Comparison between Sentinel3 A SLSTR and IASI aboard

Comparison between Sentinel-3 A SLSTR and IASI aboard Metop-A and –B EUMETSAT- Igor Tomažić Anne O’Carroll, Tim Hewison, Jorg Ackermann, Dorothee Coppens ESA RAL 1 Sentinel-3 Validation Team meeting Craig Donlon, Jens Nieke 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. 2 Sentinel-3 Validation Team meeting

Methodology • Crossovers (SNO) – Jul-Nov/2016 (Jun-Aug 17) • SNO=simultaneous nadir overpasses • Different for Metop. A and Metop. B • 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 Fo. V (all vs. sigma <0. 4 K) • Double difference 3 Sentinel-3 Validation Team meeting

S 8 nadir: td 5 min; |IASI sza|<20 deg: binned: ALL/homo: no_signal filtered Homo: std<0. 4 K ALL 4 Sentinel-3 Validation Team meeting Jul 16 -Nov 16 Jun 17 -Aug 17

S 8: td 5 min; |IASI sza|<20 deg: binned: homo: no_signal filtered: detector 0/1 S 8: detector 0/1 S 9: detector 0/1 • Good agreement between detectors, but not the same! • Difference slightly more pronounced for S 9 • SLSTR - two IR radiometers! 5 Sentinel-3 Validation Team meeting

Overall statistics for BT>220 K S 8 S 9 6 All/det 0/ det 1 homo ALL all 0. 05+-0. 11 (72863) 0. 00+-0. 64 (291396) det 0 0. 04+-0. 12 (73128) -0. 01+-0. 66 (291155) det 1 0. 05+-0. 12 (73291) 0. 00+-0. 65 (291488) all 0. 08+-0. 11 (73606) 0. 03+-0. 66 (287830) det 0 0. 07+-0. 12 (73963) 0. 02+-0. 67 (287570) det 1 0. 09+-0. 11 (74056) 0. 04+-0. 67 (287900) Sentinel-3 Validation Team meeting

IASI B – IASI A (over SLSTR A) 7 Sentinel-3 Validation Team meeting

IASI: Statistics of Double difference Time Series – MSG 3 (MSG 3 -IASIA)-(MSG 3 -IASIB) Demo RAC Standard Bias over 2013 -03/2016 -02: Channel IR 3. 9 IR 10. 8 IR 12. 0 Double Difference Trend [K/yr] -0. 016 + 0. 008 0. 004 + 0. 009 -0. 009 + 0. 009 • No statistically significant trend • in any channel • Within standard uncertainty of 10 m. K/yr • Consistent results from other Meteosats • But larger uncertainties Mean Double Difference [K] 0. 001 + 0. 005 -0. 016 + 0. 006 -0. 018 + 0. 006 • 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) 8 Sentinel-3 Validation Team meeting

Summary • Stable calibration within requirements (220 -280 K) • Apr 16 -Aug 16 ~= Jul 16 -Nov 16 ~= Jun 17 -Aug 17 • Near zero nadir view bias (<0. 1 K) in S 8 and S 9 (220 K – 280 K) • Cold temperature bias (~>0. 2 K) • Nonlinearity? - BB 250 -300 • S 8 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: • S 8 – OK, S 9 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 • S 3 A/S 3 B tandem phase: S 3 A/S 3 B (30 sec) vs IASI-A/IASI-B 9 Sentinel-3 Validation Team meeting