Soil salinity, a yield-limiting condition, has plagued crop production for centuries by reducing crop productivity. Research has introduced methods for successfully managing soil salinity. This research discusses the adaptation of established management methods to create new soil salinity management techniques. One adapted technique is an automated crop screening apparatus. A new design was created and successfully used in rapidly screening two strawberry cultivars to determine their tolerance to salinity. Screening crops and determining their tolerance to yield-limiting conditions are essential in managing soil salinity. Another salinity management tool used in this research was electromagnetic induction (EMI). EMI was used to complete a basin-scale inventory over an 18,000 ha study area in Cache County, Utah. The data obtained during the inventory were used to create EMI calibration models and a basin-scale map showing the spatial distribution of apparent soil electrical conductivity (ECa). These new methods for crop tolerance screenings and basin-scale salinity inventories will assist in successfully managing soil salinity and decrease its effect on the global food supply.

Over fifty small sinkholes (~1 meter in depth and width) were found in conjunction with structural damage to homes in an area south of Cleveland, TX. The local geology lacks carbonate and evaporite deposits associated with normal sinkhole development through dissolution. The morphology and distribution of sinkholes, and the geologic setting of the site are consistent with piping erosion. However, the site lacked the significant hydraulic gradient or exit points for sediment associated with traditional piping erosion. In areas of sinkholes, geophysical measurements of apparent electrical conductivity delineated anomalously high conductivity levels that are interpreted as a brine release from a nearby oil-field waste injection well. The contaminated areas have sodium adsorption ratios (SAR) as high as 19, compared to background levels of 3. Sodium has been shown to cause dispersion of soil colloids, allowing for sediment transport at very low velocities. Thus, subsurface erosion of dispersed sediment could be possible without significant hydraulic gradients. This hypothesis is backed by the observation of the depletion of colloidal particles within the E-horizon of sinkholes. However, there is a lack of precedence of waste brines initiating colloid dispersion. Also, sodium dispersion is not thought to be an important process in piping erosion in humid settings such as this one. Therefore, laboratory experiments on samples from the site area, designed to simulate field conditions, were conducted to measure dispersion verses pH, SAR and electrical conductivity (EC). Analysis of the experimental data with neural networks showed that an increase in SAR did increase dispersion. A dispersion prediction map, constructed with the trained neural network and calibrated geophysical data, showed correlation between sinkhole locations and increased predicted dispersion. This research indicates that a contaminant high in sodium content has caused colloidal dispersion, which may have allowed nontraditional subsurface erosion to occur in an area lacking a significant hydraulic gradient.

Remediation of unexploded ordnance (UXO) and prioritization of excavation procedures for archaeological artifacts using electromagnetic (EM) induction are studied in this dissertation. Lowering of the false alarm rates that require excavation and artifact excavation prioritization can reduce the costs associated with unnecessary procedures. Data were taken over 5 areas at the San Jacinto Battleground near Houston, Texas, using an EM-63 metal detection instrument. The areas were selected using the archaeological concepts of cultural and natural formation processes applied to what is thought to be areas that were involved in the 1836 Battle of San Jacinto. Innovative use of a Statistical Point Pattern Analysis (PPA) is employed to identify clustering of EM anomalies. The K-function uses point {x,y} data to look for possible clusters in relation to other points in the data set. The clusters once identified using K-function will be further examined for classification and prioritization using the Weighted K-function. The Weighted K-function uses a third variable such as millivolt values or time decay to aid in segregation and prioritization of anomalies present. Once the anomalies of interest are identified, their locations are determined using the Gi-Statistics Technique. The Gi*-Statistic uses the individual Cartesian{x, y} points as origin locations to establish a range of distances to other cluster points in the data set. The segregation and location of anomalies supplied by this analysis will have several benefits. Prioritization of excavations will narrow down what areas should be excavated first. Anomalies of interest can be located to guide excavation procedures within the areas surveyed. Knowing what anomalies are of greater importance than others will help to lower false alarm rates for UXO remediation or for archaeological artifact selection. Knowing significant anomaly location will reduce the number of excavations which will subsequently save time and money. The procedures and analyses presented here are an interdisciplinary compilation of geophysics, archaeology and statistical analysis brought together for the first time to examine problems associated with UXO remediation as well as archaeological artifact selection at historic battlegrounds using electromagnetic data.

Over fifty small sinkholes (~1 meter in depth and width) were found in conjunction with structural damage to homes in an area south of Cleveland, TX. The local geology lacks carbonate and evaporite deposits associated with normal sinkhole development through dissolution. The morphology and distribution of sinkholes, and the geologic setting of the site are consistent with piping erosion. However, the site lacked the significant hydraulic gradient or exit points for sediment associated with traditional piping erosion. In areas of sinkholes, geophysical measurements of apparent electrical conductivity delineated anomalously high conductivity levels that are interpreted as a brine release from a nearby oil-field waste injection well. The contaminated areas have sodium adsorption ratios (SAR) as high as 19, compared to background levels of 3. Sodium has been shown to cause dispersion of soil colloids, allowing for sediment transport at very low velocities. Thus, subsurface erosion of dispersed sediment could be possible without significant hydraulic gradients. This hypothesis is backed by the observation of the depletion of colloidal particles within the E-horizon of sinkholes. However, there is a lack of precedence of waste brines initiating colloid dispersion. Also, sodium dispersion is not thought to be an important process in piping erosion in humid settings such as this one. Therefore, laboratory experiments on samples from the site area, designed to simulate field conditions, were conducted to measure dispersion verses pH, SAR and electrical conductivity (EC). Analysis of the experimental data with neural networks showed that an increase in SAR did increase dispersion. A dispersion prediction map, constructed with the trained neural network and calibrated geophysical data, showed correlation between sinkhole locations and increased predicted dispersion. This research indicates that a contaminant high in sodium content has caused colloidal dispersion, which may have allowed nontraditional subsurface erosion to occur in an area lacking a significant hydraulic gradient.

Detailed soil and water data are essential to ensure the optimum long-term management of fields. The objective of this study was to estimate water table depths, spatially variable and layered soil properties using electromagnetic induction methods. Soil samples were collected and analyzed within two wild blueberry, a soybean-barley and a pasture fields. Observation wells were installed. The DualEM-2 was calibrated to predict the soil properties and groundwater depths. The apparent ground conductivity (ECa) and water table depths were measured simultaneously from each well, before and after every significant rainfall for three consecutive days. Comprehensive surveys were conducted in selected fields to measure ECa with DualEM-2. Survey data were imported in C++ program to estimate layered soil properties using mathematical models. Regression models were developed to predict soil properties and groundwater depths. The predicted soil properties and groundwater table maps were generated. This information can help to develop variable rate technologies.

Thesis (M.Sc. (Physics & Electronics)) - Rhodes University, 2009. / A thesis submitted in partial fulfilment of the requirements for the degree of Master of Science.

Electromagnetic induction (EM) methods have been utilised in a recent surge of archaeological applications across continental Europe, Ireland and Scandinavia. Development of multi-exploration depth instruments and improvements to instrument stability have improved its reputation as an effective method for mapping archaeological remains. Despite these advances, EM methods are comparatively lacking in rigour when for British sites. Through a structured scheme of experimental analysis and fieldwork, this thesis develops an understanding of the responses of EM instruments over a range of British archaeology, including earthworks, field systems, burials, modern remains, and a Cistercian abbey; the results of which demonstrate its effective over a diversity of environments. The impact of instrument-based issues on the collected measurements was quantified through a scheme of experiments targeting instrument drift, calibration and elevation. Dedicated instrument operation and processing workflows were developed based on the collective field and experimental results, which recommend best practice guidelines for improving the quality and accuracy of collected data. The link between instrument measurements and buried archaeology was further developed through a structured analysis of the EM datasets with complementary earth resistance and magnetic results. The integration of the EM, earth resistance and magnetic datasets was utilised to develop an enhanced archaeological characterisation of subsurface features. While the earth resistance and magnetic methods generally responded to different aspects of the buried archaeology, the EM surveys were able to detect a range of responses evident in the results of the former methods. Therefore, the role of EM methods within this characterisation are shown to “bridge the gap” between the earth resistance and magnetic methods, while providing a comprehensive characterisation of the remains in their own right.

Electromagnetic induction in the continental Bohai Bay coastal region of China and the island region of Japan is studied with the aid of laboratory analogue models. Detailed model measurements of the electric (Ex, Ey) and magnetic (Bx, By, Bz) field components are presented for an approximately uniform overhead horizontal source field for E- and B-polarizations. With the aid of 2D numerical models, criteria are developed for permitting approximate removal of the coast effect responses in field site measurements in coastal regions. For the Bohai Bay laboratory analogue model, large anomalous in-phase and quadrature model magnetic fields are observed over the Korea-Japan strait for E-polarization, and over the Bohai strait for B-polarization, due to current channelling through the straits. Large responses over the peninsulas in the shallow coastal areas occur at short periods but decrease abruptly with increasing period. The model induction arrows show that the induction in the local Bohai Bay is important primarily at short periods. At long periods, induction in the distant deeper Yellow Sea must be considered in any interpretation of field site measurements. In general, the analogue model results indicate that the effects of peninsulas, straits, bays and the irregularities in the coastlines play an important role in determining the electric and magnetic field responses both on-shore and off-shore for this complex coastal Bohai Bay region. For the Japan laboratory analogue model, electromagnetic field measurements are examined in detail for a series of traverses over Japan, the Korean peninsula, and the coastal region of China and the U.S.S.R. Large anomalous in-phase model magnetic fields are observed over the Korea-Japan strait for E-polarization and over Bohai strait, Tsugaru strait, and La Perouse strait for B-polarization due to off-shore current channelling. The significant responses observed at short periods over the peninsulas in the shallow coastal areas decrease with increasing period. Large gradients in the in-phase BZ are observed over all regions of Japan for E-polarization for both short and long periods due to the effects of induced currents in the surrounding oceans. Thus, induction arrow responses over all regions of Japan show the dominant effects of the ocean. The 2D numerical calculations of EM induction in continental and island coastal regions for an anomalous conductor in the form of an upwelling or a depression in the conductive substratum, show that if the anomalous conductor - ocean separation distance is at least as great as the coast effect response range YR (defined in the present work to be the range where the coast effect |Bz/Byn| has decreased to a value of 0.2), then the coast effect can be removed by vector subtraction to yield a response, approximately that of the anomalous conductor alone. For a given period (in the range 5 -120 min), YR is found to increase with increasing ocean depth, conductive substratum depth, and island width. Further, the dependan.ee on period is found to vary from model to model, but the general trend is for YR to decrease with increasing period, on account of the increasing importance of the underlying conductive substratum through the skin depth effect in the host. Empirical curves are presented showing how the response range depends on the ocean depth, the conductive substratum depth, the island width and the period. Coast effect response values for 3D laboratory analogue models are employed to approximately remove the geomagnetic coast effects in field measurements for some coastal sites in the Bohai Bay continental region of China and the island regions of Japan. The validity of the subtraction is examined for several models of conductive anomalies at sufficiently large anomalous conductor - ocean ranges to satisfy the response range criteria developed for 2D numerical models. The resulting interpretation of field site measurements in complex coastal regions is discussed. With the coast effect removed though subtraction of the model arrows from field site results available in the Bohai Bay region, the resulting difference arrows indicate a N-S striking conductor to the west of Bohai Bay. These difference arrows, as well as the 2D numerical calculations, support the premise of such a conductor, in the form of an upwelling in the conductive substratum (with conductivity 0.5Sm-1 at 80 km depth), situated at about 150 km from the Bohai Bay coastline to account for the field site observations. A comparison of laboratory analogue model and field site MT results at two sites west of Bohai Bay shows that the analogue model apparent resistivities are about an order of magnitude greater than the field site apparent resistivities. This result also supports the model of a conductive anomaly, in addition to the conductive substratum at 80 km depth. Laboratory analogue model measurements are employed to subtract the ocean effect in field measurements to yield difference arrow for these complex island regions of Japan ( the Kii Peninsula region, the central Honshu region and the regions of northern Honshu, Hokkaido and Tsugaru strait). These difference arrows as well as the 2-D numerical model result for the Kii Peninsula region, the central Honshu region, and the northern Honshu region support the premise of two conductive anomalies (with conductivity 0.5Sm-1), one beneath the Pacific Ocean and one beneath the Japan Sea at a depth of 30 km. Further, the difference arrows over the entire Japan region suggest that the two conductors roughly follow the general trend of the island arc, and eventually may be connected by an E-W striking conductor beneath Tsugaru strait to the north. / Graduate

It is a well documented fact that Geomagnetically Induced Currents (GIC’s) poses a significant threat to ground-based electric conductor networks like oil pipelines, railways and powerline networks. A study is undertaken to determine the feasibility of using artificial neural network models to predict GIC occurrence in the Southern African power grid. The magnitude of an induced current at a specific location on the Earth’s surface is directly related to the temporal derivative of the geomagnetic field (specifically its horizontal components) at that point. Hence, the focus of the problem is on the prediction of the temporal variations in the horizontal geomagnetic field (@Bx/@t and @By/@t). Artificial neural networks are used to predict @Bx/@t and @By/@t measured at Hermanus, South Africa (34.27◦ S, 19.12◦ E) with a 30 minute prediction lead time. As input parameters to the neural networks, insitu solar wind measurements made by the Advanced Composition Explorer (ACE) satellite are used. The results presented here compare well with similar models developed at high-latitude locations (e.g. Sweden, Finland, Canada) where extensive GIC research has been undertaken. It is concluded that it would indeed be feasible to use a neural network model to predict GIC occurrence in the Southern African power grid, provided that GIC measurements, powerline configuration and network parameters are made available.

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