The US Department of Defense (DoD) conducts military training and testing activities on approximately 12 million hectares of land. Training exercises in which wheeled and tracked vehicles are used can result in land conditions susceptible to wind erosion. Particulates from subsequent wind erosion events on previously trafficked landscape may drift across the installation boundary, impacting air quality downwind. Accurately assessing effects of traffic activity on the susceptibility to wind erosion as a function of soil, vehicle, and activity-specific characteristics is critical to understanding the total near-field (within 200 m of the source) impacts on downwind areas. This project sought to: 1) address after-trafficking impacts on wind erosion risk by measurement of important soil, surface, and vegetation characteristics that relate to wind erosion susceptibility; and 2) provide an initial assessment of each site’s ability to recover from the trafficking events that may decrease risk of wind erosion; and 3) develop a new particulate measuring device, a Compact Eye-safe Lidar System (CELiS) and method, to monitor particulates crossing a fence-line due to military training/testing and other activities.
The goal of the project was to use a combination of soil science, remote sensing, and meteorological and traditional air quality sampling to accurately measure traffic effects on surface erodibility. Objectives of the study were to: 1) improve understanding of fugitive dust emission potential from military activities, and 2) improve DoD’s ability to achieve source compliance and ambient fence-line monitoring for fugitive dust emissions at their installations.
Field experiments were carried out at four DoD facilities for a range of soil, vegetative, and climatic conditions. Tracked and wheeled vehicles were driven on military lands repeatedly in a “figure-8” pattern, providing multiple pass data in both turning and straight line trafficking configurations. Soil and vegetation data were also collected prior to and after each set of trafficking passes to evaluate the susceptibility to wind erosion as well as after a rest period to determine the initial recovery or change in those soil and vegetation properties as they relate to wind erosion susceptibility.
The technical approach for CELiS was to drive strongly toward a commercial-grade instrument which was small, light, and required very little training to operate. Specifically, thermal engineering and optical engineering best-practices from military/aerospace instrumentation were applied to the design and operational concept of an elastic lidar instrument. The self-imposed requirement was to maintain an athermal design over a range of at least 60ºC; implying careful matching of the coefficients of thermal expansion for all of the materials involved (structural, optical and epoxy). Good athermal design principles have the advantage of driving toward the fewest number of optical surfaces and the fewest number of user adjustments (knobs) as possible. Furthermore, ruggedized lidar control and data acquisition software – LidarView – which has over 10,000 hours of use at Dugway Proving Ground was adapted for CELiS. The wavelength of 1.547 mm was chosen because it was eye-safe at the laser aperture and greatly eases operational constraints.
The key findings are listed here by project sub-objective.
1. Characterize and model individual military vehicle (tracked and wheeled) impacts on the changes in temporal surface and soil properties as functions of the intrinsic soil properties and specific physical attributes/parameters of the vehicles involved.
i. Heavy tracked vehicles exhibited a more intense impact overall on the soil surface than the lighter wheeled vehicles tested, especially when turning.
ii. Tracked vehicle turning sheared the surface soil layer, throwing soil and vegetation outside the tracked region. This eliminated most vegetation present and developed a track rut in the turn in as little as a single trafficking pass.
iii. Wheeled vehicles also exerted a side shear force while turning with the intensity dependent upon vehicle weight, tire dimensions (diameter and width), turning radius, and travel speed, but the effect was less severe than the heavy tracked vehicles studied.
iv. Straight trafficked regions retained more vegetation cover and mass under repeated trafficking than in the curve trafficked regions for all vehicles, presumably due to less side shear forces.
v. Vegetation cover and mass decreased with increasing passes on straight trafficked areas for all vehicles with the effect more pronounced under heavier vehicles.
a. Characterize relevant temporal and intrinsic soil and surface properties, via laboratory wind tunnel tray studies, to measure total dust as well as PM10 emission potential on a range of disturbed and undisturbed military land soils.
i. An increase in particulate emission potential occurred in the straight trafficked regions due to the removal of vegetation cover and mass as well as the continual grinding of the surface soil from repeated trafficking passes for all vehicles.
ii. Few significant measurable differences were found between the inside and outside tracks in the curves at all trafficking levels for both vehicles.
b. Collect soil and plant data from plot studies conducted on selected military sites before and after training activities and seasonally thereafter to determine both the impact of the activities on erodibility and the recovery times to less degraded states for the disturbed sites.
i. Overwintering processes (freeze/thaw, freeze/dry, and wet/dry cycles) caused a reduction in the 0-5 cm depth bulk densities within the tracked regions at Ft. Riley, KS. It is expected that this will occur at any site where there is sufficient moisture in the soil near the surface and the site’s climate is conducive to providing freeze/thaw, freeze/dry and wet/dry cycles over the winter. Unfortunately, the Yakima and White Sands Missile Range soils were too dry to verify that expectation during resampling.
ii. Vegetation re-growth nearly a year (~10 months) later at White Sands Missile Range was measurably significant. The HMMWV wheeled figure-8 plots were nearly indistinguishable from the surrounding un-trafficked areas when re-sampling occurred. It is speculated that part of the reason was due to above average precipitation (128%) between the two sampling periods. Extrapolating this result, it is expected that vegetation regrowth could be enhanced by correctly timing and applying sufficient supplemental water, when feasible, to multi-trafficked areas on any military training lands in arid or semi-arid regions.
iii. At White Sands Missile Range, some of the tracked vehicle straight traffic regions, which originally contained sparse vegetation at the time of trafficking, had significant visual gramma grass growth compared to the adjacent, still nearly bare un-trafficked regions, at the time of re-sampling. In this case it is speculated that the repeated trafficking mixed existing gramma seed into the soil and the pulverizing effect on the surface created a more favorable seedbed than the adjacent un-trafficked areas. Based upon these observations, it is speculated that many similar initially bare surface regions could be coerced to generate enhanced vegetation growth by simulating these seed-bed enhancing effects on such surfaces, as witnessed at White Sands with the tracked vehicle.
c. Use data collected in tasks 1a, 1b, and 1c to develop algorithms and incorporate them into the WEPS model to predict changes in susceptibility to wind erosion due to military vehicle disturbances on DoD training lands and their natural recovery to less degraded states.
i. A trafficking compaction model has been developed from the bulk density measurements taken at the multi-pass trafficking experiments (in section: Development of a Trafficking Compaction Process Model). This compaction model has been incorporated into WEPS to allow the trafficking vehicle soil compaction effect to be simulated.
ii. A list of deficiencies in WEPS along with a discussion of the most feasible remedies have been outlined (in section: Potential use of WEPS for Off-Road Military Trafficking Scenarios). These deficiencies don’t preclude its use by military land managers, but addressing these issues would significantly enhance WEPS ability to simulate such scenarios as military trafficking under off-road conditions.
iii. An example of using the Single-event Wind Erosion Evaluation Program (SWEEP), a stand-alone version of the wind erosion submodel used in WEPS, has been provided to demonstrate how SWEEP could be applied on military training lands where off-road trafficking has occurred (in section: SWEEP use for Off-Road Military Trafficking Scenarios).
2. Develop and test a prototype, eye-safe, aerosol sensing lidar for real time fugitive dust concentration measurement suitable for monitoring installation fence-line PM levels.
i. A new rugged lidar instrument - the CELiS and its associated method - was developed and successfully tested for future use in monitoring particulates crossing a fence-line boundary due to military training/testing and other activities.
ii. The useful operational range of CELiS is from 300 meters to 4,000 meters. Physical and optical engineering constraints prevent data from being collected too close to CELiS (0-300 m) and signal-to-background constraints (not enough photons) limit the maximum useful range.
iii. CELiS is sensitive enough to observe Rayleigh scatter from the atmospheric gases at ranges from 300 – 600 m.
iv. For the accurate calculation of airborne concentrations of dust, a priori knowledge of the particle size distribution of the aerosol is required. Both on-site sampling and the use of literature values are acceptable.
v. The use of an in situ particle counter (MetOne E-Sampler) was useful when dust concentrations were above the detection threshold of the E-Sampler. Conversely, the use of the in situ E-Sampler was not useful in clean air conditions. SDL recommends against using an E-Sampler and instead using a particle size distribution measuring instrument such as a GRIMM or a MetOne 212 Profiler.
vi. While instrument sensitivity is not easily measured, in any given range bin CELiS can typically observe a minimum concentration of wind driven soil dust is 20 mg/m3 for PM10 and 10 mg/m3 for PM2.5. This lower limit is defined as a signal-to-background (S/B) ratio of 2.
Limited field data are currently available on the impact of military activities on surface characteristics affecting wind erosion susceptibility. In addition measurements of fence-line concentrations of particulate matter from such activities are rarely conducted due to the lack of suitable cost effective field deployable instrumentation. This research will provide a critical step in understanding the impact from off-road military trafficking activities during training exercises on the subsequent change in site susceptibility to wind erosion across a wide range of soils and climates. In addition, the data obtained should assist in evaluating best management practices for mitigating wind erosion events on military sites.
The development of CELiS represents a major breakthrough in providing a cost-effective, portable, field deployable measurement device for use in monitoring fence-line boundary particulate matter concentrations. A small pickup truck can transport the entire CELiS system to the measurement location and an experienced crew of two people can set up the entire CELiS instrument in under two hours. A single CELiS operator can make real time (<10 sec) measurements of airborne dust concentrations at ranges out to 4 km with range resolution of 6 m. A conservative lower limit for CELiS detection sensitivity is 20 mg m-3 for PM10 and 10 mg m-3 for PM2.5. CELiS can be scanned horizontally over 360º to observe large areas of landscape and create images, or heatmaps, of aerosol concentration. CELiS is eye-safe and does not mandate the use of special safety glasses or to alert the Federal Aviation Administration (FAA) when it is in use.