OMI follow-on Project Toekomstige missies gericht op troposfeer en klimaat

1. OMI follow-on Project Toekomstige missies gericht op troposfeer en klimaat Pieternel Levelt, KNMI

2. Importance of Tropospheric Measurements Tropospheric chemical science has very strong links to: • Climate • Air quality • Anthropogenic influence

3. Troposphere • Next challenge for satellite instrument development is to map the troposphere for air quality monitoring and climate research: • Tropospheric measurements needs: • higher spatial resolution • improved accuracy for O3, NO2, aerosols, clouds, HCHO • together with CO, CH4, CO2 and H2O • improve aerosol information • improve time-resolution • preference for daily global coverage(air quality) GOME Observations of Formaldehyde over North America Chance et al., Geo. Res. Let. 27, 3461-3464, 2000.

4. (tropospheric) Ozone Aerosols (tropospheric) NO2 SO2 Formaldehyde BrO UV/VIS CO CH4 CO2 H2O NIR Tropospheric Important Trace Species

5. Why these trace species? I • Ozone is a toxicgreenhouse gas. • Small aerosols are toxic, have direct & indirect global warming effects. I I I • CO indicates combustion; has a chemical role (CO2, CH4) • HCHO indicates VOCs; has role in O3 & aerosols • NO2 indicates NOx; is precursor to O3 & aerosols • SO2 traces combustion, is major aerosol precursor • CO2 is an important greenhouse gas • H2O is an important greenhouse gas

6. Climate Forcing Source: IPCC

7. Currently available or selected tropospheric-climate missions Few measurements from space to date: except: • MOPITT CO, TOMS residual O3, GOME NO2, BrO, HCHO, MODIS for aerosols and clouds • TES and OMI (Aura) and SCIAMACHY (ENVISAT) will provide many new measurements • Selected OCO NASA mission (2007): Measures CO2 with 1 km2 pixels and 10 km swath. • However: Tropospheric chemical science needs more and more accurate measurements

8. OMI on EOS Aura • Spectrometer in wavelength range 270 – 500 nm • Daily Global Coverage • Small Ground Pixels (13x24 km2) • Polarization Scrambler

9. OMI Measurement Principle Courtesy of Dutch Space

10. New Developments for Polar missions • Smaller Ground Pixels (will also improve accuracy) • Extending the Wavelength Range (add IR-channel) • Multi-Angle Viewing (for improved aerosol detection) • Assumption: Start from current Leo-OMI optical design: This means that a smaller spatial resolution of 10 x 10 km2 is not feasible, since this is the optical resolution of the instrument in polar orbit!

11. Chosen for a module approach: • OMI/SCIAMACHY + instrument is by itself a very complete tropospheric instrument • Depending on missions, channels can be adjusted or skipped

12. Requirements UV/VIS • Ground pixels: decreased to 12 x 13 km2 (except for UV-1, 40 x 40 km2) • Spatial sampling: 3 x • 270 - 500 nm, preferred extension to 600 nm (O3 and O2-O2) • Spectral resolution: minimal OMI, preferred GOME • Spectral sampling: 3 x • Daily global coverage • S/N ratios same as in OMI SRD, except for O3 and NO2 column

13. Requirements NIR • Ground pixels: 12 x 13 km2 • Spatial sampling: 3 x • 1,6 (CH4 and CO2) and 2,4 mm (CO) • O2A band detection for airmass factor (760 nm) • Spectral resolution: 0.08 nm (CO2), 0.15 nm (CO & CH4) and 0.08 nm for O2A band • Spectral sampling: 3 x • Daily global coverage for CO, for CH4 and CO2 not necessary (1000 km swath) • S/N ratios: see input SRON

14. Technical Challenges Identified • Size of instrument: • - NIR increases size of instrument • - High spectral resolution in combination with high spatial resolution and broad swath • S/N: smaller pixels and same or increased S/N is needed ! • CCD’s: CCD with preferred requirements at this moment non-existent; techniques to built it are however available • Scrambler for polarisation insensitivity optimal for UV/VIS and IR • Grating: New developed grating needed in order to decrease size of instrument • Temperature control of instrument, especially 2,4 mm • And more can follow ….. Caveat: in case higher spatial resolution is needed for tropospheric trace gases to obtain needed accuracy.

15. 6 options UV/VIS and IR now studied by industry (1) Climate mission: Complete UV/VIS and CO, CO2, CH4 and O2A (2) Air Quality mission: Complete UV/VIS and CO (3) Climate mission with 1000 km swath for NIR and O2A (4) Climate mission as (1), without CO (5) Same as (3) but with 2 telescopes (6) Same as (1) but with 1000 km swath

16. Monitoring Aerosol Mean aerosol optical depth in August 1997 (monthly average). Retrieved from ATSR-2 image (see Gonzalez et al., Geophys. Res. Lett., 27, 955-958, 2000 )

17. Aerosol retrieval • Use dual viewing concept for info on surface albedo for aerosol retrieval and AMF information for trace gas retrieval • - Current OMI for nadir • - Add one viewing angle looking forward • - Need for an extra CCD for forward looking channel, and second telescope • Technical Challenge: calibration of those two channels with high accuracy! Not clear if this is feasible.

18. Summary • OMI Technology is very suitable for remote sensing of the troposphere • - Spatial resolution can be improved to 10 x 10 km2 • - Wavelength range can be extended to NIR • High-level instrument requirements for UV/VIS and NIR are decided • Currently 6 possible instrument designs are studied on feasibility: many technical challenges are identified • Multi angle viewing seems to be more difficult than expected due to calibration difficulty • Caveat: in case higher spatial resolution is needed: new instrument design probably needed