Larry N. Lynch

A Suite of Models for Producing Synthetic, Small-scale Thermal Imagery of Vegetated Soil Surfaces

A high-resolution, computational suite has been constructed to produce synthetic thermal imagery of vegetated soil surfaces. Because a soil’s moisture affects its thermal response, the model suite must include both moisture and energy movement within the soil and plants. Thus, the suite consists of a soil model, a vegetation model, and a ray-casting model. The models run simultaneously on a single, parallel or serial computer and communicate using sockets. The soil model is a three-dimensional, spatially adaptive, continuous Galerkin, finite element model that simulates partially-saturated flow and heat transport, coupled to two-dimensional surface water flow. The vegetation model simulates infrared absorption, reflection, and transmission by discretized plant leaves and stems. Ray casting provides boundary conditions for the soil and vegetation thermal models, and produces multi-spectral images of energy reflected and emitted from the synthetic scene. Subsurface phase change, distributed root zone moisture uptake and transpiration, and flow through macropores and cracks are processes under construction. Example calculations to be presented include a multi-million-element simulation for an arid test site that is only a few meters in its longest dimension. The models are driven with meteorological data and are built using material property data collected at the field site. Synthetic images produced are compared against those from thermal cameras. A long-term goal of this work is to help build inversion software to estimate ground state information (soil moisture and physical property distributions) from airborne imagery.

Detecting underground objects by exploiting resonant scatterers with antiresonant antennas

When utilizing an antenna over ground as a near-field probe for detecting underground conducting objects, maximizing the variation in the antenna input impedance due to the buried object is the primary concern. Using the example of a horizontal dipole and a buried cylinder, significant variation in the dipole input impedance is obtained by carefully positioning the antiresonant dipole to excite the dominant cylinder resonance.

Locating soil anomalies using the impedance variation of a horizontal dipole over ground

A simple horizontal dipole over ground can be used as a near-field probe for buried object detection if changes in the dipole impedance produced by the presence of the buried object can be correlated to the characteristics of the object. In this paper, the wideband variation in the input impedance of a horizontal dipole over ground caused by the presence of a nearby underground anomaly (tunnel) is investigated via finite difference time-domain (FDTD) simulation. The correlation of the periodic variation in the dipole impedance difference to the location of the tunnel is demonstrated.

Coupling of underground objects to antennas and transmission lines at antiresonance

The changes in input impedance for a simple antenna or transmission line located over a soil containing a conducting object are examined near antiresonance. The near-field coupling of the underground object to the antenna or transmission line is investigated using the complex Poynting vector in order to identify the contribution of traveling and/or standing waves.

HPCMP CREATE-GV: Supporting Ground Vehicle Acquisition

The development of high-fidelity, physics-based software for analyzing ground vehicle concept designs and the mobility performance of wheeled and tracked ground vehicles is increasing important. The CREATE-GV toolset’s three modules are integrated to provide a complete performance evaluation of vehicle concept designs.

A reduced size antiresonant antenna for underground object detection

A reduced size antiresonant antenna for underground object detection is presented. The reduced size antenna is shown to provide improved differential impedance properties to that of a full size antiresonant dipole while providing a factor of eight reduction in the maximum dimension of the antenna.

Joint Resealing Project at Fairchild Air Force Base, Washington: Twenty-One-Year Field Performance

In 1989, the U.S. Army Engineer Research and Development Center and Crafco, Inc., initiated a research effort to develop improved materials and processes for sealing joints in portland cement concrete pavements. Objectives were to develop specifications for improved hot-applied, jet fuel–resistant (JFR) and non–jet fuel–resistant (non-JFR) sealants and to determine the impact of installation configuration on field performance. The laboratory phase identified desired sealant properties, evaluated sealants for those properties, and developed sealants with improved low-temperature and aging properties. The field phase was installed in June 1991 at Fairchild Air Force Base, Washington, to determine performance of developed sealants compared with standard sealants and to determine whether performance could be improved by changing installation geometry. Thirteen sealants were installed. The field study documented installation and evaluations at 6 and 12 months. After study completion, the installations were monitored several additional times. Detailed papers were prepared after 5 and 10 years. At 10 years, some sealants had greater than a 10-year life. In 2011, the installations reached 20 years of age. The JFR sections had been replaced, and non-JFR sections were still intact and were evaluated in April 2012. Results of the 21-year evaluation are presented. One silicone sealant and the improved non-JFR sealant achieved a 21-year life. Results also show that the flush-fill installation geometry increased life of the hot-applied asphalt sealants by more than 50% compared with the standard recessed configuration and should be considered for joint sealant installations.

Material Characterization of Silicone Sealants

Silicone sealants were analyzed using dynamic shear rheometry (DSR) and numerical analysis to determine if a method could be developed that would provide the basis for a performance-based specification. The research used a three-phase approach including DSR analysis of aged and unaged sealants, numerical model development using the DSR data as input, and laboratory tension experiments for model verification. Results of the investigation indicated that the average material properties determined through DSR and laboratory tensile testing appeared to be representative of the “true” material properties for elongations of up to 25 percent. The results were less accurate for 50 percent elongation but still acceptable. The DSR testing could be related to field performance; however, conducting several tests on multiple samples to develop a discrete stress-relaxation spectrum for numerical analysis would not be feasible for most users. Instead, two test temperatures should be selected for DSR testing based upon the maximum and minimum in-use temperature the sealant would be exposed to for a given application.