Remote Sensing of Snow Cover Using Spaceborne SAR: A Review

The importance of snow cover extent (SCE) has been proven to strongly link with various natural phenomenon and human activities; consequently, monitoring snow cover is one the most critical topics in studying and understanding the cryosphere. As snow cover can vary significantly within short time spans and often extends over vast areas, spaceborne remote sensing constitutes an efficient observation technique to track it continuously. However, as optical imagery is limited by cloud cover and polar darkness, synthetic aperture radar (SAR) attracted more attention for its ability to sense day-and-night under any cloud and weather condition. In addition to widely applied backscattering-based method, thanks to the advancements of spaceborne SAR sensors and image processing techniques, many new approaches based on interferometric SAR (InSAR) and polarimetric SAR (PolSAR) have been developed since the launch of ERS-1 in 1991 to monitor snow cover under both dry and wet snow conditions. Critical auxiliary data including DEM, land cover information, and local meteorological data have also been explored to aid the snow cover analysis. This review presents an overview of existing studies and discusses the advantages, constraints, and trajectories of the current developments

A prospectus for Thematic Mapper research in the Earth sciences

Earth science applications of Thematic Mapper (TM) imagery are discussed. Prospective research themes are defined in a general sense in relation to the technical measurement capabilities of the TM and the various types of Earth information that can potentially be derived from multispectral TM imagery. An overview of the system developed to acquire and reduce TM data is presented. The technical capabilities of this system are presented in detail. The orbital performance of the TM sensor is described, based upon the analysis of LANDSAT 4 and 5 TM data collected to date

Impact of spatial, spectral, and radiometric properties of multispectral imagers on glacier surface classification

Using multispectral remote sensing, glacier surfaces can be classified into a range of zones. The properties of these classes are used for a range of glaciological applications including mass balance measurements, glacial hydrology, and melt modelling. However, it is not immediately evident that multispectral data should be optimal for imaging glaciers and ice caps. Thus, this investigation takes an inverse perspective. Taking into account spectral and radiometric properties, in situ spectral reflectance data were used to simulate glacier surface response for a suite of multispectral sensors. Sensor-simulated data were classified and compared. In addition, airborne multispectral imagery was classified for a range of spatial resolutions and intercompared in three different ways. In these analyses, the most important property which determined the suitability of a multispectral imager for glacier surface classification was its radiometric range (i.e. gain settings). Low resolution imagery (250. m. pixels) is too coarse to represent the true complexity present on a glacier while medium resolution imagery (60. m, 30. m, or 20. m) accurately represented the results derived from high resolution airborne imagery. Of those studied here, the satellite imagers currently in use that are most suitable for glacier surface classification are Landsat TM/ETM. + and ASTER (each with particular gain settings). Both Sentinel-2 and the OLI on Landsat 8 are also expected to be similarly qualified. Landsat MSS is also found to be radiometrically well-suited for glacier surface classification, but its lower spatial resolution makes it a secondary selection. © 2013 Elsevier Inc.A. Pope was supported by the National Science Foundation Graduate Research Fellowship Programme under Grant No. DGE-1038596. Further research support came from UK Natural Environment Research Council's Field Spectroscopy Facility, ARCFAC (the European Centre for Arctic Environmental Research), Trinity College Cambridge, Sigma Xi, the Norwegian Marshall Fund, the Explorers Club, the National Geographic Society Young Explorers Program, the Scott Polar Research Institute, the Cambridge University Geography Department, the Cambridge University Department of Anglo-Saxon, Norse, and Celtic Studies, and the Cambridge University Worts Fund

Earth resources: A continuing bibliography (issue 26)

This bibliography lists 480 reports, articles, and other documents introduced into the NASA scientific and technical information system between April 1, 1980 and June 30, 1980. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, hydrology and water management, data processing and distribution systems, instrumentation and sensors, and economic analysis

Mapping moraines and glaciers using multispectral imagery and ancillary elevation data : An approach for Svalbard, Norwegian Arctic

Abstract This study uses multispectral Landsat satellite imagery and a high resolution Digital Elevation Model based on 1990/95 aerial stereoimagery (Norwegian Polar Institute) to map moraines and glacier terminus positions on the high Arctic archipelago of Svalbard, Norway. To accomplish the task, this methodological Master thesis investigates different approaches of classification and incorporation of ancillary elevation data. Glaciers and other ice masses are important parts of the climatic system and also eminent terrestrial indicators for climate change in the scale of tenths to thousands of years. In the context of climatic response and global sea-level rise, mass balance studies on glaciers are important means to quantify trends however they are laborious and only for a few glaciers worldwide available. The application of remote sensing may help to determine changes in volume and extent of glaciers with a greater spatial coverage. Furthermore, area-wide mapping of unvegetated moraines on Svalbard may aid to quantify past glacial dynamics, especially since the Little Ice Age (LIA). During this study a thematic map of vegetation- and glacier-cover dating to the period from 1999 to 2002 has been produced by contrast-enhancing-methods and supervised determination of class thresholds, covering almost the complete archipelago. ISODATA classifications of combined terrain statistics and primary topographic attributes are merged with multispectral data to map the extend of moraines. Combinations of VIS, NIR and SWIR spectral bands with elevation range and standard deviation, curvature and slope deliver the most promising results when joined to neighbourhood analysis. Datasets from principal component analysis deliver good results as well. However, since the morphological diversity is high, no method is superior on all moraines. Multitemporal change detection was tested for a small number of glaciers on Brøggerhalvøya, western Spitsbergen, where recent data was acquired in the field during 2006. High variation coefficients for annual retreat rates of 26 and 45% were discovered among datasets with different spatial resolutions. The overall trend was negative at all events, varying from 10 to 19 m/a horizontal retreat during the entire investigated period from 1983 to 2006. The fast losses of Svalbard glaciers are likely connected to climatic warming trends which are also obvious from direct measurements. The necessity of glacial studies becomes obvious as the retreat of the smaller glaciers and ice caps outside Greenland and Antarctica contributes to global sea level rise second only to the thermal expansion, with Svalbard being a major player. Abstrakt Diese Studie verwendet multispektrale Landsat Satellitenbilder und ein hochauflösendes digitales Geländemodel, welches auf Stereoluftbildern von 1990/95 vom Norwegischen Polarinstitut basiert, um Moränen sowie die Position von Gletscherfronten auf der hocharktischen Inselgruppe Svalbards (Norwegen) zu kartieren. Hierzu untersucht diese methodologische Masterarbeit verschiedene Ansätze zur Klassifikation und Integration ergänzender Geländedaten. Gletscher und andere Eismassen sind wichtige Bestandteile des Klimasystems und außerdem die besten Klimaindikatoren der festen Landoberfläche, bezogen auf Zeiträume einiger Jahrzehnte bis Jahrtausende. In dem Zusammenhang von Klimadynamik und weltweitem Meeresspiegelanstieg sind Massenbilanzstudien auf Gletschern wichtig um Trends zu quantifizieren, allerdings sind solche Untersuchungen aufwändig und wurden weltweit nur auf einer kleinen Zahl von Gletschern durchgeführt. Die Anwendung der Fernerkundung hilft Daten über Volumen- und Flächenänderungen von Gletschern flächendeckend zu erheben. Darüber hinaus kann die flächendeckende Kartierung vegetationsfreier Moränen auf Svalbard dabei helfen vergangene Gletscherfluktuationen, insbesondere seit der kleinen Eiszeit, zu quantifizieren. Im Rahmen dieser Studie wurde, mit Hilfe von kontrastverbessernden Bildbearbeitungsmethoden und manueller Grenzwertbestimmung, eine thematische Karte der Gletscher- und Vegetationsbedeckung aus dem Zeitraum von 1999 bis 2002 erstellt, welche einen Großteil Svalbards abdeckt. ISODATA-Klassifizierungen von kombinierten Geländestatistiken und primären Geländeattributen wurden zur Kartierung der Moränen mit multispektralen Daten kombiniert. Die gemeinsame Verwendung der spektralen Kanäle im sichtbaren, im nah-infraroten und im kurzwellig-infraroten Bereich sowie der Höhenvariabilität und -Standardabweichung, der Geländerundung und dem Gefälle lieferten die vielversprechendsten Ergebnisse, sofern Nachbarschaftsbeziehungsanalysen integriert wurden. Datensätze aus der Hauptkomponentenanalyse liefern ebenfalls gute Ergebnisse, prinzipiell gilt jedoch angesichts der morphologischen Vielfalt der Moränen dass keine Methode in allen Bereichen überlegen ist. Multitemporale Änderungskartierungen wurden für eine kleine Anzahl von Gletschern auf der Brøggerhalbinsel in Westspitzbergen getestet, auf der 2006 auch Feldkartierungen durchgeführt wurden. Hohe Variationskoeffizienten von 26 bis 45% wurden für die Messungen des jährlichen Rückgangs der Gletscher aus verschiedenen Datensätzen mit unterschiedlichen räumlichen Auflösungen festgestellt. Der allgemeine Trend war in allen Fällen negativ und variierte während des gesamten untersuchten Zeitraumes von 1983 bis 2006 zwischen 10 und 19 Metern Rückgang pro Jahr. Die raschen Verluste der Gletscher Svalbards sind vermutlich auf klimatische Veränderungen zurückzuführen welche auch in direkten Messungen deutlich werden. Die Notwendigkeit glaziologischer Untersuchungen wird durch die Tatsache, dass der Rückgang kleinerer Gletscher außerhalb Grönlands und der Antarktis bereits jetzt den zweitgrößten Beitrag zum globalen Meeresspiegelanstieg nach der Wärmeausdehnung leistet, unterstrichen. Svalbards Gletscher liefern hierzu einen der Hauptbeiträge. Abstrakt Denne studien bruker multispektrale bilder fra Landsat-satelliten og en digital terrengmodell med høy oppløsning, hvilket er basert på stereo-flybilder fra 1990/95 av Norsk Polarinstitutt. Studiens mål er å kartlegge morener og brefronter på den høy-arktiske øygruppen Svalbard (Norge). For å oppnå dette målet, undersøker denne metodologiske Masteroppgaven forskjellige adkomster til klassifikasjon med integrasjon av supplerende høydeverdier. Breer og andre ismasser er viktige deler av det klimatiske system og de viser til klimatiske forandringer på tidsrom fra tiår til tusenår. I sammenheng med klimatisk reaksjon og økning av havnivået verden rundt, er glasiologiske undersøkelser svært viktig, siden det hjelper med å kvantifisere en slik utvikling. Men glasiologiske undersøkelser er ressurskrevende, og det er derfor bare blitt gjort på et lite antall breer i verden. Bruk av fjernmåling hjelper til å undersøke breer med en utvidet dekning. I tillegg kan en arealdekkende kartlegging av morener på Svalbard hjelpe til å forstå, og måle forandring av breer i fortiden, spesielt siden den lille istiden. En tematisk kart av vegetasjon og is-dekning som omfatter nesten hele øygruppen i tidsrommet fra 1999 til 2002, blitt produsert under dette studiet. Kartleggingen er utført med hjelp av kontrastøkende metoder og manuell determinasjon av grenseverdiene. ISODATA klassifikasjoner av statistiske terrengmodeller og primære terrengattributter er blitt sammenført med multispektral data til å kartlegge utvidelse av morener. Kombinasjonen av VIS, NIR og SWIR spektrale kanaler med høydevariabilitet og standardavvikelse av høyden, runding og helning leverer de beste resultatene når de blir etterbehandlet med naboskapsanalyser. Hovedkomponentanalysen viser også gode resultater, men prinsipielt er den morfologiske variabilitet innenfor morenene stor og det finnes ingen metode som er overlegen i alle områder. Den multitemporal endringsanalyse er blitt testet på et lite antall breer på Brøggerhalvøya, Vestspitsbergen. På samme området er brefrontene og morenene blitt kartlagt i felt i 2006. Høye variasjonskoeffisienter på 45 og 26 % ble observert i målinger av årlig tilbaketrekking i areal og lengde med ulik romlig oppløsning. Den generelle trenden var negativ i alle undersøkte tilfeller, med variasjoner i tilbaketrekking fra 10 til 19 meter per år i hele studieperioden fra 1983 til 2006. Det store massetapet fra Svalbards breer er utvilsomt relatert til klimatisk oppvarming, en trend som også vises i direkte målinger. Nødvendigheten av å undersøke breer blir enda mer åpenbar av at tilbaketrekkingen av små breer og iskapper utenom Grønland og Antarktis allerede nå utgjør det nest største bidraget, etter termisk ekspansjon, til den globale økningen i havnivå – og her er Svalbard en viktig aktør

Quantification and Change Assessment Benjamin Aubrey Robson 2016 Dissertation date: 31st October 2016 of Debris-Covered Glaciers using Remote Sensing

This 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

Earth Resources: A continuing bibliography with indexes, issue 40

This bibliography lists 423 reports, articles, and other documents introduced into the NASA scientific and technical information system between October 1 and December 31, 1983. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, hydrology and water management, data processing and distribution systems, instrumentation and sensors, and economical analysis

Glacier Monitoring Based on Multi-Spectral and Multi-Temporal Satellite Data: A Case Study for Classification with Respect to Different Snow and Ice Types

Remote sensing techniques are frequently applied for the surveying of remote areas, where the use of conventional surveying techniques remains difficult and impracticable. In this paper, we focus on one of the remote glacier areas, namely the Tyndall Glacier area in the Southern Patagonian Icefield in Chile. Based on optical remote sensing data in the form of multi-spectral Sentinel-2 imagery, we analyze the extent of different snow and ice classes on the surface of the glacier by means of pixel-wise classification. Our study comprises three main steps: (1) Labeled Sentinel-2 compliant data are obtained from theoretical spectral reflectance curves, as there are no training data available for the investigated area; (2) Four different classification approaches are used and compared in their ability to identify the defined five snow and ice types, thereof two unsupervised approaches (k-means clustering and rule-based classification via snow and ice indices) and two supervised approaches (Linear Discriminant Analysis and Random Forest classifier); (3) We first focus on the pixel-wise classification of Sentinel-2 imagery, and we then use the best-performing approach for a multi-temporal analysis of the Tyndall Glacier area. While the achieved classification results reveal that all of the used classification approaches are suitable for detecting different snow and ice classes on the glacier surface, the multi-temporal analysis clearly reveals the seasonal development of the glacier. The change of snow and ice types on the glacier surface is evident, especially between the end of ablation season (April) and the end of accumulation season (September) in Southern Chile

Earth resources: A continuing bibliography with indexes (issue 52)

This bibliography lists 454 reports, articles, and other documents introduced into the NASA scientific and technical information system between October 1 and December 31, 1986. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, hydrology and water management, data processing and distribution systems, instrumentation and sensors, and economic analysis

Heterogeneous glacier thinning patterns over the last 40 years in Langtang Himal

Himalayan glaciers are losing mass at rates similar to glaciers elsewhere, but heavily debris-covered glaciers are receding less than debris-free glaciers or even have stable fronts. There is a need for multi-temporal mass balance data to determine if glacier wastage of debris-covered glaciers is accelerating. Here, we present glacier volume and mass changes of seven glaciers (5 partially debris-covered, 2 debris-free) in the upper Langtang catchment in Nepal of 28 different periods between 1974 and 2015 based on 8 digital elevation models (DEMs) derived from high-resolution stereo satellite imagery. We show that glacier volume decreased during all periods between 2006 and 2015 (2006–2015: −0.60 ± 0.34 m a−1) and at higher rates than between 1974 and 2006 (−0.28 ± 0.42 m a−1). However, the behavior of glaciers in the study area was highly heterogeneous, and the presence of debris itself does not seem to be a good predictor for mass balance trends. Debris-covered tongues have highly non-linear thinning profiles, and we show that local accelerations in thinning correlate with complex thinning patterns characteristic of areas with a high concentration of supraglacial cliffs and lakes. At stagnating glacier area near the glacier front, on the other hand, thinning rates may even decrease over time. We conclude that trends of glacier mass loss rates in this part of the Himalaya cannot be generalized, neither for debris-covered nor for debris-free glaciers