Surface topography of the Greenland Ice Sheet from satellite radar altimetry

Surface elevation maps of the southern half of the Greenland subcontinent are produced from radar altimeter data acquired by the Seasat satellite. A summary of the processing procedure and examples of return waveform data are given. The elevation data are used to generate a regular grid which is then computer contoured to provide an elevation contour map. Ancillary maps show the statistical quality of the elevation data and various characteristics of the surface. The elevation map is used to define ice flow directions and delineate the major drainage basins. Regular maps of the Jakobshavns Glacier drainage basin and the ice divide in the vicinity of Crete Station are presented. Altimeter derived elevations are compared with elevations measured both by satellite geoceivers and optical surveying

Satellite radar altimetry over ice. Volume 4: Users' guide for Antarctica elevation data from Seasat

A gridded surface-elevation data set and a geo-referenced data base for the Seasat radar altimeter data over Greenland are described. This is a user guide to accompany the data provided to data centers and other users. The grid points are on a polar stereographic projection with a nominal spacing of 20 km. The gridded elevations are derived from the elevation data in the geo-referenced data base by a weighted fitting of a surface in the neighborhood of each grid point. The gridded elevations are useful for the creating of large-scale contour maps, and the geo-referenced data base is useful for regridding, creating smaller-scale contour maps, and examinating individual elevation measurements in specific geographic areas. Tape formats are described, and a FORTRAN program for reading the data tape is listed and provided on the tape

Satellite radar altimetry over ice. Volume 1: Processing and corrections of Seasat data over Greenland

The data-processing methods and ice data products derived from Seasat radar altimeter measurements over the Greenland ice sheet and surrounding sea ice are documented. The corrections derived and applied to the Seasat radar altimeter data over ice are described in detail, including the editing and retracking algorithm to correct for height errors caused by lags in the automatic range tracking circuit. The methods for radial adjustment of the orbits and estimation of the slope-induced errors are given

Satellite radar altimetry over ice. Volume 2: Users' guide for Greenland elevation data from Seasat

A gridded surface-elevation data set and a geo-referenced data base for the Seasat radar altimeter data over Antarctica are described. It is intended to be a user's guide to accompany the data provided to data centers and other users. The grid points are on a polar stereographic projection with a nominal spacing of 20 km. The gridded elevations are derived from the elevation data in the geo-referenced data base by a weighted fitting of a surface in the neighborhood of each grid point. The gridded elevations are useful for the creating smaller-scale contour maps, and examining individual elevation measurements in specific geographic areas. Tape formats are described, and a FORTRAN program for reading the data tape is listed and provided on the tape

Satellite Altimetry, Semivariograms, and Seasonal Elevation Changes in the Ablation Zone of West Greenland

Seasonal mean changes in the surface elevation of the ablation zone of West Greenland to 72°N between spring 1985 and summer 1986 are measured using radar altimeter data from the 18-month Geosat Geodetic Mission. Semi-variograms are used to estimate the noise in the data as a function of position on the ice sheet. Mean elevation changes are computed by averaging the elevation differences measured at points where orbits ascending in latitude are later crossed by orbits descending in latitude (or the reverse), with each cross-over difference weighted in proportion to the inverse square of the noise level in the neighborhood of the cross-over point. The mean surface elevation of the ablation zone, relative to spring 1985, ranged from 1.5 ± 0.6 m lower during summer 1985 to 1.7 ± 0.4 m higher during spring 1986

ICESat-2 Photon Classification: Finding Signal Photons in the ATL03 Geolocated Photon Data Product

ICESat-2 carries NASA's next-generation laser altimeter, ATLAS, (Advanced Topographic Laser Altimeter System), designed to measure changes in ice sheet height, sea ice freeboard, and vegetation canopy height. ATLAS contains a photon-counting lidar which transmits green (532-nm) pulses at 10kHz. Each pulse is split into 3 pairs of beams (one strong and one weak). Approximately 1014 photons per pulse travel from ATLAS through the atmosphere to reflect off the Earth's surface. Some return back into the ATLAS telescope where they are recorded. Photons from sunlight and instrument noise at the same wavelength are also recorded. The flight software time tags all photons within a 500m to 6 km range window and generates histograms. Using the histograms, it selects a telemetry window which varies from 20m over flat surfaces to hundreds of meters over rougher terrain. ATL03 contains the time, height (relative to the WGS-84 ellipsoid), latitude and longitude of every photon within the telemetry window. The basic challenge is to determine which of these photons were reflected off the surface. We have developed an algorithm that identifies these signal photons and assigns a confidence level (low, medium, or high) to each signal photon based on the signal to noise ratio. We present an overview of the signal identification algorithm and show the results on actual ICESat-2 data over ice sheet, sea ice, vegetated, and water surfaces. Higher level ATLAS products work with aggregations of the photons in order to determine the ellipsoidal height of the Earth, canopy height and structure, and other quantities of geophysical interest

Multi-Year Elevation Changes Near the West Margin of the Greenland Ice Sheet from Satellite Radar Altimetry

Mean changes in the surface elevation near the west margin of the Greenland ice sheet are measured using Seasat altimetry and altimetry from the Geosat Exact Repeat Mission (ERM). The Seasat data extend from early July through early October 1978. The ERM data extend from winter 1986-87 through fall 1988. Both seasonal and multi-year changes are measured using altimetry referenced to GEM T2 orbits. The possible effects of orbit error are minimized by adjusting the orbits into a common ocean surface. Seasonal mean changes in the surface height are recognizable during the Geosat ERM. The multi-year measurements indicate the surface was lower by 0.4 +/- 0.4 m on average in late summer 1987 than in late summer 1978. The surface was lower by 0.2 +/- 0.5 m on average in late summer 1988 than in late summer 1978. As a control case, the computations art also carried out using altimetry referenced to orbits not adjusted into a common ocean surface

Mass Gains of the Antarctic Ice Sheet Exceed Losses

During 2003 to 2008, the mass gain of the Antarctic ice sheet from snow accumulation exceeded the mass loss from ice discharge by 49 Gt/yr (2.5% of input), as derived from ICESat laser measurements of elevation change. The net gain (86 Gt/yr) over the West Antarctic (WA) and East Antarctic ice sheets (WA and EA) is essentially unchanged from revised results for 1992 to 2001 from ERS radar altimetry. Imbalances in individual drainage systems (DS) are large (-68% to +103% of input), as are temporal changes (-39% to +44%). The recent 90 Gt/yr loss from three DS (Pine Island, Thwaites-Smith, and Marie-Bryd Coast) of WA exceeds the earlier 61 Gt/yr loss, consistent with reports of accelerating ice flow and dynamic thinning. Similarly, the recent 24 Gt/yr loss from three DS in the Antarctic Peninsula (AP) is consistent with glacier accelerations following breakup of the Larsen B and other ice shelves. In contrast, net increases in the five other DS of WA and AP and three of the 16 DS in East Antarctica (EA) exceed the increased losses. Alternate interpretations of the mass changes driven by accumulation variations are given using results from atmospheric-model re-analysis and a parameterization based on 5% change in accumulation per degree of observed surface temperature change. A slow increase in snowfall with climate waRMing, consistent with model predictions, may be offsetting increased dynamic losses

An Algorithm for Detection of Ground and Canopy Cover in Micropulse Photon-Counting Lidar Altimeter Data in Preparation of the ICESat-2 Mission

The Ice, Cloud and Land Elevation Satellite-II (ICESat-2) mission has been selected by NASA as a Decadal Survey mission, to be launched in 2016. Mission objectives are to measure land ice elevation, sea ice freeboard/ thickness and changes in these variables and to collect measurements over vegetation that will facilitate determination of canopy height, with an accuracy that will allow prediction of future environmental changes and estimation of sea-level rise. The importance of the ICESat-2 project in estimation of biomass and carbon levels has increased substantially, following the recent cancellation of all other planned NASA missions with vegetation-surveying lidars. Two innovative components will characterize the ICESat-2 lidar: (1) Collection of elevation data by a multi-beam system and (2) application of micropulse lidar (photon counting) technology. A micropulse photon-counting altimeter yields clouds of discrete points, which result from returns of individual photons, and hence new data analysis techniques are required for elevation determination and association of returned points to reflectors of interest including canopy and ground in forested areas. The objective of this paper is to derive and validate an algorithm that allows detection of ground under dense canopy and identification of ground and canopy levels in simulated ICESat-2-type data. Data are based on airborne observations with a Sigma Space micropulse lidar and vary with respect to signal strength, noise levels, photon sampling options and other properties. A mathematical algorithm is developed, using spatial statistical and discrete mathematical concepts, including radial basis functions, density measures, geometrical anisotropy, eigenvectors and geostatistical classification parameters and hyperparameters. Validation shows that the algorithm works very well and that ground and canopy elevation, and hence canopy height, can be expected to be observable with a high accuracy during the ICESat-2 mission. A result relevant for instrument design is that even the two weaker beam classes considered can be expected to yield useful results for vegetation measurements (93.01-99.57% correctly selected points for a beam with expected return of 0.93 mean signals per shot (msp9) and 72.85% - 98.68% for 0.48 msp (msp4)). Resampling options affect results more than noise levels. The algorithm derived here is generally applicable for analysis of micropulse lidar altimeter data collected over forested areas as well as other surfaces, including land ice, sea ice and land surfaces

Alternative methods for the treatment of post-menopausal troubles

[english] Menopause is described as the transition from the reproductive phase of a women to the non reproductive. Changes in hormone levels might lead to complaints and health consequences especially during peri- and postmenopause. Hormone therapy has a potential damaging health risk profile and is recommended for temporal limited therapy for acute vasomotor symptoms only.The present HTA-report aims to assess the effectiveness and the cost-effectiveness of alternative treatment methods for women with postmenopausal symptoms in Germany regarding patient relevant endpoints (reduction of symptoms and frequency of adverse events and improvement of quality of life).A systematic literature search was carried out in 33 relevant databases in September 2010. Citations were selected according to pre-defined criteria and were extracted and evaluated.In the systematic research 22 studies are identified for the effectiveness evaluation, 22 primary studies and one review.High doses of isolated genistein reduce the frequency/intensity of hot flashes while low doses of genistein show no significant effect. Intake of isoflavone extract such as genistein, daidzein, glycitein in various combinations does not have an effect on improvement of cognitive function or vaginal dryness. The effect of black cohosh and hop extract for menopausal complaints cannot be determined since results are heterogenous. The combination of isoflavone, black cohosh, monk’s pepper, valerian and vitamin E has a positive effect on menopause symptoms. Ginkgo biloba shows no significant effect on menopause symptoms and cognitive improvement beside mental flexibility. Acupuncture has a significant influence on hot flashes especially in severe cases.No final statement can be drawn regarding the effectiveness of alter­ne treatment methods due to qualitative shortcomings of included studies and a general limited availability of studies in this field. Furthermore, the generalization of the present HTA is limited due to the inclusion of only postmenopausal women.<br><br>[german] Als Wechseljahre wird der Übergang von der reproduktiven Phase der Frau zur nicht-reproduktiven beschrieben. Insbesondere in der Peri- und Postmenopause können Beschwerden aufgrund des sich veränderten Hormonspiegels auftreten. Aktuell wird die Hormontherapie wegen der mit dieser verbundenen Risiken nur noch zur kurzfristigen Behandlung akuter vasomotorischer Symptome empfohlen. Von den betroffenen Frauen werden alternative und komplementäre Heilmethoden eingesetzt.Im vorliegenden Health Technology Assessment (HTA) sollen die Effektivität und Kosteneffektivität alternativer Behandlungsmethoden von postmenopausalen Wechseljahresbeschwerden in Deutschland hinsichtlich der patientenrelevanten Endpunkte Verringerung der Symptomatik, Häufigkeit unerwünschter Ereignisse sowie Verbesserung der Lebensqualität bewertet werden. In 33 relevanten Datenbanken wird im September 2010 eine systematische Literatursuche durchgeführt. Gefundene und relevante Literaturstellen werden gemäß vorab definierter Kriterien selektiert. Die Daten der Literaturstellen werden gezielt herausgesucht, bewertet und zusammenfassend beurteilt.Aus der systematischen Recherche werden 22 Studien, davon 15 Primärstudien und ein Review zur Bewertung der Effektivität identifiziert.Hochdosiertes isoliertes Genistein reduziert die Anzahl/Schwere von Hitzewallungen, während niedrig dosiertes Genistein keinen signifikanten Effekt zeigt. Die Gabe von Isoflavonextrakten, die Genistein, Daidzein, Glycitein in unterschiedlicher Zusammensetzung enthalten, hat keinen signifikanten Einfluss auf die Verbesserung kognitiver Fähigkeiten oder vaginale Trockenheit. Traubensilberkerzen- und Hopfenextrakt führen zu unterschiedlichen Ergebnissen bezüglich der Wirksamkeit bei postmenopausalen Beschwerden, sodass keine abschließende Aussage zur Effektivität getroffen werden kann. Die Kombination von Isoflavonen, Traubensilberkerze, Mönchspfeffer, Baldrian und Vitamin E hat eine positive Wirkung auf postmenopausale Symptome. Ginkgo biloba zeigt keinen signifikanten Effekt auf postmenopausale Symptome und eine kognitive Verbesserung mit Ausnahme der mentalen Flexibilität. Akupunktur hat einen signifikanten Einfluss auf Hitzewallungen, insbesondere auf deren Schweregrad.Aufgrund der qualitativen Mängel (Concealment, Randomisierung, Fallzahlplanung) der eingeschlossenen Studien und der begrenzten Anzahl an Studien kann keine abschließende zusammenfassende Bewertung zur Wirksamkeit alternativer Heilmethoden gegeben werden. Die Verallgemeinerbarkeit des vorliegenden HTA wird durch die Beschränkung auf postmenopausale Frauen reduziert