Cooperation on assessing the impact of different sigma0 re-sampling on ASCAT SAF products (EUMETSAT FA 2014)
2014-02-20 – 2014-11-19
This Federated Activity intends to gather the expertise available in the different ASCAT teams in CAF and the SAFs on Level 1/2/3 processing, in order to address some of the issues explained above. It should be noted that the initial proposal was more ambitious, but available funding at both the OSI and H-SAF for federated activity work has significantly limited the final scope, which is now concerned with the following objectives:
I. Providing evidence on what are the effects (if any) on the Level 2 quality and characteristics, of applying the alternative sigma0 re-sampling approach currently available for 12.5 km coastal wind products by KNMI (circular top-hat averaging window). This should cover both surface boundary areas (coast/land) and open areas. Based on this evidence, issue a recommendation to CAF on modifying or not the current 12.5 km Hamming products.
II. Exploring and demonstrating the value of the information content in the currently available ASCAT full resolution sigma0 product to retrieve higher resolution soil moisture data, as well as to remove artefacts that can be identified at the sigma0 re-sampling stage (corner reflectors). Based on this, recommend appropriate improvements or changes in the current ASCAT CAF/SAF processing chains.
The initial objective of examining the full end-to-end processing chain methods up to high level SAF products (Level 3) and assessing the feasibility of finding a sigma0 re-sampling grid that might satisfy several applications, has been put on hold due to funding and resource constraints.
A further de-scoping has been done, due to the unavailability of resources for this activity in the OSI SAF sea ice team (ref. to Steering Group meeting discussion in November 2013). It is recognised however that any change in the sigma0 re-sampling approach may have consequences for the sea ice drift products that use ASCAT data as input and will need to be tested, in case the Level 1 product update requires algorithm or configuration changes in the OSI SAF sea ice drift processing chain at Met.no.
Note that the objectives I and II of this activity do not include an exhaustive analysis of the actual resolution of the ASCAT instrument measurements, or an assessment of optimum re-sampling techniques from more theoretical or philosophical considerations, nor indeed from the instrument design point of view. It is planned at EUMETSAT to issue a study to look into these matters, also in preparation of EPS-SG SCA, in a similar time-frame (start in Q1 2014). Consequently, the results from this FA with the additional expert point of view of the applications are indeed expected to be extremely important in the evaluation of the study results.
Note that in the currently re-scoped proposal, Objective I applies to the H-SAF soil moisture subsystem and team, while the OSI SAF wind team has a support role, since this work has already been done for the wind parameter. With respect to objective II, the H-SAF soil moisture subsystem and team are concerned.
- Stefan Hasenauer
- Royal Netherlands Meteorological Institute