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

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.

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

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

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!

Overall statistics for BT>220 K All/det0/ det1 homo ALL S8 all 0.05+-0.11 (72863) 0.00+-0.64 (291396) det0 0.04+-0.12 (73128) -0.01+-0.66 (291155) det1 0.05+-0.12 (73291) 0.00+-0.65 (291488) S9 0.08+-0.11 (73606) 0.03+-0.66 (287830) 0.07+-0.12 (73963) 0.02+-0.67 (287570) 0.09+-0.11 (74056) 0.04+-0.67 (287900)

IASI B – IASI A (over SLSTR A)

IASI: Statistics of Double difference Time Series – MSG3 (MSG3-IASIA)-(MSG3-IASIB) Demo RAC Standard Bias over 2013-03/2016-02: 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)

Summary S3A/S3B tandem phase: S3A/S3B (30 sec) vs IASI-A/IASI-B Stable calibration within requirements (220-280 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 250-300 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