Synergy between polar-orbiting and geostationary sensors:

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1 Synergy between polar-orbiting and geostationary sensors: Remote sensing of the ocean at high spatial and high temporal resolution. Quinten Vanhellemont, Griet Neukermans, Kevin Ruddick Management Unit of North Sea Mathematical Models (MUMM) Royal Belgian Institute of Natural Sciences (RBINS)

2 Sensor showdown (I): MODIS MODIS Aqua - polar orbiting radiometer - high spatial resolution (1 km) images per day (clouds!) - spectral bands designed for ocean colour MODIS global cover for 02/05/2012

3 North Sea is [240,130] pixel crop Sensor showdown (II): SEVIRI SEVIRI (Meteosat): - geostationary sensor Study area - images every 15 min - difficult atmospheric correction and low spatial resolution at at higher latitudes: 3x3 km at nadir point Study area: North Sea: ~3x6 km [48 N-56 N, 4 W-10 E] - broad bands for cloud and ice detection SEVIRI full disk image,

4 Study area: North Sea Semi-diurnal tide High turbidity in UK and BE coastal waters UK Strong relationship with bathymetry: resuspension in shallow waters MODIS Aqua Turbidity 08/03/ :00 FR BE NL

5 Marine signal from SEVIRI (I) Precusors: In a pioneering study, a marine signal was derived from SEVIRI by Neukermans et al. (2009), the red band was atmospherically corrected using the NIR band Data from 01/01/ /09/2009 was used to generate turbidity maps and related products every 15 minutes (Neukermans et al., subm.)

6 Marine signal from SEVIRI (II) The high frequency data allow the study of (semi-) diurnal variability: eg. timing of turbidity maximum SEVIRI and moored buoy measurements (Neukermans et al., subm. to RSE)

7 Potential for synergy! MODIS has a better spatial and spectral resolution, SEVIRI has a better temporal resolution MODIS: 1 image per day, 1x1 km resolution SEVIRI: images per day, 3x6 km resolution Can we modulate the high spatial resolution MODIS image with the high frequency signal from SEVIRI? Synergy product: images per day, 1x1 km resolution?

8 Data processing: SEVIRI (I) MARINE REFLECTANCE 0.6µm SEVIRI data is quite noisy (sensor limitation)

9 Data processing (I): SEVIRI noise Temporal smoothing of SEVIRI Removal of random noise (digitization effects) Moving average minutes (5 images) original smoothed

10 Data processing (II): SEVIRI noise Daily composite of SEVIRI data daily mean standard coefficient deviation of variation High CV / noisy data in clear waters The standard deviation is correlated with mean average The coefficient of variation (CV, sdev/mean) is very high in clear waters, related to the detection limit of SEVIRI

11 Data processing (III): SEVIRI noise Temporal smoothing of SEVIRI 5 image mean standard deviation Standard deviation of these composites not correlated with mean average: effective removal of noise

12 MODIS LR MODIS HR Data processing (IV): MODIS HR MODIS L2 (R2009) on SEVIRI HR grid reprojected on a 3x6 ( HR ) subset of the SEVIRI ( LR ) grid every SEVIRI pixel = 18 MODIS pixels LR = [240,130] pixels, HR = [720,780] pixels Crop over Thames Estuary and Belgian coastal zone for 12/01/2008 fine structures

13 Data processing (V): Comparison SEVIRI smoothed vs MODIS (AVG) for 43 images SEVIRI rhow6 within (detection limits) Underestimation by SEVIRI of 20-30%, more at lower reflectances detection limit -100% -50% +50%

14 Synergy (I) Combine the high temporal signal from SEVIRI with the spatial resolution from MODIS Smoothed time-series to modulate MODIS HR dataset ( SYN) w F ( t) ( t w 0 SEV ( t) ( MOD) ( SEV ) w ( SEV ) w ( t) ( t t = SEVIRI image times t 0 = image time closest to MODIS overpass )* F 0 ) SEV ( t)

15 Synergy (II) SEVIRI Synergy edge of MODIS scene MODIS AC failure clear water = MODIS only MARINE REFLECTANCE 0.6µm MARINE REFLECTANCE 0.6µm SEVIRI and MODIS-SEVIRI synergy product for 11/02/2008

16 Synergy (II) clear waters: masked Synergy product 11/02/2008 (crop) MARINE REFLECTANCE 0.6µm

17 Synergy (II) Synergy product 11/02/2008 (crop) at t(0) the synergy product = MODIS MARINE REFLECTANCE 0.6µm

18 Synergy (II) Synergy product 11/02/2008 (crop) MARINE REFLECTANCE 0.6µm

19 Synergy (III) Synergy product 11/02/2008 (crop) MARINE REFLECTANCE 0.6µm

20 Validation (I) Data courtesy of CEFAS; Smartbuoys at three locations (increasing T): Dowsing West Gabbard Warp Record turbidity several times per hour MODIS Aqua Turbidity 16/02/ :05

21 Validation (II) Smartbuoys Turbidity CV < 20% (sdev of a 10 minute average < 0.2 * mean) SEVIRI (smoothed) and Synergy timeseries only data with MODIS matchup SEVIRI marine reflectance [ ] average of 5 images per matchup (+-30min)

22 Validation (III) SEVIRI only (LR) Turbidity filter on in situ, 5 image smoothing, days with MODIS MODIS only Turbidity 01/01/ /09/2009 (WARP and WGAB only) Dowsing, West Gabbard, Warp

23 Validation (IV) Synergy (HR) Turbidity filter on in situ, 5 image smoothing Synergy (HR) Turbidity after removal of 14 outliers from 3 days 16/06/ /06/ /08/2008 Dowsing, West Gabbard, Warp

24 Validation (IV) SEVIRI (LR) Turbidity Synergy (HR) Turbidity Dowsing, West Gabbard, Warp

25 Conclusions Diurnal cycles detected with SEVIRI can be used to modulate higher resolution MODIS data The resulting synergy product, resolves temporal dynamics at high spatial resolution has a better coefficient of determination and lower errors when compared with in situ measurements, is limited to cloud position at MODIS overpass a dedicated geostationary sensor will reduce the effects of fast-moving (sparse) clouds, but increasing resolution for a geostationary sensor is very expensive enhanced with DINEOF cloud filling geostatistical analysis?

26 Acknowledgements Thanks to NASA: MODIS Aqua data EUMETSAT and KMI: SEVIRI data CEFAS: in situ Smartbuoy data BELSPO: funding of GEOCOLOUR project References Neukermans G., Ruddick K., Bernard E., Ramon D., Nechad B. & Deschamps P.-Y. (2009). Mapping total suspended matter from geostationary satellites: a feasibility study with SEVIRI in the Southern North Sea. Optics Express, Vol. 17(16), pp Neukermans, G., K. Ruddick and N. Greenwood (2012, submitted). Diurnal variability and light attenuation in the southern North Sea from the SEVIRI geostationary sensor. Rem Sens Env