The Oklahoma Mesonet is an automated network of 114 meteorological observing stations. During the winter of 1996-97, soil moisture monitoring devices were installed at 60 site locations. Due to its capability to perform as a fully-automated soil water measuring device, the Campbell Scientific model 229-L matric potential sensor was chosen for operational use. Extensive laboratory calibrations were performed to ensure the quality of matric potential (water potential) measurements by each sensor. In addition, soil analyses down to 75 cm were performed for each sensor location to determine the characteristics of the soil in which the sensors were installed. With knowledge of soil characteristics, it became possible to estimate the volumetric water content of the soil at each location and depth. Thus, the Oklahoma Mesonet has the ability to estimate two widely accepted measurements of soil moisture.
The addition of the soil moisture sensors at Mesonet locations, which routinely estimate various atmospheric parameters, created an opportunity to investigate land-atmosphere interactions on a variety of spatial and temporal scales. Initial investigation into the relationship between variations in soil moisture conditions and atmospheric conditions revealed significant trends exist which can be detected by the Oklahoma Mesonet. These trends, in turn, are important in determining the complex exchange of mass and energy between the land surface and the atmosphere.
In the fall of 1997, the Oklahoma Mesonet was awarded an NSF grant for the Oklahoma Atmospheric Surface-layer Instrumentation System (OASIS) Project. The Mesonet sites without soil moisture monitoring devices and without sensors to measure heat flux will be instrumented accordingly. In addition, ground heat flux plates and net radiometers will be installed at all site locations. Marshall et al. (1998) demonstrated that, when compared with a Bowen Ratio measuring device, calculating latent heat flux as a residual estimate compares well with those values which are measured explicitly. Thus, with the addition of the OASIS instruments, it will be possible to estimate the relative partitioning between latent and sensible heat fluxes with respect to variations in soil moisture at 114 sites across Oklahoma.