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Water & Energy Cycles

The basis for SMAP is that the synergy between active and passive measurements will enhance soil moisture retrieval capabilities in two ways: (i) the high resolution (3km) but noisy soil moisture data from radar will be used to downscale the accurate but low resolution (40km) soil moisture data from the radiometer to better than 10km; and (ii) surface parameters output from the radar retrieval algorithm at 3km resolution (soil moisture, surface roughness and a vegetation index) can be aggregated to the radiometer resolution and used as ancillary data for radiometric soil moisture retrieval (Entekhabi et al., 2004). While synthetic studies have shown the utility of the proposed downscaling approach (Zhan et al., 2006; Dunne et al., 2007), and methods have been proposed to retrieve passive microwave parameters from radar observations (Rahman et al., 2008), there have been very limited studies to test these methods. Consequently, we have proposed to the Australian Government to undertake a series of airborne field experiments using our recently funded airborne SMAP simulator to verify results from synthetic and tower based studies. This proposal represents the interest and expertise that A/Prof Walker can provide to the SMAP Science Definition Team. Specifically, we will develop and test algorithms to: i) downscale low resolution passive microwave observations using high resolution active microwave observations, and ii) use active and passive data synergistically to increase the accuracy of retrieved soil moisture as compared to using either data source alone. Up to now there has been no way to undertake such studies world-wide. By mid 2009 we will have a unique capability for undertaking high resolution active-passive microwave remote sensing at L-band with footprint resolution ratios, incidence angles and polarisations similar to those expected from SMAP. This capability arises from recent funding for a Polarimetric L-band Multibeam Radiometer (PLMR; Walker et al., 2003 --$657k) and a Polarimetric L-band Imaging Synthetic aperture radar (PLIS; Walker et al., 2007 -- $840k). When used together on the same aircraft, this configuration of Australian infrastructure will allow simulation of the SMAP satellite mission with passive microwave footprints at 1km and active microwave footprints at 10m resolution when flown at a flying height of 3000m. All other existing active-passive capabilities currently provide only active-passive data for the same footprint resolution. We believe that results from such a project, if funded (funding results will be announced in October), will be of immense interest to the SMAP mission development. Moreover, A/Prof Walker’s past experience in active-passive downscaling activities in an earlier risk reduction exercise for Hydros (Zhan et al., 2006), identification of mission design requirements (Walker and Houser, 2004), expertise in soil moisture data assimilation (eg. Walker and Houser, 2001), contribution to arguably the most reliable AMSR-E soil moisture retrieval algorithm (Owe et al., 2001), participation in AMSR-E cal/val activities (Draper et al, in review), leadership in recent airborne field campaigns in preparation for SMOS (Panciera et al., 2008; Merlin et al., 2008), current funded activities to validate SMOS and assimilate its products into a 1km resolution land surface model over Australia, and membership of the SMOS cal/val team, makes A/Prof Walker ideally suited as an international member on the SMAP Science Definition Team.

Project PI: Jeffrey Walker/University of Melbourne

Dept. of Civil and Environmental Engineering, The University of Melbourne, Victoria 3010, Australia.

Phone: 61383445590

Fax: 61383446215

Email: j.walker@unimelb.edu.au

http://www.civenv.unimelb.edu.au/about/webpage.php3?login=jwalker

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Started: Aug 10, 2010

Last Activity: Dec 16, 2010

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