H34D-01 INVITED 16:00h
On-the-go Near Infrared Reflectance Spectroscopy Analysis of Soils
Soil sensors are needed for carbon sequestration assessment, precision farming, and soil quality assessment. We tested the capabilities of a prototype for a field mobile, on-the-go, Near Infrared Reflectance (NIR) spectrometer system built by Veris Technologies, Inc. (Salina KS). The system consisted of an optical system embedded in a steel shank, which can be pulled through the soil behind a tractor at a controlled depth. The optical system consists of a sapphire window in the base of the steel shank fiber, a light source, and a fiber optic cable that transports diffusely reflected light from the soil in contact with the window to the NIR spectrometer. The system also includes a GPS unit and a computer that accumulates both the spectral and GPS data. The system was tested in two agricultural fields by collecting real time spectra (20 spectra per second, 350 to 1700 nm) along 30 or 37 transects within the fields. Approximately 150 soil samples were collected from each field at known locations from the smear face left by the steel shank at the base of the furrow. The soil samples were analyzed for moisture content, organic C, total N, pH, SMP-buffer pH, and ECEC by sum of ammonium acetate extractable Ca, Mg, K, Na, and Al. Multivariate partial least squares calibration models were developed using The Unscrambler (Camo Process, Inc.) to relate the measured soil properties to the field collected spectra. The results demonstrate the ability of the system to distinguish unique management zones (low, medium, and high) for N-fertilization, K-fertilization, and lime requirement. The system also provides a means of mapping the spatial distribution of organic C, total N, ECEC, moisture and several other soil properties in agricultural fields.
H34D-02 16:15h
Surface GPR time-lapse monitoring of hillslope processes
The hydrological dynamics along mountain slopes control many important phenomena, such as shallow landslide triggering and flood generation. The governing factors include: soil thickness, slope and bedrock morphology, rainfall pattern and subsurface groundwater conditions, both in vadose zone and under the water table. We present the results of a monitoring project currently undertaken on a large slope parcel in the Alpine region of Northern Italy. Both direct (piezometers, tensiometers, etc.) and indirect (geophysical) methods are being used to characterize slope and bedrock morphology and changes in soil moisture content. In this note, we focus on the use of ground-penetrating-radar (GPR) in surface to surface configuration. Recently, the use of multi and single offset GPR has been advocated for intermediate scale monitoring of moisture content changes in agricultural soils, e.g. in vineyards. We investigate the applicability of using similar techniques along hillslopes. The monitoring has been performed using a PulseEkko 100 radar system. The estimation of moisture content in the first couple of meters below the soil surface is based on the differential arrival time of direct waves through air and through the soil itself . In addition, information about the bedrock morphology can also be derived. However, care must be taken to identify complex wave propagation patterns in the data caused by waveguide phenomena in the soil layer and critical refraction from the soil-bedrock interface. Such energy pathways can complicate the interpretation, but also carry significant information about the site structure and hydrological dynamics.
H34D-03 16:30h
Acoustic Techniques for Measuring Surface Sealing and Crusting of Agricultural Soils
The microtopography of soils is an important surface characteristic that effects water ponding, infiltration, and consequently soil erosion. During a rainstorm event the surface microtopography and soil matrix evolve, thereby altering the erosion and runoff dynamics. The impact of raindrops cause the breakdown of soil aggregates into smaller particles, which can then be deposited into the smaller depressions. The redistribution of soil particles on the surface during rainfall produce a thin surface layer often referred to as surface sealing or crusting. For the purpose of this presentation, surface sealing will be used to describe a reduction in the ability of fluid to flow across the surface. Surface crusting will be associated with the formation of a thin layer of higher stiffness or larger mechanical strength. The sensitivity of acoustics to the effects of sealing and crusting was examined by measuring the acoustic-to seismic (A/S) transfer function and acoustic reflectivity on two different soils in a dry, wetted and rained-on state. The A/S transfer function measurement involves the use of a suspended loud speaker to impinge acoustic energy from the air onto the sample and a laser Doppler vibrometer (LDV) is used to measure the induced surface particle velocity. Therefore, the A/S transfer function is a measure of the seismic energy that has been transferred into the soil from the airborne wave. The acoustic surface reflectivity is a measurement of the amount of acoustic energy reflected from the surface and requires the use of a microphone suspended above the surface. Results suggests that the seismic energy transferred (A/S transfer function) is sensitive to crust formation but is not as sensitive to sealing. The amount of reflected acoustic energy appears to be more sensitive to sealing than crusting.
H34D-04 16:45h
Watershed Scale Surface Soil Moisture Variability in the Walnut Gulch Experimental Watershed During the 2004 North American Monsoon
In an effort to validate soil moisture satellite products, such as the Advance Microwave Scanning Radiometer (AMSR), diverse landscapes have been studied with intensive field campaigns. Semi-arid landscapes present a particular challenge to satellite remote sensing validation using traditional techniques because of the high spatial variability and potentially rapid rates of temporal change in moisture conditions. For one semi-arid watershed, temporal stability and other common techniques of geostatistical estimation are investigated for the watershed during a portion of the North American Monsoon season of 2004. The Walnut Gulch Experimental Watershed has a dense network of 88 precipitation gages of which 19 are collocated with soil moisture sensors providing an excellent location for satellite validation experiments. In conjunction with this monitoring network, intensive soil moisture field sampling, as part of the Soil Moisture Experiment in 2004 (SMEX04), contributed to the calibration of the network for large-scale estimation and added samples at additional raingages that did not have permanent sensors. Large-scale estimates can be calculated using a limited number of surface sensors with some qualifications. Geophysical aspects of the watershed, including topography and soil type are also examined for their influence on the soil moisture variability.
H34D-05 17:00h
Bulk Thermal Properties of the Active Layer in the Foothills of the Brooks Range, Alaska
In the arctic in particular, where infrastructure consists of sparsely distributed resources, we are faced with the problem of relating environmental measurements at the point scale to catchment-scale processes. We ultimately seek to use landform classifications derived from photography, NDVI and SAR imagery to distribute thermal and hydrological regime data across catchments on Alaska's North Slope. The landforms differ in the type of ground surface patterning caused by ice segregation and the heave and settling of the ground during freezing and thawing, respectively. Soil surface characteristics and bulk thermal properties affect the propagation of surface temperature changes into the subsurface system, and therefore affect the intensity, duration and distribution of these processes. Numerous studies have used models of heat transfer in the subsurface system to estimate bulk soil thermal properties from temperature records. Estimations of soil thermal properties are confounded primarily by latent heat effects during phase change, and by our inability to measure soil constituent densities (ice content, for example). Common methods for measuring thermal properties involve thermally perturbing the system, usually via a steady or transient heat source, which inherently changes the system's state. Thermal diffusivity measurements are made inherently difficult because changes in surface conductance between the thermal probe and the soil are seasonally dependent. Our goal is to estimate and measure soil thermal properties simultaneously using measured vertical temperature profiles and transient heat pulses generated in the soil. We use thermistors and thermal conductivity instruments to discuss the use of both techniques and to compare estimates. Data collected from the shallow (less than 2 m) subsurface soils at a number of patterned ground sites over a three-year period provides a range of material and surface types typical for the northern foothills of the Brooks Range. Bulk soil heat capacity is calculated from mean phase densities over a sufficiently large volume. These are estimated on the basis of soil physical properties and continuous time domain reflectometry measurements of liquid water content. Thermal conductivity is not as sensitive as diffusivity to the variations in surface conductance mentioned above, and measured conductivities are compared to those derived from temperature records.
H34D-06 17:15h
Detection of Spectral Features of Anomalous Vegetation From Reflectance Spectroscopy Related to Pipeline Leakages
Underground pipeline leakage inspection is an open problem with large economical and environmental impact. Traditional methods for investigating leakage and pollution, like drilling, are time consuming, destructive and expensive. A non-destructive and more economic exploration method would be a valuable complement to sub-surface investigative methods. Reflectance spectroscopy (or hyperspectral remote sensing) proved to be a tool that offers a non-destructive investigative method to identify anomalous spectral features in vegetation. One of the major environmental problems related to pipelines is the leakage of hydrocarbons into the environment. Hydrocarbons can establish locally anomalous zones that favor the development of a diverse array of chemical and mineralogical changes. Any vegetation present in these zones is likely to be influenced by the hostile and polluted environment. Geobotanical anomalies occur as a result of the effect of hydrocarbons on the growth of vegetation. The most likely changes in the vegetation are expected to occur in the chlorophyll concentrations which are an indicator of the health state. This is the main conclusion after an extensive field campaign in May 2004 in Holland investigating a 1 km trajectory of a 21 km long pipeline. The pipeline is `sweating' benzene condensates at approximately 50% of the connection points between the 9 meter segments of the pipeline. Spectral measurements were conducted at four different test locations in the 1 km trajectory. The test locations were covered by long grass, one of the fields was recently mown. Using different survey designs we can confirm the presence of geobotanical anomalies in different locations using various spectral interpretation techniques like linear red edge shifts, Carter stress indices, normalized difference vegetation index en yellowness index. After the interpretation of the geobotanical anomalies, derived from hyperspectral measurements, we compared the findings with information on pollution levels obtained by drilling at these specific locations. We can confirm a strong coherence between pollution levels derived from the drilling and the geobotanical anomalies interpreted from the spectral measurements. Comparison with aerial photographs in the visible and near-infra red for the same 1 km trajectory shows that our geobotanical anomalies coincide with the anomalous regions in the photographs. A combination of the three methods; drilling, aerial photography and field spectral reflectance measurements, will give an almost compete signature of the pollution present in a region. Using aerial photography for large scale analysis and field spectral reflectance measurements as a detailed follow-up investigative method we developed a very strong and effective, both in time and costs, method for pollution detection and monitoring. Ground validation in the form of drilling is still required but can be limited to only a few selected locations.
H34D-07 17:30h
MAPPING EVAPOTRANSPIRATION IN ARID RIPARIAN AREAS OF THE SOUTHWESTERN UNITED STATES USING OPTICAL REMOTELY SENSED IMAGERY
Accurate information on the distribution of evapotranspiration in arid riparian areas is needed for sustainable management of water resources as well as for a better understanding of water exchange processes between the land surface and the atmosphere. Since evapotranspiration is subject to rapid changes in time and space, it is nearly impossible to determine its spatial and temporal distributions over larger areas from ground measurements alone. Therefore, prediction from remote sensing data is very attractive as it enables large area coverage and a high repetition rate. In this study, the Surface Energy Balance Algorithms for Land (SEBAL) was selected to estimate evapotranspiration in the riparian areas of the Middle Rio Grande Basin (New Mexico), San Pedro River (Arizona) and Owens Valley (California). The objective is to compare SEBAL evapotranspiration rates derived from LandSat TM images with those measured on the ground with eddy covariance towers.
H34D-08 17:45h
Significance of Hydraulic Parameter Distribution Skewness on Effective Averaging Schemes in Heterogeneous Soils
We examined the impact of skewness (third order moment) of hydraulic parameter distributions, which was not considered in most previous studies, on effective soil hydraulic parameter averaging schemes for steady state vertical flow in heterogeneous soils. The effective soil hydraulic parameter of the heterogeneous soil formation is obtained by conceptualizing the soil as an equivalent homogeneous medium. The averaging scheme requires that the effective homogeneous soil discharge the ensemble flux. Using three widely used unsaturated hydraulic conductivity functions (i.e., Gardner, Brooks and Corey and van Genuchten) and various types of the probability distribution functions to represent variability for the nonlinear shape factor in the hydraulic conductivity function, $\alpha$, we derive the effective value for the parameter $\alpha$. Results show that distribution skewness is important in quantifying the effective parameters in addition to the commonly used mean and variance and therefore should be given more attention in future studies.