SOIL MOISTURE VARIATION PATTERNS OBSERVED IN HAND COUNTY, SOUTH DAKOTA1
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ABSTRACT: Sail moisture data were taken during nine sampling events (1976‐1978) at a test site in South Dakota as part of the ground truth used in NASA's aircraft experiments studying the microwave sensing of soil moisture. This portion of the study dealt only with the spatial variability observed with regard to the ground data. Samples were taken over three surface depths at each point, and the data reported as the mean field moisture content within each of three surface horizons. The results shed additional light on the relationship between ground sampling and remote sensing of soil moisture. First, it was found that it is best to partition data of well drained sites from poorly drained areas when attempting to characterize the surface moisture content throughout an area of varying soil and cover conditions. It was also found that the moisture coefficient of variation within a field decreased as the mean field soil moisture increased, and that the standard deviation was at a maximum in the mid‐range of observed moisture conditions (15‐25 percent). Within field sample variation also decreases as the sample is integrated over a greater surface depth. It was determined that a sampling intensity of 10 samples per kilometer was adequate to characterize the mean field soil moisture at all three depths along a transect in the areas of moderate to good drainage‐.With the combination of gradient analysis and quantitative analysis of landscape pattern,and by changing the transect width and research step,the extent effect of landscape gradient analysis of an urban-rural transect were studied.The results showed that the landscape gradient analysis of the urban-rural transect was scale-dependent,and the effect of transect width was greater than that of research step.Research step mainly affected the fluctuation degree of each landscape index along transect,and it was appropriate for the transect to be divided equally into 20 samples.There existed critical values for transect width.When the transect width was beyond the values,the fluctuation trend of each index along transect would be varied.Furthermore,different landscape metrics responded differently to the same transect.The percent coverage and edge density of each class,as well as the Shannon's diversity index of landscape,showed significant gradient characteristics,while patch density and mean patch fractal dimension were in adverse.
Belt transect
Diversity index
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A method is presented for characterizing the spatial variability of water infiltration and soil hydraulic properties at the transect and field scales. The method involves monitoring a set of 10 Beerkan runs distributed over a 1-m length of soil, and running BEST (Beerkan estimation of soil transfer parameters) methods to derive hydraulic parameters. The Beerkan multi-runs (BMR) method provides a significant amount of data at the transect scale, allowing the determination of correlations between water infiltration variables and hydraulic parameters, and the detection of specific runs affected by preferential flow or water repellence. The realization of several BMRs at several transects on the same site allows comparison of the variation between locations (spatial variability at the field scale) and at the transect scale (spatial variability at the metre scale), using analysis of variance. From the results, we determined the spatial variability of water infiltration and hydraulic parameters as well as its characteristic scale (transect versus field).
Infiltration (HVAC)
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