 (reprocessed data)

  6. SCIAMACHY vs POLDER : SCIA/5.01 • only Q/I is of importance (U/I has little effect on polarisation correction) • v5.01 data show for the first time some correlation with POLDER data • PMD 2 looks reasonable • PMD 3 looks ok • PMD 4 is clearly not ok Green = cloud-free, homogenous pixels Blue = possibly clouded, inhomogeneous pixels

  7. SCIAMACHY vs single scattering calculations : SCIA/5.01 • the grey areas indicate the unphysical domain: here the data points should ideally not be found • v5.01 data have many Stokes fractions in the unphysical domain • PMD 2 is not ok • PMD 3 looks ok • PMD 4 is clearly not ok These findings were reported and a software bug was found for PMD 4 (which was not present in SCIA/4.0x data)

  8. SCIAMACHY vs POLDER : SCIA/6.03 (“reprocessed data”) • large improvement of Q/I for PMD 2 and PMD 4 • good correlation with POLDER Q/I data

  9. SCIAMACHY vs single scattering calculations : SCIA/6.03 • as before, the grey areas indicate the unphysical domain: here the data points should not be found • v6.03 data have much less Stokes fractions in the unphysical domain • there are clear indications of “offset problems”, which are partially caused by instrument degradation In conclusion, the polarisation product has improved by quite a lot

  10. Plans WP 3/10: • Further study the (scan-angle dependent) degradation • Improve degradation correction of SC-AAI (and L2-AAI?) • Validate improvements in L2-AAI (part of the “SQWG work”) • Further validation of level-1 polarisation product via satellite intercomparisons and comparisons with RTMs; determine time dependent correction factors for the “offset problems” that were found • Validation of reflectance calibration for the entire wavelength range (channels 1 to 8) using stable Earth targets

  11. Extra slides

  12. Absorbing Aerosol Index (AAI) and the residue • Definition of the residue: • where the surface albedo A for the simulations is such that: • no clouds, no absorbing aerosols : r < 0 • clouds, no absorbing aerosols : r < 0 • absorbing aerosols, no clouds : r > 0 • B. Definition of the AAI: • AAI = residue > 0 (where residue < 0 the AAI is not defined)

  13. SCIAMACHY SC-AAI data are available on the TEMIS website http://www.temis.nl Available data: GOME SCIA : 1995–2000 : 2002–2007

  14. Degradation: AAI in 2004:(monthly mean)Normal distribution of UV-absorbing aerosols. Similar to observations by TOMS. AAI in 2006:(monthly mean)Degradation of the opticsleads to anomalously highvalues of the residue / AAI.

  15. SCIAMACHY degradation in the UV WLS: White Light Source, internal calibration lamp “Light Path Monitoring” results for 340 and 380 nm: Status: 340 : -25.9% 380 : -17.6% (27-06-2007) Status: 340 : -11.3% 380 : -8.2% (27-06-2007) Status: 340 : -16.5% 380 : -10.3% (27-06-2007)

  16. Effect of instrument degradation on the AAI/residue: (The daily global average of the residue should have a constant value) green points: daily residue, averaged over the globe. blue curve: calculated effect of instrument degradation (from LPM) on residue/AAI The trend in the residue can be more or less explained by degradation as found from “Light Path Monitoring”. Lately, the agreement has become worse…

  17. Effect of instrument degradation (c340 ; c380) on residue/AAI: • Trend in residue can be explained by degradation as found from “Light Path Monitoring” results. • Residue/AAI is very sensitive to (absolute) reflectance calibration. • Degradation correction is really important for the AAI. • Residue is recording its own degradation correction

More Related