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Institut für Umweltphysik (IUP) Institut für Fernerkundung (IFE)

CarbonSat L1L2 Study Final Presentation , 3-Jul-2013 . Universität Bremen, FB1 Physik und Elektrotechnik. Institut für Umweltphysik (IUP) Institut für Fernerkundung (IFE). CarbonSat: Validation strategy using TCCON sites ESA Study CarbonSat Earth Explorer 8 Candidate Mission

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Institut für Umweltphysik (IUP) Institut für Fernerkundung (IFE)

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  1. CarbonSat L1L2 Study Final Presentation, 3-Jul-2013 Universität Bremen, FB1 Physik und Elektrotechnik Institut für Umweltphysik (IUP) Institut für Fernerkundung (IFE) • CarbonSat:Validation strategy using TCCON sites • ESA Study CarbonSat Earth Explorer 8 Candidate Mission • “Level-2 and Level-1B Requirements Consolidation Study“ • ESA Contract No 4000105676/12/NL/AF • Related WP: 3600, Related document: TN-3f M. Reuter, H. Bovensmann, M. Buchwitz Institute of Environmental Physics (IUP) / Institute of Remote Sensing (IFE), University of Bremen (UB), Bremen, Germany 1

  2. Introduction • Validation must be useful to quantify systematic and stochastic retrieval errors, e.g, regional and seasonal errors at various scales. • Literature review shows that TCCON is the current de facto validation standard for satellite retrieved XCO2 and XCH4 • TCCON has a precision and accuracy better than 0.25% • TCCON is sparse but worldwide and covers many eco systems. • We concentrate on the 18 TCCON sites operational in 2012. 2

  3. Example: SCIAMACHY BESD XCO2vsTCCON(350 km, 2 hours) SCIAMACHY (singleobs.) TCCON (average) ORL DAR SOD BRE WOL GAR • Single measurementprecision: 2.23 ppm • Station-to-station bias: 0.66 ppm • N coloc: • Park Falls: 3576 • Lamont: 9760 • Darwin: 6295 BIA PAR KAR LAM 3 http://www.esa-ghg-cci.org/

  4. Validation Strategy and CS Orbits • One year simulated CS orbits (500 km swath, TN CS L4) used to find good-flagged co-locations (distance < 500km) with TCCON. • Good-flagged means: cloud free, sun zenith angle < 70°, land surfaces not covered with snow/ice, surface roughness < 0.5 km, ocean with glint angle < 30° • We concentrate on nadir and will show that this allows a thorough validation. 4

  5. Spatial Co-Location Criteria • Literature shows that 500 km is current state of the art. • With 500 km, CS will produce about 7x107 validation measurements per year. • Using 150km would reduce the amount by a factor of 10. • Except for NyAlesund and Lauder similar behavior at all sites but differing absolute values. • Reduced swath would of course reduce co-locations x2 7x107 x0.1 5

  6. Representativeness for USGS Surface Types • Surface type is generally related to eco-system regime. • USGS discriminates between 24 different surface types. • Histograms of surface types differ strongly (e.g., dry land, water) • However, 1% still means about 7x105 co-locations per year! • All significant surface types are well represented in the validation data set. 6

  7. Seasonal Representativeness • A maximum in the (northern hemispheric) summer months can be observed because the majority of TCCON sites are on the northern hemisphere. • The main driver for the number of co-locations per month is the criterion for the solar zenith angle which must be larger than 70° (e.g., Sodankyla). • Persistent clouds are sometimes also important (e.g., Darwin). maximum 7

  8. Filter Criteria • Most important criterion is (at most sites) the cloud coverage. • At high latitudes the solar zenith angle criterion prohibits measurements in winter months (e.g., Sodankyla). • Snow/ice coverage as well as surface roughness is less important. • Sea measurements are driven by the location of the site but also by the glint angle which is always larger than 30° at high latitudes (e.g., Bremen). 8

  9. Summary and Conclusions I • With a co-location criterion of 500 km, and CS with 500 km swath will produce about 7x107 validation measurements per year. • The absolute number of co-locations is several orders of magnitude larger that in recent validation studies of GOSAT and SCIAMACHY • Even without target mode, CarbonSat will produce more than enough validation measurements in the surrounding of the analyzed TCCON sites to perform a thorough validation, and a thorough validation is also possible for surface types which are largely under-represented. • TCCON allows to validate the seasonal cycle at most sites. • Above land, the amount of validation data is driven by cloud coverage and sun zenith angle (in high latitudes). • Above sea, the glint angle is also important and sites in high latitudes will never have glint conditions in nadir mode. • The dedicated glint mode needs to perform glint measurements also at high latitudes. 9

  10. Recommendations Validation • Glint and target mode cannot compensate neither the sparseness of TCCON in, e.g., Siberia or the tropics nor the weakness in not covering surface albedos larger 0.35. • TCCON needs to be upgraded • NOAA’s AirCore system - currently under development and expected to be cheaper and more accurate than TCCON - could be of great interest for the CarbonSat mission if it is widespread enough when CarbonSat is launched. XCO2difference / % (Non-scattering – RemoTeC)/RemoTeC A. Butz, TANSAT WS 2012 10

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