Quarterly literature review of the remote sensing of natural resources

The Technology Application Center reviewed abstracted literature sources, and selected document data and data gathering techniques which were performed or obtained remotely from space, aircraft or groundbased stations. All of the documentation was related to remote sensing sensors or the remote sensing of the natural resources. Sensors were primarily those operating within the 10 to the minus 8 power to 1 meter wavelength band. Included are NASA Tech Briefs, ARAC Industrial Applications Reports, U.S. Navy Technical Reports, U.S. Patent reports, and other technical articles and reports

Complexity revealed in the greening of the Arctic

As the Arctic warms, vegetation is responding, and satellite measures indicate widespread greening at high latitudes. This 'greening of the Arctic' is among the world’s most important large-scale ecological responses to global climate change. However, a consensus is emerging that the underlying causes and future dynamics of so-called Arctic greening and browning trends are more complex, variable and inherently scale-dependent than previously thought. Here we summarize the complexities of observing and interpreting high-latitude greening to identify priorities for future research. Incorporating satellite and proximal remote sensing with in-situ data, while accounting for uncertainties and scale issues, will advance the study of past, present and future Arctic vegetation change

Remote Sensing of Environmental Changes in Cold Regions

This Special Issue gathers papers reporting recent advances in the remote sensing of cold regions. It includes contributions presenting improvements in modeling microwave emissions from snow, assessment of satellite-based sea ice concentration products, satellite monitoring of ice jam and glacier lake outburst floods, satellite mapping of snow depth and soil freeze/thaw states, near-nadir interferometric imaging of surface water bodies, and remote sensing-based assessment of high arctic lake environment and vegetation recovery from wildfire disturbances in Alaska. A comprehensive review is presented to summarize the achievements, challenges, and opportunities of cold land remote sensing

Literature review of the remote sensing of natural resources

Abstracts of 596 documents related to remote sensors or the remote sensing of natural resources by satellite, aircraft, or ground-based stations are presented. Topics covered include general theory, geology and hydrology, agriculture and forestry, marine sciences, urban land use, and instrumentation. Recent documents not yet cited in any of the seven information sources used for the compilation are summarized. An author/key word index is provided

Serpentine (Floating) Ice Channels and their Interaction with Riverbed Permafrost in the Lena River Delta, Russia

Arctic deltas and their river channels are characterized by three components of the cryosphere: snow, river ice, and permafrost, making them especially sensitive to ongoing climate change. Thinning river ice and rising river water temperatures may affect the thermal state of permafrost beneath the riverbed, with consequences for delta hydrology, erosion, and sediment transport. In this study, we use optical and radar remote sensing to map ice frozen to the riverbed (bedfast ice) vs. ice, resting on top of the unfrozen water layer (floating or so-called serpentine ice) within the Arctic’s largest delta, the Lena River Delta. The optical data is used to differentiate elevated floating ice from bedfast ice, which is flooded ice during the spring melt, while radar data is used to differentiate floating from bedfast ice during the winter months. We use numerical modeling and geophysical field surveys to investigate the temperature field and sediment properties beneath the riverbed. Our results show that the serpentine ice identified with both types of remote sensing spatially coincides with the location of thawed riverbed sediment observed with in situ geoelectrical measurements and as simulated with the thermal model. Besides insight into sub-river thermal properties, our study shows the potential of remote sensing for identifying river channels with active sub-ice flow during winter vs. channels, presumably disconnected for winter water flow. Furthermore, our results provide viable information for the summer navigation for shallow-draught vessels

Retrieval of aerosol optical thickness over snow and ice surfaces in the Arctic using Advanced Along Track Scanning Radiometer

Aerosols in the Arctic cause radiative forcing and a variety of climatic feedbacks, which affect climate of both local and global scales. In order to assess the state of the Arctic climate, information on the aerosol type and amount is needed. Harsh conditions and remoteness of the Arctic region result in very few ground based measurements of aerosol optical thickness. Remote sensing has the potential to provide the necessary temporal and spatial coverage. A non-trivial task of aerosol retrieval over a very bright surface is being solved within the thesis; the developed retrieval consists of cloud screening over snow and two types of aerosol retrieval over snow - in the visible and infrared spectral regions. A number of validation and case studies has been performed to assess the quality of the retrieval. The developed algorithm applies to the data of Advanced Along Track Scanning Radiometer and produces maps of aerosol optical thickness over snow and ice

Drivers of permafrost degradation along the Inuvik to Tuktoyaktuk Highway (ITH)

Infrastructure construction on permafrost is challenging. Not only are northern regions undergoing a faster and more intense global warming than the rest of the world, inducing thawing of the permafrost at a worldwide scale. In addition, linear infrastructures such as gravel highways, built on embankments to protect the underlying permafrost, change environmental conditions in various ways, enhancing permafrost degradation. This work aims to utilize remote sensing data and explore the physical parameters that drive permafrost degradation in the regions adjacent to the Inuvik to Tuktoyaktuk Highway (ITH) in Northwest Territories, Canada. Within the work, snow accumulation along the embankment toe, vegetation moisture increase, surface water increase in poorly drained areas, earlier snowmelt and vegetation increase along the road are defined as factors that (I) enhance permafrost degradation and (II) are observable using remote sensing techniques. The analysis is conducted using cloud computing services, open-source software packages, and primarily freely available datasets. Snow accumulation conditions are derived using Digital Elevation Models (DEM) as baseline data. The cardinal direction of the road and the predominating wind direction significantly impact the snow accumulation. Moreover, the results indicate that the enhanced snow accumulation generally reaches further distances from the road than previous studies suggest. The impact from the road on vegetation moisture and vegetation conditions, indicated by the Normalized Difference Moisture Index (NDMI) and the Normalized Difference Vegetation Index (NDVI), respectively, demonstrated significant decreases within the first 25 m from the road edge. This is in line with previous studies. However, whether the observed effect reflects the field conditions or if the spectral signal is affected by other factors like dust is critically discussed. Furthermore, my study revealed that by normalizing the median NDMI and NDVI values on an undisturbed reference area, an additional effect is observed reaching up to 200 m from the road. The analysis of the NIR band indicates that the downstream side became wetter throughout the years compared to the upstream side. The snowmelt pattern indicated by the Normalized Difference Snow Index (NDSI), derived from Landsat images, shows that the areas next to the road are snow-free earlier in spring than the areas further away. The result indicates that the road affects the snowmelt up to 600 m from the road. The findings of this work highlight the importance of future research into the impact of dust on satellite-derived indices. Furthermore, the findings contribute to a better understanding of the spatial scale of altered permafrost drivers following the construction of the ITH

Geostatistical and statistical classification of sea-ice properties and provinces from SAR data

Recent drastic reductions in the Arctic sea-ice cover have raised an interest in understanding the role of sea ice in the global system as well as pointed out a need to understand the physical processes that lead to such changes. Satellite remote-sensing data provide important information about remote ice areas, and Synthetic Aperture Radar (SAR) data have the advantages of penetration of the omnipresent cloud cover and of high spatial resolution. A challenge addressed in this paper is how to extract information on sea-ice types and sea-ice processes from SAR data. We introduce, validate and apply geostatistical and statistical approaches to automated classification of sea ice from SAR data, to be used as individual tools for mapping sea-ice properties and provinces or in combination. A key concept of the geostatistical classification method is the analysis of spatial surface structures and their anisotropies, more generally, of spatial surface roughness, at variable, intermediate-sized scales. The geostatistical approach utilizes vario parameters extracted from directional vario functions, the parameters can be mapped or combined into feature vectors for classification. The method is flexible with respect to window sizes and parameter types and detects anisotropies. In two applications to RADARSAT and ERS-2 SAR data from the area near Point Barrow, Alaska, it is demonstrated that vario-parameter maps may be utilized to distinguish regions of different sea-ice characteristics in the Beaufort Sea, the Chukchi Sea and in Elson Lagoon. In a third and a fourth case study the analysis is taken further by utilizing multi-parameter feature vectors as inputs for unsupervised and supervised statistical classification. Field measurements and high-resolution aerial observations serve as basis for validation of the geostatistical-statistical classification methods. A combination of supervised classification and vario-parameter mapping yields best results, correctly identifying several sea-ice provinces in the shore-fast ice and the pack ice. Notably, sea ice does not have to be static to be classifiable with respect to spatial structures. In consequence, the geostatistical-statistical classification may be applied to detect changes in ice dynamics, kinematics or environmental changes, such as increased melt ponding, increased snowfall or changes in the equilibrium line

Recent (1986-2006) Vegetation-Specific NDVI Trends in Northern Canada from Satellite Data

Recent northern vegetation changes caused by climate warming have been well documented, using experimental plot warming to examine vegetation-specific changes and satellite image data to examine overall trends. Previous remote sensing efforts have employed the Normalized Difference Vegetation Index (NDVI) from AVHRR, whose 1 km to 8 km pixel size is too large for examination of broad scale vegetation-specific responses because of mixing within the pixel footprint. In this paper, we reconcile differences between field- and remote sensing-based approaches by using both medium-resolution (30 m) and coarse resolution (1 km) data to study 20 years of vegetation-specific responses to northern climate warming (1986 to 2006). Trends are compared among vegetation communities from two separate Landsat classifications in Canada’s eastern and western forest-tundra transition zone, as well as a 1 km AVHRR database recently developed over Canada. A comparison of absolute trends among mapped vegetation communities revealed lichen-dominated communities consistently exhibiting lower trends than those dominated by vascular plants, with both exhibiting increasing NDVI. Our results and those obtained from experimental warming suggest that the magnitude difference in NDVI increase between lichen and vascular vegetation is related to increasing vigor and biomass of vascular vegetation, in contrast to physiological impairment of lichen due to the short-term secondary effect of temperature on moisture. In the longer term, succession from lichen to vascular is likely responsible for the small observed NDVI increase over lichen-dominated regions. The fact that both Landsat and AVHRR exhibited similar relative vegetation-specific trends in NDVI suggests that this phenomenon may be widespread in the North.CCes derniers temps, les changements sur la végétation dans le Nord causés par le réchauffement climatique ont été bien documentés grâce à une parcelle expérimentale faisant l’objet d’un réchauffement qui permet d’examiner les changements propres à la végétation, ainsi que grâce à des données et images obtenues par satellite permettant d’examiner les tendances générales. Les travaux de télédétection antérieurs recouraient à l’indice d’activité végétale obtenu à partir d’un radiomètre perfectionné à très haute résolution (AVHRR), dont la taille de pixel de 1 km à 8 km est trop grande pour permettre l’examen des réactions à grande échelle de la végétation en raison du mélangeage dans la zone de couverture des pixels. Dans cette communication, nous faisons le rapprochement des différences entre les méthodes de prélèvement de données sur le terrain et les méthodes de prélèvement des données par télédétection en recourant à des données à moyenne résolution (30 m) et à des données à résolution grossière (1 km) dans le but d’étudier les réactions de la végétation échelonnées sur 20 ans dans le cadre du réchauffement climatique dans le Nord (de 1986 à 2006). Les tendances sont comparées entre les diverses communautés végétales à partir de deux classifications Landsat distinctes dans la zone de transition forêt-toundra de l’est et de l’ouest du Canada, ainsi qu’à partir d’une banque de données prélevées au Canada à l’aide d’un radiomètre perfectionné à très haute résolution de 1 km récemment mis au point. La comparaison des tendances absolues parmi les communautés végétales mappées a révélé des communautés dominées par le lichen affichant constamment des tendances moins élevées que les communautés dominées par les plantes vasculaires, toutes deux présentant un indice d’activité végétale accrue. Nos résultats et ceux obtenus dans le cadre du réchauffement expérimental laissent croire que la différence de magnitude en ce qui a trait à l’accroissement de l’indice d’activité végétale entre la végétation de lichen et la végétation vasculaire se rapporte à l’accroissement de la vigueur et de la biomasse de la végétation vasculaire, par contraste avec l’altération physiologique du lichen attribuable à l’effet secondaire à court terme de la température sur l’humidité. À plus long terme, la succession du lichen aux plantes vasculaires est vraisemblablement responsable des petites augmentations observées au titre de l’indice d’activité végétale dans les régions dominées par le lichen. Le fait que le Landsat et l’AVHRR aient tous deux permis de dénoter des tendances relatives semblables du point de vue de la végétation et de l’indice d’activité végétale laisse entendre que ce phénomène peut être étendu dans le Nord

The influence of shrub expansion on albedo and the winter radiation budget in the Canadian Low Arctic

Au cours des dernières décennies, le réchauffement climatique a entrainé une arbustation accélérée des écosystèmes arctiques. En modifiant l'albédo, les arbustes influencent la température de l'atmosphère, du manteau neigeux et du pergélisol, ce qui pourrait accélérer la fonte ou le dégel de ces deux derniers et initier de fortes boucles de rétroaction positive qui accentueraient les effets des changements climatiques. L'une des conséquences principales de cette arbustation est la réduction de l'albédo de la neige par les branches qui dépassent du manteau neigeux et en assombrissent la surface. De plus, des interactions complexes entre neige et arbustes d'une part modulent la remobilisation et le transport de la neige par le vent et d'autre part accélèrent la fonte durant les redoux. Ainsi, la présence d'arbustes au sein du manteau neigeux peut affecter les propriétés physiques et optiques de la neige, altérant encore davantage l'albédo de la surface affectée. Enfin, les branches ensevelies dans la neige peuvent également influencer le budget radiatif en absorbant les rayons lumineux car ceux-ci pénètrent généralement à plus de 10 cm de profondeur dans le manteau neigeux. Pour étudier et quantifier les interactions entre la neige, les arbustes et la lumière, nous avons récolté un jeu de données unique qui compare des manteaux neigeux avec et sans arbustes. Pour tous les sites échantillonnés, nous avons mesuré l'albédo spectral in situ et les profils de propriétés physiques de la neige ainsi que d'irradiance. Nous avons récolté ces données dans le bas Arctique, à Umiujaq, Nord du Québec, Canada (56° N, 76° W), au cours de plusieurs campagnes de terrain d'automne et d'hiver. En nous basant sur les données obtenues ainsi que des données de taille et de distribution verticale de branches d'arbustes, nous avons développé et validé une paramétrisation simple mais efficace permettant de modéliser l'albédo de surfaces hétérogènes composées de neige et d'arbustes. Cette nouvelle paramétrisation nous a permis de modéliser l'albédo avec une erreur inférieure à 3 %. Elle peut être utilisée de manière prédictive et est facile à intégrer aux modèles de système terre. L'albédo ainsi modélisé nous a permis d'élucider des processus importants des interactions entre la neige, les arbustes et la lumière. Nous avons trouvé que la réduction de l'albédo par les branches qui dépassent du manteau neigeux dépend de la longueur d'ondes considérée. Tôt durant la saison nivale, les branches diminuent l'albedo de 55 % à 500 nm et 18 % à 1000 nm. En revanche, l'effet des branches sur les propriétés physiques de la neige n'étaient pas suffisamment importants pour affecter l'albédo, sauf lors d'évènements climatiques extrêmes comme les blizzards ou les épisodes de chaleur. Nos résultats suggèrent que l'impact direct de l'assombrissement par les branches est largement supérieur aux effets indirects causés par les changements des propriétés physiques de la neige. Cependant, ces derniers pourraient gagner en importance si les évènements climatiques extrêmes devenaient plus fréquents au fur et à mesure que le réchauffement de l'Arctique s'intensifie. Finalement, nous montrons que l'impact des branches ensevelies sous la neige se traduit surtout par une augmentation de la fonte durant les épisodes de chaleur ainsi que par une intensification des processus métamorphiques tôt dans la saison. Cependant ces impacts étaient extrêmement localisés et restreints à l'environnement très proche des branches. Pour cette raison, il a été difficile de quantifier l'impact des branches ensevelies sur le budget radiatif terrestre, d'autant plus que les concentrations de carbone suie élevées (185 ng g⁻¹) dans le manteau neigeux d'Umiujaq ont accentué l'incertitude quant à l'effet relatif de ces deux processus sur l'albédo. Finalement, comme notre paramétrisation pour modéliser l'albédo a été développée sur la base de données provenant d'un seul site, nous croyons qu'il serait nécessaire de la tester de manière plus générale, avec des données provenant d'autres endroits. De cette manière, elle pourrait ensuite être intégrée aux modèles de surface continentale, ce qui permettrait d'inclure un effet réaliste de l'arbustation actuelle et future de l'Arctique sur les scénarios climatiques locaux et globaux.Arctic warming is causing an expansion of deciduous shrubs in the Arctic tundra biome. By modifying albedo, shrubs affect the temperature of the atmosphere, snowpack and permafrost, potentially increasing permafrost thawing and snow melting, and forming a powerful feedback to global warming. The most prominent impact of shrubs is a reduction of surface albedo when dark branches protrude above the bright snow surface. Additionally, complex snow-shrub interactions modify snow redistribution during windy conditions and increase snowmelt rates during warm spells. Thus, snow over shrub-covered tundra may have different physical and optical properties, leading to further modification of surface albedo. Finally, shrub branches buried in snow may still have an impact on the radiation budget because they can absorb light rays which generally penetrate deeper than 10 cm into the snowpack. To study and quantify the snow-shrub-light interactions, we collected a unique dataset comparing snowpacks with and without shrubs. For every site sampled, we measured in situ spectral albedo (400–1080 nm) and recorded snow physical properties and irradiance profiles. These data were acquired in a low Arctic site near Umiujaq, Northern Quebec, Canada (56° N, 76° W), during several field campaigns in autumn and winter. Based on these field data and a dataset of branch sizes and vertical distribution, a simple yet accurate parameterization for modeling albedo of mixed snow-shrub surfaces was developed and validated. This new parameterization had an accuracy of 3 %, can be used in a predictive way, and is easy to implement in earth system models. We uncovered important insights on snow-shrub-light interactions. Surface darkening by protruding branches was wavelength-dependent, and decreased albedo early in the snow season by 55 % at 500 nm and 18 % at 1000 nm. Changes in snow physical properties that were significant enough to impact albedo only occurred in conjunction with extreme weather events like after blizzards or during warm spells. Thus, the direct impact of darkening from shrubs likely dominates over the indirect impact from changes in snow physical properties, however the latter may gain in importance if extreme weather events become more frequent as Arctic warming progresses. The impact of buried branches was very localized, increasing snow melting during warm spells and enhancing snow metamorphic processes early in the season in the direct vicinity of branches. However, quantifying the impact of buried branches on the radiation budget was challenging due to their highly localized effect and because of high black carbon concentrations in the snowpack at our study site, which reached 185 ng g-1. We suggest that future research test the parameterization developed here more broadly, as this study was based on data from just one study site. The parametrization can then be implemented into land surface models, allowing for reliable estimates of the effect of current and projected Arctic shrubification on global and regional warming