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Murray Williams

Publications and source records attributed to Murray Williams.

10 recordsLinked to original sources
USGS2013

Remote sensing of soil moisture using airborne hyperspectral data

Landscape assessment of soil moisture is critical to understanding the hydrological cycle at the regional scale and in broad-scale studies of biophysical processes affected by global climate changes in temperature and precipitation. Traditional efforts to measure soil moisture have been principally restricted to in situ measurements, so remote sensing techniques are often employed. Hyperspectral sensors with finer spatial resolution and narrow band widths may offer an alternative to traditional multispectral analysis of soil moisture, particularly in landscapes with high spatial heterogeneity. This preliminary research evaluates the ability of remotely sensed hyperspectral data to quantify soil moisture for the Little River Experimental Watershed (LREW), Georgia. An airborne hyperspectral instrument with a short-wavelength infrared (SWIR) sensor was flown in 2005 and 2007 and the results were correlated to in situ soil moisture values. A significant statistical correlation ( R 2 value above 0.7 for both sampling dates) for the hyperspectral instrument data and the soil moisture probe data at 5.08 cm (2 inches) was determined. While models for the 20.32 cm (8 inches) and 30.48 cm (12 inches) depths were tested, they were not able to estimate soil moisture to the same degree.

GIScience and Remote Sensing↗
USGS2012

An assessment of the carbon balance of arctic tundra: comparisons among observations, process models, and atmospheric inversions

Although arctic tundra has been estimated to cover only 8% of the global land surface, the large and potentially labile carbon pools currently stored in tundra soils have the potential for large emissions of carbon (C) under a warming climate. These emissions as radiatively active greenhouse gases in the form of both CO 2 and CH 4 could amplify global warming. Given the potential sensitivity of these ecosystems to climate change and the expectation that the Arctic will experience appreciable warming over the next century, it is important to assess whether responses of C exchange in tundra regions are likely to enhance or mitigate warming. In this study we compared analyses of C exchange of Arctic tundra between 1990–1999 and 2000–2006 among observations, regional and global applications of process-based terrestrial biosphere models, and atmospheric inversion models. Syntheses of the compilation of flux observations and of inversion model results indicate that the annual exchange of CO 2 between arctic tundra and the atmosphere has large uncertainties that cannot be distinguished from neutral balance. The mean estimate from an ensemble of process-based model simulations suggests that arctic tundra acted as a sink for atmospheric CO 2 in recent decades, but based on the uncertainty estimates it cannot be determined with confidence whether these ecosystems represent a weak or a strong sink. Tundra was 0.6 °C warmer in the 2000s compared to the 1990s. The central estimates of the observations, process-based models, and inversion models each identify stronger sinks in the 2000s compared with the 1990s. Similarly, the observations and the applications of regional process-based models suggest that CH 4 emissions from arctic tundra have increased from the 1990s to 2000s. Based on our analyses of the estimates from observations, process-based models, and inversion models, we estimate that arctic tundra was a sink for atmospheric CO 2 of 110 Tg C yr -1 (uncertainty between a sink of 291 Tg C yr -1 and a source of 80 Tg C yr -1 ) and a source of CH 4 to the atmosphere of 19 Tg C yr -1 (uncertainty between sources of 8 and 29 Tg C yr -1 ). The suite of analyses conducted in this study indicate that it is clearly important to reduce uncertainties in the observations, process-based models, and inversions in order to better understand the degree to which Arctic tundra is influencing atmospheric CO 2 and CH 4 concentrations. The reduction of uncertainties can be accomplished through (1) the strategic placement of more CO 2 and CH 4 monitoring stations to reduce uncertainties in inversions, (2) improved observation networks of ground-based measurements of CO 2 and CH 4 exchange to understand exchange in response to disturbance and across gradients of hydrological variability, and (3) the effective transfer of information from enhanced observation networks into process-based models to improve the simulation of CO 2 and CH 4 exchange from arctic tundra to the atmosphere.

Biogeosciences↗
USGS2011

Are there pre-Quaternary geological analogues for a future greenhouse warming?

Given the inherent uncertainties in predicting how climate and environments will respond to anthropogenic emissions of greenhouse gases, it would be beneficial to society if science could identify geological analogues to the human race’s current grand climate experiment . This has been a focus of the geological and palaeoclimate communities over the last 30 years, with many scientific papers claiming that intervals in Earth history can be used as an analogue for future climate change. Using a coupled ocean–atmosphere modelling approach, we test this assertion for the most probable pre-Quaternary candidates of the last 100 million years: the Mid- and Late Cretaceous, the Palaeocene–Eocene Thermal Maximum (PETM), the Early Eocene, as well as warm intervals within the Miocene and Pliocene epochs. These intervals fail as true direct analogues since they either represent equilibrium climate states to a long-term CO 2 forcing—whereas anthropogenic emissions of greenhouse gases provide a progressive (transient) forcing on climate—or the sensitivity of the climate system itself to CO 2 was different. While no close geological analogue exists, past warm intervals in Earth history provide a unique opportunity to investigate processes that operated during warm (high CO 2 ) climate states. Palaeoclimate and environmental reconstruction/modelling are facilitating the assessment and calculation of the response of global temperatures to increasing CO 2 concentrations in the longer term (multiple centuries); this is now referred to as the Earth System Sensitivity, which is critical in identifying CO 2 thresholds in the atmosphere that must not be crossed to avoid dangerous levels of climate change in the long term. Palaeoclimatology also provides a unique and independent way to evaluate the qualities of climate and Earth system models used to predict future climate.

Philosophical Transactions of the Royal Society A:↗
USGS2010

Glaciers of Asia

This chapter is the ninth to be released in U.S. Geological Survey Professional Paper 1386, Satellite Image Atlas of Glaciers of the World, a series of 11 chapters. In each of the geographic area chapters, remotely sensed images, primarily from the Landsat 1, 2, and 3 series of spacecraft, are used to analyze the specific glacierized region of our planet under consideration and to monitor glacier changes. Landsat images, acquired primarily during the middle to late 1970s and early 1980s, were used by an international team of glaciologists and other scientists to study various geographic regions and (or) to discuss related glaciological topics. In each glacierized geographic region, the present areal distribution of glaciers is compared, wherever possible, with historical information about their past extent. The atlas provides an accurate regional inventory of the areal extent of glacier ice on our planet during the 1970s as part of a growing international scientific effort to measure global environmental change on the Earth’s surface. The chapter is divided into seven geographic parts and one topical part: Glaciers of the Former Soviet Union (F–1), Glaciers of China (F–2), Glaciers of Afghanistan (F–3), Glaciers of Pakistan (F–4), Glaciers of India (F–5), Glaciers of Nepal (F–6), Glaciers of Bhutan (F–7), and the Paleoenvironmental Record Preserved in Middle-Latitude, High-Mountain Glaciers (F–8). Each geographic section describes the glacier extent during the 1970s and 1980s, the benchmark time period (1972–1981) of this volume, but has been updated to include more recent information. Glaciers of the Former Soviet Union are located in the Russian Arctic and various mountain ranges of Russia and the Republics of Georgia, Kyrgyzstan, Tajikistan, and Kazakstun. The Glacier Inventory of the USSR and the World Atlas of Ice and Snow Resources recorded a total of 28,881 glaciers covering an area of 78,938 square kilometers (km 2 ). China includes many of the mountain-glacier systems of the world including the Himalaya, Karakorum, Tien Shan and Altay mountain ranges. The glaciers are widely scattered and cover an area of about 59,425 km 2 . The mountain glaciers may be classified as maritime, subcontinental or extreme continental. In Afghanistan, more than 3,000 small glaciers occur in the Hindu Kush and Pamir mountains. Most glaciers occur on north-facing slopes shaded by mountain peaks and on east and southeast slopes that are shaded by monsoon clouds. The glaciers provide vital water resources to the region and cover an area of about 2,700 km 2 . Glaciers of northern Pakistan are some of the largest and longest mid-latitude glaciers on Earth. They are located in the Hindu Kush, Himalaya, and Karakoram mountains and cover an area of about 15,000 km 2 . Glaciers here are important for their role in providing water resources and their hazard potential. The glaciers in India are located in the Himalaya and cover about 8,500 km 2 . The Himalaya contains one of the largest reservoirs of snow and ice outside the polar regions. The glaciers are a major source of fresh water and supply meltwater to all the rivers in northern India, thereby affecting the quality of life of millions of people. In Nepal, the glaciers are located in the Himalaya as individual glaciers; the glacierized area covers about 5,324 km 2 . The region is the highest mountainous region on Earth and includes the Mt. Everest region. Glaciers in the Bhutan Himalaya have a total area of about 1,317 km 2 . Many recent glacier studies are focused on glacier lakes that have the potential of generating dangerous glacier lake outburst floods. Research on the glaciers of the middle-latitude, high-mountain glaciers of Asia has also focused on the information contained in the ice cores from the glaciers. This information helps in the reconstruction of paleoclimatic records, and the computer modeling of global climate change.

Professional Paper↗
USGS2008

Investigation of bioaerosols released from swine farms using conventional and alternative waste treatment and management technologies

Microbial air pollution from concentrated animal feeding operations (CAFOs) has raised concerns about potential public health and environmental impacts. We investigated the levels of bioaerosols released from two swine farms using conventional lagoon-sprayfield technology and ten farms using alternative waste treatment and management technologies in the United States. In total, 424 microbial air samples taken at the 12 CAFOs were analyzed for several indicator and pathogenic microorganisms, including culturable bacteria and fungi, fecal coliform, Escherichia coli, Clostridium perfringens, bacteriophage, and Salmonella. At all of the investigated farms, bacterial concentrations at the downwind boundary were higher than those at the upwind boundary, suggesting that the farms are sources of microbial air contamination. In addition, fecal indicator microorganisms were found more frequently near barns and treatment technology sites than upwind or downwind of the farms. Approximately 4.5% (19/424), 1.2% (5/424), 22.2% (94/424), and 12.3% (53/424) of samples were positive for fecal coliform, E. coli, Clostridium, and total coliphage, respectively. Based on statistical comparison of airborne fecal indicator concentrations at alternative treatment technology farms compared to control farms with conventional technology, three alternative waste treatment technologies appear to perform better at reducing the airborne release of fecal indicator microorganisms during on-farm treatment and management processes. These results demonstrate that airborne microbial contaminants are released from swine farms and pose possible exposure risks to farm workers and nearby neighbors. However, the release of airborne microorganisms appears to decrease significantly through the use of certain alternative waste management and treatment technologies. ?? 2008 American Chemical Society.

Environmental Science & Technology↗
USGS2002

Application of XTOP_PRMS model in Green Lakes Valley, Colorado front range: Runoff simulation and flowpath identification

Stream runoff was simulated from 1996 to 2000 using XTOP_PRMS (coupling of TOPMODEL and Precipitation Runoff Modeling System) model under Modular Modeling System at Martinelli and Green Lake 4 catchments in Green Lakes Valley, Colorado Front Range. Two flowpaths determined by XTOP_PRMS model, surface flow (infiltration-excess overland flow) and subsurface flow, were compared against the flowpaths determined by mixing model using isotopic and chemical tracers. Three tracers (DOC, K/Si, and ??18O) were used in mixing model to identify four flowpaths, i.e., overland, upper soil horizon, lower soil horizon, and base flow. The results showed that the runoff simulation using XTOP_PRMS model is reasonably successful for Martinelli catchment (8 ha in drainage area). The Nash-Sutcliffe efficiency is 0.76. The t-test of two means for paired sample showed that the difference between the observed and modeled runoff was not significantly different at ??=0.05 at Martinelli catchment (n = 1611, p = 0.6). The flowpaths identified by XTOP_PRMS model matched the flowpaths determined by the tracer-mixing model reasonably well in magnitude, but poorly in pattern. The surface flow primarily occurred in the beginning of snowmelt at Martinelli as illustrated by the tracer-mixing model. Both runoff simulation and flowpath identification using XTOP_PRMS model were relatively poor at Green Lake 4 catchment, which has a drainage area of 220 ha. The runoff peaks observed in May and June were not captured in runoff simulation. The problem may be caused by poor understanding of behaviors of flowpath parameters and insensitivity of snowmelt to daily mean air temperature.

Conference Paper↗
USGS1998

Satellite tracking of threatened species

In 1990, a joint effort of two U.S. federal agencies, NASA Goddard Space Flight Center (GSFC) and the Patuxent Wildlife Research Center, began. We initially joined forces in a project that used satellite telemetry to discover the winter home of a tiny dwindling population of Siberian Cranes. Since then several projects have emerged, and a web site was created to follow some of these activities. This web site is called the Satellite Tracking of Threatened Species and its location is http://sdcd.gsfc.nasa.gov/ISTO/satellite_tracking. It describes the overall program, and links you to three subsections that describe the projects in more detail: Satellite Direct Readout, Birdtracks, and Birdworld.

Argos Newsletter↗
USGS1991

Survival and band recovery rates of sympatric grey ducks and mallards in New Zealand

We used band recovery data from grey ducks ( Anas superciliosa ) and mallards. ( A. platyrhynchos ) banded sympatrically during 1957-74 to estimate annual survival and recovery rates. Young birds tended to have higher recovery rates and lower survival rates than adults for both species. Both species showed strong evidence of year-to-year variation in annual survival rates. Survival rates of male mallards were higher than those in females, as is typical for this species in North America, but there was no evidence of sex-specific survival differences in grey ducks. Recovery rate estimates for grey ducks were high and were significantly higher than those for mallards. However, survival rates did not differ significantly between the 2 species within any age-sex class. The similar survival rates, when mallard populations were increasing and grey ducks were decreasing, suggest that mallard reproductive rates have been greater than those of grey ducks.

Journal of Wildlife Management↗
USGS1990

Survival and band recovery rates of mallards in New Zealand

Mallards ( Anas platyrhynchos ) were banded at 4 discrete study areas in New Zealand. We used hunting season recoveries in conjunction with band recovery models to estimate annual survival and recovery rates and to test hypotheses about sources of variation in these rates. Recovery rates varied among the 4 areas and from year to year within areas. Recovery rates were generally higher for young mallards than for adults, and recovery rates of males were higher than those of females. Survival rates varied among the 4 areas and from year to year within some areas. Survival rates of females were lower than those of males, but survival rates of young birds were not consistently lower than those of adults. Average survival rates over all 4 areas were generally lower than averages for North American mallards.

Journal of Wildlife Management↗