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Title: The NAFE'06 data set: Towards soil moisture retrieval at intermediate resolution

Author
item MERLIN, O - UNIVERSITY OF MELBOURNE
item WALKER, J - UNIVERSITY OF MELBOURNE
item KALMA, J - UNIVERSITY OF NEWCASTLE
item KIM, E - NASA
item HACKER, J - FLINDERS UNIVERSITY
item PANCIERA, R - UNIVERSITY OF MELBOURNE
item YOUNG, R - UNISERSITY OF MELBOURNE
item SUMMERELL, G - CSIRO
item HORNBUCKLE, J - UNIVERSITY OF MELBOURNE
item HAFEEZ, M - CSIRO
item Jackson, Thomas

Submitted to: Advances in Water Resources
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2008
Publication Date: 11/1/2008
Citation: Merlin, O., Walker, J.P., Kalma, J.D., Kim, E.J., Hacker, J., Panciera, R., Young, R., Summerell, G., Hornbuckle, J., Hafeez, M., Jackson, T.J. 2008. The NAFE'06 data set: Towards soil moisture retrieval at intermediate resolution. Advances in Water Resources. 31:1444-1455.

Interpretive Summary: An extensive field campaign was conducted to assess the calibration and assimilation of remotely sensed soil moisture at scales appropriate for satellite applications. Soil moisture estimates at high spatial and temporal resolutions are critical in hydrology, meteorology, climate change studies and related disciplines. Passive radiometry at L-band is one of the most promising techniques for measuring and monitoring soil moisture at global scale. The National Airborne Field Experiment 2006 (NAFE'06) was conducted during a three week period of November 2006 in the Murrumbidgee River catchment, located in southeastern Australia to develop this approach. Airborne L-band brightness temperature was mapped over two large domains concurrent with ground observations of soil moisture, surface temperature, surface reflectance, lidar data and aerial photos were acquired over selected areas to investigate scaling issues, and test multi-angle and multi-spectral retrieval approaches. Preliminary analyses indicate that the uncertainty of a single measurement was typically less than 5%, the spatial variability of ground measurements at 1km resolution was up to 10% vol. and the validation of 1km resolution L-band data is facilitated by selecting pixels with soil moisture variability lower than the point-scale uncertainty. The possibility of exploiting the synergy of passive microwave and optical data for soil moisture monitoring at improved accuracy and resolution was also evaluated. This investigation provides an adequate data set for addressing science questions related to the operational use of the Soil Moisture and Ocean Salinity (SMOS) mission satellite scheduled for launch in 2008, which will be the first satellite dedicated to this application.

Technical Abstract: The National Airborne Field Experiment 2006 (NAFE'06) was conducted during a three week period of November 2006 in the Murrumbidgee River catchment, located in southeastern Australia. One objective of NAFE'06 was to provide data at intermediate spatial resolution for SMOS (Soil Moisture and Ocean Salinity) calibration/ validation, downscaling and assimilation. Airborne L-band brightness temperature was mapped at 1km resolution 11 times (every 1-3 days) over a 40 by 55km area in Yanco and 3 times over a 40 by 50km area in Kyeamba. Moreover, multiresolution, multi-angle and multi-spectral airborne data including surface temperature, surface reflectance, lidar data and aerial photos were acquired over selected areas to investigate scaling issues, and test multi-angle and multi-spectral retrieval approaches. The near-surface soil moisture was measured extensively on the ground in 8 sampling areas concurrently with aircraft flights, and the soil moisture profile was continuously monitored at 41 sites. Preliminary analyses indicate that (i) the uncertainty of a single measurement was typically less than 5% vol. (ii) the spatial variability of ground measurements at 1km resolution was up to 10% vol. and (iii) the validation of 1km resolution L-band data is facilitated by selecting pixels with a soil moisture variability lower than the point-scale uncertainty. The sensitivity of passive microwave and optical data is also compared at 1km resolution to illustrate the multi-spectral synergy for soil moisture monitoring at improved accuracy and resolution.