Observing CO 2 from a highly elliptical orbit for studies of the carbon cycle in the Arctic and boreal regions

Transcription

1 Observing CO 2 from a highly elliptical orbit for studies of the carbon cycle in the Arctic and boreal regions Ray Nassar 1, Chris Sioris 2, Dylan B.A. Jones 3, Kaley A. Walker 3, Chris McLinden 4, C. Tom McElroy 5 1 Environment Canada - Climate Research Division, ray.nassar@ec.gc.ca 2 University of Saskatchewan 3 University of Toronto 4 Environment Canada - Air Quality Research Division 5 York University Arctic Products Validation and Evolution (APVE) workshop,

2 Boreal and Arctic Carbon Boreal Forests Longer growing season and increase in disturbances may enhance or reduce their net carbon flux McDonald et al. (2004) Tarnocai et al. (2009) Permafrost 1672 PgC, twice atm mass (835 PgC) with potential for release as CO 2, CH 4 ~85 PgC by 2100 ( PgC/yr) from extrapolation of measurements at an Alaskan site (Schurr et al. 2009) Models: 104±37 PgC (Schaefer et al. 2011) and PgC (Schneider von Deimling et al. 2012) by 2100 How can satellites play a role?

3 Satellite Orbits and Coverage Low Earth Orbit (LEO) Near-polar plane Below ~1000 km altitude If sun-synchronous, global sampling at fixed overpass time GOSAT, OCO-2, TanSat Geostationary Orbit (GEO) Near-equatorial plane ~35,800 km altitude Synchronized with Earth rotation, continuous coverage over selected area (< 60 N/S) Communications, Weather, Trop Chemistry (TEMPO, GEO-CAPE, Sentinel-4, GEMS) Some proposed CO 2 and CH 4 missions GOSAT (NIES v averaged at 0.9 x 0.9 )

4 Satellite Orbits and Coverage Low Earth Orbit (LEO) Near-polar plane Below ~1000 km altitude If sun-synchronous, global sampling at fixed overpass time GOSAT, OCO-2, TanSat Geostationary Orbit (GEO) Near-equatorial plane ~35,800 km altitude Synchronized with Earth rotation, continuous coverage over selected area (< 60 N/S) Communications, Weather, Trop Chemistry (TEMPO, GEO-CAPE, Sentinel-4, GEMS) Some proposed CO 2 and CH 4 missions Example of Geostationary Fields of Regard

5 Highly Elliptical Orbit (HEO) WMO Vision for the Global Observing System (GOS) in 2025 Conservation of angular momentum requires faster motion when close to Earth (perigee), slower motion when far from Earth (apogee) Apogee Tundra Orbit (2 apogees): T = 24 hr, H a = 48,300 km Three Apogee (TAP) Orbit: T= 16 hr, H a = 43,500 km Molniya Orbit (4 apogees): T = 12 hr, H a = 39,800 km T = period, H a = apogee altitude (higher than GEO 35,800 km) Perigee HEO options summarized in Garand, Trishchenko, Trichtchenko and Nassar (2014), Physics in Canada, 70, (4), in press.

6 Polar Communications and Weather (PCW) Canadian mission with 2 satellites in Highly Elliptical Orbit (HEO) configuration, under consideration for launch ~ 2020 Main objectives are to expand Arctic communications capabilities and provide meteorological observations Canadian Space Agency (CSA) is separately considering additional science instruments under the Polar Highly Elliptical Orbit Science (PHEOS) program The Weather, Climate and Air quality (WCA) mission concept is an atmospheric research option that completed Phase A in 2012 (PHEOS-WCA PI was Jack McConnell of York U)

7 PCW-PHEOS-WCA Spectral Bands / Species Fourier Transform Spectrometer (FTS) UV-Visible Spectrometer (UVS) FTS Band (µm) Band (cm -1 ) Resolution Target species cm -1 T, H 2 O, O 3, CO, CO 2, cm -1 CH 4, HNO 3, CH 3 OH, HCOOH, PAN, HCN, NH 3, SO 2 3a cm -1 CH 4 columns 3b cm -1 CO 2 / CH 4 columns cm -1 O 2 A band (p surf, aerosol) UVS ~ 1 nm O 3, NO 2, aerosol, BrO, HCHO, SO 2, Mass/Volume Compliant Instrument has red bands, but not blue

8 PCW-PHEOS-WCA Instrument Configurations Fourier Transform Spectrometer (FTS) UV-Visible Spectrometer (UVS) CSA Allocations Size: 30 x 30 x 30 cm 3 ( cm 3 ) Optimal Configuration Lite All Bands Configuration Compliant Configuration Mass: 50 kg Power: 100 W FTS (aperture 15 cm) with UVS, 85 kg ~ * cm 3 FTS (aperture 10 cm) with UVS, 45 kg ~35 128* cm 3 FTS (aperture 10 cm) No O 2 A band or SWIR CO 2 O 2 A band and SWIR CO 2 No UVS, 37 kg ~25 184* cm 3 *configuration volumes given with 20% contingency

9 Observing System Simulation Experiment (OSSE) Objective: Compare the potential information from HEO vs. LEO for constraining boreal and Arctic CO 2 surface fluxes by data assimilation of atmospheric CO 2 observations Approach: Designate a CO 2 model simulation as the Truth Create synthetic observations for LEO and HEO by sampling the model at hypothetical observation locations/times then adding noise Assimilate each set of synthetic observations to optimize biospheric CO 2 fluxes and assess posterior fluxes and uncertainties relative to the Truth Nassar, Sioris, Jones, McConnell (2014), Satellite observations of CO 2 from a highly elliptical orbit for studies of the Arctic and boreal carbon cycle, J. Geophys. Res. 119, , doi: /2013jd AGU Research Spotlight: EOS 95, no. 29, 2014-July-22

10 Generating Synthetic Observations GOSAT: Simulated orbit using SPENVIS (ESA), 3 cross track obs: orbit track, ±263 km, glint subsolar±20 PCW-PHEOS-WCA: Three Apogee Orbit 2 satellites, 8h apart in co-planar 16h orbit Apogee ~43,500 km, Perigee ~8100 km 3 Apogees/day (8:00 and 16:00 local time) observing ±4 h from apogee giving up to 16 h of data per 48 h per region Region/apogee: 48 scans consisting of 56x56 array of 10x10 km 2 pixels in 80 min. Checkerboard pattern in FOV to thin data and meet downlink requirement. Observations every other repeat cycle to accommodate other observing priorities.

11 Solar Zenith Angle, Albedo, Cloud Only retain when Solar Zenith Angle (SZA) < 85 Spectral Albedo Values from MODTRAN AVHRR* 1 x1 surface types *Advanced Very High Resolution Radiometer GEOS-5 Cloud Fraction 0.5x Signal-to-noise ratio (SNR) depends on surface albedo. Nadir XCO 2 retrievals over ocean, sea-ice and old snow are assumed unlikely. Used GOSAT v2.0 averaging kernels for each surface type.

12 Comparison of observations per 1 x1 No observations over snow Obs over seasonal snow included* Number of observations per month GOSAT mean simulated obs per month: 13031(no snow) and (snow) (NIES v2, 1 st year of mission) Post-filtered *Precision of obs over snow degraded by a factor of 2

13 Summary of Key Findings CO 2 flux TgC/month Mean HEO/LEO uncertainty for 14 Arctic and boreal regions Configuration Obs over Snow Jun Jul Aug Annual Optimal Lite Yes No Yes No PHEOS-FTS offers significant flux uncertainty reductions relative to GOSAT with the largest gain in the summer Largest interannual variability, uncertainty and potential for change to Arctic/boreal carbon cycle (forest disturbances and permafrost thaw) is in the summer, when PHEOS-FTS offers the greatest potential constraints

14 CO 2 and CH 4 Validation Validation of column-average CO 2 and CH 4 mole fractions (XCO 2, XCH 4 ) requires column measurements by ground-based remote sensing The Total Carbon Column Observing Network (TCCON) is the only widely accepted method TCCON instrumentation and retrievals are standardized and data are calibrated to the WMO scale by in situ profile measurements from aircraft overflights TCCON stations in the NH (white dots)

15 Cross Validation for GEO Missions LEO, GEO and HEO missions could be used to validate each other, but sun-synchronous LEO only give one point in the diurnal cycle. HEO can be compared with GEO FORs that do not overlap.

16 PHEOS-FTS Balloon Demonstrator Test PHEOS-FTS design readiness for CO 2 / CH 4 imaging, pointing stability/control over 100 s scan from a high altitude balloon launched from CNES-CSA balloon facility in Timmins, Canada * NEXT TALK * (48.6 N, 81.4 W) Credit: CSA