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Results for “Journal of Geophysical Research - Earth Surface”

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USGS1999

Retention of an atmosphere on early Mars

The presence of valley networks and indications of high erosion rates in ancient terrains on Mars suggest that Mars was warm and wet during heavy bombardment. Various processes that could occur on early Mars were integrated into a self-consistent model to determine what circumstances might lead to warm temperatures during and at the end of heavy bombardment. Included were weathering and burial of CO 2 as carbonates, impact erosion, sputtering, and recycling of CO 2 back into the atmosphere by burial and heating. The models suggest that despite losses from the atmosphere by weathering and impact erosion, Mars could retain a 0.5 to 1 bar atmosphere at the end of heavy bombardment partly because weathering temporarily sequesters CO 2 in the ground and protects it from impact erosion while the impact rate is declining and impact erosion is becoming less effective. Because of the low output of the early Sun, surface temperatures can be above freezing only for a very efficient greenhouse, such as that suggested by Forget and Pierrehumbert [1997]. With weak greenhouse models, temperatures are below freezing throughout heavy bombardment, and such a large amount of CO 2 is left in the atmosphere at the end of heavy bombardment that it is difficult to eliminate subsequently to arrive at the present surface inventory. With strong greenhouse models, temperatures are well above freezing during heavy bombardment and drop to close to freezing at the end of heavy bombardment, at which time the atmosphere contains 0.5 to 1 bar of CO 2 . This can be largely eliminated subsequently by sputtering and low-temperature weathering. Such a model is consistent with the change in erosion rate and the declining rate of valley formation at the end of heavy bombardment. Conditions that favor warm temperatures at the end of heavy bombardment are an efficient greenhouse, low weathering rates, low impact erosion rates, and a smaller fraction of heat lost by conduction as opposed to transport of lava to the surface.

Journal of Geophysical Research E: Planets↗

USGS1997

Land cover mapping, fire regeneration, and scaling studies in the Canadian boreal forest with 1 km AVHRR and Landsat TM data

A multitemporal 1 km advanced very high resolution radiometer (AVHRR) land cover analysis approach was used as the basis for regional land cover mapping, fire disturbance-regeneration, and multiresolution land cover scaling studies in the boreal forest ecosystem of central Canada. The land cover classification was developed by using regional field observations from ground and low-level aircraft transits to analyze spectral-temporal clusters that were derived from an unsupervised cluster analysis of monthly normalized difference vegetation index (NDVI) image composites (April-September 1992). Quantitative areal proportions of the major boreal forest components were determined for a 821 km ?? 619 km region, ranging from the southern grasslands-boreal forest ecotone to the northern boreal transitional forest. The boreal wetlands (mostly lowland black spruce, tamarack, mosses, fens, and bogs) occupied approximately 33% of the region, while lakes accounted for another 13%. Upland mixed coniferous-deciduous forests represented 23% of the ecosystem. A SW-NE productivity gradient across the region is manifested by three levels of tree stand density for both the boreal wetland conifer and the mixed forest classes, which are generally aligned with isopleths of regional growing degree days. Approximately 30% of the region was directly affected by fire disturbance within the preceding 30-35 years, especially in the Canadian Shield Zone where large fire-regeneration patterns contribute to the heterogeneous boreal landscape. Intercomparisons with land cover classifications derived from 30-m Landsat Thematic Mapper (TM) data provided important insights into the relative accuracy of the 1 km AVHRR land cover classification. Primarily due to the multitemporal NDVI image compositing process, the 1 km AVHRR land cover classes have an effective spatial resolution in the 3-4 km range; therefore fens, bogs, small water bodies, and small patches of dry jack pine cannot be resolved within the wet conifer mosaic. Major differences in the 1-km AVHRR and 30-m Landsat TM-derived land cover classes are most likely due to differences in the spatial resolution of the data sets. In general, the 1 km AVHRR land cover classes are vegetation mosaics consisting of mixed combinations of the Landsat classes. Detailed mapping of the global boreal forest with this approach will benefit from algorithms for cloud screening and to atmospherically correct reflectance data for both aerosol and water vapor effects. We believe that this 1 km AVHRR land cover analysis provides new and useful information for regional water, energy, carbon, and trace gases studies in BOREAS, especially given the significant spatial variability in land cover type and associated biophysical land cover parameters (e.g., albedo, leaf area index, FPAR, and surface roughness). Multiresolution land cover comparisons (30 m, 1 km, and 100 km grid cells) also illustrated how heterogeneous landscape patterns are represented in land cover maps with differing spatial scales and provided insights on the requirements and challenges for parameterizing landscape heterogeneity as part of land surface process research.

Journal of Geophysical Research D: Atmospheres↗

USGS2017

A probabilistic approach to remote compositional analysis of planetary surfaces

Reflected light from planetary surfaces provides information, including mineral/ice compositions and grain sizes, by study of albedo and absorption features as a function of wavelength. However, deconvolving the compositional signal in spectra is complicated by the nonuniqueness of the inverse problem. Trade-offs between mineral abundances and grain sizes in setting reflectance, instrument noise, and systematic errors in the forward model are potential sources of uncertainty, which are often unquantified. Here we adopt a Bayesian implementation of the Hapke model to determine sets of acceptable-fit mineral assemblages, as opposed to single best fit solutions. We quantify errors and uncertainties in mineral abundances and grain sizes that arise from instrument noise, compositional end members, optical constants, and systematic forward model errors for two suites of ternary mixtures (olivine-enstatite-anorthite and olivine-nontronite-basaltic glass) in a series of six experiments in the visible-shortwave infrared (VSWIR) wavelength range. We show that grain sizes are generally poorly constrained from VSWIR spectroscopy. Abundance and grain size trade-offs lead to typical abundance errors of ≤1 wt % (occasionally up to ~5 wt %), while ~3% noise in the data increases errors by up to ~2 wt %. Systematic errors further increase inaccuracies by a factor of 4. Finally, phases with low spectral contrast or inaccurate optical constants can further increase errors. Overall, typical errors in abundance are <10%, but sometimes significantly increase for specific mixtures, prone to abundance/grain-size trade-offs that lead to high unmixing uncertainties. These results highlight the need for probabilistic approaches to remote determination of planetary surface composition.

Journal of Geophysical Research E: Planets↗

USGS2002

Dust coatings on basaltic rocks and implications for thermal infrared spectroscopy of Mars

Thin coatings of atmospherically deposited dust can mask the spectral characteristics of underlying surfaces on Mars from the visible to thermal infrared wavelengths, making identification of substrate and coating mineralogy difficult from lander and orbiter spectrometer data. To study the spectral effects of dust coatings, we acquired thermal emission and hemispherical reflectance spectra (5–25 μm; 2000–400 cm −1 ) of basaltic andesite coated with different thicknesses of air fall‐deposited palagonitic soils, fine‐grained ceramic clay powders, and terrestrial loess. The results show that thin coatings (10–20 μm) reduce the spectral contrast of the rock substrate substantially, consistent with previous work. This contrast reduction continues linearly with increasing coating thickness until a “saturation thickness” is reached, after which little further change is observed. The saturation thickness of the spectrally flat palagonite coatings is ∼100–120 μm, whereas that for coatings with higher spectral contrast is only ∼50–75 μm. Spectral differences among coated and uncoated samples correlate with measured coating thicknesses in a quadratic manner, whereas correlations with estimated surface area coverage are better fit by linear functions. Linear mixture modeling of coated samples using the rock substrate and coating materials as end‐members is also consistent with their measured coating thicknesses and areal coverage. A comparison of ratios of Thermal Emission Spectrometer (TES) spectra of dark and bright intracrater and windstreak deposits associated with Radau crater suggests that the dark windstreak material may be coated with as much as 90% areal coverage of palagonitic dust. The data presented here also will help improve interpretations of upcoming mini‐TES and Thermal Emission Imaging System (THEMIS) observations of coated Mars surface materials.

Journal of Geophysical Research E: Planets↗

USGS2012

An instrument system for long-term sediment transport studies on the continental shelf

A bottom-mounted instrument system has been designed and built to monitor processes of bottom sediment movement on the continental shelf. The system measures bottom current speed and direction, pressure, temperature, and light transmission and photographs the bottom. The system can be deployed for periods of 2–6 months to monitor intermitent processes of sediment movement such as storms and to assess seasonal variability. Deployments of the system on the U.S. east coast continental shelf show sediment resuspension and changes in bottom microtopography due to surface waves, tidal currents, and storms.

Journal of Geophysical Research: Oceans↗

USGS2025

Origins of the water ice excavated by the Christmas Eve crater formation on Mars

On the 24th of December, 2021, a meteoroid struck the martian surface, producing a 150-m wide crater and excavating the lowest-latitude water ice observed on Mars to date. Knowledge of the preimpact depth, thickness and lateral continuity of the excavated ice would provide new insight into past environmental changes such as temperature and humidity of the atmosphere. In this work, we use the iSALE3D shock physics code to simulate the crater formation and constrain both the impact parameters and the original location of excavated ice. Analysis of the distal ejecta pattern suggests that the impact angle was 20±2.5◦ from horizontal. Based on a comparison of the simulated and observed crater morphology, we find the preimpact subsurface likely contained a stronger bedrock layer overlain by 15 m thick regolith layer. Our simulation results show that the ejected ice blocks visible in orbital images originated from shallow depths 3.2–11 m and from radii 30–60 m from the crater center. We conclude that the ice most likely originated from a massive ice layer at 3.2-11 m depth. The ice was likely also laterally discontinuous under the preimpact surface.

Journal of Geophysical Research: Planets↗

USGS2009

Fluorescence-based proxies for lignin in freshwater dissolved organic matter

Lignin phenols have proven to be powerful biomarkers in environmental studies; however, the complexity of lignin analysis limits the number of samples and thus spatial and temporal resolution in any given study. In contrast, spectrophotometric characterization of dissolved organic matter (DOM) is rapid, noninvasive, relatively inexpensive, requires small sample volumes, and can even be measured in situ to capture fine-scale temporal and spatial detail of DOM cycling. Here we present a series of cross-validated Partial Least Squares models that use fluorescence properties of DOM to explain up to 91% of lignin compositional and concentration variability in samples collected seasonally over 2 years in the Sacramento River/San Joaquin River Delta in California, United States. These models were subsequently used to predict lignin composition and concentration from fluorescence measurements collected during a diurnal study in the San Joaquin River. While modeled lignin composition remained largely unchanged over the diurnal cycle, changes in modeled lignin concentrations were much greater than expected and indicate that the sensitivity of fluorescence-based proxies for lignin may prove invaluable as a tool for selecting the most informative samples for detailed lignin characterization. With adequate calibration, similar models could be used to significantly expand our ability to study sources and processing of DOM in complex surface water systems.

Journal of Geophysical Research G: Biogeosciences↗

USGS2008

Surface albedo observations at Gusev Crater and Meridiani Planum, Mars

During the Mars Exploration Rover mission, the Pancam instrument has periodically acquired large-scale panoramic images with its broadband (739??338 nm) filter in order to estimate the Lambert bolometric albedo of the surface along each rover's traverse. In this work we present the full suite of such estimated albedo values measured to date by the Spirit and Opportunity rovers along their traverses in Gusev Crater and Meridiani Planum, respectively. We include estimated bolometric albedo values of individual surface features (e.g., outcrops, dusty plains, aeolian bed forms, wheel tracks, light-toned soils, and crater walls) as well as overall surface averages of the 43 total panoramic albedo data sets acquired to date. We also present comparisons to estimated Lambert albedo values taken from the Mars Global Surveyor Mars Orbiter Camera (MOC) along the rovers' traverses, and to the large-scale bolometric albedos of the sites from the Viking Orbiter Infrared Thermal Mapper (IRTM) and Mars Global Surveyor/Thermal Emission Spectrometer (TES). The ranges of Pancam-derived albedos at Gusev Crater (0.14 to 0.25) and in Meridiani Planum. (0.10 to 0.18) are in good agreement with IRTM, TES, and MOC orbital measurements. These data sets will be a useful tool and benchmark for future investigations of albodo variations with time, including measurements from orbital instruments like the Context Camera and High Resolution Imaging Science Experiment on Mars Reconnaissance Orbiter. Long-term, accurate albedo measurements could also be important for future efforts in climate modeling as well as for studies of active surface processes. Copyright 2008 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗

USGS1996

Origin of Bermuda's clay-rich Quaternary paleosols and their paleoclimatic significance

Red clayey paleosols that are chiefly the product of aerosolic dust deposition are interbedded in the Quaternary carbonate formations of the Bermuda oceanic island system. These paleosols provide a basis for reconstructing Quaternary atmospheric circulation patterns in the northwestern Atlantic. Geochemical analyses were performed on representative paleosol samples to identify their parent dust source. Fine-grained fractions were analyzed by energy-dispersive X ray fluorescence to determine trace element (Zr, Y, La, Ti, and Nb) concentrations and to derive geochemical signatures based on immobile element ratios. These ratios were compared with geochemical signatures determined for three possible sources of airborne dust: (1) Great Plains loess, (2) Mississippi River Valley loess, and (3) Saharan dust. The Zr/Y and Zr/La ratios provided the clearest distinction between the hypothesized dust sources. The low ratios in the paleosol B horizons most closely resemble Saharan dust in the <2-μm size class fraction. Contributions from the two North American loessial source areas could not be clearly detected. Thus Bermuda paleosols have a predominantly Saharan aerosolic dust signature. Saharan dust deposition on Bermuda during successive Quaternary glacial periods is consistent with patterns of general circulation models, which indicate that during glacial maxima the northeast summer trade winds were stronger than at present and reached latitudes higher than 30°N despite lower-than-present sea surface temperatures in the North Atlantic.

Journal of Geophysical Research D: Atmospheres↗

USGS2012

Sea ice melting in the marginal ice zone

The heat and salt flux boundary conditions together with the freezing curve relationship are a necessary component of any ice-sea water thermodynamic model. A neutral two-layer oceanic planetary boundary layer model that incorporates these boundary conditions gives the following results: The interfacial salinity is within 10% of the far-field salinity for conditions commonly encountered in the MIZ and depends only on the turbulent Lewis number and the far-field temperature and salinity. The predicted melt rates agree with the limited field observations, of the order of 1 m day −1 . The Obukov lengths, determined from the predicted interface conditions and melt rates, are generally much greater than the Ekman layer thicknesses; hence, the surface buoyancy flux has little effect on the turbulence in the planetary boundary layer.

Journal of Geophysical Research - Oceans↗

USGS2013

Emissions of carbon dioxide and methane from a headwater stream network of interior Alaska

Boreal ecosystems store significant quantities of organic carbon (C) that may be vulnerable to degradation as a result of a warming climate. Despite their limited coverage on the landscape, streams play a significant role in the processing, gaseous emission, and downstream export of C, and small streams are thought to be particularly important because of their close connection with the surrounding landscape. However, ecosystem carbon studies do not commonly incorporate the role of the aquatic conduit. We measured carbon dioxide (CO 2 ) and methane (CH 4 ) concentrations and emissions in a headwater stream network of interior Alaska underlain by permafrost to assess the potential role of stream gas emissions in the regional carbon balance. First-order streams exhibited the greatest variability in fluxes of CO 2 and CH 4, and the greatest mean p CO 2 . High-resolution time series of stream p CO 2 and discharge at two locations on one first-order stream showed opposing p CO 2 responses to storm events, indicating the importance of hydrologic flowpaths connecting CO 2 -rich soils with surface waters. Repeated longitudinal surveys on the stream showed consistent areas of elevated p CO 2 and p CH 4 , indicative of discrete hydrologic flowpaths delivering soil water and groundwater having varying chemistry. Up-scaled basin estimates of stream gas emissions suggest that streams may contribute significantly to catchment-wide CH 4 emissions. Overall, our results indicate that while stream-specific gas emission rates are disproportionately high relative to the terrestrial landscape, both stream surface area and catchment normalized emission rates were lower than those documented for the Yukon River Basin as a whole. This may be due to limitations of C sources and/or C transport to surface waters.

Journal of Geophysical Research G: Biogeosciences↗

USGS2010

Parametric study of the physical properties of hydrate-bearing sand, silt, and clay sediments: 1. Electromagnetic properties

The marked decrease in bulk electrical conductivity of sediments in the presence of gas hydrates has been used to interpret borehole electrical resistivity logs and, to a lesser extent, the results of controlled source electromagnetic surveys to constrain the spatial distribution and predicted concentration of gas hydrate in natural settings. Until now, an exhaustive laboratory data set that could be used to assess the impact of gas hydrate on the electromagnetic properties of different soils (sand, silt, and clay) at different effective stress and with different saturations of hydrate has been lacking. The laboratory results reported here are obtained using a standard geotechnical cell and the hydrate-formed tetrahydrofuran (THF), a liquid that is fully miscible in water and able to produce closely controlled saturations of hydrate from dissolved phase. Both permittivity and electrical conductivity are good indicators of the volume fraction of free water in the sediment, which is in turn dependent on hydrate saturation. Permittivity in the microwave frequency range is particularly predictive of free water content since it is barely affected by ionic concentration, pore structure, and surface conduction. Electrical conductivity (or resistivity) is less reliable for constraining water content or hydrate saturation: In addition to fluid-filled porosity, other factors, such as the ionic concentration of the pore fluid and possibly other conduction effects (e.g., surface conduction in high specific surface soils having low conductivity pore fluid), also influence electrical conductivity.

Journal of Geophysical Research↗

USGS2000

Identification of a basaltic component on the Martian surface from Thermal Emission Spectrometer data

The Mars Global Surveyor Thermal Emission Spectrometer (TES) instrument collected 4.8×10 6 spectra of Mars during the initial aerobraking and science‐phasing periods of the mission (September 14, 1997, through April 29, 1998). Two previously developed atmosphere‐removal models were applied to data from Cimmeria Terra (25°S, 213°W). The surface spectra derived for these two models agree well, indicating that the surface and atmosphere emission can be separated and that the exact atmosphere‐removal model used has little effect on the derived surface composition. The Cimmeria spectra do not match terrestrial high‐silica igneous rocks (granite and rhyolite), ultramafic igneous rocks, limestone, or quartz‐ and clay‐rich sandstone and siltstone. A particulate (sand‐sized) sample of terrestrial flood basalt does provide an excellent match in both spectral shape and band depth to the Cimmeria spectrum over the entire TES spectral range. No unusual particle size effects are required to account for the observed spectral shape and depth. The implied grain size is consistent with the thermal inertia and albedo of this region, which indicate a sand‐sized surface with little dust. The identification of basalt is consistent with previous indications of pyroxene and basalt‐like compositions from visible/near‐infrared and thermal‐infrared spectral measurements. A linear spectral deconvolution model was applied to both surface‐only Cimmeria spectra using a library of 60 minerals to determine the composition and abundance of the component minerals. Plagioclase feldspar (45%; 53%) and clinopyroxene (26%; 19%) were positively identified above an estimated detection threshold of 10–15% for these minerals. The TES observations provide the first identification of feldspars on Mars. The best fit to the Mars data includes only clinopyroxene compositions; no orthopyroxene compositions are required to match the Cimmeria spectra. Olivine (12%; 12%) and sheet silicate (15%; 11%) were identified with lower confidence. Carbonates, quartz, and sulfates were not identified in Cimmeria at detection limits of ∼5, 5, and 10%, respectively. Their presence elsewhere, however, remains open. The Cimmeria spectra are not well matched by any one SNC meteorite spectrum, indicating that this region is not characterized by a single SNC lithology. The occurrence of unweathered feldspar and pyroxene in Cimmeria, together with the inferred presence of pyroxene and unweathered basalts in other dark regions and at the Viking and Pathfinder landing sites, provides evidence that extensive global chemical weathering of materials currently exposed on the Martian surface has not occurred.

Journal of Geophysical Research: Planets↗

USGS2012

Lg and Rg waves on the California regional networks from the December 23, 1985 Nahanni earthquake

We investigate Lg and Rg propagation in California using the central and southern California regional networks. Approximately 550 stations constitute these two short-period networks providing a dense coverage of almost the entire state. The waveforms recorded from the December 23, 1985, Nahanni, Canada, earthquake are used to construct three profiles along the propagation path (almost N-S) and three perpendicular to the propagation path (almost E-W) to look at the nature of propagation of these two types of surface waves. Groups of records from stations in various geological and tectonic provinces in California are also examined in order to establish regional characteristics of the surface waves. We find that the propagation characteristics of Lg differ from those of Rg across California; Lg waves are apparently more sensitive to crustal heterogeneities. The most striking observations are the similarity of coda for both the Lg and the Rg waves within geologic provinces and the marked difference in coda between regions. These differences are seen in the amplitudes, coda duration, shape of the energy envelope, frequency content, and sharpness of the phase initiation. In general, a decrease in the Moho depth near the Pacific Coast is correlated with a decrease in the surface wave amplitude, especially at higher frequencies (0.15–0.2 Hz). Most interesting is the association of the San Andreas fault with abrupt changes in the wave train amplitudes. The surface waves are amplified in the vicinity of the fault zone and then decrease in amplitude after the zone is crossed. In the Coast Ranges, amplitudes are low and waveform coherence is poor. The Rg phase dominates the record in the Sierra Nevada, and both surface waves are amplified by the thick sedimentary sequence of the Great Valley.

Journal of Geophysical Research↗

USGS1997

Sedimentary history and mass flow structures of Chryse and Acidalia Planitiae, Mars

Geologic mapping and crater counting in Chryse and Acidalia Planitiae (GAP) reveal five major sedimentary deposits of Hesperian to Early Amazonian age, including (1) a mass flow deposited during the Early Hesperian near Deuteronilus Mensae (northeast of the map region) that may have resulted from the carving of Kasei Valles, >3000 km southwest of the exposed part of the deposit; (2) knobby plains material consisting of channel (likely; from Simud and Tiu Valles and possibly Ares and Shalbatana Valles) and mass-wasting deposits in central and eastern CAP; (3) material largely from Maja and Ares Valles emplaced in at least western and southern CAP (outcrops in southern Chryse Planitia developed thermokarst); (4) a thin mass flow covering much of southern Chryse Planitia that emanated from Simud and Tiu Valles; and (5) a thick, extensive (perhaps >3500 km across) mass flow deposit in central and northern CAP derived from accumulation and backflow of the preceding thin mass flow or perhaps melting of polar deposits. Other possible deposits may not be recognizable owing to burial by younger materials or a lack of morphologic signature. Various associated landforms appear to be consistent with the mass flow interpretations, including lobate and linear scarps along deposit edges, fractures related to desiccation of thick sediments, troughs, and ridges near the edges of the deposit indicative of secondary mass movement and deformation, pitted domes and fissure-fed flows possibly formed by sedimentary (mud) eruptions, and longitudinal channel grooves perhaps formed by roller vortices. No convincing evidence for paleoshorelines or stagnant ice sheets is found in CAP. These findings suggest that mass flow and hyperconcentrated flooding may have been the predominant processes of outflow-channel dissection in CAP. Elsewhere in the northern plains, similar landforms are prevalent. The mass flow interpretation does not require either multiple episodes of extraordinarily high water-discharge rates achieved by freeing huge volumes of water from the crust, repetitive recycling of immense volumes of water into highland aquifers at the heads of Chryse channels, or profound climate change. Mars Pathfinder will most likely land on and inspect the surface of the thin mass flow that originated from the canyons of Simud and Tiu Valles.

Journal of Geophysical Research E: Planets↗

USGS2018

Ice wedge degradation and stabilization impacts water budgets and nutrient cycling in Arctic trough ponds

Trough ponds are ubiquitous features of Arctic landscapes and an important component of freshwater aquatic ecosystems. Permafrost thaw causes ground subsidence, creating depressions that gather water, creating ponds. Permafrost thaw also releases solutes and nutrients, which may fertilize these newly formed ponds. We measured water budget elements and chloride, ammonium, and dissolved organic nitrogen (DON) across a chronosequence of trough ponds representing different stages of ice wedge degradation and stabilization. We developed a coupled hydrologic and biogeochemical model to explore how ice wedge degradation affects hydrology and nutrient availability in trough ponds in the advanced degradation stages (DAs), which are characterized by deep troughs with warmer temperatures relative to the other stages. DAs experienced greater evaporation than the other stages, and subsurface inflows entered the DAs from a wide area. Chloride accumulated in the ponds with time since thaw, implying that subsurface fluxes are delivering solutes from the thawing permafrost. Ammonium accumulated at high rates in the initial degradation stage and was seasonally depleted over the summer in all degradation stages. Ammonium trends in the DAs were consistent with high concentration inflows and in‐pond assimilation at rates between 0.37 and 2.0 mg N m −2 day −1 . Seasonal DON trends indicated that the accumulation of recalcitrant organic matter may eventually limit aquatic ecosystem production and foster pond infilling. These results provide direct evidence of nutrient release from thawing permafrost and the utilization of these nutrients by Arctic trough pond ecosystems and highlight infilling as a mechanism by which Arctic surface waters may be lost

Journal of Geophysical Research: Biogeosciences↗

USGS2008

Mars Exploration Rover Navigation Camera in-flight calibration

The Navigation Camera (Navcam) instruments on the Mars Exploration Rover (MER) spacecraft provide support for both tactical operations as well as scientific observations where color information is not necessary: large-scale morphology, atmospheric monitoring including cloud observations and dust devil movies, and context imaging for both the thermal emission spectrometer and the in situ instruments on the Instrument Deployment Device. The Navcams are a panchromatic stereoscopic imaging system built using identical charge-coupled device (CCD) detectors and nearly identical electronics boards as the other cameras on the MER spacecraft. Previous calibration efforts were primarily focused on providing a detailed geometric calibration in line with the principal function of the Navcams, to provide data for the MER navigation team. This paper provides a detailed description of a new Navcam calibration pipeline developed to provide an absolute radiometric calibration that we estimate to have an absolute accuracy of 10% and a relative precision of 2.5%. Our calibration pipeline includes steps to model and remove the bias offset, the dark current charge that accumulates in both the active and readout regions of the CCD, and the shutter smear. It also corrects pixel-to-pixel responsivity variations using flat-field images, and converts from raw instrument-corrected digital number values per second to units of radiance (W m-2 nm-1 sr-1), or to radiance factor (I/F). We also describe here the initial results of two applications where radiance-calibrated Navcam data provide unique information for surface photometric and atmospheric aerosol studies. Copyright 2008 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗

USGS2015

Coupling geophysical investigation with hydrothermal modeling to constrain the enthalpy classification of a potential geothermal resource.

An appreciable challenge in volcanology and geothermal resource development is to understand the relationships between volcanic systems and low-enthalpy geothermal resources. The enthalpy of an undeveloped geothermal resource in the Karckar region of Armenia is investigated by coupling geophysical and hydrothermal modeling. The results of 3-dimensional inversion of gravity data provide key inputs into a hydrothermal circulation model of the system and associated hot springs, which is used to evaluate possible geothermal system configurations. Hydraulic and thermal properties are specified using maximum a priori estimates. Limited constraints provided by temperature data collected from an existing down-gradient borehole indicate that the geothermal system can most likely be classified as low-enthalpy and liquid dominated. We find the heat source for the system is likely cooling quartz monzonite intrusions in the shallow subsurface and that meteoric recharge in the pull-apart basin circulates to depth, rises along basin-bounding faults and discharges at the hot springs. While other combinations of subsurface properties and geothermal system configurations may fit the temperature distribution equally well, we demonstrate that the low-enthalpy system is reasonably explained based largely on interpretation of surface geophysical data and relatively simple models.

Karckar Region↗