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At least 55 records · Page 3Linked to original sources
USGS2011

Observations of debris flows at Chalk Cliffs, Colorado, USA: Part 2, changes in surface morphometry from terrestrial laser scanning in the summer of 2009

High resolution topographic data that quantify changes in channel form caused by sequential debris flows in natural channels are rare at the reach scale. Terrestrial laser scanning (TLS) techniques are utilized to capture morphological changes brought about by a high-frequency of debris-flow events at Chalk Cliffs, Colorado. The purpose of this paper is to compare and contrast the topographic response of a natural channel to the documented debris-flow events. TLS survey data allowed for the generation of high-resolution (2-cm) digital terrain models (DTM) of the channel. A robust network of twelve permanent control points permitted repeat scanning sessions that provided multiple DTM to evaluate fine-scale topographic change associated with three debris-flow events. Difference surfaces from the DTM permit the interpretations of spatial variations in channel morphometry and net volume of material deposited and eroded within and between a series of channel reaches. Each channel reach experienced erosion, deposition, and both net volumetric gains and losses were measured. Analysis of potential relationships between erosion and deposition magnitudes yielded no strong correlations with measures of channel-reach morphometry, suggesting that channel reach-specific predictions of potential erosion or deposition locations or rates cannot be adequately derived from statistical analyses of pre-event channel-reach morphometry.

Colorado↗
USGS1984

PROCESSING OF SCANNED IMAGERY FOR CARTOGRAPHIC FEATURE EXTRACTION.

Digital cartographic data are usually captured by manually digitizing a map or an interpreted photograph or by automatically scanning a map. Both techniques first require manual photointerpretation to describe features of interest. A new approach, bypassing the laborious photointerpretation phase, is being explored using direct digital image analysis. Aerial photographs are scanned and color separated to create raster data. These are then enhanced and classified using several techniques to identify roads and buildings. Finally, the raster representation of these features is refined and vectorized. 11 refs.

Conference Paper↗
USGS2007

Survey report of NOAA Ship McArthur II cruises AR-04-04, AR-05-05 and AR-06-03: habitat classification of side scan sonar imagery in support of deep-sea coral/sponge explorations at the Olympic Coast National Marine Sanctuary

Habitat mapping and characterization has been defined as a high-priority management issue for the Olympic Coast National Marine Sanctuary (OCNMS), especially for poorly known deep-sea habitats that may be sensitive to anthropogenic disturbance. As a result, a team of scientists from OCNMS, National Centers for Coastal Ocean Science (NCCOS), and other partnering institutions initiated a series of surveys to assess the distribution of deep-sea coral/sponge assemblages within the sanctuary and to look for evidence of potential anthropogenic impacts in these critical habitats. Initial results indicated that remotely delineating areas of hard bottom substrate through acoustic sensing could be a useful tool to increase the efficiency and success of subsequent ROV-based surveys of the associated deep-sea fauna. Accordingly, side scan sonar surveys were conducted in May 2004, June 2005, and April 2006 aboard the NOAA Ship McArthur II to: (1) obtain additional imagery of the seafloor for broader habitat-mapping coverage of sanctuary waters, and (2) help delineate suitable deep-sea coral-sponge habitat, in areas of both high and low commercial-fishing activities, to serve as sites for surveying-in more detail using an ROV on subsequent cruises, Several regions of the sea floor throughout the OCNMS were surveyed and mosaicked at 1-meter pixel resolution. Imagery from the side scan sonar mapping efforts was integrated with other complementary data from a towed camera sled, ROVs, sedentary samples, and bathymetry records to describe geological and biological (where possible) aspects of habitat. Using a hierarchical deep-water marine benthic classification scheme (Greene et al. 1999), we created a preliminary map of various habitat polygon features for use in a geographical information system (GIS). This report provides a description of the mapping and groundtruthing efforts as well as results of the image classification procedure for each of the areas surveyed.

Washington↗
USGS2022

Finalization of the Confocal Laser Scanning Microscopy (CLSM) working group

A working group in Commission II to investigate applications of confocal laser scanning microscopy (CLSM) for organic petrology investigations has finalized with publication of the manuscript “Characterization of bituminite in Kimmeridge Clay by confocal laser scanning and atomic force microscopy” in the International Journal of Coal Geology. The manuscript is available via Open Access from https://doi.org/10.1016/j.coal.2022.103927 and also from the Commission II working group (WG) webpage https://www.iccop.org/workinggroup/confocal-laser-scanning-microscopy-clsm/. A report detailing the full history and results from the WG also is available from the Commission II WG webpage. The working group investigated the application of CLSM to an organic-rich (44 wt.% TOC), thermally immature sample (VRo 0.42%) of the Kimmeridge Clay Formation. CLSM imaging and spectroscopy and atomic force microscopy (AFM) were used to characterize bituminite.

ICCP News↗
USGS2006

Rime and graupel: Description and characterization as revealed by low-temperature scanning electron microscopy

Snow crystals, which form by vapor deposition, occasionally come in contact with supercooled cloud droplets during their formation and descent. When this occurs, the droplets adhere and freeze to the snow crystals in a process known as accretion. During the early stages of accretion, discrete snow crystals exhibiting frozen cloud droplets are referred to as rime. If this process continues, the snow crystal may become completely engulfed in frozen cloud droplets. The resulting particle is known as graupel. Light microscopic investigations have studied rime and graupel for nearly 100 years. However, the limiting resolution and depth of field associated with the light microscope have prevented detailed descriptions of the microscopic cloud droplets and the three-dimensional topography of the rime and graupel particles. This study uses low-temperature scanning electron microscopy to characterize the frozen precipitates that are commonly known as rime and graupel. Rime, consisting of frozen cloud droplets, is observed on all types of snow crystals including needles, columns, plates, and dendrites. The droplets, which vary in size from 10 to 100 μm, frequently accumulate along one face of a single snow crystal, but are found more randomly distributed on aggregations consisting of two or more snow crystals (snowflakes). The early stages of riming are characterized by the presence of frozen cloud droplets that appear as a layer of flattened hemispheres on the surface of the snow crystal. As this process continues, the cloud droplets appear more sinuous and elongate as they contact and freeze to the rimed crystals. The advanced stages of this process result in graupel, a particle 1 to 3 mm across, composed of hundreds of frozen cloud droplets interspersed with considerable air spaces; the original snow crystal is no longer discernible. This study increases our knowledge about the process and characteristics of riming and suggests that the initial appearance of the flattened hemispheres may result from impact of the leading face of the snow crystal with cloud droplets. The elongated and sinuous configurations of frozen cloud droplets that are encountered on the more advanced stages suggest that aerodynamic forces propel cloud droplets to the trailing face of the descending crystal where they make contact and freeze.

Scanning↗
USGS2024

Side-scan sonar as a tool for measuring fish populations: Current state of the science and future directions

Side-scan sonar (SSS) is a powerful tool that can be used to address many key questions in fisheries science. In principle, SSS uses dual transducers to transmit a narrow-beam, wide-angle acoustic signal as the survey vessel transits an area. The intensity of reflected sound is recorded to generate an image mosaic comprised of benthic substrates and targets in the water column, including organisms such as fish. Although SSS has been around for decades, recent advancements have opened new opportunities to leverage this technology to directly measure fish populations. In this paper, we review the current state of the science and identify opportunities to further refine SSS for fisheries applications.

Fisheries↗
USGS2003

Collecting, shipping, storing, and imaging snow crystals and ice grains with low-temperature scanning electron microscopy

Methods to collect, transport, and store samples of snow and ice have been developed that enable detailed observations of these samples with a technique known as low-temperature scanning electron microscopy (LTSEM). This technique increases the resolution and ease with which samples of snow and ice can be observed, studied, and photographed. Samples are easily collected in the field and have been shipped to the electron microscopy laboratory by common air carrier from distances as far as 5,000 miles. Delicate specimens of snow crystals and ice grains survive the shipment procedures and have been stored for as long as 3 years without undergoing any structural changes. The samples are not subjected to the melting or sublimation artifacts. LTSEM allows individual crystals to be observed for several hours with no detectable changes. Furthermore, the instrument permits recording of photographs containing the parallax information necessary for three-dimensional imaging of the true shapes of snowflakes, snow crystals, snow clusters, ice grains, and interspersed air spaces. This study presents detailed descriptions of the procedures that have been used successfully in the field and the laboratory to collect, ship, store, and image snow crystals and ice grains. Published 2003 Wiley-Liss, Inc.

Microscopy Research and Technique↗
USGS2020

Surface elevation change evaluation in mangrove forests using a low‐cost, rapid‐scan terrestrial laser scanner

Mangrove forests have adapted to sea level rise (SLR) increases by maintaining their forest floor elevation via belowground root growth and surface sediment deposits. Researchers use surface elevation tables (SETs) to monitor surface elevation change (SEC) in mangrove forests, after which this information is used to assess SLR resiliency or to dictate active forest management for vulnerable systems. This method requires significant investments in terms of time and human resources and is limited in the number of points it can measure per plot. We use a low‐cost, portable terrestrial laser scanning (TLS) system to assess SEC for three mangrove forests on Pohnpei Island (Federated States of Micronesia). Cloth simulation filtering was used for ground detection, after which results were refined by filtering points using angular orientation. Digital elevation models then were generated via kriging interpolation for data collected in 2017 and 2019, after which the heights of corresponding points were compared across years. Extreme elevation changes, due to disturbances such as footprints or fallen logs, were removed using interquartile range analysis. The TLS‐obtained average SEC ranged between −6.92 and +6.01 mm, which exhibited an average consistency of 72% when compared to simultaneously collected SET data (root mean square error = 1.36 mm). We contend that this approach represents an improvement over the manual method, where very few points typically are used, that is, ≅ 36 points vs. ≅ 30,000 points in the case of TLS, and could contribute to improved monitoring and management of these rapidly changing forest environments.

Limnology and Oceanography Methods↗
USGS2019

Semiautomated process for enumeration of fishes from recreational-grade side-scan sonar imagery

The use of hydroacoustic techniques is increasing as scientists search for less invasive ways to monitor fish populations, and using recreational side‐scan sonar (SSS) imagery for monitoring has become more common in aquatic resource management over the last 15 years due in part to its low cost and user‐friendly interface. The time‐consuming nature of manually counting fish targets has limited the use of the data that is collected by these systems in research or management contexts. To reduce the time and effort that is required to enumerate acoustic targets that are presumed to be fish, we developed a semiautomated process that rapidly quantifies targets from recreational SSS imagery by using an open‐source image processing software. Perceived fish targets were enumerated using a set of macroinstructions that performed similarly to manual enumeration by three experienced assessors. This method reduced variation that arises from individual assessors and eliminated the prohibitive time constraints that are associated with manual processing. Herein, we describe how our semiautomated process could be used in fisheries management contexts after further research and development of sampling methods. Future research will focus on field validation, quantifying relative abundance, testing across a broader range of environmental conditions, and exploring other applications for fisheries management.N

North American Journal of Fisheries Management↗
USGS2022

Combination of acoustic telemetry and side-scan sonar advances suppression efforts for invasive lake trout in a submontane lake

Expansion of an invasive Lake Trout Salvelinus namaycush population in Swan Lake, Montana, threatens a core area population of Bull Trout S. confluentus . Given the recent development of novel suppression methods, such as use of carcass analog pellets to cause high mortality of embryos, there was a need to quantify spawning season aggregation sites, site use, and spawning habitat for Lake Trout in Swan Lake. Acoustic tags were implanted in 85 Lake Trout during the summer in 2018 and 2019. Nightly tracking efforts during autumn in both years resulted in 1,744 relocations for 49 individual Lake Trout. Kernel density analysis was used to evaluate Lake Trout aggregation sites, identifying 10 distinct sites. All spawning sites were located in the littoral zone along areas of steep bathymetric relief, and these sites composed 48% of total relocations during both spawning seasons. In 2019, side-scan sonar imaging was used to classify and quantify the total area of spawning substrate, which constituted 12.8% of the total surface area estimated for spawning sites 1, 6, and 9 and 11.4% of the total surface area for aggregation sites 2–5, 7, 8, and 10. Simultaneous treatment of all spawning sites would require 205,709 ± 86 kg of carcass analog pellet material, resulting in 370.4 ± 0.2 kg of phosphorus inputs and 7,487.9 ± 3.1 kg of nitrogen inputs to Swan Lake. Thus, pellet treatment would increase the Carlson's trophic state index (TSI) values from 20.8 to 27.7 for total phosphorus and from 22.1 to 26.2 for total nitrogen. Based on a TSI threshold of less than 40 for an oligotrophic lake, the use of carcass analog pellets could be feasible for supplementing the gill-netting suppression of Lake Trout in Swan Lake.

Montana↗
USGS1992

Interference fringes on GLORIA side-scan sonar images from the Bering Sea and their implications

GLORIA side-scan sonographs from the Bering Sea Basin show a complex pattern of interference fringes sub-parallel to the ship's track. Surveys along the same trackline made in 1986 and 1987 show nearly identical patterns. It is concluded from this that the interference patterns are caused by features in the shallow subsurface rather than in the water column. The fringes are interpreted as a thin-layer interference effect that occurs when some of the sound reaching the seafloor passes through it and is reflected off a subsurface layer. The backscattered sound interferes (constructively or desctructively) with the reflected sound. Constructive/destructive interference occurs when the difference in the length of the two soundpaths is a whole/half multiple of GLORIA's 25 cm wavelength. Thus as range from the ship increases, sound moves in and out of phase causing bands of greater and lesser intensity on the GLORIA sonograph. Fluctuations (or 'wiggles') of the fringes on the GLORIA sonographs relate to changes in layer thickness. In principle, a simple three dimensional image of the subsurface layer may be obtained using GLORIA and bathymetric data from adjacent (parallel) ship's tracks. These patterns have also been identified in images from two other systems; SeaMARC II (12 kHz) long-range sonar, and TOBI (30 kHz) deep-towed sonar. In these, and other cases world-wide, the fringes do not appear with the same persistence as those seen in the Bering Sea. ?? 1992 Kluwer Academic Publishers.

Marine Geophysical Research↗
USGS1991

Petrography of Permian “Gondwana” coals from boreholes in northwestern Bangladesh, based on semiautomated reflectance scanning

Drilling through Quaternary alluvium and Tertiary cover at low-gravity anomalies in northwestern Bangladesh showed the presence of Permian sedimentary rocks in depressions that may be as much as a thousand meters deep in the crystalline basement. These Permian strata include low-sulfur, high-volatile bituminous coals in beds as thick as 15 m. The maceral group composition of these coals was determined by semiautomated reflectance scanning with a motorized microscope stage, rather than by point counting. This method was chosen to give objectively recorded raw analytical data and to provide a graphical picture of each sample. The coals are mostly “Gondwana” type (poorly layered “plum pudding” with abundant minerals and inertinite in a vitrinite groundmass) that would be classed as semi-dull (inerto-gelitite) coals. However, six samples have more than 70% vitrinite. None of the samples would be classed as sapropelic (liptinitic). The upper, middle, and lower main seams in borehole GDH-45 were sampled in 10 benches (0.1–3 m thick) each. Inertinite ranges from 7 to 100 vol% (mineral free basis) in individual benches, but composite seam averages are 41, 54 and 67%. Inertinite increases toward the top of two main seams so the bottom would yield the most valuable first mine slices. Some benches with extremely high inertinite content, such as the top 7 m of the lower thick seam, might be mined specially for blending with foreign low-inert coals to increase coke strength. The free swelling index reaches 7.5 in several vitrinite-rich benches, which can indicate good coking coal. Much of the vitrinite is fluorescent, which indicates secondary bituminization characteristic of vitrinite in good coking coals. Ash yields range from 8 to 52%, with composite seam averages of 15, 14 and 24%. Rare visible pyrite is in veinlets or small nodules; framboids and dispersed pyrite are absent. In borehole GDH-40 near Barapukuria (200–500 m depth), the mean random reflectance of vitrinite “A” ranges from 0.60 to 0.80% R o and vitrinite “B” ranges from 0.55 to 0.65%. In borehole GDH-45 near Khalaspir (287–442 m), the reflectance of vitrinite ranges from 0.79 to 0.94%. In individual cases, the vitrinite is difficult to define because of semivitrinite at higher reflectance (forming a separate peak on several reflectograms) and because of surface bitumen films or resinous (?) inclusions at lower reflectance. On the basis of vitrinite reflectance, the coals can be considered to have entered the “main phase of bitumen generation” of organic thermal maturation as understood in petroleum geochemistry.

Organic Geochemistry↗
USGS2022

Characterization of bituminite in Kimmeridge Clay by confocal laser scanning and atomic force microscopy

This work investigates bituminite (amorphous sedimentary organic matter) in Upper Jurassic Kimmeridge Clay source rock via confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM). These petrographic tools were used to provide better understanding of the nature of bituminite, which has been historically difficult to identify and differentiate from similar organic matter types in source rocks. As part of an International Committee for Coal and Organic Petrology (ICCP) working group, an immature (0.42% vitrinite reflectance), organic-rich (44.1 wt% total organic carbon content) sample of Kimmeridge Clay was distributed to multiple laboratories for CLSM characterization. The primary observations from CLSM imaging and spectroscopy include: 1) the interpreted presence of Botryococcus algae as a contributor to bituminite precursors; 2) color red-shift of sulfide reflectance and bituminite auto-fluorescence from below the sample surface; 3) positive alteration of bituminite from laser-induced photo-oxidation of the sample surface, including fluorescence blue-shift; 4) fluorescence blue-shift associated to higher fluorescence intensity regions in bituminite indicative of compositional (fluorophore) differences; 5) the need for fluorescence spectroscopy standardization as applied via CLSM; and 6) the suitability of CLSM fluorescence spectroscopy to predict solid bitumen reflectance from bituminite spectral emission via calibration to an extant dataset. Secondary CLSM observations include detection of reflected laser light from highly reflective inclusions in bituminite, including sulfides and fusinite, and radiolytic alteration of bituminite caused by substitution of U for Fe in sulfides. Findings from AFM include the observation that surface roughening or surface flattening of bituminite are induced by differential broad ion beam (BIB) milling and are dependent on the location and scale of AFM topology measurement. This result highlights our still limited understanding of the effects of BIB milling on sedimentary organic matter and indicates the need for further research before this technique can be advanced as a standard practice in petrographic sample preparation. Collectively, the results of this study illustrate the general applicability and versatility of AFM and CLSM as tools for organic petrology research, specifically for better understanding of the nature and properties of the bituminite maceral.

Kimmeridge↗
USGS2023

Scanning electron microscopic evaluation of broad ion beam milling effects to sedimentary organic matter: Sputter-induced artifacts or naturally occurring porosity?

Research examining organic-matter hosted porosity has significantly increased during the last decade due to greater focus on understanding hydrocarbon migration and storage in source-rock reservoirs, and technological advances in scanning electron microscopy (SEM) capabilities. The examination of nanometer-scale organic-matter hosted porosity by SEM requires the preparation of exceptionally flat geologic samples beyond the abilities of traditional mechanical polishing, which can deform or otherwise obscure organic surfaces. To meet this demand, broad ion beam (BIB) milling was introduced as a sample preparation technique for SEM petrographic analysis of geologic samples. As with any sample preparation technique, there can be unintended consequences. In this study, we examined the development of nanometer-scale sputter-induced voids caused by BIB milling of thermoset plastic binder material [poly(methyl methacrylate), PMMA] used for the mounting of geologic samples, and artifact sputter-induced voids in the organic matter of Green River Formation and Kimmeridge Clay Formation source rocks. Development of artifact sputter-induced voids was evaluated in relation to variations in the slope of the sample examination surface (0.0–4.9% slope), effectively varying the angle of ion incidence. The results indicate that only minor variations in the angle of ion incidence can generate sputter-induced voids in both PMMA (10.0–386.2 nm diameter sputter-induced voids) and sample sedimentary organic matter (solid bitumen; 12.2–103.6 nm diameter sputter-induced voids). Overall, average artifact pore diameters increased with increasing ion incidence angle within PMMA. Although sputter-induced voids within solid bitumen in the Green River Formation sample were only found in limited extent, the size of these void artifacts falls within the same size range as naturally occurring meso-macroporosity. That is, the pore-like artifacts could easily be misconstrued as naturally developed organic porosity, which is a major concern for SEM-based porosity evaluation methods. This study describes the factors that contribute to the creation of artifact sputter-induced voids, their distinguishing characteristics, and best practices for avoiding the creation of ion-induced artifacts.

International Journal of Coal Geology↗
USGS2025

Confocal laser-scanning microscopy (CLSM)-based thermal maturity of Tasmanites and progress in standardization of fluorescence microspectrometry

Evaluation of thermal maturity in vitrinite-free or vitrinite-deficient sediments via fluorescence microspectrometry can provide relevant information related to petroleum exploration and thermal history assessment. However, variation in spectral fluorescence properties of alginite macerals with increasing thermal maturity is largely underexplored. Here, authors of this study have applied confocal laser-scanning microscopy (CLSM) in conjunction with fluorescence microspectrometry to a maturity series of marine Upper Devonian Tasmanites algae from the Ohio Shale (Huron Member) and a single sample from the Marcellus Formation of the Appalachian Basin. Spectral fluorescence properties of Tasmanites were evaluated in relation to orientation, measurement location, and the number of measurements per sample, and were compared to published literature. Emission spectra of Tasmanites from continuous wave laser excitation (405 nm) were acquired from sections perpendicular and parallel to bedding and at different positions within individual Tasmanites bodies. The results showed a progressive red-shift in emission maxima (λ max ) in a large sample sized maturity series ( N = 19), e.g., 493 to 578 nm for the perpendicular section at middle position. Further, blue-shifted apex and mineral-adjacent positions within sections perpendicular to bedding were observed, with the latter being reported here for the first time. While blue-shift at apex positions can be attributed to mechanical deformation-induced reorientation of photoselected fluorophores, the blue-shifted mineral-adjacent positions could result from strain loading and development of a plastic deformation region at the mineral contact zone with Tasmanites . A decrease in standard deviation with increasing number of measured emission maxima is well-observed, and 15 to 20 individual measurements per sample appears sufficient for low standard deviation and coefficient of variance. CLSM-derived thermal maturity parameters indicated that a moderate positive correlation of red/green quotient (Q 650/500 ; R 2 = 0.67) with solid bitumen reflectance (BR o in %) exists. For reproducible results, the determination of λ max and Q 650/500 should be conducted exclusively in the middle position at perpendicular and parallel sections of the polished whole-rock pellets, where the lowest standard deviation in measurement was observed. These results strengthen the suitability and relevance of the CLSM technique in thermal maturity studies of dispersed organic matter (DOM) and contribute to the standardization of fluorescence microspectrometry methods in organic petrology investigation.

Kentucky, Ohio, Virginia, West Virginia↗
USGS2015

Thermal maturity of Tasmanites microfossils from confocal laser scanning fluorescence microscopy

We report here, for the first time, spectral properties of Tasmanites microfossils determined by confocal laser scanning fluorescence microscopy (CLSM, using Ar 458 nm excitation). The Tasmanites occur in a well-characterized natural maturation sequence ( R o 0.48–0.74%) of Devonian shale ( n = 3 samples) from the Appalachian Basin. Spectral property λ max shows excellent agreement ( r 2 = 0.99) with extant spectra from interlaboratory studies which used conventional fluorescence microscopy techniques. This result suggests spectral measurements from CLSM can be used to infer thermal maturity of fluorescent organic materials in geologic samples. Spectra of regions with high fluorescence intensity at fold apices and flanks in individual Tasmanites are blue-shifted relative to less-deformed areas in the same body that have lower fluorescence intensity. This is interpreted to result from decreased quenching moiety concentration at these locations, and indicates caution is needed in the selection of measurement regions in conventional fluorescence microscopy, where it is common practice to select high intensity regions for improved signal intensity and better signal to noise ratios. This study also documents application of CLSM to microstructural characterization of Tasmanites microfossils. Finally, based on an extant empirical relation between conventional λ max values and bitumen reflectance, λ max values from CLSM of Tasmanites microfossils can be used to calculate a bitumen reflectance equivalent value. The results presented herein can be used as a basis to broaden the future application of CLSM in the geological sciences into hydrocarbon prospecting and basin analysis.

Fuel↗
USGS2014

Characterizing the primary material sources and dominant erosional processes for post-fire debris-flow initiation in a headwater basin using multi-temporal terrestrial laser scanning data

Wildfire dramatically alters the hydrologic response of a watershed such that even modest rainstorms can produce hazardous debris flows. Relative to shallow landslides, the primary sources of material and dominant erosional processes that contribute to post-fire debris-flow initiation are poorly constrained. Improving our understanding of how and where material is eroded from a watershed during a post-fire debris-flow requires (1) precise measurements of topographic change to calculate volumetric measurements of erosion and deposition, and (2) the identification of relevant morphometrically defined process domains to spatially constrain these measurements of erosion and deposition. In this study, we combine the morphometric analysis of a steep, small (0.01 km 2 ) headwater drainage basin with measurements of topographic change using high-resolution (2.5 cm) multi-temporal terrestrial laser scanning data made before and after a post-fire debris flow. The results of the morphometric analysis are used to define four process domains: hillslope-divergent, hillslope-convergent, transitional, and channelized incision. We determine that hillslope-divergent and hillslope-convergent process domains represent the primary sources of material over the period of analysis in the study basin. From these results we conclude that raindrop-impact induced erosion, ravel, surface wash, and rilling are the primary erosional processes contributing to post-fire debris-flow initiation in the small, steep headwater basin. Further work is needed to determine (1) how these results vary with increasing drainage basin size, (2) how these data might scale upward for use with coarser resolution measurements of topography, and (3) how these results change with evolving sediment supply conditions and vegetation recovery.

California↗
USGS2020

Quantifying 40 years of rockfall activity in Yosemite Valley with historical Structure-from-Motion photogrammetry and terrestrial laser scanning

Rockfalls and rockslides are often dominant geomorphic processes in steep bedrock landscapes, but documenting their occurrence can be challenging, requiring frequent monitoring and well resolved spatial data. Repeat application of remote sensing methods such as Terrestrial Laser Scanning (TLS) and Structure-from-Motion (SfM) photogrammetry can detect even very small rockfalls, but typically these acquisitions span only years and may not record rockfall activity representative of longer-term rates of cliff erosion. Inventory databases can extend rockfall records, but are commonly incomplete and prone to observation bias. We employed TLS and SfM on two adjacent cliffs (El Capitan and Middle Brother) in Yosemite Valley, integrating semi-annual data collections from 2010 to 2017 with “historical” (archival) SfM models derived from oblique photographs taken in 1976. Comparing the 1976 SfM models against more recent data allows for more accurate and precise rockfall detection and volume measurement over a 40-year period. Change detection indicates that 235 rockfalls occurred from the two cliffs, more than twice as many events as are recorded in Yosemite's inventory database. Although individual rockfall volumes reported in the inventory database vary from those measured by SfM-TLS, reported cumulative volumes are similar to measured volumes, likely because the large-volume events that account for most of the cumulative volume tend to be widely observed and well-documented. Volume-frequency relationships indicate that the cliffs erode predominantly by less frequent, larger-volume rockfalls, at rates of 0.9 to 1.7 mm/yr. Our study demonstrates how integrated SfM and TLS measurements, especially utilizing SfM models derived from historical imagery, allow detection and quantification of rockfalls spanning several decades, complementing and improving inventory databases, informing rockfall hazard assessment, and providing longer-term rates of cliff erosion.

California↗