(1) Calibration of AIRS SRFs (2) AIRS Forward Model...
Transcript of (1) Calibration of AIRS SRFs (2) AIRS Forward Model...
AIRS: February 2000 STM
(1) Calibration of AIRS SRFs
(2) AIRS Forward Model Schedule & Validation
L. Larrabee Strow
Scott E. Hannon
Sergio De Souza-Machado
Howard E. Motteler
U M B C
UN
IVE
RSI
TY
OF
MARYLAND BALTIM
OR
E C
OU
NTY
1 9 6 6
Department of Physics
University of Maryland Baltimore County (UMBC)
Baltimore, MD 21250
L. Strow, UMBC 1
AIRS: February 2000 STM
Overview
• SRF Calibration Review and Status
• Forward Model Schedule, pre-launch
• Forward Model Schedule, post-launch
• Validation Requirements
L. Strow, UMBC 2
AIRS: February 2000 STM
Overview: SRF Calibration
• Grating Model Fits and Fringe Removal
• Sensitivity of Centroids (Y-offset), Focal Length, Widths to
Temperature
• Model Fits to SRF Shapes: Wings, Center Region
• Absolute Calibration with CO Trace Gas, Air Gap Spectra
L. Strow, UMBC 3
AIRS: February 2000 STM
Grating Model Fits and Temperature Sensitivity
• Fringe removal using summed SRFs very successful
• SRF Centroids all move together nicely with temperature
• Focal length, widths insensitive to temperature
• Slight quadratic error in grating model fits to centroids (1% of
width level)
L. Strow, UMBC 4
AIRS: February 2000 STM
Example Grating Model Fits (Red=Raw Data, Blue=Fringes Removed)
−1
−0.5
0
0.5
1
% o
bs−
calc
cen
ters
Test:1621, Module: M4d, Gain:Opt, Good Chans:93%
1210 1220 1230 1240 1250 1260 1270 1280−15
−10
−5
0
% o
bs−
calc
wid
ths
Wavenumber (cm−1)
−2
−1
0
1
2
% o
bs−
calc
cen
ters
Test:1621, Module: M5, Gain:Opt, Good Chans:93%
1040 1060 1080 1100 1120 1140−15
−10
−5
0
% o
bs−
calc
wid
ths
Wavenumber (cm−1)
L. Strow, UMBC 5
AIRS: February 2000 STM
GM Fit Errors if Channels 82/83, 118/119 Removed
−2
−1
0
1
2%
obs
−ca
lc c
ente
rs
Test:1621, Module: M12, Gain:Opt, Good Chans:95%
645 650 655 660 665 670 675 680 685−20
−15
−10
−5
% o
bs−
calc
wid
ths
Wavenumber (cm−1)
L. Strow, UMBC 6
AIRS: February 2000 STM
Variation of Focal Length with Temperature
148 150 152 154 156 158 160 162−30
−20
−10
0
10
20
30
40
Grating Temperature (K)
Foc
al L
engt
h (m
icro
ns) Green line: M12
Red line: M5
L. Strow, UMBC 7
AIRS: February 2000 STM
Sensitivity of Centroids to Focal Length
500 1000 1500 2000 2500−5
−4
−3
−2
−1
0
1
2
3
4
5
Wavenumber (cm−1)
Cen
troi
d E
rror
in %
of W
idth
50 µm error20 µm error10 µm error
L. Strow, UMBC 8
AIRS: February 2000 STM
Variation of SRF Width with Temperature – I
148 150 152 154 156 158 160 162−0.6
−0.4
−0.2
0
0.2
0.4
0.6
0.8
1
Grating Temperature (K)
Wid
th V
aria
tion
in %
Green line: M12Red line: M8
L. Strow, UMBC 9
AIRS: February 2000 STM
Variation of SRF Width with Temperature – II
1000 1500 2000 2500
−1.5
−1
−0.5
0
0.5
1
1.5
2
Wavenumber (cm−1)
Wid
th V
aria
tion
in %
T149 vs T155T155 vs T161T149 vs T161
L. Strow, UMBC 10
AIRS: February 2000 STM
Fitting SRFs to an Analytic Model
• Eventually fit wings and center portions separately (maybe 3 wings will
be used for short/mid/long-wave).
• Data shown here are fits to wing and center together, with good starting
estimates for the wing. Actually fit: 20% of log of SRF plus 80% linear SRF.
• Primarily interested in quality of analytical model fits to center region.
• Using H. Aumann’s hybrid Gaussian/Lorentz model
• Main conclusions:
– Slight wavenumber dependence on wing level (scattering?)
– sinc2 diffraction evident in SRFs at the 1.5 - 4% level? Quite large for
M11/M12.
– Taking diffraction into account in model may improve computation of
fringe signal!
– Small residual asymmetries remain in SRFs, easy to handle
– Bruker aligned, our Bruker model follows data
L. Strow, UMBC 11
AIRS: February 2000 STM
Averaged SRFs, Dotted Line is Standard Deviation over Arrays
−300 −200 −100 0 100 200 300
10−3
10−2
10−1
100
Microns from SRF Center
SR
F M
agni
tude
Longwave Midwave Shortwave
L. Strow, UMBC 12
AIRS: February 2000 STM
SRF Model Fit Results: Wings
2598 2600 2602 2604 2606 2608 261010
−4
10−3
10−2
10−1
100
Wavenumber (cm−1)
SR
F V
alue
Data Fit |Obs−Calc|
2356 2358 2360 2362 2364 2366 236810
−4
10−3
10−2
10−1
100
Wavenumber (cm−1)
SR
F V
alue
Data Fit |Obs−Calc|
L. Strow, UMBC 13
AIRS: February 2000 STM
SRF Model Fit Results: Wings
875 876 877 878 879 880 881
10−3
10−2
10−1
100
Wavenumber (cm−1)
SR
F V
alue
Data Fit |Obs−Calc|
817 818 819 820 821 82210
−4
10−3
10−2
10−1
100
Wavenumber (cm−1)
SR
F V
alue
Data Fit |Obs−Calc|
L. Strow, UMBC 14
AIRS: February 2000 STM
SRF Model Fit Results: Wings
750 752 754 756 758
10−2
10−1
100
Wavenumber (cm−1)
SR
F V
alue
+ 0
.005
Data Fit |Obs−Calc|
702 704 706 708 710 712
10−2
10−1
100
Wavenumber (cm−1)
SR
F V
alue
+ 0
.005
Data Fit |Obs−Calc|
L. Strow, UMBC 15
AIRS: February 2000 STM
SRF Model Fit Results: Wings
662 664 666 668 670 672
10−2
10−1
100
Wavenumber (cm−1)
SR
F V
alue
+ 0
.005
Data Fit |Obs−Calc|
L. Strow, UMBC 16
AIRS: February 2000 STM
�3% Peak-Peak Oscillations in Center Part of SRFs
• All arrays exhibit these oscillations in their obs-calcs for a
symmetric SRF model.
• These oscillations are coherent between arrays (in
position-units)
• Maximum modulation is about 4%, in M12.
• They are probably due to sinc2 oscillations in SRF due to
diffraction. H. Aumann has modelled this behavior 5+ years
ago, appears consistent.
• Very possible that neglecting these features has hampered
our ability to recover the pure fringe signal from the SRFs
L. Strow, UMBC 17
AIRS: February 2000 STM
SRF Model Fit Results: Center Region
0
0.51
Blu
e: S
RF
; R
ed: 1
0 x
(obs
−ca
lc)
0
0.51 0
0.51
−15
0−
100
−50
050
100
150
0
0.51
SR
F P
ositi
on in
Mic
rons
<−−− SRF Magnitude −−−>
M1a
M2a
M1b
M2b
L. Strow, UMBC 18
AIRS: February 2000 STM
SRF Model Fit Results: Center Region
−150 −100 −50 0 50 100 150−0.2
0
0.2
0.4
0.6
0.8
1
SRF Position in Microns
SR
F M
agni
tude
SRF 10 x (obs−calcs)
M12
L. Strow, UMBC 19
AIRS: February 2000 STM
Short/Mid/Long-wave Obs-Calc Averages
−0.02
0
0.02
−0.01
0
0.01
0.02
−100 −50 0 50 100−0.01
0
0.01
0.02
Microns from SRF Center
<−
−−
SR
F F
it O
bs−
Cal
c −
−−
>
Shortwave
Midwave
Longwave
L. Strow, UMBC 20
AIRS: February 2000 STM
SRF Asymmetry
−150 −100 −50 0 50 100 1500
0.2
0.4
0.6
0.8
1
1.2
Y−Offset in Microns
SR
F M
agni
tude
SRF Obs/Calc
M1a
−150 −100 −50 0 50 100 1500
0.2
0.4
0.6
0.8
1
1.2
1.4
Y−Offset in Microns
SR
F M
agni
tude
SRF Obs/Calc
M2a
L. Strow, UMBC 21
AIRS: February 2000 STM
Fringe Signal Polluted with Temperature Independent Features?
−0.05
0
0.051
− F
ringe
1290 1300 1310 1320 1330−0.05
0
0.05
Wavenumber (cm−1)
T−
shift
Err
or
Red: 6K InterpBlack: 12K Interp
L. Strow, UMBC 22
AIRS: February 2000 STM
Absolute Calibration
• CO trace gas data indicates that we need to subtract 0.09 cm�1 from the
apodization corrected wavenumber scale at 2193 cm�1.
• Combined apodization correction and offset correction is
�true � �1� 6:944� 10�5 � 0:09=2193�� �obs
• Comparison with air gap data shows a difference of 0.03 cm�1 between
what we measure, and what is calculated with the above equation (so far
this includes on 149 and 155K data).
• This comparison assumes that we have correctly computed the
apodization correction (uniform beam, known size, etc.)
• Another way to say this: the Bruker apodization correction is always
about 3x too large.
• This comparison does indicate that our absolute wavenumber scale is
probably sufficient for calibration of the channel spectra.
• CO spectra appear very symmetric! Bruker well-aligned.
L. Strow, UMBC 23
AIRS: February 2000 STM
CO Trace Gas Spectrum
2190 2200 2210 2220 2230 2240 22500.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1P
seud
o T
rans
mis
sion
Wavenumber (cm−1)
L. Strow, UMBC 24
AIRS: February 2000 STM
CO Trace Gas Spectrum – Zoom
2186 2188 2190 2192 21940.4
0.5
0.6
0.7
0.8
0.9
1
1.1P
seud
o T
rans
mis
sion
Wavenumber (cm−1)
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AIRS: February 2000 STM
Forward Model Schedule: Pre-Launch
• Proposal is to deliver 10 different AIRS-RTA’s, each offset by 5% of a
width, so the max offset RTA offset at launch will be 2.5% of a width.
These SRFs will be “pure”, no fringing.
• This is a big job! Calibration has taken our attention away from
automating this procedure.
• Optimistic delivery schedule (if get 8 more processors!):
March: Finish SRF analysis for “pure” SRFs
April: Finish new kCARTA spectroscopy
May: Start RTA convolutions (maybe late April)
June: Deliver RTA #1
August: Deliver RTA #2,#3 (now automated production begins)
September: Deliver RTA #4,#5
. . . Deliver 2 RTA’s per month
December: Deliver RTA #10
L. Strow, UMBC 26
AIRS: February 2000 STM
Production of AIRS-RTA, Flow Diagram
kCARTA
Layer-to-SpaceTransmittances
Line ShapesContinuum
Profiles
GENLN2
Layers
kCompressedDatabase
SVDCompression
HITRAN 9X
Fast ModelRadiative Transfer
MonochromaticAbs. Coeffs (k)
Fast ModelRegressions
Fast ModelParameters
Radiances
CustomLBL
SRFConvolutions
ConvolvedTransmittances
Retrieval
L. Strow, UMBC 27
AIRS: February 2000 STM
AIRS-RTA Production: Automation
• Main steps in putting RTA together after convolutions:
– 7 sets of predictors
– OPTRAN for water
– Variable CO2 correction
– Water continuum (1 shot)
– Solar at top of atmosphere (1 shot)
– Reflected Thermal (1 shot)
• Only 5% speed-up doing the (1 shot) steps only once
• System can be automated, but that is 1-2 months work
L. Strow, UMBC 28
AIRS: February 2000 STM
Other Pre-Launch RTA Activities
• Finish SRF shape analysis
– Wings
– Diffraction effects (important for separating out fringes)
– Optimization of SRF shape parameters (connect wing to center region)
• New UMBC-LBL finished, have generated monochromatic transmittancesfor input to kCARTA. These include new Toth H2O and P/R-branch mixingin CO2.
• Compress transmittances for input to kCARTA (starting soon). 1-2months of work to do this.
• Install into kCARTA. Can then start AIRS-RTA convolutions with new SRFs.(Could use old spectroscopy for launch ready software, but would rathernot.)
• We really need to test our forward model against an independentstatistical set of profiles. That has not be done for several years witholder, less accurate?, RTA models.
L. Strow, UMBC 29
AIRS: February 2000 STM
Forward Model Schedule: Post-Launch
Launch + 60 days Start comparing radiances to model radiances computed using
kCARTA; need clear flag, over ocean only
Launch + 75 days Spot check AIRS-RTA with kCARTA convolved output, any
obvious large errors?
Launch + 90 days Receive standard frequency set, start computing new AIRS-RTA,
“pure” SRFs
Launch + 100 days Receive fringe position data, start computing new AIRS-RTA,
“true” SRFs
Launch + 120 days Deliver new AIRS-RTA with “pure” SRFs. Start providing kCARTA
convolved radiances for subset of co-locations, automated
Launch + 130 days Deliver new AIRS-RTA, “true” SRFs. Start making any obvious
fixes to spectroscopy, fast model in our local software
Launch + 140 days Compute new AIRS-RTA, “true” SRFs, new spectroscopy/fast
model.
Launch + 170 days Could deliver new AIRS-RTA to JPL. Too close to other
activities... When?
L. Strow, UMBC 30
AIRS: February 2000 STM
AIRS-RTA Accuracy Before Launch + 13x days
• At launch AIRS-RTA will contain two known errors because;
– Using “pure” SRFs without fringing effects
– Possible wavenumber offset error of up to 2.5% of a width
• See next 3 graphs for error estimates for these two effects.
• At launch + 120 days, AIRS-RTA will be on exact channel centers
• At launch + 130 days, propose? to provide AIRS-RTA with fringing
• We need the “pure” SRF AIRS-RTA to help verify if we put the fringes intothe SRFs correctly.
• Need to decide on how to handle CO2 variability, and spot-check N2Ovariability.
• We need to be careful about the truth. Better agreement withradiosondes does not always mean the AIRS-RTA is better.
• Spectroscopy errors will take longer to fix.
• How will we decide on what channels are tuned, which are not?
L. Strow, UMBC 31
AIRS: February 2000 STM
B(T) Errors for a 5 �m Offset in SRF Centers
800 1000 1200 1400 1600−1
−0.5
0
0.5
1
Err
or in
B(T
) in
K
Wavenumber (cm−1)
220
240
260
280B
(T)
in K
L. Strow, UMBC 32
AIRS: February 2000 STM
B(T) Errors for a 5 �m Offset in SRF Centers
220
240
260
280B
(T)
in K
2200 2300 2400 2500 2600
−0.2
0
0.2
Err
or in
B(T
) in
K
Wavenumber (cm−1)
L. Strow, UMBC 33
AIRS: February 2000 STM
B(T) Errors if Use “Pure” SRFs vs SRF’s with Fringes
220
240
260
280
300
B(T
) in
K
1000 1500 2000 2500
−0.5
0
0.5
Wavenumber (cm−1)
B(T
) E
rror
L. Strow, UMBC 34
AIRS: February 2000 STM
Validation Requirements/Suggestions
• At Launch + 60 days we can start comparing AIRS radiances to those
computed with kCARTA using co-located radiosondes. We can determine
wavenumber scale ourselves.
• Spectroscopy and SRF/Fast Model errors take a long time to fix. We need
co-located radiosondes ASAP after launch + 60 days.
• Need CLEAR tags on co-locations.
• Initial work must be done over water so the surface emissivity is known.
• If scene shows proper wavenumber dependence due to sea-surface
emissivity, that is an excellent double-check on CLEAR flag.
• Several individual high-quality radiosonde co-locations over water are far
preferable to 10-100 questionable co-locations over land. Start limited
special radiosonde launches at launch + 60-90 days.
• Suggested Locations: Acension Island, already does ozone sondes. ARM
Pacific Site, too cloudy? Hawaii? Puerto Rico?
L. Strow, UMBC 35
AIRS: February 2000 STM
Validation Software
• Prefer “standing order query” for radiosonde co-locations. Put circularqueue of radiosonde reports and Level 1B data in a directory that we canread. Whenever new reports appear we will download them to UMBC andprocess. Old reports will stay in directory for X days, maybe X=5-10.
• We then upload our results to another directory on a daily/weekly basis?Or provide to Science Team via WWW at UMBC?
• We need to pull files from the Data Warehouse in an automated mannerfrom a remote site (UMBC). The “standing order query” can only be usedsparingly, I think.
• For us to design/test software to do automated processing, we needdocuments that describe the architecture of the Validation Warehouseand the details of the software interfaces.
• Lessons from AIRS ground calibration: Tell me how to get the dataremotely, and what you did to it first.
• Sharing of “private” calibration data at Launch + xx days needs to beworked out. We can’t share 30 Mbyte spreadsheets.
L. Strow, UMBC 36