CrIS, Three Years of Operation, Stability and Comparison

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Synopsis SNPP Stability Deconvolution and Translation SNO

CrIS, Three Years of Operation, Stability andComparison to AIRS

Chris Hepplewhite, L. Larrabee Strow, Howard Motteler,Sergio De Souza-Machado, and Steven Buczkowski

UMBCDepartment of Physics and

Joint Center for Earth Systems Technology

AIRS Science Team MeetingGreenbelt, MD, 13 - 16 October 2015

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What, Why and How

Goal: create climate data records from differenthyperspectral sensorsRequirement: need well understood error characteristics,inter-instrument biases, and instrument stabilityApproach: Convert individual instrument radiance recordsto a common spectral gridThis Work:

Demonstrate CrIS sensor stabilityOverview of AIRS–>CrIS conversionAIRS - CrIS bias with common spectral gridStability of the above bias with time

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Estimation of CrIS In-Orbit Stability: Approach

Start with CCAST processed SDRs (stable algorithm)CCAST converts to normal-resolution post Dec. 2015Subset for clear, ocean tropical scenes (uniformity filter)Match each scene of ERA Interim re-analysis and computesimulated radianceCreate daily average of observed and simulated radiances(365 x 3) long time series.Fit time series bias (Obs-Simulated) for linear rate (andseasonal terms).Perform an Optimal Estimation retrieval on bias time series(d(bias)/dt) spectrum to determine geophysical timederivatives. (O3 is only column offset.)

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CrIS Linear B(T) Bias Rate over Three Years

1000 1500 2000 2500−0.2

−0.1

0

0.1

0.2

0.3

Wavenumber (cm−1

)

dB

ias/d

t in

K/y

ear

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2-σ Uncertainty in CrIS Linear B(T) Bias Rate

1000 1500 2000 25000

0.005

0.01

0.015

0.02

0.025

Wavenumber (cm−1

)

95%

Confidence L

evel in

dB

(T)/

dt (K

/year)

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OE Fit ResultsUnits are all per year

CO2 (ppm) 2.35 +- 0.008 Full rateO3 (%) -1.22 +- 0.006 Relative to ERAN2O (ppb) 0.82 +- 0.014 Full rateCH4 (ppb) 7.79 +- 0.182 Full rateCFC11 (ppt) 0.10 +- 0.016 Full rateSST (K) 0.016 +- 0.000 Relative to ERA

Comparison to In-Situ for CO2

NOAA/ESRL Global Mean CO2Rate for 2012-2014: 2.25 ppm/yearCrIS - ESRL = 0.1 ppm/year impliesCrIS stability of 0.005K/year.

Comparison to In-Situ for SST

ERA SST is a measurement:GHRSSTCrIS - ERA = 0.016K/year

NOAA/ESRL CH4 from 2012-2015 varies from 5-10 ppb/year

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CO2 Contribution to Spectral Bias

1000 1500 2000 2500

−0.1

−0.05

0

0.05

0.1

Wavenumber (cm−1

)

dB

(T)/

dt in

K/y

ear

ObsCO2

Issue in stratospheric sounding channels, we should differ from ERA by0.04K/year! Could ERA not be able to bias correct for CO2 in the upper strat?

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OE Profile Differences from ERA

−0.01 0 0.01

10

100

1000

H2O Fraction/Year

Pre

ssu

re (

mb

ar)

−0.05 0 0.05

10

100

1000

Temperature (K/Year)

Profile Differences from ERA

For these altitude it is difficult to find a standard for temperature biascorrection? Or is the CO2 rate not constant with altitude?

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Fit ResidualsRequirements for Inter-Instrument Agreement

500 1000 1500 2000 2500 3000−0.1

−0.05

0

0.05

0.1

Wavenumber (cm−1

)

dB

(T)/

dt

in K

/Ye

ar

Obs RateFit RateObs−Calc Rate

How well can we fit CrIS radiance time derivatives?

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Fit ResidualsRequirements for Inter-Instrument Agreement

500 1000 1500 2000 2500 3000−0.04

−0.02

0

0.02

0.04

Wavenumber (cm−1

)

dB

(T)/

dt

in K

/Ye

ar

Obs−Calc Rate

How well can we fit CrIS radiance time derivatives?

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AIRS–>CrIS SRF Conversion: Basis of MethodObjectives

To create a common radiance climate record for differentsensors.To aid comparison and bias estimates between differentsensors.In this case use the CrIS standard resolution as thecommon and convert the measured AIRS and IASI signalto CrIS, but in principle to any other.Method developed by Howard Motteler

Source code for deconvolutions:https://github.com/strow/airs/deconv.git

https://github.com/strow/iasi/decon.git

https://github.com/strow/airs/deconv.git

https://github.com/strow/iasi/decon.git

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Basis of MethodBackground

Use the AIRS SRFs from TVAC to deconvolve themeasured spectral radiance to a finer user grid (0.1 cm−1)is optimum.Reconvolve to the common sensor spectral response(CrIS).Works best for continuous spectral band with uniformresponse and sensors with parameterized ILS.AIRS conversion uses L1C which fills gaps and repairs badchannels.Method validated using TOA radiance calculated for 49atmospheric profiles that cover wide dynamic range.TOA calculated using kcarta LBL at native 0.0025 cm−1

resolution.

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CrIS −→ AIRS Conversion

This topic is far beyond the scope of this talk, so just a summary.

Basic methodologySa is a matrix of AIRS SRFs on 0.1 cm-1 grid.

c = Sar,

where: c = AIRS observed channel radiances, r = higher resolutionrepresentation of true radiances, on 0.1 cm-1 grid. (For bestresults, as in forward model development, we use a 0.0025 cm-1

spacing.) Thenr = (Sa)

−1c

and we can obtain simulated CrIS by convolving r with the CrIS ILS.Sa condition number is very high for L1b, and drops to ≈250 forL1c if we drop four channels. The key is a uniform channelspacing.

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Example of De-convolved AIRS SpectrumDe-convolved SRF similar to 0.2 wide sinc

680 700 720 740 760

210

220

230

240

250

260

270

280

290

Wavenumber (cm−1

)

B(T

) in

K

AIRS L1c

AIRS Deconvolved

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Basis of MethodIASI to CrIS

IASI to CrIS is an easy translation because IASI spans the CrISbands and has a nominal (though strongly apodized) higherresolution. The main steps, for each CrIS band, are

apply a bandpass filter to the IASI channel radiances torestrict them to a single CrIS band with a rolloff outside theCrIS user gridtake the filtered radiances to an interferogram with aninverse Fourier transformapply the pointwise inverse of the IASI Gaussian over theIASI 1 cm opd and truncate this to the 0.8 cm CrIS opd.take the interferogram back to radiance at the CrIS 0.625wn channel spacing with a forward Fourier transform

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AIRS IASI SNOs2014 average

BT

(K

)

220

240

260

Airs, Iasi, Iasi2Airs SNO Full average

Airs 1bIasiiasi2airs

wn (cm-1)

1000 1500 2000 2500

Bia

s A

-I (

K)

-1

-0.5

0

0.5

1

Airs - Iasi2Airs

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AIRS CrIS2014 average

BT

(K

)

220

240

260

280

SNO 2013 AIRS l1b (b) CRIS (g) AtoC (r)

wn (cm-1)

1000 1500 2000 2500

BT

(K

)

-2

0

2

4

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AIRS CrIS Zoom

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CrIS (HR) IASI SNO2013 average

−0.5

0

0.5

1

1.5

BT

diff

(K)

cris−iasi

1000 1500 2000 25000

1

2

3

4

wavenumber (cm−1)

BT

(K

)

st.dev

st.err.

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CrIS Bias from SNOBias Trending

Take CCAST standard resolution CrIS and AIRS L1bconverted to L1c.but note - these AIRS data are not spectrally corrected fordrift (my next task!).Create SNO based on 20 minute 13 km separation ofFOVs from May 2012 to current time.Get approx 650 SNO days. Restrict to Tropical ocean (< 40latitude) and drop > 3-sigma samples.Evaluate bias for averages of each SNO day, and trend (asyou like!).Investigate and compare to IASI CrIS bias (to do).

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CrIS AIRS Bias from SNOLW band

wn cm-1

700 800 900 1000 1100

Bia

s s

lop

e K

/yr

-0.05

0

0.05Sno Airs CrIS BT Bias trend LW (2012-15)

Figure: LW band AIRS CRIS SNO Linear fitted

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CrIS AIRS Bias from SNOLW band with std. dev.

wn cm-1

600 700 800 900 1000 1100

Bia

s s

lop

e K

/yr

-0.05

0

0.05Sno Airs CrIS BT Bias trend LW (2012-15)

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CrIS AIRS Bias from SNOWindow channel detail

2012 2013 2014 2015

Bia

s K

-1.5

-1

-0.5

0

0.5

1AIRS CrIS sno 901wn Bias trend

901: slope: -2.32e-05 1.24e-06 offset: -0.0010 0.00092

901: slope: -8.46e-03 4.53e-04 offset: -0.0010 0.00092

901: slope: -0.0085 0.0005 offset: -0.0010 0.00092

901: K/yr: -0.0085 0.0005 offset: -0.0010 0.00092

901: K/yr: -0.0085 0.0005 offset: -0.0010 0.00092 K

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CrIS AIRS Bias from SNOChannel at 796 wn detail

2012 2013 2014 2015

Bia

s K

-1.5

-1

-0.5

0

0.5

1

1.5

2AIRS CrIS sno 796wn Bias trend

796: K/yr: -0.0409 0.0004 offset: 0.0632 0.00086 K

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CriS AIRS Bias from SNOChannel at 696 wn detail

2012 2013 2014 2015

Bia

s K

-0.5

-0.45

-0.4

-0.35

-0.3

-0.25

-0.2

-0.15

-0.1

-0.05AIRS CrIS sno 696wn Bias trend

696: K/yr: 0.0135 0.0032 offset: -0.2020 0.00644 K

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Conclusions and Future Work

Comparison with CO2 growth rates indicates CrIS is stableto about 5 mK/year.Comparison with SST linear rate indicates CrIS is stable to16 mK/year (includes cloud leakage).Premature to conclude comparison with AIRS and CrIS,worst case from this work suggests they are within 9mK/year of each other (LW window region).Apply frequency correction to AIRS and repeat. Comparewith IASI.Evaluate uncertainty of method (SNO method alonedoesnot tell who is nearer the truth, but is guide to stability).Evaluate optimum method to null out the bias of (merge)the two radiance records.

Documents

CrIS, Three Years of Operation, Stability and Comparison