Airborne Laser Swath Mapping Data Research Articles

Impact of flow routing on catchment area calculations, slope estimates, and numerical simulations of landscape development

[1] Flow routing across real or modeled topography determines the modeled discharge and wetness index and thus plays a central role in predicting surface lowering rate, runoff generation, likelihood of slope failure, and transition from hillslope to channel forming processes. In this contribution, we compare commonly used flow-routing rules as well as a new routing rule, to commonly used benchmarks. We also compare results for different routing rules using Airborne Laser Swath Mapping (ALSM) topography to explore the impact of different flow-routing schemes on inferring the generation of saturation overland flow and the transition between hillslope to channel forming processes, as well as on location of saturation overland flow. Finally, we examined the impact of flow-routing and slope-calculation rules on modeled topography produced by Geomorphic Transport Law (GTL)-based simulations. We found that different rules produce substantive differences in the structure of the modeled topography and flow patterns over ALSM data. Our results highlight the impact of flow-routing and slope-calculation rules on modeled topography, as well as on calculated geomorphic metrics across real landscapes. As such, studies that use a variety of routing rules to analyze and simulate topography are necessary to determine those aspects that most strongly depend on a chosen routing rule.

Morphology-based approaches for detecting stream channels from ALSM data

To map the Earth's surface at remarkable resolution, Airborne Laser Swath Mapping (ALSM) instrument technology and subsequent algorithms have been used over the last several years. Since forested watersheds have commonly been problematic to study with remote sensing techniques, the ability of ALSM technology to densely sample ground elevations beneath forest canopies is especially considerable. Stream network detection from digital elevation models (DEMs) is a key role in modelling spatially distributed hydrological processes. To detect stream channels, we have developed two approaches. The first approach is based on an encoding of mathematical morphological operators. In the second approach, a composition of geodesic top-hat and bot-hat operations of different sizes is used in order to build a morphological profile (P M) that records the image structural information. The two proposed methods perform well in terms of detection results and classification accuracies. The second approach is more general than the first, but it also requires training and more computation.

Automatic Urban Water-Body Detection and Segmentation From Sparse ALSM Data via Spatially Constrained Model-Driven Clustering

Identifying hydrological features is important for urban planning and disaster assessment. Data spatial resolution poses challenges in automatic processing. In this letter, we present a novel spatially constrained model-driven clustering method that automatically detects and delineates water bodies in an urban area using airborne laser swath mapping (ALSM) data and imagery. Our method analyzes the modality of the sparseness histogram to decide the existence of water body, followed by clustering. Using the sparseness, clusters are decided by selecting candidate sites. In the iteration of clustering process, new sites are recruited within a close spatial vicinity of the boundary sites. Experiments were conducted using data sets from the city of New Orleans. Our method demonstrated superior robustness regardless of the density of ALSM sample and data discrepancy and very competitive accuracy in comparison with manual tracing, with an overall accuracy above 98%.

Fold geometry at Sheep Mountain anticline, Wyoming, constructed using airborne laser swath mapping data, outcrop‐scale geologic mapping, and numerical interpolation

Constraints available at the Earth's surface on the geometry of geologic folds often are discontinuous, consisting of scattered bedding surface outcrops representing the position and orientation of different stratigraphic surfaces. For this reason, characterization of fold geometry from surface data, by methods such as sequential balanced cross sections, remains a subjective and interpretive process. We present a new method for modeling the geometry of kilometer‐scale folds using dense, precise topographic data available from airborne laser swath mapping (ALSM), outcrop‐scale geologic mapping, and a reproducible numerical interpolation method that is free of subjectivity. Geologic mapping at Sheep Mountain anticline, Wyoming, enables the association of hundreds of thousands of ALSM data points with 14 weathering‐resistant bedding surfaces from seven different stratigraphic units ranging in age from Mississippian to Cretaceous. These data, supplemented by several hundred strike and dip measurements constraining local orientation of folded strata, are projected to the stratigraphic position of a single surface and used as constraint for a smoothed minimum curvature spline interpolation to generate a continuous representation of fold geometry. Both strengths and weaknesses of the new method are discussed in the context of comparison between the new surface model and an existing model constructed by traditional methods.

Structural geometry of Raplee Ridge monocline and thrust fault imaged using inverse Boundary Element Modeling and ALSM data

We model the Raplee Ridge monocline in southwest Utah, where Airborne Laser Swath Mapping (ALSM) topographic data define the geometry of exposed marker layers within this fold. The spatial extent of five surfaces were mapped using the ALSM data, elevations were extracted from the topography, and points on these surfaces were used to infer the underlying fault geometry and remote strain conditions. First, we compare elevations extracted from the ALSM data to the publicly available National Elevation Dataset 10-m DEM (Digital Elevation Model; NED-10) and 30-m DEM (NED-30). While the spatial resolution of the NED datasets was too coarse to locate the surfaces accurately, the elevations extracted at points spaced ∼50 m apart from each mapped surface yield similar values to the ALSM data. Next, we used a Boundary Element Model (BEM) to infer the geometry of the underlying fault and the remote strain tensor that is most consistent with the deformation recorded by strata exposed within the fold. Using a Bayesian sampling method, we assess the uncertainties within, and covariation between, the fault geometric parameters and remote strain tensor inferred using the model. We apply these methods to the Raplee Ridge monocline, and find that the resolution and precision of the ALSM data are unnecessary for inferring the fault geometry and remote strain tensor using our approach. However, the ALSM data were necessary for the mapping of the spatial distribution of surface outcrops. Our models considered two scenarios: one in which fault geometry and remote strains were inferred using a single deformed stratum, and another in which all mapped strata were used in the inversion. Modeled elevations match those observed to within a root-mean-squared error of 16–18 m, and show little bias with position along the fold. Both single- and multilayer inversions image a fault that is broadly constrained to be ∼4.5–14 km in down-dip height, 13–30 km in along-strike width, with a tip-line 2.0–9.5 km below the surface at the time of deformation. Poisson's ratio was not well resolved by the inversion. The idealized elastic model is oversimplified when considering the complicated layered nature of this fold, however, it provides a good fit to the observations. Thus, comparable surface displacements may be produced with a variety of rheological models, so independent constraints on factors such as the fault geometry may be required to ascertain the appropriate rheology of the fold.

Surface Variability of Alluvial Fans Generated by Disparate Processes, Eastern Death Valley, CA*

This study explores the surface variability of alluvial fans from digital elevations model (DEM) derivatives generated from 1-m planimetric resolution airborne laser swath mapping data. Channel and interfluve dimensions of debris flow (DF) fans and fans generated from predominantly fluvial flows and some older debris flows (mixed flow [MF]) are extracted with the aid of a planimetric curvature classification. Significant differences are identified between the fan surface topography of DF and MF fans. MF fans tend to have smaller channel and interfluve widths, have smaller elevation differences between the crest of the interfluve and channel, and are more dissected than DF fans. The morphometric differences between the two fan classes can be explained by differences in the primary processes that develop the surficial features, but also the preponderance for secondary erosional processes acting on the MF fans.

Quantifying fault‐zone activity in arid environments with high‐resolution topography

High‐resolution airborne laser swath‐mapping (ALSM) topography illuminates active faulting with unprecedented clarity. We contrast ALSM topography of two dextral faults in arid regions of California with slip rates that differ by an order of magnitude: The Lenwood fault, with rate of ∼1 mm/yr, and the Clark fault, a strand of the San Jacinto fault with net slip rate >10 mm/yr. Visualization of ALSM data reveals abundant fault scarps and deflected channels that when reconstructed can yield powerful slip constraints. Though many of these features may also be detected in existing aerial photography, these data are limited by stereo depth resolution and fixed illumination angle.

Airborne Laser Swath Mapping: Achieving the resolution and accuracy required for geosurficial research

Modern Airborne Laser Swath Mapping (ALSM) instrumentation, with laser pulse rates in excess of 100,000 Hz, has made it possible to map topography over hundreds of square kilometers per day, with sufficient resolution to answer long standing questions and test new theories pertaining to land surface processes. But sensor technology is changing rapidly, and its operation is sufficiently complex that data collection and processing methods must continue to evolve to take advantage of sensor advances. In 2003, the National Science Foundation established the National Center for Airborne Laser Mapping (NCALM) to collect and process ALSM data. As a result, more research‐quality ALSM observations have become available to the earth science community. But as the amount of available ALSM data rapidly increases, it becomes imperative to identify and describe the parameters that control data quality, so that data sets may be evaluated as to whether they are adequate for particular applications.

Timing and patterns of debris flow deposition on Shepherd and Symmes creek fans, Owens Valley, California, deduced from cosmogenic 10Be

Debris flow fans on the western side of Owens Valley, California, show differences in their depths of fan head incision and thus preserve significantly different surface records of sedimentation over glacial‐interglacial cycles. We mapped fan lobes on two fans (Symmes and Shepherd creeks) on the basis of the geometry of the deposits using field observations and high‐resolution airborne laser swath mapping data and established an absolute fan lobe chronology by using cosmogenic radionuclide exposure dating of large debris flow boulders. While both fans and their associated catchments were subject to similar tectonic and base level conditions, the Shepherd Creek catchment was significantly glaciated while that of Symmes Creek experienced only minor glaciation. Differences in the depth of fan head incision have led to cosmogenic surface age chronologies that differ in the length of the preserved depositional records. Symmes Creek fan preserves evidence of exclusively Holocene deposition with cosmogenic 10Be ages ranging from 8 to 3 ka. In contrast, the Shepherd Creek fan surface was formed by late Pleistocene and Holocene debris flow activity, with major deposition between 86–74, 33–15, and 11–3 ka. These age constraints on the depositional timing in Owens Valley show that debris flow deposition in Owens Valley occurred during both glacial and interglacial periods but may have been enhanced during marine isotope stages 4 and 2. The striking differences in the surface record of debris flow deposition on adjacent fans have implications for the use of fan surfaces as paleoenvironmental recorders and for the preservation of debris flow deposits in the stratigraphic record.

Cosmogenic 10Be and 36Cl geochronology of offset alluvial fans along the northern Death Valley fault zone: Implications for transient strain in the eastern California shear zone

The northern Death Valley fault zone (NDVFZ) has long been recognized as a major right‐lateral strike‐slip fault in the eastern California shear zone (ECSZ). However, its geologic slip rate has been difficult to determine. Using high‐resolution digital topographic imagery and terrestrial cosmogenic nuclide dating, we present the first geochronologically determined slip rate for the NDVFZ. Our study focuses on the Red Wall Canyon alluvial fan, which exposes clean dextral offsets of seven channels. Analysis of airborne laser swath mapping data indicates ∼297 ± 9 m of right‐lateral displacement on the fault system since the late Pleistocene. In situ terrestrial cosmogenic 10Be and 36Cl geochronology was used to date the Red Wall Canyon fan and a second, correlative fan also cut by the fault. Beryllium 10 dates from large cobbles and boulders provide a maximum age of 70 +22/−20 ka for the offset landforms. The minimum age of the alluvial fan deposits based on 36Cl depth profiles is 63 ± 8 ka. Combining the offset measurement with the cosmogenic 10Be date yields a geologic fault slip rate of 4.2 +1.9/−1.1 mm yr−1, whereas the 36Cl data indicate 4.7 +0.9/−0.6 mm yr−1 of slip. Summing these slip rates with known rates on the Owens Valley, Hunter Mountain, and Stateline faults at similar latitudes suggests a total geologic slip rate across the northern ECSZ of ∼8.5 to 10 mm yr−1. This rate is commensurate with the overall geodetic rate and implies that the apparent discrepancy between geologic and geodetic data observed in the Mojave section of the ECSZ does not extend north of the Garlock fault. Although the overall geodetic rates are similar, the best estimates based on geology predict higher strain rates in the eastern part of the ECSZ than to the west, whereas the observed geodetic strain is relatively constant.

Characterizing arid region alluvial fan surface roughness with airborne laser swath mapping digital topographic data

Range‐front alluvial fan deposition in arid environments is episodic and results in multiple fan surfaces and ages. These distinct landforms are often defined by descriptions of their surface morphology, desert varnish accumulation, clast rubification, desert pavement formation, soil development, and stratigraphy. Although quantifying surface roughness differences between alluvial fan units has proven to be difficult in the past, high‐resolution airborne laser swath mapping (ALSM) digital topographic data are now providing researchers with an opportunity to study topography in unprecedented detail. Here we use ALSM data to calculate surface roughness on two alluvial fans in northern Death Valley, California. We define surface roughness as the standard deviation of slope in a 5‐m by 5‐m moving window. Comparison of surface roughness values between mapped fan surfaces shows that each unit is statistically unique at the 99% confidence level. Furthermore, there is an obvious smoothing trend from the presently active channel to a deposit with cosmogenic 10Be and 36Cl surface exposure ages of ∼70 ka. Beyond 70 ka, alluvial landforms become progressively rougher with age. These data suggest that alluvial fans in arid regions smooth out with time until a threshold is crossed where roughness increases at greater wavelength with age as a result of surface runoff and headward tributary incision into the oldest surfaces.

Surficial patterns of debris flow deposition on alluvial fans in Death Valley, CA using airborne laser swath mapping data

Debris flows are a common event in mountainous environments. They often possess the greatest potential for destruction of property and loss of lives in these regions. Delimiting the spatial extent of potential damage from debris flows relies on detailed studies of the location of depositional zones. Current research indicates debris flow fans have two distinct depositional zones. However, the two zones were derived from studies containing detailed analyses of only a few fans. High resolution airborne laser swath mapping (ALSM) data is used to calculate profile curvature and surface gradient on 19 debris flow fans on the eastern side of Death Valley. The relationship between these parameters is assessed to 1) identify if debris flow fans are accurately represented by two depositional zones, and 2) to assess how these terrain parameters relate to one another at the individual fan scale. The results show at least three zones of deposition exist within the sampled fans. These zones do not hold consistent when individual fan morphometry is analyzed in conjunction with localized fan surface gradients. Fans with consistently shallower gradients exhibit numerous depositional zones with more subtle changes in profile curvature. Steeper gradient fans exhibit significantly fewer zones with more pronounced local changes in profile curvature. The surface complexity of debris flow fans is evident from these analyses and must be accounted for in any type of hazard studies related to these features.

Analysis of spatial and temporal stability of airborne laser swath mapping data in feature space

Several features extracted from airborne laser swath mapping (ALSM) data are examined to determine their effectiveness in separating buildings from trees across geographically and temporally diverse landscapes. These two classes are often spatially mixed in urban and suburban areas and can be quite difficult to separate based solely on geometric information due to the discrete sampling of ALSM. New median-based distance measures are used to quantify the separability of the classes using the different features. Information-based measures are also applied to the same data. For each of the test cases, it is possible to identify a common feature space in which the distance between the two classes is large. This distance information is an indication of the separability between classes and is therefore indicative of the potential success likely when trying to classify ALSM data. This analysis provides new insights into the richness of simple two-return ALSM data and to the spatial and temporal stability of ALSM features when discriminating between classes.

Airborne Laser Swath Mapping: Quantifying changes in sandy beaches over time scales of weeks to years

The University of Florida (UF) and the Florida Department of Environmental Protection (FDEP) are collaborating on a program to improve the quantitative monitoring of Florida's beaches, which are subject to erosion and catastrophic damage from seasonal storms. Each year, a segment of the Florida coastline will be mapped using Airborne Laser Swath Mapping (ALSM) technology (also referred to as LIDAR). The ALSM surveys, conducted by UF staff and students, nominally extend from a few hundred feet offshore to about 1500 ft inland. GPS observations are manually collected by FDEP personnel and used to generate profiles across the beach for comparison with profiles generated from the ALSM observations. Results from the first survey segment completed under the program, covering approximately 35 miles of beaches in northeast Florida, are presented. Additional results that demonstrate the ability to precisely quantify changes in beach topography and volume using ALSM data are also presented.

Identification and Analysis of Airborne Laser Swath Mapping Data in a Novel Feature Space

Several novel features are examined to determine their effectiveness in separating buildings from trees in airborne laser swath mapping (ALSM) data. New one- and two-dimensional distance measures are created to quantify the separability of the classes using the different features. Several features involving the intensity of the laser returns were found to be highly effective at separating the classes. The new distance measure provides insight into what makes a good/bad feature when discriminating between classes. It also lays the groundwork for future classification of ALSM data by providing a systematic method of ranking features to be used for classification.

National center for airborne laser mapping proposed

Researchers from universities, U.S. government agencies, U.S. national laboratories, and private industry met in the spring to learn about the current capabilities of Airborne Laser Swath Mapping (ALSM), share their experiences in using the technology for a wide variety of research applications, outline research that would be made possible by research‐grade ALSM data, and discuss the proposed operation and management of the brand new National Center for Airborne Laser Mapping (NCALM).The workshop successfully identified a community of researchers with common interests in the advancement and use of ALSM—a community which strongly supports the immediate establishment of the NCALM.