Remote-sensing Resources for Monitoring Glacier Fluctuations on Axel Heiberg Island

We document the abundant resources available for the photographic reconstruction of glacier terminus positions in the Canadian High Arctic, with particular reference to Axel Heiberg Island. Early terrestrial photographs may yet be discovered in the archives of explorers, but systematic photography of the High Arctic began with aerial coverage by the U.S. Air Force's Operation Polaris in the early 1940s. This oblique (trimetrogon) coverage was completed by the Royal Canadian Air Force in the early 1950s, and the coverage of vertical photography was completed in the late 1950s. Thereafter the resources become intermittent, but Axel Heiberg Island glaciers have been imaged quite frequently from the air. Visible-band satellite imagery is available from as early as 1962, but the number of useful archived images is limited by persistent, extensive cloud cover and, for some satellites, by distance of the region from ground receiving stations. Radar imagery, which is free of the cloud constraint, has recently become available both from the air and from space. We illustrate the potential of the photographic record by extending back to 1948 an earlier analysis of the terminus fluctuations of White and Thompson Glaciers. Analysis of an oblique photograph demonstrates a significantly more rapid retreat of White Glacier during 1948-60 than during 1960-95, while the advance of Thompson Glacier between 1948 and 1960, at 58 m/a, was almost three times faster than thereafter.Nous documentons les importantes ressources disponibles pour la reconstruction photographique des positions du front des glaciers dans l'Extrême-Arctique canadien, en particulier sur l'île Axel Heiberg. On peut encore découvrir d'anciennes photographies terrestres dans les archives des explorateurs, mais les premières photographies systématiques de l'Extrême-Arctique ont été prises par des avions américains dans le cadre de l'opération Polaris au début des années 1940. Cette couverture par prise de vue oblique (trimétrogon) a été achevée par l'Aviation royale du Canada au début des années 1950 et celle par photographie verticale a été terminée à la fin des années 1950. Pour la période qui suit, les ressources deviennent intermittentes, mais des images aériennes des glaciers de l'île Axel Heiberg ont été prises assez souvent. Dès 1962, les capteurs de satellite ont fourni des clichés dans la bande du visible, mais le contenu utilisable de l'archive est limité par la couverture nuageuse étendue et persistante de cette région et, pour quelques satellites, par la distance entre la région et les stations de réception. L'imagerie radar, qui n'a pas à s'inquiéter des nuages, a récemment fourni des clichés pris des airs comme de l'espace. Nous illustrons les possibilités des dossiers photographiques en faisant remonter jusqu'en 1948 une analyse antérieure des déplacements du front des glaciers White et Thompson. L'analyse d'une photographie oblique montre un recul significativement plus rapide du glacier White durant la période 1948-1960 que durant la période 1960-1995, tandis que, entre 1948 et 1960, l'avancée du glacier Thompson, à 58 m/a, a été près de trois fois plus rapide que par la suite

Global glacier mass changes and their contributions to sea-level rise from 1961 to 2016

International audienc

Present and future states of Himalaya and Karakoram glaciers, Ann

Total area and total mass would each decrease by about one-half (constant-rate assumption) or three-quarters (constant-trend assumption). These projections, which are uncertain and neglect some possibly important mitigating controls, such as variable extents of debris cover and the feedback due to retreat to higher elevations, demonstrate the need for more complete analyses to inform public perceptions of, and policy decisions relating to, the health of H-K glaciers

General or miscellaneous; 1827 Hydrology: Glaciology (1863); 1863 Hydrology: Snow and ice (1827); Citation: Cogley

[1] Total surface accumulation (total snowfall minus total sublimation) on the Greenland Ice Sheet is estimated as 299 ± 23 kg m À2 yr À1 for an assumed 30-year span, the uncertainty being quoted as twice the standard error. The estimate is very similar to earlier estimates because it relies largely on the same compiled observations, but it is the first to be accompanied by formal error bars. An error model was developed for this purpose. It incorporates uncertainties due to measurement error, record length or span, and spatial bias in the distribution and density of the observations. Measurement errors, although dominant over large parts of the interior, make only a small contribution to uncertainty in the accumulation of the whole ice sheet. Time series of accumulation are shown to be stationary and independent, which means that the date of any given observation is of no importance when evaluating its uncertainty as an estimate of accumulation at any other date. However, as found earlier, the span of the observation is a leading contributor to uncertainty, and a means of placing short-and long-span measurements on an equal footing is developed. Spatial bias is the other leading contributor, to judge from modeling of the standard error of averages of pairs of observations as a function of their separation and from a map of the standard error of accumulation. The standard error of interpolated point estimates of accumulation is small where measurements are dense and welldistributed in the interior, but grows rapidly where measurements are more thinly or unevenly distributed. Estimates of accumulation are therefore most uncertain in the peripheral ablation zone. It is suggested that uncertainty in accumulation needs to be reduced by a factor of two or more if the measurements are to contribute reliably to explaining the observed sea level rise