1. SSMIS and the Unified Pre-Processor (UPP)
Bill Bell1 and Steve Swadley2
1 European Centre for Medium Range Weather Forecasting, Reading, UK
2 US Naval Research Laboratory, Monterey

2. Overview Microwave Imager Data in NWP The SSMIS Instrument
Calibration Anomalies in F16, F17 & F18
Reflector Emission
Solar Intrusions / Gain Anomalies
Scan Biases
Spillover Correction*
SSMIS UPP data quality in NWP
Summary, Conclusions & Questions

3. Planned Operational MW Imaging & Imaging/Sounding MissionsUS
China
Russia
Japan
Research platforms not shown, eg: Windsat, AMSR, TMI, GMI, Mega-Tropiques …

4. Assimilation of MWI data at NWP Centres
Model/DA
SSMI
SSMIS
AMSR-E
TMI
Windsat
ECMWF
(Europe)
T1279/L91
4D-Var
F15 only
F16
Radiances
F17/F18
Met Office
(UK)
N512/L70
F16 (LAS)
(u,v)
JMA
(Japan)
T959/L60
F16/F17 ENV
F16 LAS
radiances
F18
NRL
(US)
T239/L42
WS/TCWV
WS / TCWV
F16/F17/F18
Canada
35km/L80
Sea ice
Meteo-France
T798/L70
Assimilated
Monitored
Planned in 2010

5. SSMIS Instrument 24 Channel Microwave Imager/Sounder
Conical Scan (53° Incidence Angle)
0.61 m Graphite Reflector (VDA/SiOx)
Res. (km) Freq. (GHz)
Imaging 12.5 km (5) km 19 – 37 (5)
LAS T km (8)
LAS Hum km 150, 183 (3)
UAS T km (5)

6. Biases in SSMIS Radiances
Reflector Emission
Solar Intrusions/ Gain Anomalies
Cross Scan Biases
Spillover Correction Errors
Residual Doppler Signals

7. Biases in SSMIS Radiances
Reflector Emission
Solar Intrusions/ Gain Anomalies
Cross Scan Biases
Spillover Correction Errors
Residual Doppler Signals

8. Biases in SSMIS Radiances: Reflector Emission
Difference between
Observation &
Model (in TB space):
(OB-BK)
(also known as
First Guess Departure)
Un-corrected OB-BK / K
Solar Intrusion
Earth Shadow
Scan Non-Uniformity

9. Frequency Dependence of the SSMIS Reflector Emission Bias
Time series of Scan Averaged OB-BK for SSMIS Channels 5 and 11
These are plots of the scan averaged OB-BK departure vs. time for channels 5 and 11 (55.5 and 183±1 GHz) for the F-16 on the left and F- 17 on the right.
The horizontal GRAY bars show the times of the earth and spacecraft shadow for F-16, and the earth and solar array shadowing for F-17.
The GREEN line is the reflector rim temperature for F-16, and the rear refelector temperature for F-17.
F GHz Channel
Shows 1.5 K Jump
at emergence from Earth Shadow
F GHz Channel
Shows 7 K Jump
at emergence from Earth Shadow
ε(55.5)Rflct ~
ε(183)Rflct ~

10. Reflector emission: entering Earth shadow
Visualisation Software (DGS)
Mike Werner, Aerospace Corp.
Main reflector
ε ≠ 0
(Imperfect VDA coating,
reducing reflectivity
from → )
Effects correctable, if TANT & ε known
ε NOT known from pre-launch measurements,
TANT measured NOT representative for F16
Main reflector
exposed to direct sunlight
on exiting & entering
earth shadow

11. Characterising TANT & ε : Channels 2 – 7
Temp sounding channels
trop – lower strat
(AMSU-A like channels)
Ch : ε = 0.01
6,7 : ε = 0.02
T corr = 30 – 40 K
(effectively calibrating
reflector emissivity
using NWP T fields)
Assume :
Chs ( GHz)
ε = 0
(Status in 2007)

12. Analysis and Verification of Root Causes
Precise Effective Conductivity
Measurements Of Reflector
Surfaces Using Cylindrical TE01
Mode Resonant Cavities
Aluizio Prata, Jr. (USC)‏
Ezra M. Long and Shannon T. Brown (JPL)‏
A new technology was being developed by researchers at JPL and USC, to measure the effective conductivity of the reflector surfaces, and from that measurement compute the resulting emissivity.

13. Effective Conductivity and Thermal Emissivity
For Large Effective Conductivities, the approximate v and h polarized
emissivities are:
Effective Conductivity, σ [MS/m]
Example:
183 GHz Pure Al at 300 K
Өi = 18°
σ = MS/m
: Frequency [Hz]
: Free-space permittivity
[F/m]
: Surface Incidence angle
The equations governing the relationship between the Effective Conductivity measurements, which are independent of frequency, and the vertical and horizontal polarized emissivities at a given incidence angle and frequency.
θi = 18° corresponds to the SSMIS reflector offset from the focus of the parent paraboloid.
[MS/m] = MegaSiemens/m
Ideally, we want an εRflct
approaching that of Pure Al

14. JPL/USC Effective Conductivity Measurements
SSMIS Mass Model
Bare Graphite Composite
Reflector
SSMIS F18
(Spare Reflector)
MS/m‏
SSMIS SN03
Original F18
SSMIS SN04
Original F19
CMIS Coupon
AMR Anomalous
Coupons
60.0
Pure Al
Reflector Emissivity
Emissivity vs. Effective Conductivity
Effective Conductivity vs. Computed Emissivity for various SSMIS frequencies.
Clearly , the uncertainty in the current surface coating process cannot guarantee a reflector that meets the needs of precision microwave radiometry.
Pre-flight measurements of this nature must be made a requirement.
Effective Conductivity [MS/m]
A. Prata & S. Brown,

15. Analysis and Verification of Root Causes
Roughened Surface
Smooth Surface
VDA* Layer
Carbon Fibers of the Unidirectional Cross-Layered Tape (P75S/ERL1962) forming the Epoxy Shell
32 GHz σE = 3.4 MS/m
55 GHz ε =
32 GHz σE = 33 MS/m
55 GHz ε =
JPL surface roughening methods included differing degrees of Scotch- Brite applications. Yes, Scotch-Brite scrubbing pads just like the ones at home.
Here is the result of aggressively applying the Scotch-Brite roughening (pressing hard).
Note the discontinuous VDA layer, i.e. a poor conductor
*VDA: Vapor Deposited Aluminum

16. Reflector Emission Model
Assume Reflector Emissivity can be estimated by the slope of an ensemble of:

17. F17
Ch. 3
εRflct ~ 0.019
OB-BK
TRflct-OB

18. F16 Reflector Emissivity Estimates
LAS Channels 3-7, 24, DTG:
F16

19. F17 Reflector Emissivity Estimates
LAS Channels 3-7, 24, DTG:
F17

20. F18 F18 Reflector Emissivity Estimates
LAS Channels 3-7, 24, DTG:
Verifies Pre-Flight Conductivity Measurements
F18

21. Scan-Averaged OB-BK Time Series
F18
OB-BK
F18
Scan-Averaged OB-BK Time Series
F17
OB-BK
F17
Scan-Averaged OB-BK Time Series

22. F18
OB-BK
Ch 3
F17
OB-BK

23. F18
OB-BK
Ch 11
F17
OB-BK

24. Biases in SSMIS Radiances
Reflector Emission
Solar Intrusions/ Gain Anomalies
Cross Scan Biases
Spillover Correction Errors
Residual Doppler Signals

25. Solar Intrusions into the Warm Calibration Load
Visualisation Software (DGS)
Mike Werner, Aerospace Corp.
warm load
SSMIS can suffer
from both
DIRECT and
INDIRECT
(reflected)
Intrusions into
the warm load
F16 had both
Fence mitigated
direct intrusions
in F17 onwards
Attempt to eliminate
INDIRECT intrusions
may have led to
new problems in F18

26. Calibration anomalies: warm load solar intrusions
Effect of
intrusions wc cc wl
radiometer
counts
Brightness
temperature
Tb0 Tb sc
UPP V2 uses modified gain data, based on Fourier filtering of the actual gain, to correct for intrusions.
Direct & indirect for F16
Indirect only for F17 onwards

27. Biases in SSMIS Radiances
Reflector Emission
Solar Intrusions/ Gain Anomalies
Cross Scan Biases
Spillover Correction Errors
Residual Doppler Signals

28. F-17 SSMIS LAS Scan Dependence
Instrument dependent
Due to spacecraft
obstructions &
RT modelling errors
These biases are
corrected in the UPP V2
using a fov dependent
scaling factor

29. Biases in SSMIS Radiances
Reflector Emission
Solar Intrusions/ Gain Anomalies
Cross Scan Biases
Spillover Correction Errors
Residual Doppler Signals

30. Spillover Correction Errors
F15 SSMI
Tscene : Estimated scene TB
TREFL: Reflector temperature
ε : Reflector emissivity
K: Spillover factor
Errors in K will be manifested
as biases in TSCENE
F17 SSMIS
Biases are currently large for
SSMIS, due to errors in
imager channel spillover
factors
This will be critical for
climate applications
of the data:
but not difficult to tune
Bias correction / K

31. DMSP SSMIS UPP UPP Before After UPP V2 includes
Reflector Emission Corrections (F16 and F17)
Spatial Averaging to reduce NEΔT to K level (NRL only)
Uses Operational NGES Fourier Filtered Gain Files to Correct Gain Anomalies
Produces ASCII and BUFR TDR output files at full and/or filtered resolution
Performs Scan Non-uniformity corrections
SSMIS UPP V2 Operational at FNMOC (F /2008, F /2009, F18 – Apr ’10)
FNMOC distributes UPP data to NESDIS for use by the NWP Community
The SSMIS Unified Preprocessor was jointly developed by the Met Office and NRL to specifically meet NWP DA needs.
The UPP Produces SSMIS data that Meet the Stringent NWP Radiance Assimilation Accuracy Requirements for Temperature Sounding Channels
Plans are to allow for user specified Averaging to meet specific application requirements. i.e. Mesoscale NWP
SSMIS UAS Radiance Assimilation will also Require Pre-Processed SSMIS TDR data with the required Geomagnetic Parameters
F-17 SSMIS Data Present an New Challenge for the Radiance Assimilation Community to Produce TDR Data meeting the NWP DA Requirements

32. F16 & F17 SSMIS UPP Imager Channel Data Quality: comparison with SSMI, AMSR-E and TMI
STD (FG departures)
F16 – F18 SSMIS
imager data quality
similar to currently
used imagers.
(NB. Variational bias
correction deals with
relatively large TB
biases – due to spillover
correction error)

33. ECMWF MWI Upgrade (replacing F15 with F17, adding TMI)
Improved forecast fit to IR Radiances
First Guess departures for HIRS, AIRS and IASI
(normalised to F15+AMSR-E fits)
Tropics only
F15 + AMSR-E (current operations)
F17 + AMSR-E
F17 + AMSR-E + TMI (CY36R4)

34. ECMWF MWI Upgrade (replacing F15 with F17, adding TMI)
Improved forecast fit to MW Radiances
First Guess departures for AMSU-B/MHS, AMSR-E and AMSU-A
(normalised to F15+AMSR-E fits)
Tropics only
F15 + AMSR-E (current operations)
F17 + AMSR-E
F17 + AMSR-E + TMI (CY36R4)

35. ECMWF MWI Upgrade (replacing F15 with F17, adding TMI)
Improved forecasts NH SH
100 hPa
200 hPa
500 hPa
degradation
+5%
improvement
-5%
T799 DJF 2009/10
RMSE Z scores
CY36R4 vs current
configuration

36. Summary
SSMIS has become the most important MWI data set for NWP data assimilation
F16 - F18 SSMIS suffer from a range of systematic biases, which has required the development of corrections & modifications to instrument design and pre-flight testing. F18 performs better than F16, but work remains to be done !
The UPP was envisaged as a community unified ‘pre-processor’, feedback welcomed.
UPP data from F16 - F18 available from FNMOC, via NESDIS for NWP applications
UPP-CP under development (see Joe’s talk next !)