Water content measurements by gravimetric methods involve weighing a wet sample, removing the water via drying in an oven, and reweighing the sample to determine the amount of water removed. Water content then is obtained by dividing the difference between wet and dry masses by the mass of the dry sample to obtain the ratio of the mass of water to the mass of dry soil. When multiplied by 100, this becomes the percentage of water in the sample on a dry-mass (or, as often expressed, on a dry-weight) basis. Soil moisture determined using the gravimetric method was measured at 800 sites along 24 transects. These transects were over flown by the airborne Gamma Radiation System used to measure soil moisture. These data are useful for comparison of airborne and ground soil moisture data. This analysis for the airborne Gamma Radiation System, using completely independent soil moisture data showed that the root mean square error of 97 flights was 3.02 percent soil moisture, with a bias of less than 0.5 percent soil moisture (Carroll et al., 1988).

This data set contains percent soil moisture ground measurements. These data were collected on the ground along the various flight lines flown in the Southern and Northern Study Areas (SSA and NSA) during 1994 by the gamma ray instrument. This data set contains information on the locations of field in-site measurements of soil moisture, depth of moss/humus layer, and water content of the moss/humus layer and contains information on soil conditions and vegetative cover around the sites.

During the 1989 FIFE field campaign, measurements were made of soil moisture release parameters and hydraulic conductivity. Bulk density and soil moisture release data were collected at five FIFE sites representing the major soil types in the FIFE study area. These data were used to model the porosity, saturated water potential, and the b-factor (the exponent of the power curve function) following the method of Clapp and Hormberger (1978). These soil moisture characteristics can be used to describe plant-available water and water movement through soils.

This data product was created based on the hypothesis that a variety of ground truth observations of soil moisture could be combined to estimate equal soil moisture contours across a large area (e.g., the FIFE area). A second stage required interpolating from these contours, using the methods of spatial statistics, to average soil moisture values at the nodes of a uniform grid. The grid node values in this product represent the average soil moisture of a 0.5 km x 0.5 km area centered at the node location. The correlation area method (CAM) was used to combine in situ measurements and airborne gamma remote sensing estimates to obtain areal averages of soil moisture. Information on biomass and the spatial distribution of vegetation in a model was also used to estimate soil moisture from PBMR measurements. Another simple method, using only ground soil moisture data, was also used to compute soil moisture from the PBMR measurements. All soil moisture data collected from the aircraft platforms and ground measurements were entered into the ARC/INFO GIS along with the UTM coordinates of each observation. All available and usable measurements of soil moisture were considered in an analysis that produced isolines of soil moisture.

This dataset contains in-situ soil moisture profile and soil temperature data collected at 30-minute intervals at SoilSCAPE (Soil moisture Sensing Controller and oPtimal Estimator) project sites since 2021 in the United States and New Zealand. The SoilSCAPE network has used wireless sensor technology to acquire high temporal resolution soil moisture and temperature data over varying durations since 2011. Since 2021, the SoilSCAPE has upgraded the two previously active sites in Arizona and added several new sites in the United States and New Zealand. These new sites typically use the METER Teros-12 soil moisture sensor. At its maximum, the new network consisted of 57 wireless sensor installations (nodes), with a range of 6 to 8 nodes per site. Each SoilSCAPE site contains multiple wireless end-devices (EDs). Each ED supports up to five soil moisture probes typically installed at 5, 10, 20, and 30 cm below the surface. Sites in Arizona have soil moisture probes installed at up to 75 cm below the surface. Soil conditions (e.g., hard soil or rocks) may have limited sensor placement. The data enables estimation of local-scale soil moisture at high temporal resolution and validation of remote sensing estimates of soil moisture at regional and national (e.g. NASA's Cyclone Global Navigation Satellite System - CYGNSS and Soil Moisture Active Passive - SMAP) scales. The data are provided in NetCDF format.

The parameters for this data set include gravimetric soil moisture, volumetric soil moisture, bulk density, and surface and soil temperature for the Georgia study region. This data set is part of the Soil Moisture Experiment 2003 (SMEX03). The United States portion of SMEX03 was conducted during June and July, 2003. Data are provided in a tab-delimited ASCII text file, and are available via FTP.These data were collected as part of a validation study for the Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E). AMSR-E is a mission instrument launched aboard NASA's Aqua Satellite on 04 May 2002. AMSR-E validation studies linked to SMEX are designed to evaluate the accuracy of AMSR-E soil moisture data. Specific validation objectives include assessing and refining soil moisture algorithm performance; verifying soil moisture estimation accuracy; investigating the effects of vegetation, surface temperature, topography, and soil texture on soil moisture accuracy; and determining the regions that are useful for AMSR-E soil moisture measurements.

The aim of the FIFE soil moisture transect work was to characterize spatial and temporal patterns of soil moisture along selected transects at the FIFE study area. Two levels of ground data were collected to support the passive microwave (PBMR) flights over the Konza experimental area. The water content measurements were collected using gravimetric methods. Soil moisture measured along a transect is necessary to calibrate airborne moisture instruments or compare data obtained from them. Soil units in a landscape are inherently heterogeneous, which leads to variations in moisture content along an aircraft flight path on the ground. In order to reduce errors, values on the flight path were sampled at close intervals.