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Title: Introduction to Soil Moisture Experiments 2004 (SMEX04)

Author
item Jackson, Thomas
item Moran, Mary
item O'NEILL, PEGGY - NASA-GSFC

Submitted to: Remote Sensing of Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2007
Publication Date: 2/15/2008
Citation: Jackson, T.J., Moran, M.S., O'Neill, P.E. 2008. Introduction to Soil Moisture Experiments 2007 (SMEX04). Remote Sensing of Environment. 112:301-303.

Interpretive Summary: Land surface antecedent boundary conditions may control the onset and intensity of the summer monsoon rainfall in the southwestern U.S. and northern Mexico. The influence of the land surface is relayed through surface evaporation and associated surface cooling (dependent on soil moisture), terrain, and vegetation cover. Increased soil moisture after precipitation promotes evapotranspiration between storm events. This may contribute to enhanced convection and further precipitation, all of which influence agriculture throughout the western U.S. Soil Moisture Experiments 2004 (SMEX04) addressed the goal of studying these processes using ground based and remotely sensed observations. This Special Issue of Remote Sensing of Environment includes a number of accomplishments that point to the success of SMEX04. These include soil moisture network validation, the spatial scaling and temporal variability of surface soil moisture for large footprint validation in mountainous terrain, the scaling of tower fluxes and the effect of remote sensing spatial resolution on land surface models, using remote sensing to determine the spatial and temporal patterns of vegetation water content, aircraft-based microwave remote sensing of soil moisture, broader issues of modeling root-zone soil moisture using data assimilation and characterizing the land surface water cycle within the NAME region with a multi-sensor approach. The results will contribute to better models and forecasts of seasonal climate in the region.

Technical Abstract: Land surface antecedent boundary conditions may control the onset and intensity of the summer monsoon rainfall in the southwestern U.S. and northern Mexico. The influence of the land surface is relayed through surface evaporation and associated surface cooling (dependent on soil moisture), terrain, and vegetation cover. Increased soil moisture after precipitation promotes evapotranspiration between storm events. This may contribute to enhanced convection and further precipitation, all of which influence agriculture throughout the western U.S. Soil Moisture Experiments 2004 (SMEX04) addressed the goal of studying these processes using ground based and remotely sensed observations. Over much of the NAME region soil moisture observations are sparse and even precipitation observations that might be used to derive estimates of surface wetness are inadequate. Therefore, it would be difficult to address the hypothesis of NAME without additional soil moisture information. Remote sensing provides an alternative means of observing spatial and temporal variations in surface wetness over the region. Frequent derived estimates of soil moisture over the NAME region are available from the Advanced Microwave Scanning Radiometer (AMSR-E) on Aqua. However, these products have yet to be validated and are known to be of limited value in heavily vegetated regions. SMEX04 provided an excellent opportunity to evaluate AMSR products because much of the region has relatively sparse vegetation. In addition to NAME, SMEX04 extends previous research. Field experiments in support of remote sensing, hydrology and climate have included catchments throughout North America (Oklahoma: SGP97, SGP99, SMEX03; Alabama and Georgia SMEX03; and Iowa: SMEX02). These experiments have been intensive efforts ranging from one to six weeks in duration. The basic approach used in these experiments has been to collect ground-based samples of soil moisture and surface fluxes in conjunction with aircraft flights at the same time as satellite overpasses. SMEX04 builds on the preceding experiments by focusing specifically on topography, vegetation, and strengthening the soil moisture components of the North American Monsoon Experiment (NAME). The timing of SMEX04 and NAME were driven by the NAMS. Rainfall statistics demonstrate quite clearly that the field experiment should be centered on the period of roughly mid-July to mid-August, when the number of rainy days is large and the possibility of having flights prior to and subsequent to heavy rainfall is high. This Special Issue of Remote Sensing of Environment includes a number of accomplishments that point to the success of SMEX04. These include soil moisture network validation, the spatial scaling and temporal variability of surface soil moisture for large footprint validation in mountainous terrain, the scaling of tower fluxes and the effect of remote sensing spatial resolution on land surface models, using remote sensing to determine the spatial and temporal patterns of vegetation water content, aircraft-based microwave remote sensing of soil moisture, broader issues of modeling root-zone soil moisture using data assimilation and characterizing the land surface water cycle within the NAME region with a multi-sensor approach. In addition to the science results presented in this Special Issue, SMEX04 has also resulted in a data archive (http://nsidc.org/data/amsr_validation/soil_moisture/smex04/]) and on-going continuous measurements of soil moisture and associated parameters (http://tucson.ars.ag.gov/dap/). The resulting databases will be of value in the next phase of NAME science investigations and expand our knowledge of the effects of key land surface features and the potential of new technologies for soil moisture mapping.