17 research outputs found
Western Alaska Lake Database
No full textThis vector data layer covers 6 major lake districts (Baldwin Peninsula, Kobuk Delta, Selawik Lowland, Northern Seward Peninsula, Central Seward Peninsula, and Yukon-Kuskokwim Delta) in the northern and central sub-regions of the Western Alaska Landscape Conservation Cooperative (WALCC) region and consists of polygons of lakes with areas equal or greater than 1.0 ha. More than 58000 Lakes were mapped from Landsat TM and ETM+ imagery acquired between 1972 and 1975, 2002 and 2009, and 2013 and 2014 using Object-Based Image Analysis (OBIA) techniques with an classification accuracy of 96%. The spatial image resolution of Landsat TM and ETM+ is 30 m. Permafrost characteristics and surficial geology associated with lake polygons were determined from the Alaska permafrost map (Jorgenson et al. 2008)
Remote sensing of lake dynamics in Alaska
No full textDissertation (Ph.D.) University of Alaska Fairbanks, 2016Lakes are abundant in high northern latitude permafrost regions. They are important ecosystem components forming a complex and dynamic landscape with repeated cycles of lake formation and drainage affecting regional hydrological and terrestrial characteristics, biogeochemical processes and carbon cycling, wildlife habitats, and human communities living in the permafrost region. Remote sensing is a useful tool to map the spatial distribution of lakes and assess its change, understand lake dynamics, and to extract useful information to study their associated feedbacks in a changing climate. In this dissertation, I focused on remote sensing studies associated with (1) methane ebullition from a thermokarst lake, (2) post-drainage succession patterns in drained thermokarst lake basins, and (3) lake change dynamics. I developed a semi-automatic classification method based on an Object-based Image Analysis (OBIA) framework to detect methane ebullition bubbles trapped in a snow-free ice-covered lake using high-resolution airborne images of Goldstream lake, Fairbanks, Alaska acquired following freeze up in October of 2011 and 2012. This study showed that remote sensing is a valuable tool to map ebullition bubbles (bubble patches) on the entire lake surface with an accuracy of > 95%, a task that is difficult to achieve through field-based survey alone. The image analysis performed by combining the mapping results from the OBIA and field-based observations showed a relationship between bubble patch brightness and ground-measured methane flux, which was then used to estimate the whole-lake methane flux. A strong inverse exponential relationship (R2 >= 0.79) was found between the percent of the surface area of lake ice covered with bubble patches and distance from the active thermokarst lake margin, indicating high methane production as a response to thermokarst activity that released labile organic-rich carbon along the eroding lake margin. Despite the influence of atmospheric pressure conditions on distribution of ebullition bubble patches following the lake freeze-up events, the spatiotemporal regularity of bubble patches revealed that a larger number of seeps are stable over at least annual timescales. This remote sensing technique is applicable to other regions for mapping ebullition bubbles trapped in snow-free ice-covered lakes, identifying their relative flux, and assessing their spatiotemporal dynamics. By using TerraSAR-X (TSX) Synthetic Aperture Radar (SAR) backscatter data and the Normalized Difference Vegetation Index (NDVI) derived from a Landsat-5 image from the year 2009, I characterized drained thermokarst lake basins (DTLBs) of various age ranging between 0 to 10,000 years since drainage in the northern Seward Peninsula, Alaska. In the study I found logarithmic relationships of basin age from 0 to 10,000 years with mean basin TSX backscatter (R2 = 0.36) and with mean basin NDVI (R2 = 0.53). However, TSX data performed much better to discriminate older basins in the age class 50–10,000 years with R2 = 0.58, while no significant relationship was found between NDVI and basin age. Results of this study demonstrated the potential application of X-band SAR data in combination with NDVI data to enhance differentiation of soil moisture and vegetation status on drained basins for mapping long-term succession dynamics of DTLBs. Finally, I demonstrated the utility of Landsat imagery to identify lake distribution patterns and changes between 1972 and 2014 in six major lake-rich study regions across various permafrost zones covering an area of 68,830 km2 in western Alaska. Even though lake area change was found to be positive (increase by less than 4%) in some study areas while negative (decrease by 4-15%) in others, there was a widespread drainage of mainly large lakes in all regions creating remnant ponds that increased the abundance of lakes <10 ha in all study regions by 2-27%. The average lake area decline observed in various permafrost zones did not represent the trend of individual sites due to spatial heterogeneity in lake characteristics. While lake drainage dominated the non-continuous permafrost zones, areas of continuous permafrost showed both trends of negative and positive lake area change accompanied by major lake drainage events that led to a regional lake area loss in the continuous permafrost zone. This remote sensing technique proved to be useful in identifying ongoing lake drainage and expansion events within study regions and a regional shift in lake distribution (i.e. lake area loss) that is happening in western Alaska. Based upon my research, there is an immense opportunity to use and combine various remote sensing tools to study lake dynamics and to evaluate associated environmental changes. Future work should be directed towards collaborative research for combining field-based observations and remote sensing tools to improve the understanding of how lakes and drained lake basins change in a changing climate as well as extend the scale of observations of methane ebullition features by covering many lakes in an environmentally diverse set of regions. This will guide us to understanding the feedback of lake dynamics to the surrounding ecosystem, global carbon budget, and to upscale the response of lakes to changing climate and permafrost environments to larger regions.Chapter 1. Introduction -- Chapter 2. An object-based classification method to detect methane ebullition bubbles in early winter lake ice -- Chapter 3. Detection and spatiotemporal analysis of methane ebullition on thermokarst lake ice using high-resolution optical aerial imagery -- Chapter 4. Characterizing post-drainage succession in thermokarst lake basins on the Seward Peninsula, Alaska with TerraSAR-X backscatter and Landsat-based NDVI data -- Chapter 5. Landsat-based lake distribution and changes in western Alaska between 1972 and 2014 -- Chapter 6. Summary
Landsat-based lake distribution and changes in western Alaska permafrost regions between the 1970s and 2010s
No full textLakes are an important ecosystem component and geomorphological agent in northern high latitudes and it is important to understand how lake initiation, expansion and drainage may change as high latitudes continue to warm. In this study, we utilized Landsat Multispectral Scanner System (MSS) images from the 1970s (1972, 1974, and 1975) and Operational Land Imager (OLI) images from the 2010s (2013, 2014, and 2015) to assess broad-scale distribution and changes of lakes larger than 1 ha across the four permafrost zones (continuous, discontinuous, sporadic, and isolated extent) in western Alaska. Across our ca 70,000 km2study area, we saw a decline in overall lake coverage across all permafrost zones with the exception of the sporadic permafrost zone. In the continuous permafrost zone lake area declined by -6.7 % (-65.3 km2), in the discontinuous permafrost zone by -1.6 % (-55.0 km2), in the isolated permafrost zone by -6.9 % (-31.5 km2) while lake cover increased by 2.7 % (117.2 km2) in the sporadic permafrost zone. Overall, we observed a net drainage of lakes larger than 10 ha in the study region. Partial drainage of these medium to large lakes created an increase in the area covered by small water bodies <10 ha, in the form of remnant lakes and ponds by 7.1 % (12.6 km2) in continuous permafrost, 2.5 % (15.5 km2) in discontinuous permafrost, 14.4 % (74.6 km2) in sporadic permafrost, and 10.4 % (17.2 km2) in isolated permafrost. In general, our observations indicate that lake expansion and drainage in western Alaska are occurring in parallel. As the climate continues to warm and permafrost continues to thaw, we expect an increase in the number of drainage events in this region leading to the formation of higher numbers of small remnant lakes
A bibliometric study of publications by Indian ophthalmologists and vision researchers, 2001-06
No full textObjective: The objective was to conduct a bibliometric analysis of Indian ophthalmic papers published from 2001 to 2006 in the peer-reviewed journals, to assess productivity, trends in journal choice, publication types, research funding, and collaborative research. Materials and Methods: We searched PubMed for articles indicating both vision-related content and author affiliation with an Indian research center. We identified research collaborations and funding from indexing for research support, and classified articles as reporting basic science, clinical science, or clinically descriptive research. Impact factors were determined from Journal Citation Reports for 2006. Results: The total number of published articles that were retrieved for the years 2001 to 2006 was 2163. During the six-year period studied, the annual output of research articles has nearly doubled, from 284 in 2001 to 460 in 2006. Two-thirds of these were published in international journals; 41% in vision-related journals with 2006 impact factors; and 3% in impact factor journals which were not vision-related. Fifty percent of the publications came from nine major eye hospitals. Clinical science articles were most frequently published whereas basic science the least. Publications resulting from international collaborations increased from 3% in 2001 to 8% in 2006. The focus of the journal with the highest number of publications corresponds to the most common cause of bilateral blindness in India, cataract. Conclusion: This bibliometric study of publications of research from India in the field of ophthalmic and vision research shows that research productivity, as measured in both the number of publications in peer-reviewed journals and qualitative measures of those journals, has increased during the period of this study
Detection and spatiotemporal analysis of methane ebullition on thermokarst lake ice using high-resolution optical aerial imagery
No full textThermokarst lakes are important emitters of methane, a potent greenhouse gas. However, accurate estimation of methane flux from thermokarst lakes is difficult due to their remoteness and observational challenges associated with the heterogeneous nature of ebullition. We used high-resolution (9–11 cm) snow-free aerial images of an interior Alaskan thermokarst lake acquired 2 and 4 days following freeze-up in 2011 and 2012, respectively, to detect and characterize methane ebullition seeps and to estimate whole-lake ebullition. Bubbles impeded by the lake ice sheet form distinct white patches as a function of bubbling when lake ice grows downward and around them, trapping the gas in the ice. Our aerial imagery thus captured a snapshot of bubbles trapped in lake ice during the ebullition events that occurred before the image acquisition. Image analysis showed that low-flux A- and B-type seeps are associated with low brightness patches and are statistically distinct from high-flux C-type and hotspot seeps associated with high brightness patches. Mean whole-lake ebullition based on optical image analysis in combination with bubble-trap flux measurements was estimated to be 174 ± 28 and 216 ± 33 mL gas m−2 d−1 for the years 2011 and 2012, respectively. A large number of seeps demonstrated spatiotemporal stability over our 2-year study period. A strong inverse exponential relationship (R2 > = 0.79) was found between the percent of the surface area of lake ice covered with bubble patches and distance from the active thermokarst lake margin. Even though the narrow timing of optical image acquisition is a critical factor, with respect to both atmospheric pressure changes and snow/no-snow conditions during early lake freeze-up, our study shows that optical remote sensing is a powerful tool to map ebullition seeps on lake ice, to identify their relative strength of ebullition, and to assess their spatiotemporal variability
Remote sensing observations of lake change in Bering Land Bridge National Preserve, Northern Seward Peninsula, from 1949-2015
No full text
