1. Comparison between Sentinel-3A SLSTR and IASI aboard Metop-A and –B
EUMETSAT- Igor Tomažić
Anne O’Carroll, Tim Hewison, Jorg Ackermann, Dorothee Coppens
ESA
Craig Donlon, Jens Nieke
RAL
Dave Smith

2. SLSTR: IR requirement
The absolute radiometric accuracy of the data acquired in the IR channels shall be smaller than 0.2 K (0.1 K goal) traceable to the ITS-90.
As a minimum, this requirement shall be met in the blackbody temperature range (~250 K - ~300 K), provided that the on-ground characterization covers the complete temperature range specified.

3. Crossovers (SNO) – Jul-Nov/2016 (Jun-Aug 17)
Methodology
Crossovers (SNO) – Jul-Nov/2016 (Jun-Aug 17)
SNO=simultaneous nadir overpasses
Different for MetopA and MetopB
Collocations (matchups)
spatio/temporal/geometry (within pix/5 min/20 deg)
Spectral convolution
Convolve IASI radiance spectra with SLSTR SRF
Aggregate (average)
SLSTR pixels in IASI FoV (all vs. sigma <0.4 K)
Double difference

4. S8 nadir: td5 min; |IASI sza|<20deg:binned: ALL/homo: no_signal filtered
Homo:std<0.4 K
ALL
Jul16-Nov16
Jul16-Nov16
Jun17-Aug17
Jun17-Aug17

5. S8: td5 min; |IASI sza|<20deg:binned: homo: no_signal filtered: detector0/1
S8: detector 0/1
S9: detector 0/1
Good agreement between detectors, but not the same!
Difference slightly more pronounced for S9
SLSTR - two IR radiometers!

6. Overall statistics for BT>220 K
All/det0/ det1
homo
ALL S8
all
(72863)
(291396)
det0
(73128)
(291155)
det1
(73291)
(291488) S9
(73606)
(287830)
(73963)
(287570)
(74056)
(287900)

7. IASI B – IASI A (over SLSTR A)

8. IASI: Statistics of Double difference Time Series – MSG3
(MSG3-IASIA)-(MSG3-IASIB) Demo RAC Standard Bias over / :
Channel
Double Difference Trend [K/yr]
Mean Double Difference [K]
IR3.9
 -0.016 +
  0.008
0.001
0.005
IR10.8
  0.004
  0.009
-0.016
0.006
IR12.0
 -0.009
-0.018
No statistically significant trend
in any channel
Within standard uncertainty of 10mK/yr
Consistent results from other Meteosats
But larger uncertainties
No statistically significant difference
between IASI-A and -B
in Short- and Mid-bands
in any channel
Small, but significant difference
in long-wave band
Larger for colder scenes
After Hewison, 2016 (IASI WG 2106)

9. Summary S3A/S3B tandem phase: S3A/S3B (30 sec) vs IASI-A/IASI-B
Stable calibration within requirements ( K)
Apr16-Aug16 ~= Jul16-Nov16 ~= Jun17-Aug17
Near zero nadir view bias (<0.1 K) in S8 and S9 (220 K – 280 K)
Cold temperature bias (~>0.2 K)
Nonlinearity? - BB
S8 cold temp. calibration issue ~200 K (dynamic range, “no_signal”)
Small difference in dynamic range for two detectors (will be lowered to ~183 K)
Small negative bias for >280 K  to be further investigated with QSNO
Different detectors response:
S8 – OK, S9 small offset between detectors (~0.08 K)
SLSTR IR  2 radiometers
Straylight error observed during the SLSTR pre-flight calibration?
IASIA/IASIB double differences:
Small bias ~ 0.05 K – function of SNO event, scene temperature
Similar trend compared to MSG/SEVIRI
S3A/S3B tandem phase: S3A/S3B (30 sec) vs IASI-A/IASI-B