Soil moisture links the hydrologic cycle and the energy budget of land surfaces by regulating the partitioning of surface radiative energy between latent and sensible heat fluxes. Therefore, accurate assessment of the spatial and temporal variation of soil moisture is important for the study, understanding, and management of surface biogeophysical processes. However, soil moisture exhibits a high degree of variability whose cause has been elusive, but is thought to be determined by heterogeneity in soil properties, vegetation, topography, water table depth, precipitation, and other meteorological factors. Understanding and assessment of these variations across a range of scales will enable the definition of the vertical and horizontal soil moisture error correlation structures which are essential in soil moisture data assimilation studies and for understanding the processes that drive soil moisture variability.
During the Southern Great Plains 1997 Experiment (SGP97), soil moisture, soil properties, vegetation characteristics, and meteorological information was measured for 30 days at a wide range of scales ranging from 1 meter to 250 km. A preliminary analysis of these observations will be presented here. This analysis is focused on the assessment of the spatial and temporal structure of profile (0-1 m below the soil surface) soil moisture at a scales ranging from one square meter to 10 thousand square meters over the 30 days of the experiment. Specific issues include: 1) the relation of point measurements to area averages, 2) the examination of in-field soil moisture structure with implications for soil and/or topographic controlled variability, 3) the cross-field soil moisture structure with implications on vegetation controlled variability, 4) the regional soil moisture structures with implications for meteorological controlled variability, and 5) the change of the dominant control on variability with moisture content.
Jackson, Tom, 1997: Southern Great Plains 1997 Experiment Plan. http://hydrolab.arsusda.gov/~tjackson/