2,639 research outputs found
Quantification and Change Assessment Benjamin Aubrey Robson 2016 Dissertation date: 31st October 2016 of Debris-Covered Glaciers using Remote Sensing
No full textThis thesis investigates how remote sensing data can be used to assess the changing state of debris-covered ice. The principal study areas are the Manaslu Region in Nepal (papers I and III) and the Hohe Tauern National Park, Austria (paper II). Clean glacier ice is straightforward to semi-automatically classify using multi-spectral satellite imagery owing to the strong spectral signature of clean ice in the visible and near-infrared sections of the electromagnetic spectrum. Since the ablation zones of clean ice glaciers are at the pressure melting point, a change in terminus position or glacier area can be directly linked to a change in climate. Debris-covered ice is however more complicated to map and to interpret temporal change. Supraglacial debris is spectrally indistinguishable from the surrounding paraglacial terrain, and requires auxiliary data such as a Digital Elevation Model (DEM), thermal band data, or flow data. Object-Based Image Analysis (OBIA) provides a framework for combining multiple datasets in one analysis, while additionally allowing shape, contextual, hierarchical and textural criteria to be used to classify imagery. Paper I combines optical (Landsat-8), topographic (void-filled SRTM) and SAR coherence (ALOS PALSAR) data within an OBIA workflow to semi-automatically classify both clean ice and debris-covered ice in the challenging area surrounding Mount Manaslu in Nepal. When compared with manually delineated outlines, the classification achieved an accuracy of 91% (93% for clean ice and 83% for debriscovered ice). The classification was affected by seasonal snow and shadows while the debris-covered ice mapping was influenced by the datasets being temporally inconsistent, and the mountainous topography causing inconsistencies in the SAR coherence data. The method compares well with other automated techniques for classifying debris-covered ice, but has two additional advantages: firstly, that SAR coherence data can distinguish active ice from stagnant ice based on whether motion or significant downwasting has occured, and secondly, that the method is applicable over a large study area using just space-borne data. Paper II explores the potential of using high-resolution (10 m) topographic data and an edge detection algorithm to morphologically map the extent of debris-covered ice. The method was applied in the Hohe Tauern National Park, Austria, using a 10 m DEM derived from airborne Light Detection and Radar (LiDAR) acquisitions. Additionally, the end-of-summer transient snowline (TSL) was also mapped, which approximates the annual Equilibrium Line Altitude (ELA). Our classification was applied on three Landsat satellite images from 1985, 2003 and 2013 and compared the results to the Austrian Glacier Inventories from 1969 and 1998 to derive decadal-scale glacial changes. A mean rate of glacier area reduction of 1.4 km2a-1 was calculated between 1969 and 2013 with a total reduction in area of 33%. The TSL rose by 92 m between 1985 and 2013 to an altitude of 3005 m. By comparing our results with manually delineated outlines an accuracy of 97.5% was determined. When a confusion matrix was calculated it could be seen that the results contained few false positives but some false negatives which were attributed to seasonal snow, shadows and misclassified debris. Our results correspond broadly with those found in other areas of the European Alps although a heterogeneity in glacier change is observable. We recommend that future glacier mapping investigations should utilise a combination of both SAR coherence data and high-resolution topographic data in order to delineate the extent of both active and stagnant glacier ice. Paper III investigates decadal scale changes in glacier area, velocity and volume in the previously undocumented Manaslu Region, Nepal. Between 2001 and 2013 the glacier area reduced by 8.2% (-0.68% a-1). Simultaneously, the glaciers lowered by -0.21 ± 0.08 m a-1 and had a slightly negative specific mass balance of -0.05 ± 016 m w.e a-1 although mass balances ranged -2.49 ± 2.24 to +0.27 ± 0.30 m w.e a-1 throughout the region. The geodetic mass balance for select glaciers covered by a Corona DEM between 1970 and 2013 was -0.24 ± 0.12 m w.e a-1 which became more negative (-0.51 ± 0.12 m w.e. a-1) between 2005 and 2013. Rates of surface lowering over debriscovered ice increasing by 168% between 1970 – 2000 (0.40 ± 0.18 m a-1) and 2005 – 2013 (1.07 ±0.48 m a-1). The rate of glacier melt varies due to presumed increases in debris thickness at the upper and lower boundaries of the ablation zone, while an area of enhanced glacier downwasting corresponds to the presence of supraglacial lakes and exposed ice. The glacier velocity varies across the region. Many glaciers have stagnant sections towards the glacier termini, and a trend of ongoing stagnation is observable. No relationship exists between trends in glacier area and glacier volume or velocity, although a weak relationship exists between trends in the changes of volume and velocity. The rates of glacier area and velocity change appear to be similar, although the number of glaciers that had records of area, velocity, and volume was few. Our results are comparable to studies looking at mean surface lowerings and geodetic mass balances in other areas of the Himalayas, and point towards heterogeneous yet pronounced mass losses across the Himalaya region
Organizational Factors and Office Workers’ Health After the World Trade Center Terrorist Attacks: Long-Term Physical Symptoms, Psychological Distress, and Work Productivity
No full textObjective: To assess if organizational factors are predictors of workers' health and productivity after the World Trade Center attacks.Methods: We conducted a survey of 750 workers and compared those who had direct exposures to the World Trade Center attacks (south of Canal Street workers; primary victims) with those less directly exposed (north of Canal Street workers; other victims and non-victims).Results: South of Canal Street workers reported headache more frequently than north of Canal Street workers did (P = 0.0202). Primary victims reported headache and cough more frequently than did other victims and non-victims (P = 0.0086 and 0.0043, respectively). Defensive organizational culture was an independent predictor of cough and job stress, and job stress was an independent predictor of on-the-job productivity losses.Conclusion: Organizational variables may modify health and productivity outcomes after a large-scale traumatic event in the workplace.This research was supported in part by the Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health (NIOSH) Grant 5 R21 OH007713-02, and the NIEHS sponsored UMDNJ Center for Environmental Exposures and Disease, Grant NIEHS P30ES005022.This is a non-final version of an article published in final form in Journal of Occupational and Environmental Medicine (50(2):112-25, 2008 Feb) a publication of Lippincott, Williams & Wilkins. The published article is available at http://journals.lww.com/joem/Fulltext/2008/02000/Organizational_Factors_and_Office_Workers__Health.4.asp
Holding Canada's Cities to Account: an Assessment of Municipal Fiscal Management
No full textCities are the most visible level of government for most Canadians, providing services such as waste collection, policing and transit. Yet their budgets are the most opaque of any level of government. Municipalities generally use accounting in their budgets that does not match what they use in their financial reports. Peering through the messy numbers reveals that most cities routinely miss budget targets by large amounts. Councillors and taxpayers who seek to hold these municipal governments to account face a daunting task. Amid the mixed record, however, are some municipalities with clearer numbers and better records for spending control. That fact, along with improvements that have occurred at the federal and provincial levels in recent years, shows that progress is possible. The authors suggest five basic reforms would create clearer, more consistent budgets and would bring the financial management of Canada’s municipalities into line with their fiscal impact and their importance in Canadians’ lives.Fiscal & Tax Competitiveness, Governance and Public Institutions, Urban Issues Series, Canadian municipalities, fiscal management, municipal budgets
The seasonal evolution of subglacial drainage pathways beneath a soft-bedded glacier
No full textSubglacial hydrology is a key element in glacier response to climate change, but investigations of this environment are logistically difficult. Most models are based on summer data from glaciers resting on rigid bedrocks. However a significant number of glaciers rest on soft (unconsolidated sedimentary) beds. Here we present a unique multi-year instrumented record of the development of seasonal subglacial behavior associated with an Icelandic temperate glacier resting on a deformable sediment layer. We observe a distinct annual pattern in the subglacial hydrology based on self-organizing anastomosing braided channels. Water is stored within the subglacial system itself (till, braided system and ‘ponds’), allowing the rapid access of water to enable glacier speed-up events to occur throughout the year, particularly in winter
Long‐term impact of the proglacial lake Jökulsárlón on the flow velocity and stability of Breiðamerkurjökull glacier, Iceland
No full textProglacial lakes are becoming ubiquitous at the termini of many glaciers worldwide due to continued climate warming and glacier retreat, and such lakes have important consequences for the dynamics and future stability of these glaciers. In light of this, we quantified decadal changes in glacier velocity since 1991 using satellite remote sensing for Breiðamerkurjökull, a large lake-terminating glacier in Iceland. We investigated its frontal retreat, lake area change and ice surface elevation change, combined with bed topography data, to understand its recent rapid retreat and future stability. We observed highly spatially variable velocity change from 1991 to 2015, with a substantial increase in peak velocity observed at the terminus of the lake-terminating eastern arm from ~1.00±0.36m day1 in 1991 to 3.50±0.25m day1 in 2015, with mean velocities remaining elevated from 2008 onwards. This is in stark comparison to the predominately land-terminating arms, which saw no discernible change in their velocity over the same period. We also observed a substantial increase in the area of the main proglacial lake (Jökulsárlón) since 1982 of ~20 km2, equating to an annual growth rate of 0.55km2 year1. Over the same period, the eastern arm retreated by ~3.50km, which is significantly greater than the other arms. Such discrepancies between the different arms are due to the growth and, importantly, depth increase of Jökulsárlón, as the eastern arm has retreated into its ~300m-deep reverse-sloping subglacial trough. We suggest that this growth in lake area, forced initially by rising air temperatures, combined with the increase in lake depth, triggered an increase in flow acceleration, leading to further rapid retreat and the initiation of a positive feedback mechanism. These findings may have important implications for how increased melt and calving forced by climate change will affect the future stability of large soft-bedded, reverse-sloped, subaqueous-terminating glaciers elsewhere
Assessing and Improving Bioterrorism Preparedness Among First Responders: A Pilot Study
No full textFollowing the September 11 terrorist attacks, the vulnerability of the United States became apparent. It also became evident that there was a need for respiratory protection. The purpose of this study was to determine the prior knowledge and perceptions of emergency medical technicians with respect to bioterrorism and to enhance their current knowledge to better prepare them for possible future events. The study was also designed to create a certified pool of trainers who would be capable of fit-testing all squad members with N-100 respirators. Representatives were recruited from each of the Hunterdon County, New Jersey, rescue squads. Participants attended a train-the-trainer session. Before the session and after, they were tested on knowledge and perceptions about relevant bioterrorism issues and were given an educational presentation on bioterrorism, threatening agents, respiratory health, and proper protection, along with being introduced to the fit-test steps for N-100 respirator masks. The response rate for the training was 94 percent. The authors measured and compared responses on the pre-test and the post-test with respect to knowledge, behaviors, and perceptions, and the results indicated a change following the training. The study thus provided evidence that the train-the-trainer program is an effective method of providing public health preparedness training to members of community organizations and agencies.Reprinted with permission from the Journal of Environmental Health, a publication of the National Environmental Health Association, www.neha.org.Supported by NIEHS Grants ES07148 and ES05022 and the Environmental and Occupational Health Sciences Institute.Peer reviewe
Erosional and depositional subglacial streamlining processes at Skálafellsjökull, Iceland: an analogue for a new bedform continuum model
No full textWe combine the use of the unique Glacsweb in situ embedded sensors, surface velocity measurements (from dGPS and remote sensing), and UAV and field photographic surveys, to understand the subglacial processes responsible for the formation of a series of subglacial bedforms composed of both till andbedrock. There is till deformation throughout the year, with spatial and temporal variations. We estimate the ice velocity associated with the formation of a range of subglacial bedforms (9.2–31 m a−1) and the erosion rate on the bedrock flutes (2.13 mm a−1). We show that there is simultaneous deposition and erosion (either at the base of till or directly by ice) which generates flutes, large flutes and drumlins (rather than just depositional processes required by the instability theory). The flutes form behind obstacles associated with mobile till. Where a stationary obstacle is below a threshold height (which at this site is 1.56 m), either till tails will form behind the obstacle or a large flute will develop. Where a stationary obstacle is above a threshold height, then drumlins may form. Using these results as an analogue for larger bedforms, we discuss the bedform continuum in relation to elongation ratio, height, glacier velocity and bed mobility.These bedforms form associated with an overall net erosional regime, and once bedforms are produced, they may become fixed due to the presence of stationary obstacles, and so the resultant bedforms result from the most recent, as well as legacy, processes as they evolve over time
Knowledge, Attitude, and Practice toward Clostridium Botulinum Outbreak in Home-Canned Bamboo Shoots at Pakaluang Subdistrict, Ban Luang District, Nan Province, Thailand
No full textThis study aims to assess the level of knowledge, attitude, and practice (KAP) toward Clostridium botulinum outbreak in home-canned bamboo shoots at Pakalung SubDistrict, Ban Luang District, Nan Province, Thailand. A cross-sectional approach was conducted to assess KAP using a structured questionnaire. A total of 280 people, randomly selected responded by face to face interview. The results indicated that the knowledge and attitude of the participants were moderate and neutral (57.9 % and 51.8 %, respectively). The prevalence of good practice level was 89.6 %. Furthermore, the knowledge was significantly associated with social-demographic characteristics (Chi-square, p<0.05) i.e. education level (p<0.001), occupation (p<0.029), monthly incomes (p<0.001). The attitude was associated with age group (p<0.001), education level (p<0.002), monthly incomes (p<0.001) and monthly incomes (p<0.001) are associated with practice level. The information gained would be utilized for health promotion and use of appropriate tools to increase more knowledge, and changing wrong beliefs concerning food habits and changing some people’s practices that might increase risk related to C. botulinum foodborne.Peer reviewed
The Fréchet Distance Unleashed: Approximating a Dog with a Frog
No full textWe show that a variant of the continuous Fréchet distance between polygonal curves can be computed using essentially the same algorithm used to solve the discrete version. The new variant is not necessarily monotone, but this shortcoming can be easily handled via refinement.
Combined with a Dijkstra/Prim type algorithm, this leads to a realization of the Fréchet distance (i.e., a morphing) that is locally optimal (aka locally correct), that is both easy to compute, and in practice, takes near linear time on many inputs. The new morphing has the property that the leash is always as short as possible. These matchings/morphings are more natural, and are better than the ones computed by standard algorithms - in particular, they handle noise more graciously. This should make the Fréchet distance more useful for real world applications.
We implemented the new algorithm, and various strategies to obtain fast practical performance. We performed extensive experiments with our new algorithm, and released publicly available (and easily installable and usable) Julia and Python packages. In particular, the Julia implementation, for computing the regular Fréchet distance, seems to be {significantly faster} than other currently available implementations. See Table 2.2. Our algorithms can be used to compute the almost-exact Fréchet distance between polygonal curves.
Implementations and numerous examples are available here: https://frechet.xyz
Increased winter warm events in Iceland drive enhanced glacier velocity and melting
No full textA key element in the comprehension of the response of glaciers to climate change is an understanding of the bed conditions, and these are a vital component of ice sheet models. The West Antarctic ice streams are potentially highly unstable, with implications for rapid sea level rise. These are underlain by unconsolidated sediments (soft-bed), which have a distinct but rarely studied subglacial hydrology. We present a detailed data set from Skálafellsjökull, a soft-bedded glacier in Iceland, as an analogue for other soft-bedded glaciers. These data include wireless in situ till water pressure, meteorological, surface melt, discharge and glacier surface velocity from GPS as well as remote sensing imagery. We show how short-term warm events during winter can effect annual velocity, and how the number of warm events has increased over the last 10 years. We argue this was because water was stored in a soft-bed subglacial reservoir where it could be rapidly released during winter, with the resultant storage levels effecting the following summer dynamics. To test whether warm winter events are unique to Iceland, we analyzed the daily air temperatures record of 18 World Glacier Monitoring Service ‘reference’ glaciers (1979-2018). We were able to show that periods of warm temperatures during winter were present in maritime locations, and the number of these events had increased in locations where winter temperatures had also increased. We propose that winter events are an important component of glacier retreat and sea level rise that have hitherto not been examined in detail
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