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At least 487 records · Page 27Linked to original sources
USGS2008

Scaling sap flux measurements of grazed and ungrazed shrub communities with fine and coarse-resolution remote sensing

We measured transpiration by black greasewood ( Sarcobatus vermiculatus ) (SAVE) and fourwing saltbush ( Atriplex canescens ) (ATCA) over a nitrate-contaminated aquifer in Monument Valley, Arizona, on the Colorado Plateau. Heat balance sap flow sensors were used to measure transpiration by shrubs in 2006 and 2007 and results were scaled to larger landscape units and longer time scales using leaf area index (LAI), fractional vegetation cover, meteorological data, and the enhanced vegetation index (EVI) from MODIS sensors on the Terra satellite. Transpiration was high depending on leaf area (2·95–6·72 kg m −2 d −1 ) and was controlled by vapour pressure deficit ( D ) in the atmosphere. SAVE tended to have higher transpiration rates than ATCA and had a steeper response to D , but both exhibited midday depression of leaf conductance. Over most of the site, fractional vegetation cover ( f c ) and area-wide LAI were low (0·10 and 0·37, respectively) due to heavy grazing by cattle and sheep. However, a portion of the plume that had been protected from grazing for 10 years had f c = 0·75, LAI = 2·88. Transpiration rates on a ground-area basis varied with LAI, with midsummer daily values ranging from 1·44 mm d −1 (LAI = 0·36) to 13·1 mm d −1 (LAI = 2·88 mm) over the site, corresponding to projected annual values of 159–1447 mm year −1 . Controlling grazing could, theoretically, slow or halt the movement of the contamination plume by allowing the shrub community to extract more water than is recharged in the aquifer.

Utah↗
USGS2021

Hydrologic and geomorphic effects on riparian plant species occurrence and encroachment: Remote sensing of 360 km of the Colorado River in Grand Canyon

A common impact on riparian ecosystem function following river regulation is the expansion and encroachment of riparian plant species in the active river channels and floodplain, which reduces flow of water and suspended sediment between the river, riparian area, and upland ecosystems. We characterized riparian plant species occurrence and quantified encroachment within the dam-regulated Colorado River in Grand Canyon, Arizona, USA. We mapped 10 riparian species with high-resolution multispectral imagery and examined effects of river hydrology and geomorphology on the spatial distribution of plant species and open sand. Analysis spanned an image time-series from 2002-2009-2013; a period when plant species and sand were spatially dynamic, and operations of Glen Canyon Dam included daily hydro-peaking and small episodic controlled flood releases. Plant species occurrence and encroachment rates varied with hydrology, geomorphology, and local species pool. Encroachment was greatest on surfaces frequently inundated by hydro-peaking. Seep willow ( Baccharis spp .), tamarisk ( Tamarix spp .) and arrowweed ( Pluchea sericea ) were the primary encroaching woody species. Common reed ( Phragmites australis ) and horsetail ( Equisetum xferrissii ) were the primary encroaching herbaceous species. Encroachment composition from 2002 to 2009 was similar to the entire riparian landscape, whereas encroachment from 2009 to 2013 primarily consisted of seep willow and early-colonizing herbaceous species. Emergence of seep willow and arrowweed after burial by sand deposited by controlled floods indicated that those species were resilient to this form of disturbance. Describing patterns of species encroachment is an important step towards designing flow regimes that favor riparian species and ecosystem functions valued by stakeholders.

Arizona↗
USGS2008

Wide-area estimates of saltcedar (Tamarix spp.) evapotranspiration on the lower Colorado River measured by heat balance and remote sensing methods

In many places along the lower Colorado River, saltcedar ( Tamarix spp) has replaced the native shrubs and trees, including arrowweed, mesquite, cottonwood and willows. Some have advocated that by removing saltcedar, we could save water and create environments more favourable to these native species. To test these assumptions we compared sap flux measurements of water used by native species in contrast to saltcedar, and compared soil salinity, ground water depth and soil moisture across a gradient of 200–1500 m from the river's edge on a floodplain terrace at Cibola National Wildlife Refuge (CNWR). We found that the fraction of land covered ( f c ) with vegetation in 2005–2007 was similar to that occupied by native vegetation in 1938 using satellite-derived estimates and reprocessed aerial photographs scaled to comparable spatial resolutions (3–4 m). We converted f c to estimates of leaf area index (LAI) through point sampling and destructive analyses ( r 2 = 0·82). Saltcedar LAI averaged 2·54 with an f c of 0·80, and reached a maximum of 3·7 with an f c of 0·95. The ranges in f c and LAI are similar to those reported for native vegetation elsewhere and from the 1938 photographs over the study site. On-site measurements of water use and soil and aquifer properties confirmed that although saltcedar grows in areas where salinity has increased much better than native shrubs and trees, rates of transpiration are similar. Annual water use over CNWR was about 1·15 m year −1 .

Arizona, California↗
USGS2013

Linkages between lake shrinkage/expansion and sublacustrine permafrost distribution determined from remote sensing of interior Alaska, USA

[1] Linkages between permafrost distribution and lake surface-area changes in cold regions have not been previously examined over a large scale because of the paucity of subsurface permafrost information. Here, a first large-scale examination of these linkages is made over a 5150 km 2 area of Yukon Flats, Alaska, USA, by evaluating the relationship between lake surface-area changes during 1979–2009, derived from Landsat satellite data, and sublacustrine groundwater flow-path connectivity inferred from a pioneering, airborne geophysical survey of permafrost. The results suggest that the shallow (few tens of meters) thaw state of permafrost has more influence than deeper permafrost conditions on the evolving water budgets of lakes on a multidecadal time scale. In the region studied, these key shallow aquifers have high hydraulic conductivity and great spatial variability in thaw state, making groundwater flow and associated lake level evolution particularly sensitive to climate change owing to the close proximity of these aquifers to the atmosphere.

Alaska↗
USGS2013

Comparison of elevation and remote sensing derived products as auxiliary data for climate surface interpolation

Climate models may be limited in their inferential use if they cannot be locally validated or do not account for spatial uncertainty. Much of the focus has gone into determining which interpolation method is best suited for creating gridded climate surfaces, which often a covariate such as elevation (Digital Elevation Model, DEM) is used to improve the interpolation accuracy. One key area where little research has addressed is in determining which covariate best improves the accuracy in the interpolation. In this study, a comprehensive evaluation was carried out in determining which covariates were most suitable for interpolating climatic variables (e.g. precipitation, mean temperature, minimum temperature, and maximum temperature). We compiled data for each climate variable from 1950 to 1999 from approximately 500 weather stations across the Western United States (32° to 49° latitude and −124.7° to −112.9° longitude). In addition, we examined the uncertainty of the interpolated climate surface. Specifically, Thin Plate Spline (TPS) was used as the interpolation method since it is one of the most popular interpolation techniques to generate climate surfaces. We considered several covariates, including DEM, slope, distance to coast (Euclidean distance), aspect, solar potential, radar, and two Normalized Difference Vegetation Index (NDVI) products derived from Advanced Very High Resolution Radiometer (AVHRR) and Moderate Resolution Imaging Spectroradiometer (MODIS). A tenfold cross-validation was applied to determine the uncertainty of the interpolation based on each covariate. In general, the leading covariate for precipitation was radar, while DEM was the leading covariate for maximum, mean, and minimum temperatures. A comparison to other products such as PRISM and WorldClim showed strong agreement across large geographic areas but climate surfaces generated in this study (ClimSurf) had greater variability at high elevation regions, such as in the Sierra Nevada Mountains.

International Journal of Climatology↗
USGS2001

Combined use of remote sensing and continuous monitoring to analyse the variability of suspended-sediment concentrations in San Francisco Bay, California

Analysis of suspended-sediment concentration data in San Francisco Bay is complicated by spatial and temporal variability. In situ optical backscatterance sensors provide continuous suspended-sediment concentration data, but inaccessibility, vandalism, and cost limit the number of potential monitoring stations. Satellite imagery reveals the spatial distribution of surficial-suspended sediment concentrations in the Bay; however, temporal resolution is poor. Analysis of the in situ sensor data in conjunction with the satellite reflectance data shows the effects of physical processes on both the spatial and temporal distribution of suspended sediment in San Francisco Bay. Plumes can be created by large freshwater flows. Zones of high suspended-sediment concentrations in shallow subembayments are associated with wind-wave resuspension and the spring-neap cycle. Filaments of clear and turbid water are caused by different transport processes in deep channels, as opposed to adjacent shallow water.

Estuarine, Coastal and Shelf Science↗
USGS2009

An integrated approach to benthic habitat mapping using remote sensing and GIS: An example from the Hawaiian Islands

This chapter documents our effort to map benthic habitats within the KalokoHonokohau National Historic Park, Hawai`i, USA. We produce detailed benthichabitat maps by using a combination of color aerial photography, high-resolution bathymetry, and georeferenced underwater video and still photography. We classify individual habitat polygons using five basic attributes and additional information regarding geology, morphology, and coral species. Derivative data sets including isobaths, hillshades, and slope maps are also generated. The mapping shows that benthic habitat and seafloor morphology varies greatly throughout the study area. Nearly 73% of the study area consists of a hardbottom structure that is potentially available for coral habitation; the remaining 27% includes unconsolidated sediment and artificial or historical features. Coral cover is generally low and increases with water depth. The offshore geology is predominantly composed of smooth to undulating pahoehoe-type basalt flows that form flat to gently sloping benches, vertical walls, and steep escarpments. In some locations the basalt surface is irregular and mounded into ridges, pinnacles, and arches. Large rounded basaltic boulders and smaller scattered rocks are common throughout the marine portions of the park. Coral or accreted carbonate reef obscures the underlying volcanic surface in only a few areas. The underlying geologic framework and morphology of the submerged volcanic flows within Kaloko-Honokohau National Historical Park provide the primary control on benthic habitats within the park. The habitat maps and associated data can be used as a stand-alone product or in a GIS to provide useful baseline information to scientists, managers and the general public.

Hawaii↗
USGS1986

Determination of total, commonality, and uniqueness of interpreted structural elements from remotely sensed data in Alaska

Statistical analysis is conducted to determine the unique value of real- and synthetic-aperture side-looking airborne radar (SLAR) to detect interpreted structural elements. SLAR images were compared to standard and digitally enhanced Landsat multispectral scanner (MSS) images and to aerial photographs. After interpretation of the imagery, data were cumulated by total length in miles and by frequency of counts. Maximum uniqueness is obtained first from real-aperture SLAR, 58.3% of total, and, second, from digitally enhanced Landsat MSS images, 54.1% of total. ?? 1986 Plenum Publishing Corporation.

Mathematical Geology↗
USGS1978

Microwave remote sensing of sea ice in the AIDJEX Main Experiment

During the AIDJEX Main Experiment, April 1975 through May 1976, a comprehensive microwave sensing program was performed on the sea ice of the Beaufort Sea. Surface and aircraft measurements were obtained during all seasons using a wide variety of active and passive microwave sensors. The surface program obtained passive microwave measurements of various ice types using four antennas mounted on a tracked vehicle. In three test regions, each with an area of approximately 1.5 ?? 104 m2, detailed ice crystallographic, dielectric properties, and brightness temperatures of first-year, multiyear, and first-year/multiyear mixtures were measured. A NASA aircraft obtained passive microwave measurements of the entire area of the AIDJEX manned station array (triangle) during each of 18 flights. This verified the earlier reported ability to distinguish first-year and multiyear ice types and concentration and gave new information on ways to observe ice mixtures and thin ice types. The active microwave measurements from aircraft included those from an X- and L-band radar and from a scatterometer. The former is used to study a wide variety of ice features and to estimate deformations, while both are equally usable to observe ice types. With the present data, only the scatterometer can be used to distinguish positively multiyear from first-year and various types of thin ice. This is best done using coupled active and passive microwave sensing. ?? 1978 D. Reidel Publishing Company.

Boundary-Layer Meteorology↗
USGS2004

Use of remote sensing techniques to determine the effects of grazing on vegetation cover and dune elevation at assateague island national seashore: Impact of horses

The effects of grazing by feral horses on vegetation and dune topography at Assateague Island National Seashore were investigated using color-infrared imagery, lidar surveys, and field measurements. Five pairs of fenced and unfenced plots (300 m2) established in 1993 on sand flats and small dunes with similar elevation, topography, and vegetation cover were used for this study. Color-infrared imagery from 1998 and field measurements from 2001 indicated that there was a significant difference in vegetation cover between the fenced and unfenced plot-pairs over the study period. Fenced plots contained a higher percentage of vegetation cover that was dominated by American beachgrass (Ammophila breviligulata). Lidar surveys from 1997, 1999, and 2000 showed that there were significant differences in elevation and topography between fenced and unfenced plot-pairs. Fenced plots were, on average, 0.63 m higher than unfenced plots, whereas unfenced plots had generally decreased in elevation after establishment in 1993. Results demonstrate that feral horse grazing has had a significant impact on dune formation and has contributed to the erosion of dunes at Assateague Island. The findings suggest that unless the size of the feral horse population is reduced, grazing will continue to foster unnaturally high rates of dune erosion into the future. In order to maintain the natural processes that historically occurred on barrier islands, much larger fenced exclosures would be required to prevent horse grazing. ?? 2004 Springer Science+Business Media, Inc.

Environmental Management↗
USGS2021

Evolution in eruptive style of the 2018 eruption of Veniaminof volcano, Alaska, reflected in groundmass textures and remote sensing

Variable eruptive style and explosivity is common in basaltic to basaltic andesite volcanoes but can have uncertain origins. Veniaminof volcano in the Alaska-Aleutian arc is a frequently active open-vent center, regularly producing Strombolian eruptions and small lava flows from an intracaldera cone within an intracaldera ice cap. The September–December 2018 eruption of Veniaminof evolved in explosivity over time. The eruption was documented with frequent satellite observations, syn- and post-eruption structure-from-motion photo surveys, and post-eruption sampling of lava flows and tephra preserved in the syn-eruption snowpack. Lava flows with a total volume of ~ 6 × 10 6 m 3 flowed down the cone flanks into the ice cap, overthickening at ice marginal flow fronts. Smaller tephra deposits were estimated at ~ 1–2 × 10 6 m 3 dense rock equivalent, with almost half of this volume deposited directly on the eruptive cone itself. Erupted products were basaltic andesite, and composition (54 ± 0.7 wt% bulk rock, 58 ± 0.7 wt% glass SiO 2 ), sideromelane microlite crystallinity (20–30%), and microlite number density (plagioclase 6.4 ± 2.6 × 10 5 n/mm 3 ) did not change significantly over the eruption suggesting a similar magma source and ascent rate. We defined tephra componentry with groundmass microcrystalline textures using backscatter electron images. The componentry of tephra groundmass showed significant increases in tachylite grains, defined here by the presence of dendritic interstitial nanolites, corresponding to increasing seismic tremor and periods of increased ash emissions. We suggest that these componentry changes reflect increasing undercooled zones on the conduit margins that increased brittle shearing, fragmentation, and ultimately ash emissions.

Alaska↗
USGS2023

The 2022 Chaos Canyon landslide in Colorado: Insights revealed by seismic analysis, field investigations, and remote sensing

An unusual, high-alpine, rapid debris slide originating in ice-rich debris occurred on June 28, 2022, at 16:33:16 MDT at the head of Chaos Canyon, a formerly glacier-covered valley in Rocky Mountain National Park, CO, USA. In this study, we integrate eyewitness videos and seismic records of the event with meteorological data, field observations, pre- and post-event satellite imagery, and uncrewed aircraft vehicle imagery to characterize the event and future hazards it may pose. Deformation of the eventual slide mass preceded rapid failure by decades, starting in the early to mid-2000s, accelerating in 2018 (the warmest year on record), and reaching ~ 20 m/year in 2021. The main event, which was preceded by smaller sliding episodes earlier that day, had a volume of ~ 2.1 million m 3 , reached peak velocities of about 5 m/s, slid on a surface up to 80 m deep, and moved up to ~ 245 m downslope in < 2 min. We observed blocks of frozen debris (permafrost) in the landslide deposits. Within ~ 2 weeks, these blocks had melted and became dry, conical debris mounds (molards). We hypothesize that the rapid slide was induced by gradually increasing long-term air temperatures that thawed ice and increased pore pressures. The presence and suspected influence of permafrost on the occurrence of this landslide indicate other slopes in the park, and other moderate-to-low latitude alpine regions may experience similar slope stability issues as temperatures continue to warm.

Colorado↗
USGS2010

Vegetation index methods for estimating evapotranspiration by remote sensing

Evapotranspiration (ET) is the largest term after precipitation in terrestrial water budgets. Accurate estimates of ET are needed for numerous agricultural and natural resource management tasks and to project changes in hydrological cycles due to potential climate change. We explore recent methods that combine vegetation indices (VI) from satellites with ground measurements of actual ET (ETa) and meteorological data to project ETa over a wide range of biome types and scales of measurement, from local to global estimates. The majority of these use time-series imagery from the Moderate Resolution Imaging Spectrometer on the Terra satellite to project ET over seasons and years. The review explores the theoretical basis for the methods, the types of ancillary data needed, and their accuracy and limitations. Coefficients of determination between modeled ETa and measured ETa are in the range of 0.45&ndash;0.95, and root mean square errors are in the range of 10&ndash;30% of mean ETa values across biomes, similar to methods that use thermal infrared bands to estimate ETa and within the range of accuracy of the ground measurements by which they are calibrated or validated. The advent of frequent-return satellites such as Terra and planed replacement platforms, and the increasing number of moisture and carbon flux tower sites over the globe, have made these methods feasible. Examples of operational algorithms for ET in agricultural and natural ecosystems are presented. The goal of the review is to enable potential end-users from different disciplines to adapt these methods to new applications that require spatially-distributed ET estimates.

Surveys in Geophysics↗
USGS2026

Leveraging time-series remote sensing to predict post-fire invasive annual grass response in western US rangelands

Context Understanding the relationship between Exotic Annual Grass (EAG) expansion, drought, and fire frequency across western US rangelands is complex, but critical for maintaining ecological integrity. Objectives We quantified the impacts of wildfire on EAGs, with emphasis on understanding the factors driving the spatial and temporal variability of those impacts, highlighting the role of drought. Methods We investigate two study periods using 1985–2024 and 2016–2024 EAG cover datasets to better understand EAG dynamics in relation to fire. We, 1) leverage mapped EAG cover responses to fire in the context of various biophysical variables to model expected change in EAG cover (ΔG) given a fire in a specific location, even if no fire has occurred in that location in the period of record; 2) evaluate the influence of drought and other biophysical variables on the ΔG; 3) combine our ΔG values with burn probability and ecological integrity data to evaluate the profile of EAG risk due to fire in sagebrush habitats. Results Our results show that fire impacts on EAG are often delayed, with limited effects in the first post-fire year followed by increasing cover over subsequent years. Importantly, areas with low pre-fire EAG cover exhibited the greatest potential for post-fire increases, whereas heavily invaded sites showed lower incremental responses, suggesting saturation or carrying-capacity constraints. Conclusions Understanding the connections among EAGs, drought, and wildfire is critical for maintaining the ecological integrity of western rangelands. Identifying the magnitude of fire impacts to EAG cover provides critical insight for land managers.

western United States↗