1. Assimilation of surface sensitive infrared channels over land at Environment Canada
L. Garand, S.K. Dutta, and S. Heilliette
DAOS Meeting
Montreal, Qc
August 15-16, 2014

2. Outline Context & motivation Approach Assimilation results
________________________
Also: Update on PCW mission

3. Context & motivation
Env. Can. moving to ensemble-variational system with:
Flow-dependent background errors including surface skin temperature correlations with other variables
Analysis grid at 50 km, increments interpolated to model 25 km grid (15 km in 2015)
~140 AIRS and IASI channels assimilated: many sensitive to low level T, q, and Ts. RTM is RTTOV-10.
Favorable context to attempt assimilating surface-sensitive IR channels over land and sea-ice vs earlier work with GOES (Garand et al. JAM, 2004) with analysis grid at 150 km and no hyperspectral IR.

4. Ensemble spread of Ts (Feb-Mar 2011)
00 UTC UTC
Maximum ~15h local
In SH (summer)
Maximum at night
Tibetan area (winter)
Ts background error
over land in 4Dvar is
Constant: 3 K.
In EnVar, B is
0.5(BENKF+ BNMC)
12 UTC UTC

5. Ensemble T(~964 hpa) spread (Jan-Feb 2011)
00 UTC UTC
Only minor
variations with
local time
Values < 0.5 K in SH
seem underestimated
12 UTC UTC

6. Key factors to consider
Reliable cloud mask
Spectral emissivity definition (CERES, U-Wisconsin)
Highly variable topography
Radiance bias correction
Background and observation error definition

7. Approach guided by prudence
Assimilate under these restrictive conditions over land and sea ice:
Estimate of cloud fraction < 0.01
High surface emissivity (> 0.97)
Relatively flat terrain (local height STD < 100 m)
Diff between background Ts and retrieval
based on inverting RTE limited to 4K
Radiance bias correction approach:
For channels flagged as being surface sensitive, use only ocean
data to update bias coefficients

8. Assigned observation error to radiances
Assigned = f std(O-P) Desroziers = <(O-P)(O-A)>
15.0mm
4.13mm
15.3mm
4.50mm
f typically in range

9. Limitation linked to topography
Criterion used: local STD of topography < 50 m (on 3X3 ~50 km areas)
RED: accepted, white std > 100 m, blue 100>std>50 m

10. Limitation linked to surface emissivity
AIRS ch 787
Emissivity based on
CERES land types
(~15 km)
+ weighted average
for water/ice/snow
fraction.
Accept only emissivity > 0.97 ; Bare soil, open shrub regions excluded.

11. Examples of emissivity from CERES
10.7 micron micron
water: water: 0.977
A large portion of land masses have surface emissivity > 0.97

12. First attempt: negative impact in region 60-90 N/S
00 hr hr
Possible cause: cloud contamination ?

13. Second attempt: added constraints
Cut latitudes > 60 deg
Local gradient of topography < 50 m (was 100 m)
Strong impact on (O-B) stats for surface channels

14. T std error diff. (CNTL-EXP) NH-Extratropics 6 Feb to 31March 2011
vs ERA Interim vs own analysis
Consistent positive impact vs ERA Interim and own

15. T std diff (CNTL-EXP) vs ERA-Interim
Tropics SH Extratropics

16. Zonal T STD difference (CNTL-EXP) vs ERA-Interim
72-h
120-h

17. Time series of T std diff at 850 hPa
(b)
(a)
CNTL
EXP
NH extratropics Tropics
EXP superior to CNTL % of cases at days 3-5

18. 850 hPa TT anomaly cor.
CNTL
EXP
NH extratropics Tropics

19. 120-h N-Extr vs ERA-Interim
CNTL
EXP
U HR
GZ T

20. Validation vs raobs 120-h Feb-Mar 2011 (59 days)
CNTL
EXP
SH-extratropics NH-extratropics
U V U V
GZ T GZ T

21. Validation vs raobs 120-h FEB-Mar 2011 (59 days)
CNTL
EXP
North America Europe
U V U V
GZ T GZ T

22. Added yield: about 15% (for surface sensitive channels)
CNTL
EXP
Number of radiances assimilated for surface channel AIRS 787
CNTL: ~1400/6h EXP: ~1600/6h
Region: world, EXP excludes surface-sensitive channels at latitudes > 60
Radiance thinning is at 150 km

23. Std/bias of (O-P) and (O-A), AIRS 787 CNTL EXP
No major impact on bias. Strong assimilation over land,
with std (O-P) of ~1.7 K, std (O-A) of 0.40 K (not shown)

24. Conclusion Very encouraging results, especially in NH where most
of new data are assimilated
Next steps:
Relax limitations on emissivity, use MODIS-derived atlas
Run a summer cycle
Seek operational implementation
Longer term
Evaluate problems specific to high latitudes

25. Update on Polar Communications and Weather (PCW) mission
Goal:
Fill communication and meteorological
observation gaps in the Arctic
Most likely configuration:
2 satellites in highly elliptical orbits
Status:
Seeking approval from Government
in early Could start
operating in 2021.
Meteorological instrument:
Similar to ABI or FCI
A possible 2-sat HEO system

26. Weather: High-Level Requirements
Capabilities
‘GEO-like’ continuous imaging of Arctic circumpolar region
‘GEO-like’ spatial (1-3 km) and temporal (15 min) resolution
‘Next-generation’ meteorological imager (ABI, FCI, 16+ channels)
Near-real time processing to L1c for delivery to Environment Canada
Compatibility with GEO imagers as part of WMO Global Observing System.

27. Orbit Comparison (2-sat Constellation)
Molniya (12-h)
Apogee: 39,800 km
TAP (16-h)
Apogee: 43,500 km
Tundra (24-h)
Apogee: 48,300 km
The Highly Elliptical Orbits “quasi-geostationary” imaging and communications services at high latitudes:
High temporal sequences
Simultaneous retrievals
Stereo views
12hr HEO:
Provides excellent area coverage with apogee height similar to GEO
Critical inclination 63.4 deg makes apogee location stable
24hr HEO
Inclination > 80 deg needed to get reasonable imaging coverage
High apogee and ground speed and are not ideal for imaging
Significant Orbital maintenance required
Communications services are more difficult because a satellite cannot see the opposite hemisphere as it descends from apogee and is then at much lower latitude
16 hr HEO has intermediate features of both
Critical inclination gives reasonable coverage , but 66 deg inclination is better
Larger Orbital maintenance required for 66 deg
TAP is unique in that both sats follow same ground track. In contrast Molniya and Tundra sats each have their own ground track (and apogees).

28. Science Studies: Uniqueness of HEO System vs LEO
23 LEO satellites needed to get 15 min
Imagery at 60 N, versus 2 HEO
Trichchenko and Garand,
Can. J. Remote Sensing, 2012
Also, capability to get image triplets for AMV vastly superior to LEO

29. Science Studies: Impact on NWP
OSSE showing significant impact of PCW
AMVs filling gap in polar areas
Garand et al., JAMC, 2013
Positive impact (blue) at 120-h
In both polar regions from 4 satellites

30. Example of PCW Geometry Matching [16-hr TAP Orbit] for intercalibration
VIIRS/SNPP
GEO
Trishchenko and Garand, GSICS Newsletter, 2012