1. GHRSST 8 th Science Team Melbourne, May 2007 GHRSST Sea Ice Working Group Peter Minnett RSMAS University of Miami

2. GHRSST 8 th Science Team Melbourne, May 2007 Background GHRSTT SI WG was set up at the 6 th Science Team Meeting in Exeter.GHRSTT SI WG was set up at the 6 th Science Team Meeting in Exeter. Objectives:Objectives: –To determine best ice-mask for high latitude SST fields –To improve accuracy of high latitude SST fields

3. GHRSST 8 th Science Team Melbourne, May 2007 Membership Peter Minnett (U. Miami)Peter Minnett (U. Miami) Chelle Gentemann (RSS & U. Miami)Chelle Gentemann (RSS & U. Miami) Søren Andersen (DMI)Søren Andersen (DMI) John Stark (UK Met O)John Stark (UK Met O) With input from Ron Vincent (Royal Military College of Canada) & Steinar Eastwood (Norwegian Met Service [met.no])With input from Ron Vincent (Royal Military College of Canada) & Steinar Eastwood (Norwegian Met Service [met.no])

4. GHRSST 8 th Science Team Melbourne, May 2007 IR - Issues There are four specific issues associated with the accurate retrieval of sea surface temperature (SST) at high latitudes using infrared radiometry: The discrimination between ice-free and ice-covered water at the resolution (temporal and spatial) of the GHRSST SST retrieval schemes.The discrimination between ice-free and ice-covered water at the resolution (temporal and spatial) of the GHRSST SST retrieval schemes. The discrimination between ice-free and ice-covered water at the resolution (temporal and spatial) of the GHRSST SST global analyses schemes.The discrimination between ice-free and ice-covered water at the resolution (temporal and spatial) of the GHRSST SST global analyses schemes. The accurate correction of the effects of the atmosphere on the infrared radiation as it propagates from the sea surface to the satellite radiometer.The accurate correction of the effects of the atmosphere on the infrared radiation as it propagates from the sea surface to the satellite radiometer. How feasible is the reconstruction of SST in the marginal ice zone based on ice concentration, typically needed in climate– related, long-term data sets such as HadISST?How feasible is the reconstruction of SST in the marginal ice zone based on ice concentration, typically needed in climate– related, long-term data sets such as HadISST?

5. GHRSST 8 th Science Team Melbourne, May 2007 μW - Issues Microwave radiometry is very good at all- weather determination of SST and ice cover, but: –Spatial resolution is poor –Side-lobe contamination – more of an issue for SST than for ice cover –Calibration of AMSR-E is potentially an issue

6. GHRSST 8 th Science Team Melbourne, May 2007 GHRSST Sea Ice Requirements Ice mask, not ice properties:Ice mask, not ice properties: –1- 4 -10km resolution @ 6hrs Procedure very analogous to cloud screeningProcedure very analogous to cloud screening Could make use of ice properties retrievals, but it is not clear that objectives are the sameCould make use of ice properties retrievals, but it is not clear that objectives are the same Complementary to the GCOS SST & Sea Ice Working Group which is comparing different ice concentration products in order to obtain better knowledge of their error properties.Complementary to the GCOS SST & Sea Ice Working Group which is comparing different ice concentration products in order to obtain better knowledge of their error properties.

7. GHRSST 8 th Science Team Melbourne, May 2007 GHRSST Sea Ice Requirements - II Atmospheric correction algorithm improvements for high-latitude, near ice edge factorsAtmospheric correction algorithm improvements for high-latitude, near ice edge factors –Dry atmospheres –Large air-sea temperature differences –Temperature dependence of infrared emissivity see Newman, S. M., J. A. Smith, M. D. Glew, S. M. Rogers, and J. P. Taylor, 2005: Temperature and salinity dependence of sea surface emissivity in the thermal infrared. Quarterly Journal of the Royal Meteorological Society, 131, 2539-2557. doi: 10.1256/qj.04.150see Newman, S. M., J. A. Smith, M. D. Glew, S. M. Rogers, and J. P. Taylor, 2005: Temperature and salinity dependence of sea surface emissivity in the thermal infrared. Quarterly Journal of the Royal Meteorological Society, 131, 2539-2557. doi: 10.1256/qj.04.150

8. GHRSST 8 th Science Team Melbourne, May 2007 Sea Ice Sea ice includes ice pack, land fast ice and tide-water glaciers that extend beyond the conventional, time-invariant land-mask.Sea ice includes ice pack, land fast ice and tide-water glaciers that extend beyond the conventional, time-invariant land-mask. Highly variable in space and timeHighly variable in space and time Does not necessarily have a well defined edgeDoes not necessarily have a well defined edge –Comparable to cloud edge

9. GHRSST 8 th Science Team Melbourne, May 2007 OLS image of katabatic winds blowing over open water in the Ross Sea, Antarctica. Streamers of frazil ice forming at the surface are oriented in the direction of air flow. (Courtesy of Arctic Antarctic Research Center - arcane.ucsd.edu)

10. GHRSST 8 th Science Team Melbourne, May 2007 Large tabular icebergs calved off Antarctica provide a dynamic ice edge

11. GHRSST 8 th Science Team Melbourne, May 2007 Data sources High resolution (<1 km) SAR and visible imageryHigh resolution (<1 km) SAR and visible imagery High resolution (~1 km) infrared imageryHigh resolution (~1 km) infrared imagery Medium resolution (~12 km) high frequency microwave imagery (ice cover)Medium resolution (~12 km) high frequency microwave imagery (ice cover) Low resolution (~50-100 km) low frequency microwaves (SST)Low resolution (~50-100 km) low frequency microwaves (SST)

12. GHRSST 8 th Science Team Melbourne, May 2007 Spatial resolution Spatial resolution in the micro- wave images relatively poor. Generally over-sampled to a 25km grid. Microwave data less influenced by clouds, and contain complementary information to the visible or infrared imagery.

13. GHRSST 8 th Science Team Melbourne, May 2007 Terra MODIS true color June 29, 2004. 21:59 UTC

14. GHRSST 8 th Science Team Melbourne, May 2007 Terra MODIS true color June 16, 2004.

15. GHRSST 8 th Science Team Melbourne, May 2007 MODIS cloud & ice mask

16. GHRSST 8 th Science Team Melbourne, May 2007 Example of SAR image

17. GHRSST 8 th Science Team Melbourne, May 2007 Summary – ice mask During summer, cloud screening algorithms using reflected sunlight can be applied to IR dataDuring summer, cloud screening algorithms using reflected sunlight can be applied to IR data During winter, lack if reflected sunlight means IR techniques have to be applied (e.g. spatial coherence), or reduced-resolution microwave ice product:During winter, lack if reflected sunlight means IR techniques have to be applied (e.g. spatial coherence), or reduced-resolution microwave ice product: –Dr Gentemann has an “operational” 9-km, daily μw ice mask –Aqua has MODIS and AMSR-E so elapsed time not an issue; all other combinations of ir/mw sensors have uncertainties with ice movement between overpasses –SAR images, very high resolution, but difficult to interpret, and displacement between overpasses can be an issue.

18. GHRSST 8 th Science Team Melbourne, May 2007 Atmospheric correction algorithms And now for the high latitude effects on SST:And now for the high latitude effects on SST: –Atmospheric transmissivity (water vapor distribution) –Air-sea temperature differences

19. GHRSST 8 th Science Team Melbourne, May 2007 Variability of atmospheric transmission

20. GHRSST 8 th Science Team Melbourne, May 2007 Ocham’s razor – simple is good AVHRR NLSST algorithms: NLSST = a + bT 4 + c(T 4 – T 5 ) + d[(T 4 – T 5 ) * (sec  – 1)] CASSTA (Composite Arctic Sea Surface Temperature Algorithm; Vincent et al, 2007 a, b) uses the form: Arctic SST = a + bT 4 with coefficients derived by AVHRR BT & ship- based skin-SST measurements

21. GHRSST 8 th Science Team Melbourne, May 2007 Marine-Atmospheric Emitted Radiance Interferometer (M-AERI)

22. GHRSST 8 th Science Team Melbourne, May 2007 Temperatures are traced to NIST 1.M-AERI on-board black-body cavities have thermometers calibrated to NIST-traceable thermometers. 2.Periodic calibration using a 3 rd black body in M-AERI zenith view. 3.Periodic calibration of M-AERI system with a NIST-designed Water-Bath Black-Body target at RSMAS, using NIST-traceable reference thermometers. 4.RSMAS Water-Bath Black-Body target characterized with NIST EOS TXR NIST EOS TXR TXR characterizing the RSMAS WBBB

23. GHRSST 8 th Science Team Melbourne, May 2007 Dry Arctic Atmospheres

24. GHRSST 8 th Science Team Melbourne, May 2007 North Water Polynya Expedition March-July 1998 M-AERI

25. GHRSST 8 th Science Team Melbourne, May 2007 AVHRR SST retrievals in the NOW region From Vincent, R. F., R. F. Marsden, P. J. Minnett, K. A. M. Creber, and J. R. Buckley, 2007: Arctic Waters and Marginal Ice Zones: Part 1 - A Composite Arctic Sea Surface Temperature Algorithm using Satellite Thermal Data. In reparation. Preliminary results

26. GHRSST 8 th Science Team Melbourne, May 2007 AVHRR SST retrievals in the NOW region From Vincent, R. F., R. F. Marsden, P. J. Minnett, K. A. M. Creber, and J. R. Buckley, 2007: Arctic Waters and Marginal Ice Zones: Part 1 - A Composite Arctic Sea Surface Temperature Algorithm using Satellite Thermal Data. In reparation.

27. GHRSST 8 th Science Team Melbourne, May 2007 Radiometric measurements of air- sea temperature difference

28. GHRSST 8 th Science Team Melbourne, May 2007 Air-sea temperature differences Over most of the oceans the air-sea temperature difference is very constrained. Close to the ice, the spread of values is greater.

29. GHRSST 8 th Science Team Melbourne, May 2007 Dependence on air-sea temperature difference

30. GHRSST 8 th Science Team Melbourne, May 2007 Dependence on air-sea temperature difference Simulations have 5 air-sea temperature differences under each atmosphere: 0, ±1, ±2K

31. GHRSST 8 th Science Team Melbourne, May 2007 Summary Ice mask for IR SST can be derived in the summer using the same tools as the cloud mask.Ice mask for IR SST can be derived in the summer using the same tools as the cloud mask. –Use information in the data streams for SST, not necessary to wait for an ice product. –New approaches may need to be defined for winter measurements Ice amount can be retrieved from microwave channelsIce amount can be retrieved from microwave channels –Use information in the data streams for SST, not necessary to wait for an ice product. Physics of high-latitude SSTs reasonably well understood in terms of the problems, solutions are being developed.Physics of high-latitude SSTs reasonably well understood in terms of the problems, solutions are being developed. –Requires better characterization of polar conditions; more in situ measurements.