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At least 1,387 records · Page 77Linked to original sources
USGS2020

The pervasive and multifaceted influence of biocrusts on water in the world’s drylands

The capture and use of water are critically important in drylands, which collectively constitute Earth's largest biome. Drylands will likely experience lower and more unreliable rainfall as climatic conditions change over the next century. Dryland soils support a rich community of microphytic organisms (biocrusts), which are critically important because they regulate the delivery and retention of water. Yet despite their hydrological significance, a global synthesis of their effects on hydrology is lacking. We synthesized 2,997 observations from 109 publications to explore how biocrusts affected five hydrological processes (times to ponding and runoff, early [sorptivity] and final [infiltration] stages of water flow into soil, and the rate or volume of runoff) and two hydrological outcomes (moisture storage, sediment production). We found that increasing biocrust cover reduced the time for water to pond on the surface (−40%) and commence runoff (−33%), and reduced infiltration (−34%) and sediment production (−68%). Greater biocrust cover had no significant effect on sorptivity or runoff rate/amount, but increased moisture storage (+14%). Infiltration declined most (−56%) at fine scales, and moisture storage was greatest (+36%) at large scales. Effects of biocrust type (cyanobacteria, lichen, moss, mixed), soil texture (sand, loam, clay), and climatic zone (arid, semiarid, dry subhumid) were nuanced. Our synthesis provides novel insights into the magnitude, processes, and contexts of biocrust effects in drylands. This information is critical to improve our capacity to manage dwindling dryland water supplies as Earth becomes hotter and drier.

Global Change Biology↗
USGS2022

Representing plant diversity in land models: An evolutionary approach to make ‘Functional Types’ more functional

Plants are critical mediators of terrestrial mass and energy fluxes, and their structural and functional traits have profound impacts on local and global climate, biogeochemistry, biodiversity, and hydrology. Yet Earth System Models (ESMs), our most powerful tools for predicting the effects of humans on the coupled biosphere-atmosphere system, simplify the incredible diversity of land plants into a handful of coarse categories of ‘Plant Functional Types’ (PFTs) that often fail to capture ecological dynamics such as biome distributions. The inclusion of more realistic functional diversity is a recognized goal for ESMs, yet there is currently no consistent, widely accepted way to add diversity to models, i.e. to determine what new PFTs to add and with what data to constrain their parameters. We review approaches to representing plant diversity in ESMs and draw on recent ecological and evolutionary findings to present an evolution-based functional type approach for further disaggregating functional diversity. Specifically, the prevalence of niche conservatism, or the tendency of closely related taxa to retain similar ecological and functional attributes through evolutionary time, reveals that evolutionary relatedness is a powerful framework for summarizing functional similarities and differences among plant types. We advocate that Plant Functional Types based on dominant evolutionary lineages (‘Lineage Functional Types’) will provide an ecologically defensible, tractable, and scalable framework for representing plant diversity in next-generation ESMs, with the potential to improve parameterization, process representation, and model benchmarking. We highlight how the importance of evolutionary history for plant function can unify the work of disparate fields to improve predictive modeling of the Earth system.

Global Change Biology↗
USGS2007

Coseismic and post-seismic signatures of the Sumatra 2004 December and 2005 March earthquakes in GRACE satellite gravity

The GRACE satellite mission has been measuring the Earth's gravity field and its temporal variations since 2002 April. Although these variations are mainly due to mass transfer within the geofluid envelops, they also result from mass displacements associated with phenomena including glacial isostatic adjustment and earthquakes. However, these last contributions are difficult to isolate because of the presence of noise and of geofluid signals, and because of GRACE's coarse spatial resolution (>400 km half-wavelength). In this paper, we show that a wavelet analysis on the sphere helps to retrieve earthquake signatures from GRACE geoid products. Using a wavelet analysis of GRACE geoids products, we show that the geoid variations caused by the 2004 December ( M w = 9.2) and 2005 March ( M w = 8.7) Sumatra earthquakes can be detected. At GRACE resolution, the 2004 December earthquake produced a strong coseismic decrease of the gravity field in the Andaman Sea, followed by relaxation in the area affected by both the Andaman 2004 and the Nias 2005 earthquakes. We find two characteristic timescales for the relaxation, with a fast variation occurring in the vicinity of the Central Andaman ridge. We discuss our coseismic observations in terms of density changes of crustal and upper-mantle rocks, and of the vertical displacements in the Andaman Sea. We interpret the post-seismic signal in terms of the viscoelastic response of the Earth's mantle. The transient component of the relaxation may indicate the presence of hot, viscous material beneath the active Central Andaman Basin.

Geophysical Journal International↗
USGS2010

Time-dependent seismic tomography

Of methods for measuring temporal changes in seismic-wave speeds in the Earth, seismic tomography is among those that offer the highest spatial resolution. 3-D tomographic methods are commonly applied in this context by inverting seismic wave arrival time data sets from different epochs independently and assuming that differences in the derived structures represent real temporal variations. This assumption is dangerous because the results of independent inversions would differ even if the structure in the Earth did not change, due to observational errors and differences in the seismic ray distributions. The latter effect may be especially severe when data sets include earthquake swarms or aftershock sequences, and may produce the appearance of correlation between structural changes and seismicity when the wave speeds are actually temporally invariant. A better approach, which makes it possible to assess what changes are truly required by the data, is to invert multiple data sets simultaneously, minimizing the difference between models for different epochs as well as the rms arrival-time residuals. This problem leads, in the case of two epochs, to a system of normal equations whose order is twice as great as for a single epoch. The direct solution of this system would require twice as much memory and four times as much computational effort as would independent inversions. We present an algorithm, tomo4d, that takes advantage of the structure and sparseness of the system to obtain the solution with essentially no more effort than independent inversions require. No claim to original US government works Journal compilation ?? 2010 RAS.

Geophysical Journal International↗
USGS2011

High-frequency Born synthetic seismograms based on coupled normal modes

High-frequency and full waveform synthetic seismograms on a 3-D laterally heterogeneous earth model are simulated using the theory of coupled normal modes. The set of coupled integral equations that describe the 3-D response are simplified into a set of uncoupled integral equations by using the Born approximation to calculate scattered wavefields and the pure-path approximation to modulate the phase of incident and scattered wavefields. This depends upon a decomposition of the aspherical structure into smooth and rough components. The uncoupled integral equations are discretized and solved in the frequency domain, and time domain results are obtained by inverse Fourier transform. Examples show the utility of the normal mode approach to synthesize the seismic wavefields resulting from interaction with a combination of rough and smooth structural heterogeneities. This approach is applied to an ∼4 Hz shallow crustal wave propagation around the site of the San Andreas Fault Observatory at Depth (SAFOD).

Geophysical Journal International↗
USGS2006

Natural controls involved in shallow aquifer contamination

Shallow aquifers, commonly the most important sources of ground water, are also those most susceptible to contamination . The mode of entry of contaminants to shallow aquifers is (1) directly, via wells or secondary openings in consolidated rocks, (2) percolation through the zone of aeration, (3) induced infiltration through the zone of saturation, and (4) interaquifer leakage or flow through open holes. Natural removal or degradation of contaminants is by filtration, dispersion, sorption, ion exchange, oxidation, and various biochemical processes. These phenomena are controlled by the physical environment, structure; mineralogy, and hydraulic characteristics of the earth materials contacted by the liquid wastes. When liquid wastes enter an aquifer directly, there is little or no natural treatment by filtration, sorption, or oxidation. Purification is only by those processes that operate within the aquifer under anaerobic conditions. Contaminants from natural sources that enter aquifers under saturated‐flow conditions are degraded primarily by dilution. The natural processes effective in reducing contamination from surface‐water sources depend on the hydraulic regimen involved , which vary with individual cases. Liquid wastes percolating through the zone of aeration are those most likely to be purified by natural environment processes. Natural processes, however, do not effectively remove or degrade all contaminants, especially some of the many highly stable compounds that have gained widespread use in recent years, such as synthetic detergents. Comprehensive interdisciplinary research into the ability of various earth materials to remove many types of contaminants under varying hydrologic conditions is needed.

Groundwater↗
USGS2007

Assessment of gully-control structures in the Rio Nutria watershed, Zuni reservation, New Mexico

During the latter part of the 19th century and the early part of the 20th century, a major cycle of erosion, arroyo cutting, and gullying occurred in the southwestern United States. Since this erosion cycle began, many projects to control erosion, such as the Civilian Conservation Corps projects in the 1930s, were initiated. However, in the Southwestern United States few studies have documented the effect of these structures in reducing erosion or their effect on gully systems. As part of a watershed rehabilitation project on the Zuni Reservation, New Mexico, 47 structures made either of earth or rocks and 23 rock and brush structures were assessed. Sixty percent of the 47 earth or rock structures have breached and relative to dam height, 65 percent of 47 structures are more than 50 percent silted. Of the 23 rock and brush structures, 22 percent have breached or are close to breaching. Reasons for breaching of all structural types may be piping, scour immediately below the structures, large runoff and large drainage area, poor maintenance, headcutting, and active arroyo deepening and widening. In most cases, documentation does not exist on structure design, the specific purpose for a structure, or when these structures were built.

Water Resources Bulletin↗
USGS2023

Report of the Science Community Workshop on the proposed First Sample Depot for the Mars Sample Return Campaign

The Mars 2020/Mars Sample Return (MSR) Sample Depot Science Community Workshop was held on September 28 and 30, 2022, to assess the Scientifically-Return Worthy (SRW) value of the full collection of samples acquired by the rover Perseverance at Jezero Crater, and of a proposed subset of samples to be left as a First Depot at a location within Jezero Crater called Three Forks. The primary outcome of the workshop was that the community is in consensus on the following statement: The proposed set of ten sample tubes that includes seven rock samples, one regolith sample, one atmospheric sample, and one witness tube constitutes a SRW collection that: (1) represents the diversity of the explored region around the landing site, (2) covers partially or fully, in a balanced way, all of the International MSR Objectives and Samples Team scientific objectives that are applicable to Jezero Crater, and (3) the analyses of samples in this First Depot on Earth would be of fundamental importance, providing a substantial improvement in our understanding of Mars. At the conclusion of the meeting, there was overall community support for forming the First Depot as described at the workshop and placing it at the Three Forks site. The community also recognized that the diversity of the Rover Cache (the sample collection that remains on the rover after placing the First Depot) will significantly improve with the samples that are planned to be obtained in the future by the Perseverance rover and that the Rover Cache is the primary target for MSR to return to Earth.

Meteoritics and Planetary Science↗
USGS2018

Science at the frontier: Multimethod research to evaluate ecosystem change across multiple scales

Changes in the Earth system occur across the full spectrum of spatial and temporal scales, yet our research approaches to understanding and predicting those changes are typically restricted to a pre-defined window of space and time. For this reason, there is substantial power in integrating different approaches, particularly for research associated with the multifaceted nature of ecosystem responses to global change. Within a given research approach – for example, remote sensing, field experimentation, modeling – science promotes the continued advancement of tools and techniques. As technical advancements continue at an unprecedented rate, new opportunities for integrated, multi-approach research emerge, which could more effectively capture the mechanisms and patterns that drive ecosystem structure and function. A capacity to move beyond comparison and into the realm of integration shows promise for promoting significant advances in Earth system science, as evidenced by the Organized Session Science at the Frontier: Using Multimethod Research to Create New Knowledge and Assess Tools Across Spatial and Temporal Scales on December 12, 2017 at the Fall meeting of the American Geophysical Union in New Orleans, Louisiana.

New Phytologist↗
USGS2022

Geomorphology shapes relationships between animal communities and ecosystem function in large rivers

Understanding how the Earth's surface (i.e. ‘nature's stage') influences connections between biodiversity and ecosystem function (BEF) is a central objective in ecology. Despite recent calls to examine these connections at multiple trophic levels and at more complex and realistic scales, little is known about how landscape structure shapes BEF relationships among animal communities in nature. We coupled high-resolution habitat mapping with extensive field sampling to quantify connections among the geophysical habitat templet, invertebrate assemblages and secondary production in two large North American riverscapes. Patterns of sediment size governed invertebrate assemblage structure, with particularly strong effects on composition, richness and taxonomic and functional diversity. These relationships propagated to drive positive relationships between biodiversity and secondary production that were modified by scale, context-dependencies and anthropogenic modification. Finally, leveraging spatially-explicit descriptions of geophysical and biological properties, we uncovered distinct and nested spatial scales of biodiversity and secondary production, and suggest that multiple geophysical processes simultaneously influence these patterns at different scales. Together, our findings advance our understanding of relationships between the physical templet and patterns of BEF, and help to predict how perturbations to the Earth's surface may propagate to influence biodiversity and energy flux through food webs.

Oikos↗
USGS2019

Evidence for plunging river plume deposits in the Pahrump Hills member of the Murray formation, Gale crater, Mars

Recent robotic missions to Mars have offered new insights into the extent, diversity and habitability of the Martian sedimentary rock record. Since the Curiosity rover landed in Gale crater in August 2012, the Mars Science Laboratory Science Team has explored the origins and habitability of ancient fluvial, deltaic, lacustrine and aeolian deposits preserved within the crater. This study describes the sedimentology of a ca 13 m thick succession named the Pahrump Hills member of the Murray formation, the first thick fine‐grained deposit discovered in situ on Mars. This work evaluates the depositional processes responsible for its formation and reconstructs its palaeoenvironmental setting. The Pahrump Hills succession can be sub‐divided into four distinct sedimentary facies: (i) thinly laminated mudstone; (ii) low‐angle cross‐stratified mudstone; (iii) cross‐stratified sandstone; and (iv) thickly laminated mudstone–sandstone. The very fine grain size of the mudstone facies and abundant millimetre‐scale and sub‐millimetre‐scale laminations exhibiting quasi‐uniform thickness throughout the Pahrump Hills succession are most consistent with lacustrine deposition. Low‐angle geometric discordances in the mudstone facies are interpreted as ‘scour and drape’ structures and suggest the action of currents, such as those associated with hyperpycnal river‐generated plumes plunging into a lake. Observation of an overall upward coarsening in grain size and thickening of laminae throughout the Pahrump Hills succession is consistent with deposition from basinward progradation of a fluvial‐deltaic system derived from the northern crater rim into the Gale crater lake. Palaeohydraulic modelling constrains the salinity of the ancient lake in Gale crater: assuming river sediment concentrations typical of floods on Earth, plunging river plumes and sedimentary structures like those observed at Pahrump Hills would have required lake densities near freshwater to form. The depositional model for the Pahrump Hills member presented here implies the presence of an ancient sustained, habitable freshwater lake in Gale crater for at least ca 10 3 to 10 7 Earth years.

Sedimentology↗
USGS2021

Landsat 9: Ready for Launch

Landsat 9 is in its final preparations for launch from Vandenberg Space Force Base on 16 September 2021. It has completed its environmental testing at Northrop Grumman Space (NGSP) in Gilbert, Arizona and has been transported to its California launch site. It will be launched into a 705 km orbit replacing Landsat 7 to provide 8-day Earth land mass coverage in concert with Landsat 8. Landsat 8 carries the first Operational Land Imager (OLI) and the Thermal Infrared Sensor (TIRS); Landsat 9 carries the second of each: OLI-2 and TIRS-2. Once launched it will undergo a 90-day activation, checkout, characterization and calibration, a.k.a. commissioning phase before transitioning to operations. For a several-day period during this commissioning phase, Landsat 9 will under-fly Landsat 8, allowing near simultaneous data collection by both sensors of common Earth targets. These data will be used to compare the radiometric calibrations of the instruments and allow for adjustments of processing parameters to provide more consistent data products.

Conference Paper↗
USGS2002

Archiving, processing, and disseminating ASTER products at the USGS EROS Data Center

The U.S. Geological Survey EROS Data Center archives, processes, and disseminates Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data products. The ASTER instrument is one of five sensors onboard the Earth Observing System's Terra satellite launched December 18, 1999. ASTER collects broad spectral coverage with high spatial resolution at near infrared, shortwave infrared, and thermal infrared wavelengths with ground resolutions of 15, 30, and 90 meters, respectively. The ASTER data are used in many ways to understand local and regional earth-surface processes. Applications include land-surface climatology, volcanology, hazards monitoring, geology, agronomy, land cover change, and hydrology. The ASTER data are available for purchase from the ASTER Ground Data System in Japan and from the Land Processes Distributed Active Archive Center in the United States, which receives level 1A and level 1B data from Japan on a routine basis. These products are archived and made available to the public within 48 hours of receipt. The level 1A and level 1B data are used to generate higher level products that include routine and on-demand decorrelation stretch, brightness temperature at the sensor, emissivity, surface reflectance, surface kinetic temperature, surface radiance, polar surface and cloud classification, and digital elevation models. This paper describes the processes and procedures used to archive, process, and disseminate standard and on-demand higher level ASTER products at the Land Processes Distributed Active Archive Center.

Conference Paper↗
USGS2005

Landsat-4 and Landsat-5 thematic mapper band 6 historical performance and calibration

Launched in 1982 and 1984 respectively, the Landsat-4 and -5 Thematic Mappers (TM) are the backbone of an extensive archive of moderate resolution Earth imagery. However, these sensors and their data products were not subjected to the type of intensive monitoring that has been part of the Landsat-7 system since its launch in 1999. With Landsat-4's 11 year and Landsat-5's 20+ year data record, there is a need to understand the historical behavior of the instruments in order to verify the scientific integrity of the archive and processed products. Performance indicators of the Landsat-4 and -5 thermal bands have recently been extracted from a processing system database allowing for a more complete study of thermal band characteristics and calibration than was previously possible. The database records responses to the internal calibration system, instrument temperatures and applied gains and offsets for each band for every scene processed through the National Landsat Archive Production System (NLAPS). Analysis of this database has allowed for greater understanding of the calibration and improvement in the processing system. This paper will cover the trends in the Landsat-4 and -5 thermal bands, the effect of the changes seen in the trends, and how these trends affect the use of the thermal data.

Conference Paper↗
USGS2005

Improvement in absolute calibration accuracy of Landsat-5 TM with Landsat-7 ETM+ data

The ability to detect and quantify changes in the Earth's environment depends on satellites sensors that can provide calibrated, consistent measurements of Earth's surface features through time. A critical step in this process is to put image data from subsequent generations of sensors onto a common radiometric scale. To evaluate Landsat-5 (L5) Thematic Mapper's (TM) utility in this role, image pairs from the L5 TM and Landsat-7 (L7) Enhanced Thematic Mapper Plus (ETM+) sensors were compared. This approach involves comparison of surface observations based on image statistics from large common areas observed eight days apart by the two sensors. The results indicate a significant improvement in the consistency of L5 TM data with respect to L7 ETM+ data, achieved using a revised Look-Up-Table (LUT) procedure as opposed to the historical Internal Calibrator (IC) procedure previously used in the L5 TM product generation system. The average percent difference in reflectance estimates obtained from the L5 TM agree with those from the L7 ETM+ in the Visible and Near Infrared (VNIR) bands to within four percent and in the Short Wave Infrared (SWIR) bands to within six percent.

Conference Paper↗
USGS2005

Outgassing models for Landsat-4 thematic mapper short wave infrared bands

Detector responses to the Internal Calibrator (IC) pulses in the Landsat-4 Thematic Mapper (TM) have been observed to follow an oscillatory behavior. This phenomenon is present only in the Short Wave Infrared (SWIR) bands and has been observed throughout the lifetime of the instrument, which was launched in July 1982 and imaged the Earth's surface until late 1993. These periodic changes in amplitude, which can be as large as 7.5 percent, are known as outgassing effects and are believed to be due to optical interference caused by a gradual buildup of an ice-like material on the window of the cryogenically cooled dewar containing the SWIR detectors. Similar outgassing effects in the Landsat-5 TM have been characterized using an optical thin-film model that relates detector behavior to the ice film growth rate, which was found to gradually decrease with time. A similar approach, which takes into consideration the different operational history of the instrument, has been applied in this study to three closely sampled data sets acquired throughout the lifetime of the Landsat-4 TM. Although Landsat-4 and Landsat-5 Thematic Mappers are essentially identical instruments, data generated from analyses of outgassing effects indicate subtle, but important, differences between the two. The estimated lifetime model could improve radiometric accuracy by as much as five percent.

Conference Paper↗
USGS2006

Absolute calibration accuracy of L4 TM and L5 TM sensor image pairs

The Landsat suite of satellites has collected the longest continuous archive of multispectral data of any land-observing space program. From the Landsat program's inception in 1972 to the present, the Earth science user community has benefited from a historical record of remotely sensed data. However, little attention has been paid to ensuring that the data are calibrated and comparable from mission to mission, Launched in 1982 and 1984 respectively, the Landsat 4 (L4) and Landsat 5 (L5) Thematic Mappers (TM) are the backbone of an extensive archive of moderate resolution Earth imagery. To evaluate the "current" absolute accuracy of these two sensors, image pairs from the L5 TM and L4 TM sensors were compared. The approach involves comparing image statistics derived from large common areas observed eight days apart by the two sensors. The average percent differences in reflectance estimates obtained from the L4 TM agree with those from the L5 TM to within 15 percent. Additional work to characterize the absolute differences between the two sensors over the entire mission is in progress.

Conference Paper↗
USGS2007

Consistency of L4 TM absolute calibration with respect to the L5 TM sensor based on near-simultaneous image acquisition

The Landsat archive provides more than 35 years of uninterrupted multispectral remotely sensed data of Earth observations. Since 1972, Landsat missions have carried different types of sensors, from the Return Beam Vidicon (RBV) camera to the Enhanced Thematic Mapper Plus (ETM+). However, the Thematic Mapper (TM) sensors on Landsat 4 (L4) and Landsat 5 (L5), launched in 1982 and 1984 respectively, are the backbone of an extensive archive. Effective April 2, 2007, the radiometric calibration of L5 TM data processed and distributed by the U.S. Geological Survey (USGS) Center for Earth Resources Observation and Science (EROS) was updated to use an improved lifetime gain model, based on the instrument's detector response to pseudo-invariant desert site data and cross-calibration with the L7 ETM+. However, no modifications were ever made to the radiometric calibration procedure of the Landsat 4 (L4) TM data. The L4 TM radiometric calibration procedure has continued to use the Internal Calibrator (IC) based calibration algorithms and the post calibration dynamic ranges, as previously defined. To evaluate the "current" absolute accuracy of these two sensors, image pairs from the L5 TM and L4 TM sensors were compared. The number of coincident image pairs in the USGS EROS archive is limited, so the scene selection for the cross-calibration studies proved to be a challenge. Additionally, because of the lack of near-simultaneous images available over well-characterized and traditionally used calibration sites, alternate sites that have high reflectance, large dynamic range, high spatial uniformity, high sun elevation, and minimal cloud cover were investigated. The alternate sites were identified in Yuma, Iraq, Egypt, Libya, and Algeria. The cross-calibration approach involved comparing image statistics derived from large common areas observed eight days apart by the two sensors. This paper summarizes the average percent differences in reflectance estimates obtained between the two sensors. The work presented in this paper is a first step in understanding the current performance of L4 TM absolute calibration and potentially serves as a platform to revise and improve the radiometric calibration procedures implemented for the processing of L4 TM data.

Conference Paper↗