ERNESST meeting. October 14, Minutes (H. Roquet, P. Le Borgne)

Transcription

1 ERNESST meeting October 14, 2009 Minutes (H. Roquet, P. Le Borgne) Introduction (C. Merchant) The first idea of a European Research Network dedicated to satellites SST was discussed in Spring 2009 (ERNESST = European Research Network for Estimation from Space of Surface Temperature). A lot of efforts have been put recently in Europe on the exploitation of satellite SST measurements downstream the SST retrieval step (ex : Medspiration, MyOcean). However, it was felt that there was a need for a research effort on the retrieval step from satellite radiances to SSTs. The scientific issues identified up to now are : SST algorithms, optimal estimation Cloud (or rain for microwave) detection and biases Exploiting the system of SST sensors (referencing, bias adjustment) Accounting for diurnal variability The proposed top level objectives and activities of ERNESST are : increased communication between members research priorities and strategies opportunities for co-ordinated new investigations coordination with GHRSST groups, namely: DW group: Gary Wick STVAL group: Gary Corlett EAR group: Andy Harris Hlat group: Jacob Hoyer future generation of scientists seeking financial support for network activities New contacts have been already looked for (37 people answered ERNESST s and declared their interest). Among interested people who were not able to come, are an Israelian group (working on the Dead Sea), and a Finnish group (working on lakes).

2 Recent research results as an example (C. Merchant) The current SST bias correction schemes, based on AATSR, and developed and implemented for instance in the context of MERSEA and MyOcean, rely on strong assumptions on the spatial and time scales of the biases. Ideally, it would be better to tackle the bias problem at sensors level, and to use their differential sensitivities to detect and perform mutual corrections between them. For SST retrieval, great improvements are expected from optimal estimation techniques. However, the improvements were very clear in the METOP/AVHRR study, but the same approach didn t give comparable improvements in the MSG/SEVIRI study, showing that a lot of problems still need to be better understood. Among the other SST issues expected to be discussed during the meeting, there are : analysis and understanding of satellite SST retrieval errors in difficult regions (ex : Arctic) use and understanding of in-situ observation climate challenge analysis, merging/blending techniques for satellite SSTs SST algorithms (P. Le Borgne) Operational SST retrieval is now facing the challenge of using real time information on the state of the atmosphere, provided by NWP outputs. Ongoing research at CMS in that field bears on: BT simulation correction and cloud mask determination Multispectral SST algorithm anomalies and improvements to OE techniques SST in the Arctic (S. Eastwood) Arctic regions are very challenging for SST retrieval. Extreme cases are the Polynias ( lakes of the Arctic), where atmosphere is extremely dry and were single-channel SST IR algorithms work better than traditional multi-channel ones. SST in the Arctic (J. Hoyer) Another difficult case for SST retrieval in the Arctic region is the marginal ice zone, where ice fog (due to very large Tair Tsea differences) occurs frequently. DMI is currently setting up a

3 METOP processing chain based on the CASSTA algorithms, to derive (with different algorithms) surface temperatures in the open ocean, in the transition zone, over ice and in Polynias. Merging SSTs (P.Le Borgne) The bias correction method based on using the AATSR as a reference gives satisfying result on a global scale (Ifremer) and atlantic scale (CMS); it is questionable at smaller scale over Europe and should be reconsidered in Polar conditions or in closed seas such as the Mediterranean. Identifying DW contaminated data is an other issue, that can be solved by using observations or model outputs. Validation is needed. Three research topics are envisaged in this context: 1) large bias correction 2) bias correction and Diurnal Warming in polar conditions 3) bias correction and Diurnal Warming in the Mediterranean area Use of drifting buoy SST in remote sensing (C. Merchant) From a triple collocation study, C. Merchant presented estimates of the drifting buoy SST real accuracy (0.2 K standard deviation), which contradicts the accuracy expected by the drifting buoy operators (0.1 K standard deviation). The accuracy requirement established by the GHRSST is 0.05 K, and should be achievable with improved drifting buoy thermistance calibration procedures. He showed also that with the current drifting buoy accuracy, it is extremely difficult to detect an improvement in the accuracy of the satellite SSTs (at least for the most accurate ones). Time of Day and depth effects in satellite in situ comparisons (O.Embury) Within the ARC project (toward version 3 of ATSR SST) drifter-depth SSTs are experimentally estimated from satellite SSTs, adjusting for skin effect, diurnal stratification and time-of-day. For time-of-day adjustment, rates of cooling/warming can be parameterized in terms of solar zenith angle. Time series of global and regional average SST from ATSR (K. Veal) In the operational (version 2) ATSR SST archive, different types of SST retrieval (dual and nadir, two-channel and three-channel) have inconsistent discontinuities and biases. Simple methods of adjusting the mean produce more convincing time series, but stability errors associated with such methods have not been assessed.

4 Satellite SST retrievals in the Adriatic Sea (I. Tomazic) The main objective of these activities is the production of improved SST analyses over the Adriatic Sea, for use by regional oceanographic models. SST retrievals display various dependencies which were analyzed, and can be improved. Discussion (all) From the presentations hereabove, a list of potential additional research topics/issues for ERNESST was established : The addition of inland water bodies in the research area of ERNESST was proposed and supported by the participants. However land temperature is not included. Coastal areas Fundamental radiative transfer issues (spectroscopy, emissivity, diffusion etc ) Extending insights from current system(s) to the past ERNESST capability in microwave radiometry Surface Temperature definition in the Arctic region (in particular in case of sub-pixel ice) Ice surface temperature Regionality of retrievals Cloud detection and classification In-situ observations (complementary data sets, geographical lines of radiometers, integration with satellite systems.) Actions 1. Enlarging ERNESST: H. Roquet to get in touch with other potential European partners having expertise in microwave radiometry (ex : University of Bremen) B. Buongiorno to contact people active on the Black Sea 2. Develop the ERNESST web pages (could be a wiki hosted by Met.no?) 3. Set up a subgroup to bid for financial support for network activities. Explore European options. 4. Until finance is available, participation of ERNESST members in meetings on an opportunistic basis is encouraged.

5 CMS is hosting a meeting on SST validation on the 1 st and 2 nd of December 2009 PAGE 3