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At least 379 records · Page 21Linked to original sources
USGS1988

Radarclinometry: Bootstrapping the radar reflectance function from the image pixel-signal frequency distribution and an altimetry profile

A method is derived for determining the dependence of radar backscatter on incidence angle that is applicable to the region corresponding to a particular radar image. The method is based on enforcing mathematical consistency between the frequency distribution of the image's pixel signals (histogram of DN values with suitable normalizations) and a one-dimensional frequency distribution of slope component, as might be obtained from a radar or laser altimetry profile in or near the area imaged. In order to achieve a unique solution, the auxiliary assumption is made that the two-dimensional frequency distribution of slope is isotropic. The backscatter is not derived in absolute units. The method is developed in such a way as to separate the reflectance function from the pixel-signal transfer characteristic. However, these two sources of variation are distinguishable only on the basis of a weak dependence on the azimuthal component of slope; therefore such an approach can be expected to be ill-conditioned unless the revision of the transfer characteristic is limited to the determination of an additive instrumental background level. The altimetry profile does not have to be registered in the image, and the statistical nature of the approach minimizes pixel noise effects and the effects of a disparity between the resolutions of the image and the altimetry profile, except in the wings of the distribution where low-number statistics preclude accuracy anyway. The problem of dealing with unknown slope components perpendicular to the profiling traverse, which besets the one-to-one comparison between individual slope components and pixel-signal values, disappears in the present approach. In order to test the resulting algorithm, an artificial radar image was generated from the digitized topographic map of the Lake Champlain West quadrangle in the Adirondack Mountains, U.S.A., using an arbitrarily selected reflectance function. From the same map, a one-dimensional frequency distribution of slope component was extracted. The algorithm recaptured the original reflectance function to the degree that, for the central 90% of the data, the discrepancy translates to a RMS slope error of 0.1 ???. For the central 99% of the data, the maximum error translates to 1 ???; at the absolute extremes of the data the error grows to 6 ???. ?? 1988 Kluwer Academic Publishers.

Earth, Moon and Planets↗
USGS2010

Holocene aggradation of the Dry Tortugas coral reef ecosystem

Radiometric age dating of reef cores acquired at the Dry Tortugas coral reef ecosystem (DTCRE) was merged with lidar topographic mapping to examine Holocene reef development linked to spatial variation in growth and erosion under the control of sea level. Analysis of variance of lidar topography confirmed the presence of three distinct terraces on all three major DTCRE banks (Loggerhead Bank, Garden Bank, and Pulaski Bank). Reef building on the middle terrace (T2) began atop Pleistocene edifices on Loggerhead Bank by 8.0 ka (thousands of years ago) and on Garden Bank by 7.2 ka at elevations of about −16.0 m and −11.9 m, respectively, relative to present mean sea level. Following this initiation at different elevations, T2 aggraded vertically on both banks at different rates during the early Holocene under foundering conditions until a highstand at 5.2 ka, resulting in a 2.21 m offset in present mean T2 elevation between these banks. Initiation of an upper terrace (T1) occurred on both Loggerhead Bank and Garden Bank in association with sea-level fall to a lowstand at near 4.8 ka. This upper terrace initiated on Garden Bank at about 5.0 ka and then grew upward at rate of 2.5 mm year −1 until approximately 3.8 ka . On Loggerhead Bank, the upper T1 terrace formed after 4.5 ka at a higher vertical aggradation rate of 4.1 mm year −1 , but at a lower elevation than on Garden Bank. Terrace T1 aggraded on Loggerhead Bank below the elevation of lowstands during late Holocene sea-level oscillation, and consequently erosion on Loggerhead Bank was minimal and likely limited to the crest of the upper terrace. In contrast, after 3.8 ka terrace T1 on Garden Bank likely tracked sea level and consequently underwent erosion when sea level fell to second, third and fourth lowstands at 3.3, 1.1, and 0.3 ka.

Florida↗
USGS2022

Extent of sedge-grass meadow in a Lake Michigan drowned river mouth wetland dictated by topography and lake level

Water-level fluctuations are critical in maintaining diversity of plant communities in Great Lakes wetlands. Sedge-grass meadows are especially sensitive to such fluctuations. We conducted vegetation sampling in a sedge-grass dominated Lake Michigan drowned river mouth wetland in 1995, 2002, and 2010 following high lake levels in 1986 and 1997. We also conducted photointerpretation studies in 16 years dating back to 1965 to include responses to high lake levels in 1952 and 1974. Topographic data were collected to assess their influence on areal extent of sedge-grass meadow. Dominant species in short emergent and submersed/floating plant communities changed with water availability from 1995 to extreme low lake levels in 2002 and 2010. Sedge-grass meadow was dominated by Calamagrostis canadensis and Carex stricta in all years sampled, but Importance Values differed among years partly due to sampling in newly exposed areas. Photointerpretation studies showed a significant relation between percent of wetland in sedge-grass meadow and summer lake level, as well as the number of years since an extreme high lake level. From the topographic map created, we calculated the cumulative area above each 0.2-m contour to determine the percent of wetland dewatered in select years following extreme high lake levels. When compared with percent sedge-grass meadow in those years, relative changes in both predicted land surface and sedge-grass meadow demonstrated that accuracy of lake level as a predictor of area of sedge-grass meadow is dependent on topography. Our results regarding relations of plant-community response to hydrology are applicable to other Great Lakes wetlands.

Michigan↗
USGS2008

Geolocation of man-made reservoirs across terrains of varying complexity using GIS

The Reservoir Sedimentation Survey Information System (RESIS) is one of the world's most comprehensive databases of reservoir sedimentation rates, comprising nearly 6000 surveys for 1819 reservoirs across the continental United States. Sediment surveys in the database date from 1904 to 1999, though more than 95% of surveys were entered prior to 1980, making RESIS largely a historical database. The use of this database for large-scale studies has been limited by the lack of precise coordinates for the reservoirs. Many of the reservoirs are relatively small structures and do not appear on current USGS topographic maps. Others have been renamed or have only approximate (i.e. township and range) coordinates. This paper presents a method scripted in ESRI's ARC Macro Language (AML) to locate the reservoirs on digital elevation models using information available in RESIS. The script also delineates the contributing watersheds and compiles several hydrologically important parameters for each reservoir. Evaluation of the method indicates that, for watersheds larger than 5 km2, the correct outlet is identified over 80% of the time. The importance of identifying the watershed outlet correctly depends on the application. Our intent is to collect spatial data for watersheds across the continental United States and describe the land use, soils, and topography for each reservoir's watershed. Because of local landscape similarity in these properties, we show that choosing the incorrect watershed does not necessarily mean that the watershed characteristics will be misrepresented. We present a measure termed terrain complexity and examine its relationship to geolocation success rate and its influence on the similarity of nearby watersheds. ?? 2008 Elsevier Ltd. All rights reserved.

Computers & Geosciences↗
USGS2015

Sediment contributions from floodplains and legacy sediments to Piedmont streams of Baltimore County, Maryland

Disparity between watershed erosion rates and downstream sediment delivery has remained an important theme in geomorphology for many decades, with the role of floodplains in sediment storage as a common focus. In the Piedmont Province of the eastern USA, upland deforestation and agricultural land use following European settlement led to accumulation of thick packages of overbank sediment in valley bottoms, commonly referred to as legacy deposits. Previous authors have argued that legacy deposits represent a potentially important source of modern sediment loads following remobilization by lateral migration and progressive channel widening. This paper seeks to quantify (1) rates of sediment remobilization from Baltimore County floodplains by channel migration and bank erosion, (2) proportions of streambank sediment derived from legacy deposits, and (3) potential contribution of net streambank erosion and legacy sediments to downstream sediment yield within the Mid-Atlantic Piedmont. We calculated measurable gross erosion and deposition rates within the fluvial corridor along 40 valley segments from 18 watersheds with drainage areas between 0.18 and 155 km 2 in Baltimore County, Maryland. We compared stream channel and floodplain morphology from lidar-based digital elevation data collected in 2005 with channel positions recorded on 1:2400 scale topographic maps from 1959–1961 in order to quantify 44–46 years of channel change. Sediment bulk density and particle size distributions were characterized from streambank and channel deposit samples and used for volume to mass conversions and for comparison with other sediment sources. Average annual lateral migration rates ranged from 0.04 to 0.19 m/y, which represented an annual migration of 2.5% (0.9–4.4%) channel width across all study segments, suggesting that channel dimensions may be used as reasonable predictors of bank erosion rates. Gross bank erosion rates varied from 43 to 310 Mg/km/y (median = 114) and were positively correlated with drainage area. Measured deposition within channels accounted for an average of 46% (28–75%) of gross erosion, with deposition increasingly important in larger drainages. Legacy sediments accounted for 6–90% of bank erosion at individual study segments, represented about 60% of bank height at most exposures, and accounted for 57% (± 16%) of the measured gross erosion. Extrapolated results indicated that first- and second-order streams accounted for 62% (± 38%) of total streambank erosion from 1005 km 2 of northern Baltimore County. After accounting for estimated redeposition, extrapolated net streambank sediment yields (72 Mg/km 2 /y) constituted 70% of estimated average Piedmont watershed yields (104 Mg/km 2 /y). The results suggest that streambank sediments are a relatively large source of sediment from Piedmont tributaries to the Chesapeake Bay.

Maryland↗
USGS2005

Estimating discharge in rivers using remotely sensed hydraulic information

A methodology to estimate in-bank river discharge exclusively from remotely sensed hydraulic data is developed. Water-surface width and maximum channel width measured from 26 aerial and digital orthophotos of 17 single channel rivers and 41 SAR images of three braided rivers were coupled with channel slope data obtained from topographic maps to estimate the discharge. The standard error of the discharge estimates were within a factor of 1.5-2 (50-100%) of the observed, with the mean estimate accuracy within 10%. This level of accuracy was achieved using calibration functions developed from observed discharge. The calibration functions use reach specific geomorphic variables, the maximum channel width and the channel slope, to predict a correction factor. The calibration functions are related to channel type. Surface velocity and width information, obtained from a single C-band image obtained by the Jet Propulsion Laboratory's (JPL's) AirSAR was also used to estimate discharge for a reach of the Missouri River. Without using a calibration function, the estimate accuracy was +72% of the observed discharge, which is within the expected range of uncertainty for the method. However, using the observed velocity to calibrate the initial estimate improved the estimate accuracy to within +10% of the observed. Remotely sensed discharge estimates with accuracies reported in this paper could be useful for regional or continental scale hydrologic studies, or in regions where ground-based data is lacking. ?? 2004 Elsevier B.V. All rights reserved.

Journal of Hydrology↗
USGS2018

Satellite remote sensing estimation of river discharge: Application to the Yukon River Alaska

A methodology based on general hydraulic relations for rivers has been developed to estimate the discharge (flow rate) of rivers using satellite remote sensing observations. The estimates of discharge, flow depth, and flow velocity are derived from remotely observed water surface area, water surface slope, and water surface height, and demonstrated for two reaches of the Yukon River in Alaska, at Eagle (reach length 34.7 km) and near Stevens Village (reach length 38.3 km). The method is based on fundamental equations of hydraulic flow resistance in rivers, including the Manning equation and the Prandtl-von Karman universal velocity distribution equation. The method employs some new hydraulic relations to help define flow resistance and height of the zero flow boundary in the channel. Estimates are made both with and without calibration. The water surface area of the river reach is measured by using a provisional version of the U.S. Geological Survey (USGS) Landsat based product named Dynamic Surface Water Extent (DSWE). The water surface height and slope measurements require a self-consistent datum, and are derived from observations from the Jason-2 satellite altimeter mission. At both reach locations, the Jason-2 radar altimeter non-winter heights consistently tracked the stage recorded at USGS streamgages with a standard deviation of differences (error) during the non-winter periods of less than 7%. Part of the error may be due to differences in the gage and altimeter crossing locations with respect to the range of stage change and the response to changes in discharge at the upstream and downstream locations. For the non-winter periods, the radar derived slope estimates (mean = 0.0003) were constant over the mission lifetime, and in agreement with previously measured USGS water surface slopes and slopes determined from USGS topographic maps. The accuracy of the mean of the uncalibrated daily estimates of discharge varied between reaches, ranging from 13% near Stevens Village (N = 90) to −21% at Eagle (N = 246) based on the absolute error, and 5% to −6% based on the error of the log of the estimates. Calibrating to the mean of USGS daily discharge estimates from the streamflow rating for the same period of record at each streamgage resulted in mean absolute errors ranging from 1% to 2%, and log errors ranging from 1% or less. The error pattern of the estimates shows that without calibration, even though the mean is well simulated, the high and low end values over the range of estimates may have significant bias.

Alaska↗
USGS2007

Evaluating planetary digital terrain models-The HRSC DTM test

The High Resolution Stereo Camera (HRSC) has been orbiting the planet Mars since January 2004 onboard the European Space Agency (ESA) Mars Express mission and delivers imagery which is being used for topographic mapping of the planet. The HRSC team has conducted a systematic inter-comparison of different alternatives for the production of high resolution digital terrain models (DTMs) from the multi look HRSC push broom imagery. Based on carefully chosen test sites the test participants have produced DTMs which have been subsequently analysed in a quantitative and a qualitative manner. This paper reports on the results obtained in this test.

Planetary and Space Science↗
USGS2015

Examining the utility of satellite-based wind sheltering estimates for lake hydrodynamic modeling

Satellite-based measurements of vegetation canopy structure have been in common use for the last decade but have never been used to estimate canopy's impact on wind sheltering of individual lakes. Wind sheltering is caused by slower winds in the wake of topography and shoreline obstacles (e.g. forest canopy) and influences heat loss and the flux of wind-driven mixing energy into lakes, which control lake temperatures and indirectly structure lake ecosystem processes, including carbon cycling and thermal habitat partitioning. Lakeshore wind sheltering has often been parameterized by lake surface area but such empirical relationships are only based on forested lakeshores and overlook the contributions of local land cover and terrain to wind sheltering. This study is the first to examine the utility of satellite imagery-derived broad-scale estimates of wind sheltering across a diversity of land covers. Using 30 m spatial resolution ASTER GDEM2 elevation data, the mean sheltering height, h s , being the combination of local topographic rise and canopy height above the lake surface, is calculated within 100 m-wide buffers surrounding 76,000 lakes in the U.S. state of Wisconsin. Uncertainty of GDEM2-derived h s was compared to SRTM-, high-resolution G-LiHT lidar-, and ICESat-derived estimates of h s , respective influences of land cover type and buffer width on h s are examined; and the effect of including satellite-based h s on the accuracy of a statewide lake hydrodynamic model was discussed. Though GDEM2 h s uncertainty was comparable to or better than other satellite-based measures of h s , its higher spatial resolution and broader spatial coverage allowed more lakes to be included in modeling efforts. GDEM2 was shown to offer superior utility for estimating h s compared to other satellite-derived data, but was limited by its consistent underestimation of h s , inability to detect within-buffer h s variability, and differing accuracy across land cover types. Nonetheless, considering a GDEM2 h s -derived wind sheltering potential improved the modeled lake temperature root mean square error for non-forested lakes by 0.72 °C compared to a commonly used wind sheltering model based on lake area alone. While results from this study show promise, the limitations of near-global GDEM2 data in timeliness, temporal and spatial resolution, and vertical accuracy were apparent. As hydrodynamic modeling and high-resolution topographic mapping efforts both expand, future remote sensing-derived vegetation structure data must be improved to meet wind sheltering accuracy requirements to expand our understanding of lake processes.

Remote Sensing of Environment↗
USGS2012

Chryse Basin channels: low-gradients and ponded flows.

Gradients on the floors of the Martian outflow channels that are derived from radar-elevation profiles across Lunae Planum and Chryse Basin have much lower values than those obtained from the U.S. Geological Survey's topographic map. Whereas the gradients of Maja and Ares Valles are similar to those of the catastrophic flood channels in the Scablands of Washington State, the gradients of Simud and Tiu Valles are essentially level, and the movement of fluids to the N poses problems. It is proposed that ponding may have formed lakes in depressions associated with the Valles Marineris grabens, ancient craters in the chaotic terrain area, and possibly even the regional low where most chaotic terrains occur. It is envisaged that lakes eventually overflowed, forming the present channels. When dams broke, floods were released catastrophically, with a final gigantic flood from the Valles Marineris system of troughs, which would have had sufficient head to move fluids across nearly level gradients through the Simud and Tiu channels.

Journal of Geophysical Research↗
USGS1984

Topography of the shield volcano, Olympus Mons on Mars

Olympus Mons, one of the largest known shield volcanoes in the Solar System, covers an area of >3.2 ?? 105 km2and has a diameter of >600 km, excluding its vast aureole deposits. The structure is five times larger than the largest shield volcano on the Earth. It is situated on the north-west flank of the Tharsis volcanic region, a broad topographic rise on the martian surface. The volcano has three physical subdivisions: the summit caldera, the terraced upper flanks, and the lower flanks, which terminate in a scarp 2-10 km high that nearly surrounds the structure. A large block of images of the Tharsis region, including Olympus Mons, was obtained by the Viking mission1. Here we present a topographic map of Olympus Mons, compiled using various combinations of stereo pairs of these images, together with stereoscopic perspective views generated by image processing techniques. ?? 1984 Nature Publishing Group.

Nature↗
USGS2024

Detrital zircons and the magmatic history of Viti Levu, Fiji

We integrate the existing detrital zircon data from multiple modern river sediment samples on Viti Levu, Fiji, with the most current available geological and topographic mapping of the respective river drainage basins to compare detrital populations with potential bedrock sources. The temporal and spatial variations in zircon geochemistry supplement what is known from igneous rocks and confirm the petrological differences between plutonic and volcanic rocks from the Eocene to early Oligocene (Yavuna age, >30 Ma), middle Oligocene to middle Miocene (Wainimala age, 30–12.5 Ma), late Miocene (Colo age, 12.5–6.5 Ma) and latest Miocene (Namosi age, 6.5–5 Ma). The >30 Ma Yavuna-age zircons are restricted to areas that drain the previously mapped Yavuna Group. The 30–12.5 Ma zircons are found across central Viti Levu from west to east, and the 30–15 Ma zircons have distinctively low U/Yb and high Dy/Yb ratios. They are the best radiometric evidence of widespread early to middle Miocene arc magmatism in Fiji that was relatively U-poor. Peak deconvolution of the Colo age zircons from individual basins suggests the following ages for undated or poorly dated plutons from central Viti Levu. The large Mavuvu pluton is probably composed of multiple intrusions in the 12–10 Ma range, the Waiqa pluton is probably ca 10 Ma, and the Noikoro pluton is probably ca 9 Ma. There are zircons from unknown plutonic or volcanic sources between 8 and 7 Ma in western Viti Levu that have distinct Eu/Eu* ratios. We attribute the highest U/Yb ratios in some Colo age zircons to crustal anatexis. Namosi-age zircons are abundant in the Medrausucu Group and can be found scattered across Viti Levu.

Viti Levu↗
USGS1998

Objective delineation of lahar-inundation hazard zones

A new method of delineating lahar hazard zones in valleys that head on volcano flanks provides a rapid, objective, reproducible alternative to traditional methods. The rationale for the method derives from scaling analyses of generic lahar paths and statistical analyses of 27 lahar paths documented at nine volcanoes. Together these analyses yield semiempirical equations that predict inundated valley cross-sectional areas (A) and planimetric areas (B) as functions of lahar volume (V) . The predictive equations ( A = 0.05 V 2/3 and B = 200 V 2/3 ) provide all information necessary to calculate and plot inundation limits on topographic maps. By using a range of prospective lahar volumes to evaluate A and B , a range of inundation limits can be plotted for lahars of increasing volume and decreasing probability. Resulting hazard maps show graphically that lahar-inundation potentials are highest near volcanoes and along valley thalwegs, and diminish gradually as distances from volcanoes and elevations above valley floors increase. We automate hazard-zone delineation by embedding the predictive equations in a geographic information system (GIS) computer program that uses digital elevation models of topography. Lahar hazard zones computed for Mount Rainier, Washington, mimic those constructed on the basis of intensive field investigations. The computed hazard zones illustrate the potentially widespread impact of large lahars, which on average inundate planimetric areas 20 times larger than those inundated by rock avalanches of comparable volume.

Washington↗
USGS2020

Late Quaternary slip rates on the Sierra Madre fault zone and paleoseismic evidence on the size and frequency of past ruptures

The Sierra Madre fault zone is a south-vergent, active reverse fault that accommodates shortening between basins on the northern margin of the Los Angeles region and the San Gabriel Mountains. The preservation of late Quaternary alluvial fill and fan surfaces in the hanging wall of the fault provides evidence of long-term uplift. Surface rupture from the 1971 Mw 6.6 San Fernando earthquake and evidence of large prehistoric displacements from trenching investigations emphasize the ongoing hazard posed by the fault system to the region. This one-day field trip visits some of the key locations near Pasadena and San Fernando, California, where slip rates have been determined from cosmogenic and luminescence dating of abandoned surfaces dating to 50–70, ca. 30, and ca. 12 ka and surface offsets measured from lidar and pre-development topographic maps. Another stop is the site of a paleoseismic trench, which provided key evidence on the timing and displacement of past ruptures on the fault. In combination, results from these field investigations converge on a slip rate for the eastern ~100 km of the fault zone of 1–2 mm/yr, which matches or exceeds the rates for other reverse faults in southern California. This rate, in combination with trenching data that show no evidence of post–mid Holocene ruptures along the central and eastern portions of the fault, indicate the fault zone poses a significant seismic hazard to the region.

California↗
USGS2011

Faulted terrace risers place new constraints on the late Quaternary slip rate for the central Altyn Tagh fault, northwest Tibet

The active, left-lateral Altyn Tagh fault defines the northwestern margin of the Tibetan Plateau in western China. To clarify late Quaternary temporal and spatial variations in slip rate along the central portion of this fault system (85°–90°E), we have more than doubled the number of dated offset markers along the central Altyn Tagh fault. In particular, we determined offset-age relations for seven left-laterally faulted terrace risers at three sites (Kelutelage, Yukuang, and Keke Qiapu) spanning a 140-km-long fault reach by integrating surficial geologic mapping, topographic surveys (total station and tripod–light detection and ranging [T-LiDAR]), and geochronology (radiocarbon dating of organic samples, 230 Th/U dating of pedogenic carbonate coatings on buried clasts, and terrestrial cosmogenic radionuclide exposure age dating applied to quartz-rich gravels). At Kelutelage, which is the westernmost site (37.72°N, 86.67°E), two faulted terrace risers are offset 58 ± 3 m and 48 ± 4 m, and formed at 6.2–6.1 ka and 5.9–3.7 ka, respectively. At the Yukuang site (38.00°N, 87.87°E), four faulted terrace risers are offset 92 ± 12 m, 68 ± 6 m, 55 ± 13 m, and 59 ± 9 m and formed at 24.2–9.5 ka, 6.4–5.0 ka, 5.1–3.9 ka, and 24.2–6.4 ka, respectively. At the easternmost site, Keke Qiapu (38.08°N, 88.12°E), a faulted terrace riser is offset 33 ± 6 m and has an age of 17.1–2.2 ka. The displacement-age relationships derived from these markers can be satisfied by an approximately uniform slip rate of 8–12 mm/yr. However, additional analysis is required to test how much temporal variability in slip rate is permitted by this data set.

Central Altyn Tagh fault↗
USGS1992

Precipitation estimation in mountainous terrain using multivariate geostatistics. Part I: structural analysis

Values of average annual precipitation (AAP) are desired for hydrologic studies within a watershed containing Yucca Mountain, Nevada, a potential site for a high-level nuclear-waste repository. Reliable values of AAP are not yet available for most areas within this watershed because of a sparsity of precipitation measurements and the need to obtain measurements over a sufficient length of time. To estimate AAP over the entire watershed, historical precipitation data and station elevations were obtained from a network of 62 stations in southern Nevada and southeastern California. Multivariate geostatistics (cokriging) was selected as an estimation method because of a significant (p = 0.05) correlation of r = .75 between the natural log of AAP and station elevation. A sample direct variogram for the transformed variable, TAAP = ln [(AAP) 1000], was fitted with an isotropic, spherical model defined by a small nugget value of 5000, a range of 190 000 ft, and a sill value equal to the sample variance of 163 151. Elevations for 1531 additional locations were obtained from topographic maps to improve the accuracy of cokriged estimates. A sample direct variogram for elevation was fitted with an isotropic model consisting of a nugget value of 5500 and three nested transition structures: a Gaussian structure with a range of 61 000 ft, a spherical structure with a range of 70 000 ft, and a quasi-stationary, linear structure. The use of an isotropic, stationary model for elevation was considered valid within a sliding-neighborhood radius of 120 000 ft. The problem of fitting a positive-definite, nonlinear model of coregionalization to an inconsistent sample cross variogram for TAAP and elevation was solved by a modified use of the Cauchy-Schwarz inequality. A selected cross-variogram model consisted of two nested structures: a Gaussian structure with a range of 61 000 ft and a spherical structure with a range of 190 000 ft. Cross validation was used for model selection and for comparing the geostatistical model with six alternate estimation methods. Multivariate geostatistics provided the best cross-validation results.

Nevada↗
USGS2016

Comparison of measurement- and proxy-based Vs30 values in California

This study was prompted by the recent availability of a significant amount of openly accessible measured V S 30 values and the desire to investigate the trend of using proxy-based models to predict V S 30 in the absence of measurements. Comparisons between measured and model-based values were performed. The measured data included 503 V S 30 values collected from various projects for 482 seismographic station sites in California. Six proxy-based models—employing geologic mapping, topographic slope, and terrain classification—were also considered. Included was a new terrain class model based on the Yong et al. (2012) approach but recalibrated with updated measured V S 30 values. Using the measured V S 30 data as the metric for performance, the predictive capabilities of the six models were determined to be statistically indistinguishable. This study also found three models that tend to underpredict V S 30 at lower velocities (NEHRP Site Classes D–E) and overpredict at higher velocities (Site Classes B–C).

Earthquake Spectra↗
USGS2009

Basinsoft, a computer program to quantify drainage basin characteristics

Surface water runoff is a function of many interrelated factors including climate, soils, landuse, and the physiography of the drainage basin. A practical and effective method to quantify drainage basin characteristics would allow analysis of the interrelations of these factors, leading to an improved understanding of the effects of drainage basin characteristics on surface-water runoff. Historically, the quantification of drainage basin characteristics has been a tedious and time-consuming process. Recent improvements in computer hardware and software technology have enabled the developers of a program called Basinsoft to automate this process. Basinsoft requires minimal preprocessing of data and provides an efficient, automated procedure for quantifying selected morphometric characteristics and the option to area-weight characteristics for a drainage basin. The user of Basinsoft is assumed to have a limited amount of experience in the use of ARC/INFO, a proprietary geographic information system (GIS). (The use of brand names in this chapter is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey [USGS].) In 1988, the USGS began developing a program called Basinsoft. The initial program quantified 16 selected drainage basin characteristics from three source-data layers that were manually digitized from topographic maps using the versions of ARC/INFO, Fortran programs, and prime system Command Programming Language (CPL) programs available in 1988 (Majure and Soenksen, 1991). By 1991, Basinsoft was enhanced to quantify 27 selected drainage-basin characteristics from three source-data layers automatically generated from digital elevation model (DEM) data using a set of Fortran programs (Majure and Eash, 1991: Jenson and Dominique, 1988). Due to edge-matching problems encountered in 1991 with the preprocessing

Book chapter↗