A survival guide to Landsat preprocessing Young, Nicholas E.; Anderson, Ryan S.; Chignell, Stephen M. ...
Ecology,
April 2017, Letnik:
98, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Landsat data are increasingly used for ecological monitoring and research. These data often require preprocessing prior to analysis to account for sensor, solar, atmospheric, and topographic effects. ...However, ecologists using these data are faced with a literature containing inconsistent terminology, outdated methods, and a vast number of approaches with contradictory recommendations. These issues can, at best, make determining the correct preprocessing workflow a difficult and time-consuming task and, at worst, lead to erroneous results. We address these problems by providing a concise overview of the Landsat missions and sensors and by clarifying frequently conflated terms and methods. Preprocessing steps commonly applied to Landsat data are differentiated and explained, including georeferencing and co-registration, conversion to radiance, solar correction, atmospheric correction, topographic correction, and relative correction. We then synthesize this information by presenting workflows and a decision tree for determining the appropriate level of imagery preprocessing given an ecological research question, while emphasizing the need to tailor each workflow to the study site and question at hand. We recommend a parsimonious approach to Landsat preprocessing that avoids unnecessary steps and recommend approaches and data products that are well tested, easily available, and sufficiently documented. Our focus is specific to ecological applications of Landsat data, yet many of the concepts and recommendations discussed are also appropriate for other disciplines and remote sensing platforms.
Demand for traditional medicine ingredients is causing species declines globally. Due to this trade, Himalayan caterpillar fungus (Ophiocordyceps sinensis) has become one of the world’s most valuable ...biological commodities, providing a crucial source of income for hundreds of thousands of collectors. However, the resulting harvesting boom has generated widespread concern over the sustainability of its collection. We investigate whether caterpillar fungus production is decreasing—and if so, why—across its entire range. To overcome the limitations of sparse quantitative data, we use a multiple evidence base approach that makes use of complementarities between local knowledge and ecological modeling. We find that, according to collectors across four countries, caterpillar fungus production has decreased due to habitat degradation, climate change, and especially overexploitation. Our statistical models corroborate that climate change is contributing to this decline. They indicate that caterpillar fungus is more productive under colder conditions, growing in close proximity to areas likely to have permafrost. With significant warming already underway throughout much of its range, we conclude that caterpillar fungus populations have been negatively affected by a combination of overexploitation and climate change. Our results underscore that harvesting is not the sole threat to economically valuable species, and that a collapse of the caterpillar fungus system under ongoing warming and high collection pressure would have serious implications throughout the Himalayan region.
Critical physical geography (CPG) calls for integrative research on material landscapes and the socio‐political dynamics of scientific knowledge production. Network analysis, a rich tradition of ...tools and approaches for analyzing relational information, has seen little use in the CPG literature to date. This represents a fruitful opportunity, as many of CPG's core interests—knowledge politics, histories of scientific concepts, and ecosocial relations—can be effectively analyzed using network techniques. In this article, I argue for adapting network approaches to CPG. First, I provide an overview of various network concepts, approaches, and their origins. I then discuss bibliometric network techniques for “science mapping” including co‐word, co‐authorship, and citation analyses. Next, I describe discourse network analysis, a recent mixed‐method approach from political science. Finally, I discuss overlaps with emerging approaches from qualitative and visual network analysis. In each section, I provide existing and hypothetical examples, as well as software and visualization techniques, that demonstrate how network approaches could add new insights to CPG and related scholarship. Linking CPG with the diverse traditions of network analysis has the potential to produce new empirical understandings and bring the field into conversation with a growing body of research that spans the social sciences, natural sciences, and humanities.
Key Messages
Methods and concepts from network analysis can provide valuable empirics and novel insights for critical physical geography and related fields.
Network approaches can help to bridge human‐physical and qualitative‐quantitative divides in geographical research.
Critical physical geographers and network scholars have much to gain from collaboration.
Un lien manquant? L'analyse de réseau comme approche empirique à utiliser pour la géographie physique critique
La géographie physique critique revendique une approche de recherche intégrée traitant des paysages matériels et des dynamiques sociopolitiques de production de connaissances scientifiques. L'analyse de réseau, une riche tradition d'outils et d'approches pour l'analyse de l'information relationnelle, a été peu utilisée pour les études dans ce domaine, jusqu'à présent. Il s'agit pourtant d'une opportunité prometteuse, car de nombreux éléments fondamentaux de la géographie physique critique, comme l'histoire des concepts scientifiques, peuvent être analysés efficacement à l'aide des techniques de réseau. Dans cet article, nous plaidons en faveur de l'adaptation des approches de réseau à la géographie physique critique. Tout d'abord, nous présentons un aperçu des différents concepts et approches de réseau et de leurs origines. Nous abordons ensuite les techniques de réseaux bibliométriques pour la « cartographie scientifique ». Ensuite, nous décrivons l'analyse des réseaux de discours, une approche récente à méthodes mixtes issue des sciences politiques. Finalement, nous discutons des chevauchements avec les approches émergentes de l'analyse qualitative et visuelle des réseaux. Dans chaque section, des exemples existants et hypothétiques sont présentés, ainsi que des logiciels et des techniques de visualisation. L'établissement d'un lien entre ce domaine et les diverses traditions de l'analyse des réseaux pourrait permettre de produire de nouvelles données empiriques et de les croiser avec un grand nombre de recherches en sciences humaines ou naturelles.
As in many parts of the world, the management of environmental science research in Antarctica relies on cost-benefit analysis of negative environmental impact versus positive scientific gain. Several ...studies have examined the environmental impact of Antarctic field camps, but very little work looks at how the placement of these camps influences scientific research. In this study, we integrate bibliometrics, geospatial analysis, and historical research to understand the relationship between field camp placement and scientific production in the McMurdo Dry Valleys of East Antarctica. Our analysis of the scientific corpus from 1907-2016 shows that, on average, research sites have become less dispersed and closer to field camps over time. Scientific output does not necessarily correspond to the number of field camps, and constructing a field camp does not always lead to a subsequent increase in research in the local area. Our results underscore the need to consider the complex historical and spatial relationships between field camps and research sites in environmental management decision-making in Antarctica and other protected areas.
Natural and social scientists everywhere are struggling to understand how to proceed in the face of continued biodiversity loss and the injustices brought upon people living in and around ...conservation landscapes. This has resulted in increasing calls for critical reflection on the narratives driving conservation research and practice.
Narratives can be understood as part of a larger process of “framing” within an intellectual community, which includes the way studies are defined and discussed. Identifying, reflecting on and even destabilizing entrenched frames can be helpful for understanding when and where our diagnosis or understanding of a problem fails. However, we also need to understand the scholarly processes that create and reify some frames (and not others) over time.
We address these needs by developing a mixed‐method approach that integrates qualitative frame analysis and quantitative science mapping to identify the origins of the dominant frame and trace its reproduction in the scientific literature over time.
We demonstrate this approach using the case of the Bale Mountains, an internationally recognised centre of species endemism in Ethiopia. Our results show the enduring influence of the perceptions and values of a few early conservation scientists working with limited data. This led to erroneous assumptions and conclusions that, in some cases, were corrected by later research, but in many cases were not. This was a function of the social and intellectual structure of the scientific network, minor but consequential decisions in data interpretation and specific citational habits.
Synthesizing these results, we identify several linked mechanisms that helped the dominant frame retain its tenacity and may also be at work in other contexts. We close with a discussion on how others might apply our approach and how future scientific research and conservation practice could proceed differently.
Read the free Plain Language Summary for this article on the Journal blog.
Read the free Plain Language Summary for this article on the Journal blog.
Maximum flood extent-a key data need for disaster response and mitigation-is rarely quantified due to storm-related cloud cover and the low temporal resolution of optical sensors. While change ...detection approaches can circumvent these issues through the identification of inundated land and soil from post-flood imagery, their accuracy can suffer in the narrow and complex channels of increasingly developed and heterogeneous floodplains. This study explored the utility of the Operational Land Imager (OLI) and Independent Component Analysis (ICA) for addressing these challenges in the unprecedented 2013 Flood along the Colorado Front Range, USA. Pre- and post-flood images were composited and transformed with an ICA to identify change classes. Flooded pixels were extracted using image segmentation, and the resulting flood layer was refined with cloud and irrigated agricultural masks derived from the ICA. Visual assessment against aerial orthophotography showed close agreement with high water marks and scoured riverbanks, and a pixel-to-pixel validation with WorldView-2 imagery captured near peak flow yielded an overall accuracy of 87% and Kappa of 0.73. Additional tests showed a twofold increase in flood class accuracy over the commonly used modified normalized water index. The approach was able to simultaneously distinguish flood-related water and soil moisture from pre-existing water bodies and other spectrally similar classes within the narrow and braided channels of the study site. This was accomplished without the use of post-processing smoothing operations, enabling the important preservation of nuanced inundation patterns. Although flooding beneath moderate and sparse riparian vegetation canopy was captured, dense vegetation cover and paved regions of the floodplain were main sources of omission error, and commission errors occurred primarily in pixels of mixed land use and along the flood edge. Nevertheless, the unsupervised nature of ICA, in conjunction with the global availability of Landsat imagery, offers a straightforward, robust, and flexible approach to flood mapping that requires no ancillary data for rapid implementation. Finally, the spatial layer of flood extent and a summary of impacts were provided for use in the region's ongoing hydrologic research and mitigation planning.
Antarctic and Southern Ocean environments are facing increasing pressure from multiple threats. The Antarctic Treaty System regularly looks to the Scientific Committee on Antarctic Research (SCAR) ...for the provision of independent and objective advice based on the best available science to support decision-making, policy development and effective environmental management. The recently approved SCAR Scientific Research Programme Ant-ICON - ‘Integrated Science to Inform Antarctic and Southern Ocean Conservation‘ - facilitates and coordinates high-quality transdisciplinary research to inform the conservation and management of Antarctica, the Southern Ocean and the sub-Antarctic in the context of current and future impacts. The work of Ant-ICON focuses on three research themes examining 1) the current state and future projections of Antarctic systems, species and functions, 2) human impacts and sustainability and 3) socio-ecological approaches to Antarctic and Southern Ocean conservation, and one synthesis theme that seeks to facilitate the provision of timely scientific advice to support effective Antarctic conservation. Research outputs will address the most pressing environmental challenges facing Antarctica and offer high-quality science to policy and advisory bodies including the Antarctic Treaty Consultative Meeting, the Committee for Environmental Protection and the Scientific Committee of the Commission for the Conservation of Antarctic Marine Living Resources.
The Bale Mountains of Ethiopia contain the largest contiguous area of alpine habitat in Africa. The region provides critical water resources and other essential environmental services to highland ...communities, endemic wildlife, and millions of downstream people in East Africa. Increasing land use change has created concern over degradation to headwater wetlands and potential impacts on hydrologic regimes. Baseline understanding of wetland dynamics is lacking, however, and little is known about their function in the regional hydrologic system. We used remote sensing, machine learning, and field surveys to map the distribution of Afroalpine wetlands in the Bale Mountains. We developed a wetland typology based on hydrogeomorphic characteristics and a conceptual model of surface-groundwater flow. Our results show that wetland extent more than doubles between wet and dry seasons and that only 4 percent of the Afroalpine zone is saturated year-round. We also found evidence of a hydrologic continuum based on volcanic and glacial legacies, with wetlands at elevations above approximately 3,800 m asl likely to be ephemeral and wetlands at lower elevations tending to be perennial. Further interpretation suggests that local geology is a principal control on wetland distribution and hydrologic attenuation in the Bale Mountains. This lays the foundation for further research into surface-groundwater connectivity, climate change impacts, and conservation planning. Key Words: Afroalpine, Ethiopian highlands, HGM classification, mountain water tower, tropical alpine.
Over the last half century, the McMurdo Dry Valleys (MDV)
of East Antarctica have become a globally important site for scientific
research and environmental monitoring. Historical data can make ...important
contributions to current research activities and environmental management in
Antarctica but tend to be widely scattered and difficult to access. We
address this need in the MDV by compiling over 5000 historical photographs,
sketches, maps, oral interviews, publications, and other archival resources
into an online digital archive. The data have been digitized and
georeferenced using a standardized metadata structure, which enables
intuitive searches and data discovery via an online interface. The ultimate
aim of the archive is to create as comprehensive as possible a record of
human activity in the MDV to support ongoing research, management, and
conservation efforts. This is a valuable tool for scientists seeking to
understand the dynamics of change in lakes, glaciers, and other physical
systems, as well as humanistic inquiry into the history of the Southern
Continent. In addition to providing benchmarks for understanding change over
time, the data can help target field sampling for studies working under the
assumption of a pristine landscape by enabling researchers to identify the
date and extent of past human activities. The full database is accessible
via a web browser-based interface hosted by the McMurdo Long Term Ecological
Research site: http://mcmurdohistory.lternet.edu/ (last access: 5 May 2020). The complete
metadata data for all resources in the database are also available at the
Environmental Data Initiative: https://doi.org/10.6073/pasta/6744cb28a544fda827805db123d36557
(Howkins et al., 2019).
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