Julie R. Kelley

High-resolution soil moisture mapping in Afghanistan

Soil moisture conditions have an impact upon virtually all aspects of Army activities and are increasingly affecting its systems and operations. Soil moisture conditions affect operational mobility, detection of landmines and unexploded ordinance, natural material penetration/excavation, military engineering activities, blowing dust and sand, watershed responses, and flooding. This study further explores a method for high-resolution (2.7 m) soil moisture mapping using remote satellite optical imagery that is readily available from Landsat and QuickBird. The soil moisture estimations are needed for the evaluation of IED sensors using the Countermine Simulation Testbed in regions where access is difficult or impossible. The method has been tested in Helmand Province, Afghanistan, using a Landsat7 image and a QuickBird image of April 23 and 24, 2009, respectively. In previous work it was found that Landsat soil moisture can be predicted from the visual and near infra-red Landsat bands1-4. Since QuickBird bands 1-4 are almost identical to Landsat bands 1- 4, a Landsat soil moisture map can be downscaled using QuickBird bands 1-4. However, using this global approach for downscaling from Landsat to QuickBird scale yielded a small number of pixels with erroneous soil moisture values. Therefore, the objective of this study is to examine how the quality of the downscaled soil moisture maps can be improved by using a data stratification approach for the development of downscaling regression equations for each landscape class. It was found that stratification results in a reliable downscaled soil moisture map with a spatial resolution of 2.7 m.

Partially saturated soil causing significant variability in near surface seismic signals

The behaviour of dry, moist, and saturated soils has been studied for over a century without adequately investigating the behaviour associated with transient saturation in the near surface, i.e. the upper 1 m of overburden, including the effects of rapid meteorological changes, dynamic fluid flow, and variability of saturation on shallow seismic sensors. This paper presents observational data wherein the geophysical instrumentation response was significantly influenced by near-surface post-precipitation saturation and additional laboratory experimentation on the effects of saturation on shear wave velocity. The lack of partially-saturated data is primarily because transient meteorological events have not been critically important to the types of long-term deployments performed in the past, where sensors were situated in hard-rock, collecting data under idealized conditions, as opposed to sedimentary settings. Shorter-duration deployments and smaller system architectures, e.g. persistent monitoring, now necessitate detailed a priori knowledge of meteorological impacts to system design and performance. The purpose of this persistent monitoring geophysical instrumentation is to continually monitor the near surface and relate small perturbations to a specific source type(s) and distance(s) from the receiver. As such, the received signal is compared to known sources within a predetermined geological/ meteorological condition. Presented herein is the calibration signal generated by a 3.63-kg (8-lb) sledgehammer prior to and post 36 hours of steady precipitation. The resulting subsurface seismic velocity time-histories show a significant increase in signal amplitude, change in frequency content and no change in duration. Thus, the amplification effects of near-surface moisture variability combined with dynamic pore fluid could be interpreted as false positives of a specific source signature and/or instrument failure.

Steel-shot method for measuring the density of soils

The density of soil is crucial in engineering, construction, and research. Standard methods to determine density use procedures, equipment or expendable materials that limit their effectiveness in challenging field conditions. Some methods require burdensome logistics or have time requirements that limit their use or the number of tests that can be exe- cuted. A test method, similar to the sand-cone method, was developed that uses steel shot as the material to which a vol- ume of soil is compared to calculate soil density. Steel shot is easily recovered and reused, eliminating the need for specialty sand and calibrated cones or containers, and allows rapid determination of the volume of displaced soil. Exca- vated soil also provides measurements of total mass and moisture content. Volume, mass, and moisture content are applied in simple calculations to determine wet and dry densities and unit weight of the soil. Proficiency in performing the test can be achieved with minimal training, and the required kit can be assembled for a reasonable cost. Field uses of the method in dry environments in a variety of soil types demonstrated that the method can produce repeatable results within 2% of the values of soil density determined by traditional methods, with advantages in logistics.

Geotechnical Evaluation of the Brownsville Levee Cracking and Partial Slope Failure

Abstract : The U.S. International Boundary and Water Commission (IBWC) discovered cracks and a partial slope failure on a newly refurbished levee section and adjacent floodplain along the Rio Grande River in Brownsville, TX. The partial failure followed a significant drop inwater level in early April 2014. A geotechnical investigation was performed by the U.S. Army Engineer Research and Development Center (ERDC) to determine the causes for the partial levee failure and provide remediation alternatives. A series of events, combined with the local geologic conditions, led to the partial slope failure. Events included the 2012 levee construction, fluctuation and rapid drawdown conditions in the Rio Grande, and a higher elevation of Lake Brown (an oxbow of the Rio Grande) relative to the river. Progressive or creep-type failure mode was identified as the probable mechanism to explain the deformation observed in the field, and this was confirmed by seepage and stability analyses. Based on this evaluation, recommendations for remediation include: (1) implementation of a vegetation control program, (2) short-term monitoring, (3) evaluation of other locations along the river with similar river geometry and groundwater conditions, (4) efforts to minimize sudden drawdown, (5) additional analyses using the design hydrograph, and (6) incorporating cost/benefit analyses for the different alternatives.

The legacy of the 1948 underseepage and crevasse maps, Lower Mississippi River levees

Abstract : Seepage and crevasse maps showing levee performance from the 1937 and 1945 floods in the LMV were compiled as part of the comprehensive study by USACE (1956) into levee underseepage and its control. This map folio was limited in distribution, never officially published as a technical memorandum/report, and was thought to have been lost. The map folio was discovered as part of ongoing research into sand boils in the LMV and consists of 40 15-min scale maps extending from Cairo, IL, to New Orleans, LA. The complete set of maps was scanned and is being presented herein for wider dissemination. This map folio identifies sand boil locations, historic crevasses, severity of seepage, and extent of seepage control measures that were present prior to 1945. A historic summary is presented for background information and importance to ongoing studies of seepage control and internal erosion of levees.

Coaxial line measurement and analysis of electromagnetic properties of soils for sensor applications

We report complex permittivity, conductivity, magnetic susceptibility, and attenuation for soils collected from a typical site in a current theater of operations. Our experimental setup consists of three network analyzers along with custombuilt sample holders and data reduction and analysis software. The sample holder has the advantage of large sample volume and a resulting higher signal to noise ratio. This system was developed to determine the electrical properties of soils over a wide frequency range from 100 Hz to 8 GHz. The lower frequencies are applicable to capacitive sensors for small shallow targets, while the higher frequencies are applicable to ground-penetrating radar (GPR) from 50 MHz to 2 GHz and beyond. S-parameter data is collected and reduced using a method, initially developed by Nicolson and Ross (1970)1, for the determination of dielectric permittivity, magnetic permeability, and loss tangent from measured Sparameter data. Experimental results are compared with site geology and mineralogy. Applications include detection of tunnels, land mines, unexploded ordinance (UXO), concrete reinforcements, and other shallow compact targets.

Development of an integrated soils laboratory for modeling and detection applications

The Geotechnical and Structures Laboratory at the US Army Corps of Engineers, Engineer Research and Development Center (ERDC) has developed a near-surface properties laboratory to provide complete characterization of soil. Data from this laboratory is being incorporated into a comprehensive database, to enhance military force projection and protection by providing physical properties for modelers and designers of imaging and detection systems. The database will allow cross-referencing of mineralogical, electromagnetic, thermal, and optical properties to predict surface and subsurface conditions. We present an example data set from recent collection efforts including FTIR in the Near-IR, MWIR, and LWIR bands, magnetic susceptibility (500 Hz to 8 GHz), and soil conductivity and complex permittivity (10 μHz to 8 GHz) measurements. X-ray data is presented along with a discussion of site geology, sample collection and preparation methods, and mineralogy. This type of data-collection effort provides useful constraint information of soil properties for use in modeling and target detection. By establishing real ranges for critical soil properties, we are able to improve algorithms to define anomalies that can indicate the presence of land mines, unexploded ordnance (UXOs), improvised explosive devices (IEDs), tunnels, and other visually obscured threats.