Download or read book Use of Microwave Radar Data to Interpret Physical Properties of Ice and Snow on the Greenland Ice Sheet written by Christopher M. Gero and published by . This book was released on 1995 with total page 66 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 538 pages. Available in PDF, EPUB and Kindle. Book excerpt: Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
Download or read book Advancing Microwave Radar Retrievals of Snow Depth on Sea Ice written by Arttu Jutila and published by . This book was released on 2022 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Snow is a key factor in the sea-ice and Earth's climate systems that modifies the physical, climatic, and biogeochemical processes taking place. One of its most important impacts is in regulating sea-ice growth and melt. Despite its importance, little is known about the spatial and temporal distribution of snow depth on sea ice on the regional to global scales. Snow is tightly coupled to the highly dynamic sea-ice and atmospheric conditions and it is, therefore, very heterogeneous and constantly evolving both in space and in time. As a spatially and temporally representative, global, year-round product of snow depth observations on sea ice does not exist to this date, applications often have to rely on climatological values that do not necessarily hold true in the rapidly warming global climate. The unknown properties directly translate into the uncertainty of the result. This dissertation takes on the ambitious goal of working toward full characterisation of the snow and sea-ice layers. To achieve that, the focus is on advancing microwave radar retrievals of snow depth on sea ice. Enhanced snow depth observations will enable improving other measurements of sea-ice related parameters, most importantly sea-ice thickness, and in joint analysis of coincident sea-ice measurements estimating sea-ice bulk density becomes possible. In the first step, field experiments with ground-based C and K band pulse radars are carried out to investigate microwave penetration into the snow cover. The results show the K band microwaves expectedly reflect from the snow surface while the C band microwaves penetrate closer to the snow-sea-ice interface potentially enabling dual-frequency snow depth retrieval in less than half of the studied cases and only on first-year ice. In the second step, radar measurements of snow depth on sea ice are upscaled by using an airborne radar in the western Arctic Ocean in 2017-2019. A high-sensitivity, ultra-wideband, frequency-modulated continuous-wave (FMCW) radar is integrated to the instrument configuration of the Alfred Wegener Institute's (AWI) IceBird sea-ice campaigns. Snow depth retrievals with a custom algorithm based on signal peakiness from the radar measurements at a low altitude of 200 ft show good consistency against high altitude measurements at 1500 ft, which are comparable to previous acquisitions. At the nominal low altitude of the IceBird surveys, the small, two-metre radar footprint increases the spatial resolution and reduces the effect of off-nadir targets. Validation against ground measurements reveal a sub-centimetre mean bias, which is below the sensor resolution. As the main result of this step, the AWI IceBird surveys are now capable of discriminating between the snow and sea-ice layers. In the third step, the full AWI IceBird sensor configuration, including airborne laser, radar, and electromagnetic induction sounding instruments, is exploited by collocating the coincident thickness and freeboard measurements and tracking the locations of air-snow, snow-sea-ice, and sea-ice-water interfaces for more than 3000 km along survey paths over different sea-ice types. Assuming values for snow and sea-water densities and that the sea-ice cover is in isostatic equilibrium, it is possible to derive sea-ice bulk density. The results show that the ice-type averaged densities for first-year and multi-year ice are higher than and do not differ as much as widely used values from previous studies. This highlights the demand of algorithms to adapt to changing sea-ice density in satellite altimetry retrievals of sea-ice thickness. Finally, a negative-exponential parametrisation of sea-ice bulk density is derived using sea-ice freeboard as the predictor variable for future applications. In conclusion, this dissertation takes important advancing steps in characterising the snow and sea-ice layers. Previously, the airborne AWI IceBird surveys carried out in late-winter were only able to measure the combined thickness of the snow and sea-ice layers but now, after successful integration of the FMCW radar and in combination with the airborne laser scanner measurements, it is possible to track the locations of all three interfaces bounding the snow-sea-ice system. Such airborne multi-instrument measurements of snow depth, sea-ice thickness, and freeboard are important data sets in their own right to complement the scarce observations of sea-ice related parameters in remote areas of the polar regions, but a joint analysis allows deriving further key parameters like sea-ice density. The results of this dissertation can be applied to improve retrievals of geophysical sea-ice parameters from the soon 30-year long satellite altimetry data record, which in turn will contribute to enhance monitoring the climate-sensitive sea-ice cover and modelling future projections of the changing global climate.
Download or read book Microwave Remote Sensing of Sea Ice written by Frank D. Carsey and published by American Geophysical Union. This book was released on 1992-04-08 with total page 466 pages. Available in PDF, EPUB and Kindle. Book excerpt: Published by the American Geophysical Union as part of the Geophysical Monograph Series, Volume 68. Human activities in the polar regions have undergone incredible changes in this century. Among these changes is the revolution that satellites have brought about in obtaining information concerning polar geophysical processes. Satellites have flown for about three decades, and the polar regions have been the subject of their routine surveillance for more than half that time. Our observations of polar regions have evolved from happenstance ship sightings and isolated harbor icing records to routine global records obtained by those satellites. Thanks to such abundant data, we now know a great deal about the ice-covered seas, which constitute about 10% of the Earth's surface. This explosion of information about sea ice has fascinated scientists for some 20 years. We are now at a point of transition in sea ice studies; we are concerned less about ice itself and more about its role in the climate system. This change in emphasis has been the prime stimulus for this book.
Download or read book A Correlation based Approach to Modeling Interferometric Radar Observations of the Greenland Ice Sheet written by E. Weber Hoen and published by . This book was released on 2001 with total page 384 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Interferometric synthetic aperture radar (InSAR) phase observations have greatly increased our understanding of the topography and motion of ice sheets, but yield little information on the sub-surface structure, a needed description for mass-balance estimates. Inversion of a diffuse volume scatter model shows that InSAR correlation values, p, can be related to radiowave penetration depths, d, which depend on characteristics of the snow/ice volume. Application to European Research Satellite (ERS) images (VV, 5.6 cm, 23 ̊incidence angle) of the Greenland ice sheet imply C-band d of 0 m along the rocky coast, 10-20 m in the bare ice zone, and 20-35 m in the percolation zone and dry snow zone, consistent with in situ results. Moreover, volume scattering reduces the ERS critical baseline from about 1100 m to 300 m. Correlation and backscatter power (ơ0) observations can be combined for further understanding of the snow/ice volume. In particular, p and ơ0 data of 15 km-long, 50 m-high topographic undulations in the dry snow zone arc minimum on the windward side and maximum on the lee side, with 1 to 3 dB variation typical. These spatial variations in the scattering medium appear to follow from differences in snow accumulation due to prevailing winds. Assuming that snow-grains are the dominant source of backscatter, the classical independent-scatterer model is physically implausible at firn densities; a second-order dense-medium radiative transfer model also is unable to explain both the observed d and ơ0. A modified Born approach provides a better match to ơ0 and p separately, but leads to different grain size solutions for each measurement type. A buried layer model based on the incoherent addition of echoes from hoar layer interfaces, in which scattering from a single layer is derived from small-perturbation methods, reconciles the ERS ơ0 and p data, with variations in hoar layer spacing of 12-17 cm providing the needed structural fluctuations for the observed range of ơ0 and p. Translation of layer spacing into accumulation rates predicts a 40% variability in accumulation rate from the windward to lee side and, more importantly, addresses high-resolution mapping of continental accumulation rates"--Leaves iv-v.
Download or read book Remote Sensing of Snow and Ice written by W. Gareth Rees and published by CRC Press. This book was released on 2005-08-12 with total page 336 pages. Available in PDF, EPUB and Kindle. Book excerpt: Many advances in spaceborne instrumentation, remote sensing, and data analysis have occurred in recent years, but until now there has been no book that reflects these advances while delivering a uniform treatment of the remote sensing of frozen regions. Remote Sensing of Snow and Ice identifies unifying themes and ideas in these fields and presents them in a single volume. This book provides a comprehensive introduction to the remote sensing of the Earth’s cryosphere. Explaining why cryospheric observations are important and why remote sensing observations are essential, it offers thorough surveys of the physical properties of ice and snow, and of current and emerging remote sensing techniques. Presenting a technical review of how the properties of snow and ice relate to remote sensing observations, the book focuses on principles by which useful geophysical information becomes encoded into the electromagnetic radiation detected during the remote sensing process. The author then discusses in detail the application of remote sensing methods to snow, freshwater ice, glaciers, and icebergs. The book concludes with a summary that examines what remote sensing has revealed about the cryosphere, where major technical problems still exist, and how these problems can be addressed.
Download or read book Assessment of Climate Variability of the Greenland Ice Sheet Integration of in Situ and Satellite Data written by National Aeronautics and Space Adm Nasa and published by Independently Published. This book was released on 2018-10-25 with total page 30 pages. Available in PDF, EPUB and Kindle. Book excerpt: The proposed research involves the application of multispectral satellite data in combination with ground truth measurements to monitor surface properties of the Greenland Ice Sheet which are essential for describing the energy and mass of the ice sheet. Several key components of the energy balance are parameterized using satellite data and in situ measurements. The analysis will be done for a ten year time period in order to get statistics on the seasonal and interannual variations of the surface processes and the climatology. Our goal is to investigate to what accuracy and over what geographic areas large scale snow properties and radiative fluxes can be derived based upon a combination of available remote sensing and meteorological data sets. Operational satellite sensors are calibrated based on ground measurements and atmospheric modeling prior to large scale analysis to ensure the quality of the satellite data. Further, several satellite sensors of different spatial and spectral resolution are intercompared to access the parameter accuracy. Proposed parameterization schemes to derive key component of the energy balance from satellite data are validated. For the understanding of the surface processes a field program was designed to collect information on spectral albedo, specular reflectance, soot content, grain size and the physical properties of different snow types. Further, the radiative and turbulent fluxes at the ice/snow surface are monitored for the parameterization and interpretation of the satellite data. The expected results include several baseline data sets of albedo, surface temperature, radiative fluxes, and different snow types of the entire Greenland Ice Sheet. These climatological data sets will be of potential use for climate sensitivity studies in the context of future climate change. Steffen, K. and Abdalati, W. and Stroeve, J. and Key, J. Unspecified Center NAGW-2158
Download or read book NASA Technical Memorandum written by and published by . This book was released on 1963 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Earth Resources written by and published by . This book was released on 1983 with total page 758 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book International Aerospace Abstracts written by and published by . This book was released on 1999 with total page 1032 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Analysis of Surface Melting and Snow Accumulation Over the Greenland Ice Sheet from Spaceborne Microwave Sensors written by Indrajit Bhattacharya and published by . This book was released on 2010 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Continuous monitoring of changes in the Greenland ice sheet from both space and air borne sensors has been conducted since the early 1970's. Since the mid-1990's dramatic changes occurring on the Greenland ice sheet have been observed both from space borne sensors and field work. These changes, primarily mass loss from the ice sheet, are related to the observed trend of earth's warmer climate in recent decades both in peer reviewed journals and in popular media. This dissertation addresses two parameters that contribute to Greenland ice sheet mass balance estimates. The first factor is characterization of surface melting of the Greenland ice sheet from satellite-based passive and active microwave sensors. We use a wavelet based edge detection technique to delineate surface melt from brightness temperature measured by passive microwave sensors. Along with brightness temperature data, we also use normalized backscatter data from the Quick Scatterometer (QuikSCAT) as an independent sensor for comparison with the radiometer derived results. We use a semi-empirical threshold based method for surface melt detection from QuikSCAT. Our results show a step-like, consistent increase in melt area of the Greenland ice sheet since 1995. This step-like increase is also observed in the mean summer air temperature along portions of the Greenland coast. The 1995 step-like increase of melt area (and melt index, a measure of melt intensity) is correlated with a distinct change of the North Atlantic Oscillation (NAO) index (from positive to negative) after 1995. The second factor is mass accumulation in the upper reaches of the ice-sheet. We use an empirical model that correlates mean annual brightness temperature to annual accumulation rate. We apply a microwave emission model for the dry snow region of Greenland to show that 37 GHz vertically polarized brightness temperature data are better suited to capture the inter-annual variability of snow accumulation. Using our model we estimate a snow accumulation time series from brightness temperature for 150 km x 150 km area around Summit Camp in central Greenland. Using measured surface velocities and ice thickness we calculate the surface mass balance for our study area. We find a positive mass balance of 3.18 ± 6.0 cm/yr. Our mass balance derived elevation change is in agreement with satellite altimeter data and published results of other researchers.
Download or read book Arctic Research of the United States written by and published by . This book was released on 1994 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book NASA SP written by and published by . This book was released on 1984 with total page 448 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Selected Water Resources Abstracts written by and published by . This book was released on 1976 with total page 802 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Determining Greenland Ice Sheet Accumulation Rates from Radar Remote Sensing written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-06-20 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: An important component of NASA's Program for Arctic Regional Climate Assessment (PARCA) is a mass balance investigation of the Greenland Ice Sheet. The mass balance is calculated by taking the difference between the areally Integrated snow accumulation and the net ice discharge of the ice sheet. Uncertainties in this calculation Include the snow accumulation rate, which has traditionally been determined by interpolating data from ice core samples taken from isolated spots across the ice sheet. The sparse data associated with ice cores juxtaposed against the high spatial and temporal resolution provided by remote sensing , has motivated scientists to investigate relationships between accumulation rate and microwave observations as an option for obtaining spatially contiguous estimates. The objective of this PARCA continuation proposal was to complete an estimate of surface accumulation rate on the Greenland Ice Sheet derived from C-band radar backscatter data compiled in the ERS-1 SAR mosaic of data acquired during, September-November, 1992. An empirical equation, based on elevation and latitude, is used to determine the mean annual temperature. We examine the influence of accumulation rate, and mean annual temperature on C-band radar backscatter using a forward model, which incorporates snow metamorphosis and radar backscatter components. Our model is run over a range of accumulation and temperature conditions. Based on the model results, we generate a look-up table, which uniquely maps the measured radar backscatter, and mean annual temperature to accumulation rate. Our results compare favorably with in situ accumulation rate measurements falling within our study area. Jezek, Kenneth C. Goddard Space Flight Center
Download or read book Earth Resources A Continuing Bibliography with Indexes Issue 50 written by and published by . This book was released on 1986 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Geographical Abstracts written by and published by . This book was released on 1987 with total page 748 pages. Available in PDF, EPUB and Kindle. Book excerpt:
