Soil Brightness Research Articles

Determination of Soil Characteristics from Thematic Mapper Data of a Cropped Organic‐Inorganic Soil Landscape

AbstractMethods of determining soil characteristics from thematic mapper (TM) data were investigated at a site in southern Wisconsin. These methods utilized the soil‐sensitive spectral region of TM. Because there was little correlation between soil mapping units (soil phases) and the TM soil spectral classes, the former were grouped by wetness class, as determined from natural soil drainage classes, and by organic matter content. Agreement between wetness class and the April and September classifications, with absolute radiance and raw ratio transformation was 65.1, 61.3, 64.0, and 64.7%. When organic matter content was used instead of wetness class, the agreement ratio with TM was 74.0, 73.9, 68.4, and 66.0%. The April image correlated better with the soil map than the September image. Vegetative cover was a primary reason for difficulty in interpretation. The soil brightness image contributed most to classification accuracy, and can be used for manual soil interpretation. The stretched thermal IR image was also effective in discriminating between mineral soils and Histosols.

Calculation of canopy bidirectional reflectance using the Monte Carlo method

For a calculation of the plant canopy bidirectional reflectance distribution function (BRDF) the Monte Carlo method is used. The plant architecture is given by a rather universal mathematical model which allows to consider such structural parameters as canopy density and height, the number of leaves per plant, distance between leaves, dimensions and orientations of leaves and stems, etc., and their influence on the shape of the BRDF as a function of solar and view directions. To quantify these effects, a series of numerical experiments has been carried out. The information content of the BRDF about canopy architecture is the largest, if it is determined in the principal plane. The change of the BRDF in the region of “hot spot” characterizes leaf dimensions by increasing the leaf area or by decreasing the distance between leaves, the region of the “hot spot” increases. The change of the BRDF near nadir view direction is influenced by soil brightness and by arrangement of the leaves on the stem. The presence of vertical stems or nonhorizontal mat leaves increases the asymmetry of BRDF relative to nadir, in the opposite side of the sun the canopy reflectance is several times smaller than on the sun side. Adding the effect of multiple scattering to the BRDF changes the shape of BRDF only a little. The BRDF as a function of view directions contains information about canopy architecture and can be used for future progress of the remote sensing technique.

Calculations of the Microwave Brightness Temperature of Rough Soil Surfaces: Bare Field

A model for simulating the remotely sensed microwave brightness temperatures of soils with rough surfaces is developed. The surface emissivity of the soil media is calculated from one minus its reflectivity, which is obtained by the integration of the bistatic scattering coefficients for rough soil surfaces. The soil brightness temperature is obtained from the product of the surface emissivity and the effective soil temperature, which is calculated with measured soil moisture profiles and soil temperature profiles at various soil depths. The roughness of a soil surface is characterized by two parameters, the surface height standard deviation a and its horizontal correlation length l. The model calculations are compared to the measured angular variations of the polarized brightness temperatures at both L-band (1.4 GHz) and C-band (5 GHz) frequencies. A nonlinear least squares fitting method is used to match the model calculations with the data, and the best fit results produce the parameter values of a and l that best characterize the surface roughness. The effect of rough surface shadowing is also incorporated into the model by introducing a shadowing function S(θ), which represents the probability that a point on a rough surface is not shadowed by other parts of the surface. The model results for horizontal polarization are in excellent agreement with the data, both qualitatively and quantitatively. For vertical polarization, some discrepancies exist between the calculations and data. Possible causes of the discrepancy are discussed.

Estimating Soil Hydraulic Parameters Using Passive Microwave Data

Useful quantitative information about soil properties may be obtained by calibrating energy and moisture balance models with remotely sensed data. In this study, a soil physics model solves heat and moisture flux equations in the soil profile and is driven by the surface energy balance. Model-generated surface temperature and soil moisture and temperature profiles are then used in a microwave emission model to predict the soil brightness temperature. The model hydraulic parameters are varied until the predicted temperatures agree with the remotely sensed measurements. Using this method, values were estimated for hydraulic conductivity, matric potential and soil moisture at saturation, and a soil texture parameter. The conductivity agreed with values measured with an infiltration ring and the other parameters agreed with values in the literature.

Spectral response of a plant canopy with different soil backgrounds

Abstract The spectral behavior of a cotton canopy with four soil types alternately inserted underneath was examined at various levels of vegetation density. Measured composite spectra, representing various mixtures of vegetation with different soil backgrounds, were compared with existing measures of greenness, including the NIR-red band ratios, the perpendicular vegetation index (PVI), and the greenness vegetation index (GVI). Observed spectral patterns involving constant vegetation amounts with different soil backgrounds could not be explained nor predicted by either the ratio or the orthogonal greenness measures. All greenness measures were found to be strongly dependent on soil brightness. Furthermore, soil-induced greenness changes became greater with increasing amounts of vegetation up to 60% green cover. The results presented suggests that soil and plant spectra interactively mix in a nonadditive, partly correlated manner to produce composite canopy spectra.

Fracture detection by airborne microwave radiometry in parts of the Mississippi embayment, Missouri and Tennessee

Airborne microwave radiometry is a promising remote sensing technique for detecting buried fractures in areas of low relief and uniform soil cover. The technique was applied to two areas in the alluvial part of the Mississippi embayment, near Blytheville, Missouri, and Ridgely, Tennessee, where faults and fractures have been reported. Microwave and infrared soil brightness temperatures were obtained from an aircraft flying along parallel lines. These data were digitized and the values mathematically converted to microwave emissivities. The complements of emissivity (absorptivity) along the flight lines were cross-correlated. Lines of high correlation represent lineaments on the ground defined by anomalously high moisture contents. In the Blytheville area, the orientation and positions of these lines correspond well to reported fracture patterns; in the Ridgely area, the major anomaly corresponds generally to the known trend of the Ridgely and Cottonwood Grove faults. Discrepancies in correspondence are, as yet, poorly understood.

Multifrequency Measurements of the Effects of Soil Moisture, Soil Texture, And Surface Roughness

An experiment on remote sensing of soil moisture content was conducted over bare fields with microwave radiometers at the frequencies of 1.4, 5, and 10.7 GHz, during July-September of 1981. Three bare fields with different surface roughnesses and soil textures were prepared for the experiment. Ground-truth acquisition of soil temperatures and moisture contents for 5 layers down to the depths of 15 cm was made concurrently with radiometric measurements. The experimental results show that the effect of surface roughness is to increase the soil's brightness temperature and to reduce the slope of regression between brightness temperature and moisture content. The slopes of regression for soils with different textures are found to be comparable and the effect of soil texture is reflected in the difference of regression line intercepts at brightness-temperature axis. The result is consistent with laboratory measurement of soil's dielectric permittivity. Measurements on wet smooth bare fields give lower brightness temperatures at 5 than at 1.4 GHz. This phenomenon is not expected from current radiative transfer theory, using laboratory measurements of the relationship between dielectric permittivity and moisture content for different soil-water mixtures at frequencies of <5 GHz.