Robert T. Pack

Modeling of the interactions between forest vegetation, disturbances, and sediment yields

in the Idaho batholith are investigated through numerical modeling. The model simulates soil development based on continuous bedrock weathering and the divergence of diffusive sediment transport on hillslopes. Soil removal is due to episodic gully erosion, shallow landsliding, and debris flow generation. In the model, forest vegetation provides root cohesion and surface resistance to channel initiation. Forest fires and harvests reduce the vegetation. Vegetation loss leaves the land susceptible to erosion and landsliding until the vegetation cover reestablishes in time. Simulation results compare well with field observations of event sediment yields and long-term averages over � 10,000 years. When vegetation is not disturbed by wildfires over thousands of years, sediment delivery is modeled to be less frequent but with larger event magnitudes. Increased values of root cohesion (representing denser forests) lead to higher event magnitudes. Wildfires appear to control the timing of sediment delivery. Compared to undisturbed forests, erosion is concentrated during the periods with low erosion thresholds, often called accelerated erosion periods, following wildfires. Our modeling suggests that drainage density is inversely proportional to root cohesion and that reduced forest cover due to wildfires increases the drainage density. We compare the sediment yields under anthropogenic (harvest) and natural (wildfire) disturbances. Disturbances due to forest harvesting appear to increase the frequency of sediment delivery; however, the sediment delivery following wildfires seems to be more severe. These modeling-based findings have implications for engineering design and environmental management, where sediment inputs to streams and the fluctuations and episodicity of these inputs are of concern. INDEX TERMS: 1625 Global Change: Geomorphology and weathering (1824, 1886); 1815 Hydrology: Erosion and sedimentation; 1824 Hydrology: Geomorphology (1625); KEYWORDS: sediment yield, wildfires, forest management, hydrology

Effect of bedrock permeability on stream base flow mean transit time scaling relationships: 2. Process study of storage and release

In Part 1 of this two-part series, Hale and McDonnell (2016) showed that bedrock permeability controlled base flow mean transit times (MTTs) and MTT scaling relations across two different catchment geologies in western Oregon. This paper presents a process-based investigation of storage and release in the more permeable catchments to explain the longer MTTs and (catchment) area-dependent scaling. Our field-based study includes hydrometric, MTT, and groundwater dating to better understand the role of subsurface catchment storage in setting base flow MTTs. We show that base flow MTTs were controlled by a mixture of water from discrete storage zones: (1) soil, (2) shallow hillslope bedrock, (3) deep hillslope bedrock, (4) surficial alluvial plain, and (5) suballuvial bedrock. We hypothesize that the relative contributions from each component change with catchment area. Our results indicate that the positive MTT-area scaling relationship observed in Part 1 is a result of older, longer flow path water from the suballuvial zone becoming a larger proportion of streamflow in a downstream direction (i.e., with increasing catchment area). Our work suggests that the subsurface permeability structure represents the most basic control on how subsurface water is stored and therefore is perhaps the best direct predictor of base flow MTT (i.e., better than previously derived morphometric-based predictors). Our discrete storage zone concept is a process explanation for the observed scaling behavior of Hale and McDonnell (2016), thereby linking patterns and processes at scales from 0.1 to 100 km.

A co-boresighted synchronized ladar/EO imager for creating 3D images of dynamic scenes

An integrated ladar/EO imager has been developed that synchronizes and aligns CMOS digital camera readouts with the scan motion of a time-of-flight pulsed ladar . A prototype has been developed at the Utah State University Center for Advanced Imaging Ladar that reads out a 13 by 13 patch of RGB pixels within the subtended angle of a single ladar beam footprint. The readout location for the patch is slaved to the ladar and follows the ladar beam as it is scanned within the field-of-view. As the scanning occurs, the x-y-z position of each footprint and associated image patch is determined via the ladar. Multiple patches can then be mosaiked to build up a 3D image composed of 3D texture elements (texels) or 3D splats. Because of its ability to produce texels on-the-fly, the system is called a Texel Camera. The approach precludes mismatched occlusions and other ill-effects when motion occurs in the scene. The existing prototype consists of a single-channel flying-spot ladar running at approximately 470 shots/second and a color imager running at approximately 160 times the shot rate. Other designs are in development that employ line-flash and array flash ladar components that will run at pixel rates up to two orders of magnitude faster. The ability to create high-fidelity combined ladar/EO data sets in real time will be advantageous for time-critical applications such as cruise missile automatic target recognition. The design has the potential for applications in space rendezvous and dock, airborne automatic target recognition, surveillance from a tripod, and others that benefit from real-time 3D imagery creation.

Scintillometer-Based Estimates of Sensible Heat Flux Using Lidar-Derived Surface Roughness

AbstractThe estimation of sensible heat flux, H, using large aperture scintillometer (LAS) under varying surface heterogeneity conditions was investigated. Surface roughness features characterized by variable topography and vegetation height were represented using data derived from the highly accurate light detection and range (lidar) techniques as well as from traditional vegetation survey and topographic map methods. The study was conducted at the Cibola National Wildlife Refuge, Southern California, over a riparian zone covered with natural vegetation dominated by tamarisk trees interspersed with bare soil in a region characterized by arid to semiarid climatic conditions. Estimates of H were obtained using different representations of surface roughness features derived from both traditional and lidar methods to estimate LAS beam height [z(u)] at each increment u along its path, vegetation height (hc), displacement height (d), and roughness length (z0) combined with the LAS weighing function, W(u), alon...

A Handheld Texel Camera for Acquiring Near-Instantaneous 3D Images

A Texel camera is a device which synchronously captures depth information via a ladar and digital imagery of the same scene. The ladar and digital camera are co-boresighted to eliminate parallax. This configuration fuses the ladar data to the digital image at the pixel level, eliminating complex post-processing to register the datasets. This paper describes a handheld version of a Texel Camera which can be used to create near-instantaneous 3D imagery. The hardware configuration of the Texel Camera, issues and method associated with ladar/camera calibration, and representative imagery are presented.

Simulation and modeling of return waveforms from a ladar beam footprint in USU LadarSIM

Ladar systems are an emerging technology with applications in many fields. Consequently, simulations for these systems have become a valuable tool in the improvement of existing systems and the development of new ones. This paper discusses the theory and issues involved in reliably modeling the return waveform of a ladar beam footprint in the Utah State University LadarSIM simulation software. Emphasis is placed on modeling system-level effects that allow an investigation of engineering tradeoffs in preliminary designs, and validation of behaviors in fabricated designs. Efforts have been made to decrease the necessary computation time while still maintaining a usable model. A full waveform simulation is implemented that models optical signals received on detector followed by electronic signals and discriminators commonly encountered in contemporary direct-detection ladar systems. Waveforms are modeled using a novel hexagonal sampling process applied across the ladar beam footprint. Each sample is weighted using a Gaussian spatial profile for a well formed laser footprint. Model fidelity is also improved by using a bidirectional reflectance distribution function (BRDF) for target reflectance. Once photons are converted to electrons, waveform processing is used to detect first, last or multiple return pulses. The detection methods discussed in this paper are a threshold detection method, a constant fraction method, and a derivative zero-crossing method. Various detection phenomena, such as range error, walk error, drop outs and false alarms, can be studied using these detection methods.

The simulation of automatic ladar sensor control during flight operations using USU LadarSIM software

USU LadarSIM Release 2.0 is a ladar simulator that has the ability to feed high-level mission scripts into a processor that automatically generates scan commands during flight simulations. The scan generation depends on specified flight trajectories and scenes consisting of terrain and targets. The scenes and trajectories can either consist of simulated or actual data. The first modeling step produces an outline of scan footprints in xyz space. Once mission goals have been analyzed and it is determined that the scan footprints are appropriately distributed or placed, specific scans can then be chosen for the generation of complete radiometry-based range images and point clouds. The simulation is capable of quickly modeling ray-trace geometry associated with (1) various focal plane arrays and scanner configurations and (2) various scene and trajectories associated with particular maneuvers or missions.

Estimating evapotranspiration of riparian vegetation using high resolution multispectral, thermal infrared and lidar data

High resolution airborne multispectral and thermal infrared imagery was acquired over the Mojave River, California with the Utah State University airborne remote sensing system integrated with the LASSI imaging Lidar also built and operated at USU. The data were acquired in pre-established mapping blocks over a 2 day period covering approximately 144 Km of the Mojave River floodplain and riparian zone, approximately 1500 meters in width. The multispectral imagery (green, red and near-infrared bands) was ortho-rectified using the Lidar point cloud data through a direct geo-referencing technique. Thermal Infrared imagery was rectified to the multispectral ortho-mosaics. The lidar point cloud data was classified to separate ground surface returns from vegetation returns as well as structures such as buildings, bridges etc. One-meter DEMs were produced from the surface returns along with vegetation canopy height also at 1-meter grids. Two surface energy balance models that use remote sensing inputs were applied to the high resolution imagery, namely the SEBAL and the Two Source Model. The model parameterizations were slightly modified to accept high resolution imagery (1-meter) as well as the lidar-based vegetation height product, which was used to estimate the aerodynamic roughness length. Both models produced very similar results in terms of latent heat fluxes (LE). Instantaneous LE values were extrapolated to daily evapotranspiration rates (ET) using the reference ET fraction, with data obtained from a local weather station. Seasonal rates were obtained by extrapolating the reference ET fraction according to the seasonal growth habits of the different species. Vegetation species distribution and area were obtained from classification of the multispectral imagery. Results indicate that cottonwood and salt cedar (tamarisk) had the highest evapotranspiration rates followed by mesophytes, arundo, mesquite and desert shrubs. This research showed that high-resolution airborne multispectral and thermal infrared imagery integrated with precise full-waveform lidar data can be used to estimate evapotranspiration and water use by riparian vegetation.

Signal processing on waveform data from the Eyesafe Ladar Testbed (ELT)

The Eyesafe Ladar Test-bed (ELT) is a raster scanning, single-beam, energy-detection ladar with the capability of digitizing and recording the return pulse waveform at 2 GHz in the field for off-line 3D point cloud formation research in the laboratory. The ELT serves as a prime tool in understanding the behavior of ladar waveforms. Signal processing techniques have been applied to the ELT waveform in an effort to exploit the signal with respect to noise reduction, range resolution improvement, and ability to discriminate between two surfaces of similar range. This paper presents a signal processing method used on the ELT waveform. In the processing, three deconvolution techniques were investigated-the Wiener filter, Richardson-Lucy deconvolution, and a new method that synthesizes the surface response using least squares minimization. Range error and range resolution are reported for these methods.

Eyesafe ladar testbed with coaxial color imager

A new experimental full-waveform LADAR system has been developed that fuses a pixel-aligned color imager within the same optical path. The Eye-safe LADAR Test-bed (ELT) consists of a single beam energy-detection LADAR that raster scans within the same field of view as an aperture-sharing color camera. The LADAR includes a pulsed 1.54 μm Erbium-doped fiber laser; a high-bandwidth receiver; a fine steering mirror for raster scanning; and a ball joint gimbal mirror for steering over a wide field of regard are all used. The system has a 6 inch aperture and the LADAR has pulse rate of up to 100 kHz. The color imager is folded into the optical path via a cold mirror. A novel feature of the ELT is its ability to capture LADAR and color data that are registered temporally and spatially. This allows immediate direct association of LADAR-derived 3D point coordinates with pixel coordinates of the color imagery. The mapping allows accurate pointing of the instrument at targets of interest and immediate insight into the nature and source of the LADAR phenomenology observed. The system is deployed on a custom van designed to enable experimentation with a variety of objects.