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CrIS/VIIRS Comparisons David Tobin, Chris Moeller, Greg Quinn, Hank Revercomb
GSICS Annual MeeBng
Williamsburg, VA 3-‐8 March 2013
2
NOAA/STAR CrIS SDR Cal/Val;
UW efforts:
CrIS In-‐orbit Radiometric Uncertainty EsBmaBon
Internal consistency checks on Radiometric CalibraBon
Radiometric Non-‐linearity Refinement & EvaluaBon
Radiometric Noise
assessment
Variable arBfact
assessment using PCA
Early broadband comparisons with GOES and other
GEOs
Clear sky Obs minus Calc
Analysis
Internal consistency checks on spectral
calibraBon, spectral self-‐apodizaBon correcBon
and resampling
Analysis of non-‐uniform scene effects on the
ILS
SNO comparisons with IASI and AIRS
CrIS/VIIRS Radiance
Comparisons
ICT Environmental Model EvaluaBon and Refinement
Hyperspectral Infrared Satellite IntercalibraBon Studies NASA Satellite Calibra.on Interconsistency Studies (SICS11) selec.on
Monochromatic spectrum, CrIS spectrum, and VIIRS SRFs BT
(K)
wavenumber, 1/cm
BT (K
)
wavenumber, 1/cm
M13 4um
M15 10.8um
M16A 12um
4
Ø Comparisons are performed rou.nely for bands M13, M15, M16A, and I5 (not shown) Ø M15 and M16A SRFs include small OOB contribu.ons in the 8.5µm gap region
Example Daily comparisons, M15 band @ 10.8µm, Descending
CrIS convolved with VIIRS SRF VIIRS mean within CrIS FOVs
VIIRS standard deviaBon within CrIS FOVs Differences for uniform scenes
BT (K) 210 220 230 240 250 260 270 280 290 300
0 1 2 3 4 5 6 7 8 9 10 -‐5 -‐4 -‐3 -‐2 -‐1 0 1 2 3 4 5
BT (K) 210 220 230 240 250 260 270 280 290 300
BT (K) VIIRS -‐ CrIS (K)
Ø CrIS processing is ADL/CSPP with v33 Eng. Packet; VIIRS is IDPS product Ø Each day includes ~500,000 coloca.ons which pass a spa.al uniformity test
Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar−0.2
−0.15
−0.1
−0.05
0
0.05
0.1
0.15
VIIR
S −
CrIS
BT
(K)
CrIS/VIIRS Daily Mean Differences
M13, 4umM15, 10.8umM16, 12um
Ø Daily mean differences are < 0.1K since VIIRS OBC LUT change in early March Ø Slow trends are observed in all three bands, ~15 mK, over the past year Ø Discon.nui.es are due to known events (e.g. VIIRS OBC LUT change in early March, shutdown/
restart on March 24/25, VIIRS nonlinearity tests in May, Sep, Dec)
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Daily Mean Differences
200 220 240 260 280 300 320−0.5
−0.4
−0.3
−0.2
−0.1
0
0.1
0.2
0.3
0.4
0.5
BT (K)
VIIR
S −
CrIS
BT
(K)
CrIS/VIIRS Differences versus Scene BT (4/1 to 02/25)
M13, 4umM15, 10.8umM16, 12um
Ø M13 differences show li_le dependence on scene BT, except for coldest scenes Ø M15 and M16 show clear scene BT dependence of differing magnitude; Further inves.ga.ons
are underway, including signal dependence of the CrIS calibra.on uncertainty, VIIRS SRF OOB effects, and VIIRS comparisons with IASI and AIRS.
7
Scene Temperature Dependence
8
CrIS Non-‐Linearity CorrecBons
• The CrIS RU budget and SDR algorithm did not originally include NL contribu.ons; Significant quadra.c NL realized for LW and MW (MCT) bands and characterized only with system level TVAC tes.ng. SW band (InSb) is linear.
• The correc.on is FOV#, band, wavenumber, and scene dependent • The NL magnitude was observed to change between TVAC cycles, par.cularly for certain MW FOVs. • Post-‐launch, the on-‐orbit NL has been characterized using harmonic out-‐of-‐band analysis of ICT
views and FOV-‐2-‐FOV consistency analysis of Earth views.
600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600
200
220
240
260
280
300
Sample FOV7 Spectrum
wavenumber
BT (K
)
600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600−1.5
−1
−0.5
0
0.5NLC effect; NLC minus no NLC
wavenumberBT
Diff
(K)
Example correcBons
Corrected Raw Complex Spectrum = Raw Complex Spectrum × (1+ 2 a2 V) where V is DC level voltage at 1st stage of preamplifier
BT Dif (K)
BT (K
) wavenumber
Longwave
1 2 3
4 5 6
7 8 9
Midwave
1 2 3
4 5 6
7 8 9
Shortwave (linear)
1 2 3
4 5 6
7 8 9 0 1 2 3 40.5
11.5
22.5
33.5
a2 (1/V)0 0.02 0.04 0.06 0.08
Longwave
1 2 3
4 5 6
7 8 9
Midwave
1 2 3
4 5 6
7 8 9
Shortwave (linear)
1 2 3
4 5 6
7 8 9 0 1 2 3 40.5
11.5
22.5
33.5
a2 (1/V)0 0.02 0.04 0.06 0.08
Longwave
1 2 3
4 5 6
7 8 9
Midwave
1 2 3
4 5 6
7 8 9
Shortwave (linear)
1 2 3
4 5 6
7 8 9 0 1 2 3 40.5
11.5
22.5
33.5
a2 (1/V)0 0.02 0.04 0.06 0.08
Longwave
1 2 3
4 5 6
7 8 9
Midwave
1 2 3
4 5 6
7 8 9
Shortwave (linear)
1 2 3
4 5 6
7 8 9 0 1 2 3 40.5
11.5
22.5
33.5
a2 (1/V)0 0.02 0.04 0.06 0.08
CorrecBon Coefficient, a2
NLC effect:
Ø Very similar behavior observed for all CrIS FOVs 9
Scene Temperature Dependence, by CrIS FOV FOV 1 FOV 2 FOV 3
FOV 4 FOV 5 FOV 6
FOV 7 FOV 8 FOV 9
CrIS ICT Predicted Radiance
1%
RICT = εICT B(TICT) + (1-‐εICT) RICT,Reflected
ICT Emissivity
ICT Emissivity Uncertainty
T refl, modeled
Ø The predic.on includes a modeled component of the reflected radiance which varies with orbit phase.
Ø The effect is expected to be small, but largest for warm scenes in SW band and edge of MW band.
orbit time (sec)
delta
T (K
)
0 50 100 150 200 250 300 350
−0.2
−0.1
0
0.1
0.2
0.3
orbit phase
VIIR
S −
CrIS
BT
(K)
CrIS/VIIRS Differences versus Orbit Phase (4/1 to 02/26)
M13, 4um
11
Orbit Phase Dependence
Eq. Eq. N.Pole Eq. S.Pole
Ø Li_le dependence on orbit phase for M13 is a verifica.on of the CrIS ICT environmental model (blackbody reflected term) accuracy.
VIIRS-‐CrIS Comparisons During VIIRS OBC WUCD
12
Nominal biases at opera/onal OBC temperature and above converge when OBC cools to ambient
OBC Warmup Phase OBC Cooldown Phase
10-‐Sep-‐2012 11-‐Sep-‐2012
Ø For warm scenes, cooling the OBC temperature causes (1) M13 biases to converge with those of M15 and M16, as well as (2) be_er overall agreement with CrIS.
Ø Has poten.al implica.ons for developing refinements to the VIIRS OBC emissivity and/or instrument temperatures, for example.
0 10 20 30 40 50 60 70 80 90−1
−0.8
−0.6
−0.4
−0.2
0
0.2
0.4
0.6
0.8
1
cross track index
VIIR
S −
CrIS
BT
(K)
CrIS/VIIRS Differences versus Scan Angle (4/1 to 02/25)
M13, 4umM15, 10.8umM16, 12um
13
Scan Angle Dependence
Ø Differing designs and sensi.vity to poten.al scan angle biases, yet li_le dependence on scan angle is observed.
Summary ² These types of comparisons are beneficial for both VIIRS and CrIS.
² Daily mean differences are <0.1K, with very small changes (~15mK) over the past 11 months.
² The comparisons show a clear dependence on scene BT for M15, with VIIRS cooler than CrIS by ~0.4K at 205K. Root cause(s) is under inves.ga.on.
² The comparisons show very similar behavior among CrIS FOVs, including the dependence on scene temperature contribu.ng to the characteriza.on of the CrIS radiometric nonlinearity correc.on uncertainty.
² The comparisons show li_le dependence on orbit phase, contribu.ng to characteriza.on of the CrIS ICT environmental model uncertainty.
² The mean agreement between CrIS and VIIRS improves further when the VIIRS OBC is cooled during quarterly linearity characteriza.on tests, with poten.al implica.ons for small refinements to the VIIRS OBC emissivity and/or instrument temperatures.
² The comparisons show li_le dependence on scan angle. 14
200
220
240
260
280
300
BT
(K)
LW FOV 5
700 800 900 1000 1100
−0.2
−0.1
0
0.1
0.2
wavenumber
3−si
gma
RU
(K)
MW FOV 9
1200 1400 1600wavenumber
SW FOV 5
2200 2300 2400 2500wavenumber
CrIS In-‐Flight Radiometric Uncertainty (RU) Es;mates for a typical ~clear sky scene
Longwave Midwave Shortwave
3σ uncertainBes: a2 (30%LW, 15%MW) ICT Temp (112.5 mK) ICT emis (0.03) ICT Refl Tmod (6K) ICT Refl Tmeas (1.5K) RSS/Total RU
* Not including Shortwave cold scene and Gibbs ringing ar.facts
200 220 240 260 280 300−1
−0.5
0
0.5
1
BT (K)
CrIS
− IA
SI (K
)
835 cm−1
CrIS (K)
AIR
S −
CrIS
(K)
180 200 220 240 260 280 300 320−1
−0.5
0
0.5
1
coun
t
1
2
7
20
54
150
400
Scene Temperature Dependence, cont.
AIRS – CrIS SNOs @ 835 cm-‐1 AIRS – IASI SNOs @ 900 cm-‐1
CrIS – IASI SNOs @ 900 cm-‐1
• Mar 28 – Oct 16, 2012 VIIRS-‐IASI SNOs (RAD-‐12B data set). • Compare full RSR spectral radiance to in-‐band only spectral
radiance for M12–M16, I4, I5. • Filter on VIIRS uniformity (> 400 matchups aoer filtering). • OOB impact small in all bands (<0.1K). • M13 impact peak at very cold scenes; M15 also has scene
temperature dependence.
M13 (4.05um) M15 (10.8um)
17
M12 (3.70um)
M14 (8.55um)
M16 (12.0um) I4 (3.74um) I5 (11.5um)
OOB Impact on VIIRS TEB
UWisc, 2012-‐10-‐24
OOB influence is small in all bands (but not zero)
Ø As the VIIRS OBC temperature approaches the instrument temperature, the VIIRS calibra.on becomes less sensi.ve to knowledge of the OBC emissivity and to knowledge of the instrument temperatures, and also changes the nonlinearity “set point”; Changes to the CrIS/VIIRS comparisons during this test implies that small improvements to the VIIRS calibra.on parameters are possible.
Ø For warm scenes, cooling the OBC temperature causes (1) M13 biases to converge with those of M15 and M16, as well as (2) be_er overall agreement with CrIS.
18