1. Institut für Umweltphysik/Fernerkundung Physik/Elektrotechnik Fachbereich 1 CAPACITY WP3100 Geostationary Mission Concepts CAPACITY Final Presentation, 2.6.2005 Heinrich Bovensmann, University of Bremen Johannes Orphal, LISA-CNRS, Paris Contributors: J. M. Flaud, G. Bergametti, M. Beekmann, T. Steck, F. Friedl-Vallon, Th. von Clarmann, G. Stiller, O. Hasekamp, S. Noel, V. Rozanov, K.U. Eichmann, J. P. Burrows

2. Overview Relevant user requirements Impact of Clouds Measurement Technique Independent Specifications UV-VIs-Nir Sounding from Geostationary Orbit - Specifications Infrared Sounding from Geostationary Orbit - Specifications Expected Performance and Comparison with User Requirements Conclusions

3. Geostationary Orbit (GEO) serves best applications requesting for high temporal sampling (< 2 hrs) with good horizontal resolution (< 20 km) and regional to continental scale coverage (here: system covering Europe and surrounding areas), as the requirements related to European Air Quality applications (B1S-B3S). Applications asking for moderate temporal sampling (6 – 72 hrs) and/or high vertical resolution, especially in the UTLS and stratosphere, are typically better served by nadir and limb sounding instruments in LEO (see LEO WP). Synergies with GEO observation can be expected by better constraining the stratospheric concentrations. Global AQ applications can be served by a combination of GEO and LEO Study Logic

4. Summary Level 2 Requirements (WP2300) Applications are asking for sensitivity of measurements including the PBL

5. Impact of Clouds: LEO vs. GEO LEO (Kerridge et al., ACOR FR) ATSR-2/ERS-2, 1.5 km x 2 km 1 day global average GEO (Tjemkes et. Al. 2005) MVIRI/METEOSAT 4.8 km x 4.8 km (= 1 Pixel=23 km 2 ) Selected regions, seasonal averages EUROPE: DJF

6. Cloud free measurements per day and geolocation LEO GEO

7. Conclusions on Cloud Impact An instrument with 5 x 5 km 2 (SSP) in GEO will deliver over Europe on average approx. 2 (winter) to 8 (summer), (seasonal average: 5) cloud free observations per day per covered geolocation, based on MVIRI cloud statistics. An instrument with 15 x 15 km 2 (SSP) in GEO will deliver over Europe on average approx. 1.5 (winter) to 6.5 (summer), (seasonal average: 3.5) cloud free observations per day per covered geolocation, based on MVIRI cloud statistics. A LEO constellation (METOP+NPP/NPOESS+NewUV-Vis) will give on average approx. 0.4 cloud free observations per day per covered geolocation (0.15 for METOP +NPP), based on ATSR-2 cloud statistics. Note: this analysis estimates the amount of cloud free observations w.r.t. to the covered scene, not w.r.t. the number of cloud free observations in a given horizontal cell.

8. Field of View (FOV) and Temporal Sampling FOV: User „European Continent including eastern Europe and surrounding oceans“ => FOV should at least cover Europe in E-W direction from 30°W - 45°E (@40°N) and in N-S direction from 30°N - 65°N => S/C positioned around 0° -10° E Calibration requires Sahara as calibration target to be scanned (weekly – monthly) Temporal Sampling: User “0.5 – 2 hours” => The instrument shall cover the FOV within 1 hour. Horizontal Resolution: User 5 – 20 km, Clouds: 5 – 15 km => target requirement on IFOV is 5 km x 5 km (threshold 20 km x 20 km) at sub- satellite, corresponding to approx. 5 km x 10 km over Europe (latitude dependent). Target more important for UV-Vis (higher sensitivity to lowest troposphere) than for TIR.

9. Solar Backscatter Sounding from Geostationary Orbit Toulouse, 12. Sep. 2003 SeaWIFs

10. Heritage and Related Studies GOME on ERS-2 Demonstrates quantitative determination of trop. column distributions of O 3, NO 2, SO 2, HCHO, H 2 O from solar backscatter measurements SCIAMACHY on ENVISAT Demonstrates quantitative determination of trop. column distributions of CO, CH 4 and CO 2 from solar backscatter measurements Demonstrates value of improved spatial resolution (30 x 30/60 km2) OMI on AURA Demonstrates the use of 2-dimensional CCDs for solar backscatter trace gas applications GOME-2/METOP Polarisation measurement system to characterise aerosol (Hasekamp et al.) GeoSCIA Studies on requirements and instrument concepts MTG-UVS Studies on requirements and instrument concepts

11. UV-Vis-SWIR relevant spectral ranges Main purpose of the O 2 A channel (755 – 780 nm) with its high spectral resolution is to estimate a mean aerosol layer height (Rozanov and Timofeev 1994, Timofeev et al. 1995, Koopers et al. 1997, Heidinger 1998 etc.). Cloud top height and optical thickness can be determined alternatively from low spectral resolution (approx. 1 nm) O 2 A-band measurements or from O 4 absorption and/or Raman scattering (Ring effect).

12. Can polarisation improve on aerosol from GEO? Investigated by O.Hasekamp, SRON Intensity: 350 – 550 nm (w.r.t. albedo), spectral resolution 10 nm Polarisation (Q, U): 350 – 1000 nm, spectral resolution 10 nm SNR: 500 bi-modal (fine and coarse) aerosol model (here industrial aerosol) with 5 free parameters per mode: effective radius, effective variance, aerosol column, real/imaginary part of refractive index Albedo: vegetation Two SZA (45°, 50°) are used simultaneously (5° < 1 hour) Investigated: Degrees of Freedom for Signal (DFS), AOT @ 350 nm and 550 nm, SSA @ 350 nm

13. I Polarisation can improve on aerosol from GEO! Measurements of I and Q results in error on AOT well below (@ 550 nm) the requirement (0.05), DFS=6-7. Measurements of I, Q and U further reduces the error on AOT (roughly factor 2), resulting in AOT @ 350 nm also be within 0.05, DFS=7. DFS > 5 should allow for fine and coarse mode discrimination Instrument Specification (GOME-2 heritage): FOV: as trace gases IFOV: 5 km x 5 km SSP, with the goal to have 5 km x 5 km over Europe Assumption: intensity already measured with trace gas instrument Polarisation: Q, U 350 – 1000 nm, spectral resolution 10 nm SNR: 500 I+Q I+Q+U

14. Spectral Ranges and Resolution The lowest UV window 290 – 310 nm is specified to separate stratospheric from tropospheric O 3 from the combination of the Hartley and Huggins band, as demonstrated by Munro et al. and Liu et al. 2005. 755-780 nm is driven by aerosol height information, high spectral resolution is needed. 2360 nm channel is driven by CO. To minimise the CH 4 and H 2 O interference with CO, the window is somewhat enlarged. It will therefore also yield quantitative information on CH 4.

15. SNR - Earth‘s Radiance SNR derived from sensitivity studies (ESA, EUMETSAT etc.) and GOME, SCIAMACHY experience For the spectral window 290 – 310 nm (mainly strat. O 3 ) a deviation of the specified horizontal resolution to 50 km by 50 km is acceptable to reach the SNR in case this channel might be the driver for the radiometric aperture.

16. Radiometric Requirements Radiometric Calibration driven by requirements on AOT! Trace gases only require approx. 2-3 % In case the PMS is included the requirement can therefore be relaxed.

17. Conclusions and Comments Solar Backscatter Most important drivers for the Solar Backscatter instrument requirements are: –Aerosol (AOT etc.) –trace gases/accuracies –temporal resolution The products delivered by such a system are demonstrated by GOME and SCIAMACHY products Design concepts for a solar backscatter sounder in geostationary orbit were assessed for feasibility and robustness since 1998 by several studies and groups including industry (Astrium, TPD-TNO, SIRA etc.) and agencies (DLR, ESA/EUMETSAT, NERC/UK) coming to very similar conclusions that instrument concepts are mature (see for example ESA’s EEOM 2002 evaluation) and feasible (several studies available), due to the heritage of GOME, SCIAMACHY and OMI designs.

18. Thermal Infrared Sounding from Geostationary Orbit CO from IMG/ADEOS at two layers in the troposphere ( B. Barret et al. ACCENT-AT2) 1 km 10 km

19. Heritage and Related Studies Satellite projects for Nadir-observations of the atmosphere in the thermal infrared (TIR), about 500-3000 cm -1 (3-20  m) relevant to this part of Work Package 3100 are: 1) Interferometric Monitor of Greenhouse Gases (IMG), NASDA 2) Tropospheric Emission Spectrometer (TES), NASA 3) Infrared Atmospheric Sounding Interferometer (IASI), ESA-EUMETSAT 4) Meteosat Third Generation Infrared Sounder, ESA-EUMETSAT 5) Geostationary Fourier Transform Spectrometer (GIFTS), NASA 6) Geostationary Fourier Imaging Spectrometer (GeoFIS), CNRS-LISA, IMK

20. TIR Sounding from GEO Nadir geometry TIR radiative transfer calculations very well established spectroscopic databases: HITRAN 2004 / MIPAS physical effect used to extract vertical profile information: pressure-dependence of molecular lines  requirements on spectral resolution and signal/noise ratio Radiative transfer model calculations study carried out by scientists from LISA, CNES and IMK/FZK Karlsruhe KOPRA code (IMK/FZK, developed for MIPAS) varying degrees of freedom (first-order Tikhonov regularisation) investigate impact of instrument parameters (spectral resolution, signal/noise ratio, spectral coverage) on retrieval (vertical resolution, accuracy of retrieved concentrations) investigate impact of atmospheric parameters (e.g. surface temperature and accuracy of vertical temperature profiles)

21. Spectral Coverage

22. Impact of Surface Temperature

23. Note: T surf = 280 K was used in all calculations. Thermal Contrast

24. Note: Sampling must be higher or equal to twice the highest frequency component of the data. Spectral Resolution

25. Note: Digitizing noise is included (requirement on ADC dynamic range is instrument-dependent). SNR for combined TIR/UV-VIS

26. Radiom. & Spectral Calibration, Stability, ILS

27. Conclusions and Comments TIR Most important drivers for the TIR instrument requirements are: –trace gases: vertical resolutions and accuracies –temporal resolution Comment: Additional calculations have been made at IMK-FZK to assess the dependence of retrieval errors on knowledge of vertical temperature profiles. Result: temperature profiles from meteorological services will be sufficiently accurate for the TIR retrievals. Comment on dimensions and feasibility of TIR instrument: –two parallel studies: IMK-FZK and CNES-PASO (Toulouse) –good agreement with each other –reasonable size, mass, and power consumption –CNES PASO (Toulouse): TIR instrument is feasible

28. Combined Solar Backscatter-TIR

29. UV-SWIR / IR Nadir Synergy Solar Backscatter can provide during daylight total and tropospheric columns of O 3, NO 2, SO 2, HCHO, H 2 O and CO as well as AOT, including the lowest troposphere (at one hour sampling and at 5 km x 5 km (SSP)). Thermal IR can provide height-resolved information in the troposphere on O 3, CO and H 2 O (day and night) In addition, thermal IR can provide columns of C 2 H 6, HNO 3, PAN, N 2 O 5 (night), and has potential to provide columns of Organic Nitrates and SO 2 (enhanced). Combination of Solar Backscatter and IR will significantly improve height information including the lowest troposphere and accuracy (O 3 and CO).

30. UV-SWIR / IR Nadir Sounding Synergy IR retrieval used as a-priori for solar backscatter retrieval (3 level) Combined retrieval on solar backscatter and IR emission is a must to get maximum vertical resolution in the troposphere precisions in the PBL (0-2 km) which meet the requirements in this layer. Results on CO in agreement with findings from P. Coheur et al. (EUMETSAT MTG study)

31. Comparison to User Requirements

33. (Note 1): Uncertainties for HNO3, N2O5 (night) and Organic Nitrates need further studies to be established.

34. Options for a Geo Component driven by B1-B3 A) combined solar backscatter and TIR sounding mission addressing B1-B3 requirements at one hour sampling and at 5 km x 5 km SSP (solar backscatter, TIR: 15 km x 15 km) Solar backscatter will provide total and tropospheric columns of O 3, NO 2, SO 2, HCHO, CO as well as data on aerosol (AOT etc.) TIR will provide O 3 and CO profiles, tropospheric columns of C 2 H 6 and PAN during day and night and has potential to provide HNO 3, N 2 O 5 (night) and Organic Nitrates (study Meteo France: T profiles from met. offices will be precise enough for TIR) Combined Solar Backscatter – TIR sounding: height resolved O 3 and CO with enhanced sensitivity to lowest troposphere, B) a solar backscatter sounding mission addressing B1/B2 column requirements at one hour sampling and at 5 km x 5 km (SSP) Solar Backscatter provides total and tropospheric column information on O 3, NO 2, CO, SO 2, and HCHO as well as AOT, including the lowest troposphere (at one hour sampling and at 5 km x 5 km (SSP)). Addition of H 2 O can address B3 No nighttime coverage and no data on HNO 3, PAN, N 2 O 5 and Organic Nitrates No height resolved information on O 3 and CO in the troposphere.

35. Conclusion GEO The user requirements for European Air Quality Applications are best served by a combined solar backscatter and TIR sounding mission addressing B1-B3 requirements at one hour sampling and at 5 km x 5 km SSP (solar backscatter, TIR: 15 km x 15 km) Solar backscatter will provide total and tropospheric columns of O 3, NO 2, SO 2, HCHO, CO as well as data on aerosol (AOT etc.) TIR will provide O 3 and CO profiles, tropospheric columns of C 2 H 6 and PAN during day and night and has potential to provide HNO 3, N 2 O 5 (night) and Organic Nitrates (study Meteo France: T profiles from met. offices will be precise enough for TIR) Combined Solar Backscatter – TIR sounding: height resolved O 3 and CO with enhanced sensitivity to lowest troposphere,

36. Contribution of a European GEO AQ Mission