cris spectral calibration and trending · 1 spectral cal. high spectral res. mode sinc ringing obs...
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Spectral Cal. High Spectral Res. Mode Sinc Ringing Obs Cold Scene SNOs Background Slides
CrIS Spectral Calibration and Trending
L. Larrabee Strow1, Howard Motteler1, Breno Imbiriba1, ChrisHepplewhite1, and Dave Tobin2
1Department of Physics, JCETUniversity of Maryland Baltimore County (UMBC)
2Space Science Engineering CenterUniversity of Wisconsin Madison
NOAA CrIS SDR ReviewCollege Park, MD
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Spectral Cal. High Spectral Res. Mode Sinc Ringing Obs Cold Scene SNOs Background Slides
Overview
Spectral calibration and apodization corrections
High spectral resolution mode validation
Methodology: Measuring excess “sinc ringing”
Methodology and Update: Analysis of cold-scene SNOs
Terminology
LW = Long-wave band1MW = Mid-wave band2SW = Short-wave band3ν = Frequency
Focal Plane FOV Definitions
7 4 1
8 5 2
9 6 3
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Spectral Cal. High Spectral Res. Mode Sinc Ringing Obs Cold Scene SNOs Background Slides
Spectral Calibration SensitivityRemove self-apodization and shift frequency scale
Apodization Corrections
Adjust asymmetric off-axis FOVILS to on-axis
Shift spectra to fixed ν scale
Performed with CMO operator
Requires: focal plane geometry, νof metrology laser
725 730 735 740 745230
240
250
260
270
280
290
Wavenumber (cm−1
)
B(T
) in
K
Filled Spectrum
CrIS Obs
Adjustments can be very large: 20K+
1 ppm ν calibration error = ±0.06K in B(T)
CrIS ν calibration specification is 10 ppm
NWP applications require uniform calibration among FOVs
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Spectral Cal. High Spectral Res. Mode Sinc Ringing Obs Cold Scene SNOs Background Slides
Relative ν Calibration
ν calibration relative to center FOV(FOV-5)
Provides FOV positions relative tointerferometer optical axis which areused to generate self-apodizationcorrections.
Tables below are ν calibration errors(ppm) relative to FOV-5.
From Dave Tobin/SSEC
LW0.20 0.03 0.030.15 0 0.030.15 0.12 -0.01
MW-0.23 -0.12 -0.310.14 0 0.000.03 0.12 -0.18
SW-0.06 -0.41 -0.68-0.04 0 0.100.27 -0.64 -0.08
Self-apodization parameters well characterized and very stable. FOV frequencymismatches due to incorrect focal plane geometry should be well below the 1ppm level except possibly for short-wave.
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Spectral Cal. High Spectral Res. Mode Sinc Ringing Obs Cold Scene SNOs Background Slides
Absolute ν Calibration (units are ppm)
Based on CCAST radiances
Feb. 2012 CCAST agreement with TVACNeon Cal: 0.6 ppm, so Neon cal notchanged
Absolute ν calibration with IDPS SDRsproblematic: Neon lamp value used inCMO unknown until Nov. 2013
Largest ν error: IDPS requires 2 ppmNeon change to update
Absolute LW ν Calibration(CCAST SDRs in Feb. 2012)
0.1 -0.0 0.00.1 -0.6 -0.5
-0.8 -1.0 -0.4
Jan12 Apr12 Jul12 Oct12 Jan13 Apr13 Jul13 Oct13 Jan14−3.5
−3
−2.5
−2
−1.5
−1
−0.5
0
0.5
1
1.5
Time
Fre
quency C
alib
ration (
ppm
)
Upwelling (Truth)
Neon
Difference
Neon−Resamp
SW Aug. 28 ν Cal (hi-res mode) LW ν Cal minus Short-wave ν Cal
0.08 -1.37 -1.25-0.72 -0.53 -1.85-0.46 -1.10 -1.16
Mean/Std over FOV: -0.93 ± 0.58 ppm
0.02 1.37 1.250.82 -0.07 1.35
-0.34 0.10 0.76
Mean/Std over FOV: 0.58 ± 0.67 ppm
The LW and SW spectral calibration agree to <1 ppm (using CCAST).
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Spectral Cal. High Spectral Res. Mode Sinc Ringing Obs Cold Scene SNOs Background Slides
Absolute ν Calibration: Figure ZOOM
Jan12 Apr12 Jul12 Oct12 Jan13 Apr13 Jul13 Oct13 Jan14−3.5
−3
−2.5
−2
−1.5
−1
−0.5
0
0.5
1
1.5
Time
Fre
quency C
alib
ration (
ppm
)
Upwelling (Truth)
Neon
Difference
Neon−Resamp
Data using IDPS long-wave SDRs; Very few updates due to 2 ppm threshold
SDR’s exhibit ∼3 ppm variability
Correct operation of CMO generation started in Nov. 2013
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Spectral Cal. High Spectral Res. Mode Sinc Ringing Obs Cold Scene SNOs Background Slides
IDPS Upgrade
Feb. 2012: IDPS ILS parameters for FOVs (1:4, 6:9) fudgeddue to suspected SDR algorithm code errors for FOV 5. CCASTSDR results did not show these errors.
Yong Han found three errors in computation of FOV5 CMOoperator, fixed in ADL.
Fudge removed in new ENGR packets and tested via 1-day ofADL runs done at UW. Now using original CCAST derived ILSparameters.
UW relative ν calibration and UMBC absolute ν calibrationfrom new ADL SDR radiances proved that IDPS FOV-5 errorshad been corrected.
IDPS may start using corrected SDR code and new ENGRpacket in Feb. 2014.
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Spectral Cal. High Spectral Res. Mode Sinc Ringing Obs Cold Scene SNOs Background Slides
Short-Wave ν Calibration
2200 2250 2300 2350 2400 2450 2500
220
225
230
235
240
245
250
255
260
265
270
Wavenumber (cm−1)
B(T
) in
K
All ChannelsNeon Cal Channels
−80 −60 −40 −20 0 20 40 60 80−20
−15
−10
−5
0
5
10
15
20
25
Latitude
Neo
n O
ffset
in p
pm
LW High−AltitudeSW High−AltitudeLW Operational
Shortwave (SW) at high spectral resolution provides very goodν calibration
Spectral region used by IASI for all ν calibration
SW channels emit in upper-strat/mesosphere. This will allownearly continuous spectral calibration during each orbit,unlike LW.
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Spectral Cal. High Spectral Res. Mode Sinc Ringing Obs Cold Scene SNOs Background Slides
High Spectral Resolution Validation
Validate Aug. 2013 high-spectral resolution data
CCAST used to generate high-spectral resolution SDRs
Lien: No non-linear corrections for mid-wave (coming soon)
Validation approach 1: SNOs versus IASI converted to CrIS ILS
Validation approach 2: Analyze biases versus computedradiances using ECMWF and SARTA Radiative TransferAlgorithm (RTA)
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Spectral Cal. High Spectral Res. Mode Sinc Ringing Obs Cold Scene SNOs Background Slides
High Spectral Resolution SNOs with IASI
500 1000 1500 2000 2500 3000
210
220
230
240
250
260
Wavenumber (cm−1
)
B(T
) in
K
CrIS
IASI
CrIS−normal
2300 2310 2320 2330 2340 2350 2360 2370
215
220
225
230
235
240
245
250
Wavenumber (cm−1
)
B(T
) in
K
CrIS
IASI
CrIS−normal
SNO agreement is very goodBlack circles on right graph show CrIS at normal mode resolutionLine structure in 2330 cm−1 region provides very good spectralcalibration throughout most of an orbit
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Spectral Cal. High Spectral Res. Mode Sinc Ringing Obs Cold Scene SNOs Background Slides
High Spectral Resolution SNOs with IASI: Details
B(T) Diff B(T) Diff vs Radiance
1200 1400 1600 1800 2000 2200 2400 2600−1
−0.5
0
0.5
1
1.5
2
Wavenumber (cm−1
)
CrI
S −
IA
SI_
mod in K
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7−1
−0.5
0
0.5
1
1.5
2
2.5
3
3.5
Channel Radiance
BT
CrI
S−
IAS
I in
K
Note: No non-linear corrections in mid-wave bandShort-wave agreement very good (this is sinc ILS!)Larger BT differences in cold channels, noise related.
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Spectral Cal. High Spectral Res. Mode Sinc Ringing Obs Cold Scene SNOs Background Slides
High Spectral Resolution NWP Biases
B(T) Bias % Radiance BiasSTD over FOVs STD versus ECMWF
500 1000 1500 2000 2500 3000−3
−2
−1
0
1
2
3
4
5
6
Wavenumber (cm−1
)
Bia
s/S
td in
K
No Non−linear Corrections in MW!
Bias vs ECMWF
Std Bias over FOV
2150 2200 2250 2300 2350 2400 2450 2500 2550
−2
−1
0
1
2
3
4
5
Wavenumber (cm−1
)B
ias/S
td in
% o
f 2
87
K R
ad
ian
ce
Bias vs ECMWF
Std Bias
Relatively good agreement with ECMWF (clear ocean tropical)Std of bias over FOV implies accurate SW ILS correctionsRinging in short-wave accentuated by cold scene temperaturesShort-wave % radiance bias shows ringing is constant over bandIncorrect CO in RTA gives high bias errors
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Spectral Cal. High Spectral Res. Mode Sinc Ringing Obs Cold Scene SNOs Background Slides
Method for Observing Excess Sinc Ringing(See Dan Mooney’s presentation for more information.)
The CrIS ILS specification is sinc ILS.Most RTAs simulate apodized radiances.Ringing artifacts far smaller than RTA + NWP simulations.Enhance visibility of non-sinc ringing with differences (D1,2,3)
D1 ≡ biasILS = BTobs,ILS − BTcalc,ILS
where ILS = Hamming or Sinc. BTcalc,Hamming is RTA simulation fromECMWF. The Hamming forward operator reduces sinc ringing by an orderof magnitude. Create BTcalc,Sinc with the inverse Hamming operator.
D2(sweep_dir) ≡ (biassinc − biasHamming)sweep_dir
highlights non-sinc ringing. sweep_dir selected using odd or even FORs.Differential ringing bias with sweep direction is then
D3 ≡ D2(odd_FOR)−D2(even_FOR)
This approach removes model, RTA, and smooth radiance calibrationerrors, leaving non-sinc ringing in D2 and D3.
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Spectral Cal. High Spectral Res. Mode Sinc Ringing Obs Cold Scene SNOs Background Slides
Examples of Sinc Ringing MetricErrors shown as percent of a 287K blackbody radiance
Left hand side: This shows the excess (non-sinc) ringing in theCrIS spectra for odd FORs. It is quite large for the short-wave.
Right hand side: Here we form the triple difference, bysubtracting the odd FOR (biassinc − biasHamming) from the samequantity but for even FORs.
D2(odd_FOR) D3
1000 1500 2000 2500−2
−1.5
−1
−0.5
0
0.5
1
1.5
2FOV5 Sinc − Hamming Odd Bias in Percent Radiance Units at 287K
Wavenumber (cm−1
)
%R
ad
ian
ce
800 1000 1200 1400 1600 1800 2000 2200 2400
−0.5
−0.4
−0.3
−0.2
−0.1
0
0.1
0.2
0.3
0.4
0.5
FOV5 Sinc−Hamming, Odd−Even Bias in Percent Radiance Units at 287K
Wavenumber (cm−1
)
%R
ad
ian
ce
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Spectral Cal. High Spectral Res. Mode Sinc Ringing Obs Cold Scene SNOs Background Slides
SNOs: Improved MethodologyCorrects error in last SDR Review
Last Review
160 180 200 220 240 260 280 300 320180
200
220
240
260
280
300
320
AIRS B(T) in K
CrI
S B
(T)
in K
2552 cm−1
CrIS B(T)’s are warmer when AIRS SNOB(T)’s are cold.
Methodology Error
Scene subset selection based only on onesensor is biased and non gaussian. Subseton union of scenes with AIRS and CrISB(T)’s within some B(T) bin. Color scale:log(counts).
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Spectral Cal. High Spectral Res. Mode Sinc Ringing Obs Cold Scene SNOs Background Slides
Proper SNO Scene Selection and Binning
205 210 215 220 225205
210
215
220
225
AIRS BT (K)
CrI
S B
T (
K)
Sample population is union of scenesin bin for both instruments.
180 200 220 240 260 280 300−0.4
−0.3
−0.2
−0.1
0
0.1
0.2
0.3
0.4
BT_CrIS or BT_AIRS (K)
AIR
S −
CrI
S in
KGlobal SNO versus scene temperaturefor ν=900 cm−1.
See Dave Tobin’s presentation for detailed SNO results.
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Spectral Cal. High Spectral Res. Mode Sinc Ringing Obs Cold Scene SNOs Background Slides
Shortwave Cold Scene SNOsRe-visit data shown in previous review
No 10K issues as before. SNOdifferences far below noise. Bothstandard SNO and quantile resultsshown.
Same data as on left, but plottedversus scene radiances instead of B(T).Note noise level. This is quantileresult.
Short-wave cold scenes: Too sensitive to noise, avoid. However,inter-comparisons with AIRS are very good, but not perfect. No coldscene issues relative to AIRS.
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Spectral Cal. High Spectral Res. Mode Sinc Ringing Obs Cold Scene SNOs Background Slides
Conclusions
CrIS IDSP SDR spectral calibration good to ∼3 ppm.
CrIS instrument and up-welling ν calibration capable of∼1ppm absolute and <0.5 ppm relative ν calibration.
Achieving instrument capabilities require removal of IDPS 2ppm threshold for computation of new CMO. Can be achievedby interpolation of CMO operators (very smooth) as done byCCAST.
Metrology laser drifts track instrument temperaturevariations. (Not discussed.)
High-spectral resolution mode working very well, short-waveagreement with IASI to ∼0.1K, accurate ILS corrections.
High-spectral resolution mode spectral calibration veryaccurate, can be used over much of each orbit.
Improved methodology for SNOs shows that CrIS and AIRSagree very well for cold scenes (in all bands).
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Spectral Cal. High Spectral Res. Mode Sinc Ringing Obs Cold Scene SNOs Background Slides
Quantile Analysis of SNO Data
10−3
10−2
10−1
100
200
210
220
230
240
250
260
270
280
290
300
Cumulative Probability
Me
an
B(T
) in
K
Why Quantile Approach?
Tropical SNOs have large differences(small cold clouds)
Limited # of cold SNOs, poorstatistics
Quantile analysis quantifies statisticaldistribution of each instrument SNOradiances independently
Allows larger data sets?
Select a cumulative probability vector p = 0.0001:δP:1.0Sort radiances by value, find mean radiance in each δP bin.Distribution difference is difference in radiance/B(T) associatedwith same cumulative probability bin.
Does not require subtraction of SNO pairs, which may have very largeB(T) differences (especially in the tropics).
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Spectral Cal. High Spectral Res. Mode Sinc Ringing Obs Cold Scene SNOs Background Slides
CrIS Radiometric StabilityRelative to SST, CO2
Apr12 Jul12 Oct12 Jan13 Apr13 Jul13 Oct13 Jan14−0.6
−0.5
−0.4
−0.3
−0.2
−0.1
0
0.1
0.2
0.3
Bia
s in K
Tropical ocean clear
1-Year differences far below0.1K. Red curve is smoothedtime series.
Apr12 Jul12 Oct12 Jan13 Apr13 Jul13 Oct13 Jan14−0.2
−0.15
−0.1
−0.05
0
0.05
0.1
0.15
0.2
B(T
) C
hange in C
O2 L
ine D
epth
2.5 ppm CO2
CO2 from ECMWF bias (791.5cm−1) - 0.27*bias(790 cm−1).
Second term removes any SST,H2O variability.
Oct 2012 through Oct 2013shows 2.5 ppm growth rate(0.06K).