GRAVITY SURVEYS IN GLACIER‐COVERED REGIONS

Geophysics ◽  
1978 ◽  
Vol 43 (4) ◽  
pp. 819-822 ◽  
Author(s):  
Raymond D. Watts ◽  
William Isherwood

Prior to 1974, glaciologists used gravity surveys as a means of determining ice thickness, but the density variations in the underlying rocks were inherent sources of errors in their measurements. Because of these errors and because of the poor resolution of the gravity techniques, better geophysical tools for obtaining ice depths were sought. In polar regions, where the ice is below its melting temperature throughout most of the ice mass, radio echo sounders were used successfully starting about 1960. Until 1974, however, radio echo sounder experiments on temperate glaciers were unsuccessful. Temperate glaciers are found throughout the mountains of Washington, Western Canada, and Alaska. In many of these areas, terrain is so rugged that a helicopter‐borne gravity crew can find very few landing sites which are not on glaciers (Figure 1).

2019 ◽  
Vol 13 (2) ◽  
pp. 675-691 ◽  
Author(s):  
Cătălin Paţilea ◽  
Georg Heygster ◽  
Marcus Huntemann ◽  
Gunnar Spreen

Abstract. The spaceborne passive microwave sensors Soil Moisture Ocean Salinity (SMOS) and Soil Moisture Active Passive (SMAP) provide brightness temperature data in the L band (1.4 GHz). At this low frequency the atmosphere is close to transparent and in polar regions the thickness of thin sea ice can be derived. SMOS measurements cover a large incidence angle range, whereas SMAP observes at a fixed 40∘ incidence angle. By using brightness temperatures at a fixed incidence angle obtained directly (SMAP), or through interpolation (SMOS), thin sea ice thickness retrieval is more consistent as the incidence angle effects do not have to be taken into account. Here we transfer a retrieval algorithm for the thickness of thin sea ice (up to 50 cm) from SMOS data at 40 to 50∘ incidence angle to the fixed incidence angle of SMAP. The SMOS brightness temperatures (TBs) at a given incidence angle are estimated using empirical fit functions. SMAP TBs are calibrated to SMOS to provide a merged SMOS–SMAP sea ice thickness product. The new merged SMOS–SMAP thin ice thickness product was improved upon in several ways compared to previous thin ice thickness retrievals. (i) The combined product provides a better temporal and spatial coverage of the polar regions due to the usage of two sensors. (ii) The radio frequency interference (RFI) filtering method was improved, which results in higher data availability over both ocean and sea ice areas. (iii) For the intercalibration between SMOS and SMAP brightness temperatures the root mean square difference (RMSD) was reduced by 30 % relative to a prior attempt. (iv) The algorithm presented here allows also for separate retrieval from any of the two sensors, which makes the ice thickness dataset more resistant against failure of one of the sensors. A new way to estimate the uncertainty of ice thickness retrieval was implemented, which is based on the brightness temperature sensitivities.


Polar Record ◽  
1955 ◽  
Vol 7 (51) ◽  
pp. 467-485 ◽  
Author(s):  
E. J. C. Kendall

Scurvy was known from the earliest times as a condition likely to arise when men were constrained to live upon a limited diet because of crop failure, siege or extended voyaging. It was first clearly described in the thirteenth century but, although its connexion with restricted supplies and especially with paucity of vegetables and fruit in the diet, was recognized from that period, its occurrence was ascribed to many other factors. Thus, because it often affected many members of a closed community at about the same time, it was thought to be contagious; and although conditions such as cold, the diminution of daylight in polar regions and the constant humidity of sea voyages were the reason for lack of fresh fruits and vegetables, these conditions themselves were suggested as causes of the disease. Likewise poverty, resulting in overcrowding and insanitary conditions, was blamed, whilst in reality economic conditions prevented the poor from buying antiscorbutic foods.


2020 ◽  
Author(s):  
Michael Kern ◽  
Robert Cullen ◽  
Bruno Berruti ◽  
Jerome Bouffard ◽  
Tania Casal ◽  
...  

Abstract. One of the candidate missions in the evolution of the Copernicus Space Component (CSC) is the Copernicus polaR Ice and Snow Topography ALtimeter (CRISTAL). The aim of this mission is to obtain high-resolution sea-ice thickness and land ice elevation measurements and includes the capability to determine the properties of snow cover on ice to serve Copernicus’ operational products and services of direct relevance to the Polar Regions. The evolution of the CSC is foreseen in the mid-2020s to meet priority user needs not addressed by the existing infrastructure, and to reinforce the Copernicus services by expanding the monitoring capability in the thematic domains of anthropogenic emissions (CO2), polar and agriculture/forestry/emergency. This evolution will be synergetic with the enhanced continuity of services foreseen with the next generation of the existing Copernicus Sentinels. New high-priority candidate satellite missions have been identified by the European Commission (EC) for implementation in the coming years to address gaps in current capability and emerging user needs. This paper describes the CRISTAL mission objectives, main mission requirements driving its design, the payload complement currently under development and its expected contributions to the monitoring of important components of Earth’s cryosphere.


2020 ◽  
Author(s):  
Igor Mitrofanov ◽  
Lev Zelenyi ◽  
Vladislav Tretyakov

<p>The most interesting sites for future lunar outposts are thought to be located closely to poles, and South one is found to be more preferable.  But before humans could land there, the sequence of robotic missions should be implemented to study the natural environment at the selected sites, to deliver some supporting systems for ensuring conditions of habitability and also to test the innovated technology for Earth-Moon-Earth round trip.</p><p>Therefore, the Russian Lunar Program will be ignited by four robotic missions, which Russian Academy of Science has selected for the initial stage of this Program. Their names Luna-25 -28 were selected taking into account the name of the last Soviet lander Luna-24 of 1976. The objectives of these missions are critically important for accomplishment of the future polar expeditions of humans. The missions will conduct orbital mapping of polar regions with fine spatial resolution, measurements of radiation environment at the selected landing sites, testing of water and space volatiles in the polar regolith, and, in particular – testing presence of complex molecules and pre-biotic molecular complexes, the lunar dust and exosphere, etc. Mobile elements of landing missions will investigate local areas around the landing sites to determine the best spots for the future habitation modules of human missions. In addition, the researches for the basic science will also be accomplished by these missions, such as the experiments for lunar-based astronomy at long wavelengths and at gamma-rays, the experiments for lunar seismology, for monitoring of interplanetary plasma and solar wind, etc.</p><p>The talk presents in details the concept of the key mission of the first stage of the Lunar Program, the Luna-28 mission for lunar polar sample return. The mission concept is based on the several basic requirements. The mission should have the return module for direct flight from Moon to Earth. The module should be able to deliver to the Earth a set of samples of polar regolith with the total mass of about 2 kilograms. They should be quarried from different depths of the shallow subsurface from several cm down to 1 meter. Samples should be delivered to the Earth with all volatiles, including water, in the frozen state. Small moonrover “Lunokhod” with mass below 100 kg should be delivered to the Moon by the lander. Before the launch of the return module, the rover could deliver remotely selected stones for return at the nearest vicinity of the lander, after the launch, the rover should conduct scientific studies of the area around the landing site.</p><p>The mission of Luna-28 will also be supported by the ground segment for proper curation of delivered samples and for their studies in the leading domestic and international research centers. The complex molecules and organic molecular complexes will be the main objects for these studies.   </p>


2001 ◽  
Vol 33 ◽  
pp. 230-236 ◽  
Author(s):  
Takenobu Toyota ◽  
Masaaki Wakatsuchi

AbstractThe heat budget over the ice-covered area of the southern Sea of Okhotsk is estimated from in situ meteorological and ice observation for four years, 1996−99. The data are from about 1 week in early February in each of four years. Ice-thickness distributions required for calculating the heat budget are quantitatively obtained from video analysis. A one-dimensional thermodynamical model is used to calculate the heat flux. The total heat flux is obtained by summing up the area-weighted heat flux of each ice-thickness category. In addition, to determine the characteristics of the heat budget in this region, we also calculated the heat budget in the northern Sea of Okhotsk using Special Sensor Microwave/Imager ice-extent data and European Centre for Medium-range Weather Forecasts meteorological data, and compared the results. Our investigations show the following characteristics in the southern Sea of Okhotsk: (1) Due to relatively thin ice thickness, the average turbulent heat flux is upward. (2) Thin ice and open water contribute significantly to the total turbulent heat flux. (3) Thermodynamic ice growth is limited to about 1 cm d−1 on average. (4) The heat budget is largely characterized by abundant solar radiation. The first, third and fourth results are characteristic of this region located at a relatively low latitude, while the second one is similar to that for polar regions.


1997 ◽  
Vol 25 ◽  
pp. 237-240 ◽  
Author(s):  
Markus Harder

In polar regions, the exchange of heat, fresh water and salt water, and momentum between ocean and atmosphere is strongly affected by the presence of sea-ice cover. As a growing number of climate models include a dynamic–thermodynamic sea-ice component to take these effects into account, it might be asked whether sea ice is adequately represented in these simulations, and how far these simulations fit with physical observations.Sea ice in the classical models (Hibler, 1979; Parkinson and Washington, 1979) that have been available for two decades, is regarded as a two-dimensional (2-D) continuum covering the ocean surface. The prognostic variables describing the ice pack are horizontal ice velocity, areal coverage (ice concentration), and ice thickness. In numerical models, these variables and their evolution in space and time are solved on an Eulerian grid.A number of observational data are available to verify the model results. Sea-ice drift is observed from drifting buoys deployed on ice floes. Areal sea-ice coverage can be observed with satellite-borne passive-microwave sensors (SMMR, SSM/I). For ice thickness, which cannot be observed with remote-sensing techniques, rather few, scattered observations from upward-looking sonars on submarines and moorings are available.This article gives an overview of three additional variables representing sea ice in large-scale climate models. These are (1) roughness, (2) age of the ice, introduced as two prognostic variables, and (3) simulated trajectories of ice motion, which are diagnosed from the Eulerian velocity grid. The new variables enable a more detailed look at sea ice in models, helping to understand better the coupled dynamic–thermodynamic processes determining the polar ice cover. Further, the new variables offer important, additional possibilities for comparing the simulated sea-ice properties with available observations.


Polar Record ◽  
1977 ◽  
Vol 18 (115) ◽  
pp. 375-377 ◽  
Author(s):  
H. Björnsson ◽  
R. L. Ferrari ◽  
K. J. Miller ◽  
G. Owen

This brief report describes the first year of a joint Cambridge University—Iceland University two-year project to develop radio echo depth-sounding apparatus suitable for the temperate ice of the Vatnajökull ice cap. There is much interest in obtaining detailed ice thickness measurements for the 8 400 km2 Vatnajökull area, where only limited ice-depth surveys, using bore-hole and seismxic techniques, have been carried out in the past. A line of volcanic and geothermal activity extends through the western regions of the ice and creates a sub-glacial lake, Grimsvotn, which collapses every five years or so giving rise to the jökulhlaups, a catastrophic flooding which affects considerable areas of the Icelandic coast to the south of Vatnajökull. Proper understanding of the jökulhlaups phenomena can only be achieved if detailed knowledge of ice thickness and related data are available. Established radio echo sounding techniques which have been successfully applied in the polar regions do not work in water-laden ice such as is to be found in the Vatnajökull area.


Author(s):  
Jianfei Liu ◽  
Guoqing Feng ◽  
Huilong Ren ◽  
Wenjia Hu ◽  
Yuwei Sun

Abstract Ships performing their missions in the polar regions will inevitably suffer from sea ice collision, which will lead to structural safety problems. Therefore, ships should be designed according to the characteristics of polar sea ice to enable them to navigate safely in the polar regions. Based on the probability density curve of sea ice thickness and the occurrence frequency of sea ices of different sizes of the Kara Sea and the Barents Sea, this paper preliminarily designs ship’s bow sailing in the Kara Sea and the Barents Sea, establishes the ship’s bow-ice collision model and carries out numerical simulation to obtain the stress distribution. Then it optimizes the structure of the parts of the ship’s bow. After the optimization, the bow structure meets the strength requirements and the weight of the ship’s bow is relatively light.


2016 ◽  
Author(s):  
Petteri Uotila ◽  
Dorotea Iovino ◽  
Martin Vancoppenolle ◽  
Mikko Lensu ◽  
Clement Rousset

Abstract. A set of hindcast simulations with the new NEMO3.6 ocean-ice model in the ORCA1 grid and forced by the DFS5.2 atmospheric data was performed from 1958–2012. We focussed on simulations that differ only in their sea-ice component: the old standard version LIM2 and its successor LIM3. Main differences between these sea-ice models are the parameterisations of sub-grid-scale sea-ice thickness distribution, ice deformation, thermodynamic processes, and sea-ice salinity. Our main objective was to diagnose the ocean-ice sensitivity to the updated NEMO-LIM sea-ice physics. Results of such analysis have not been published for this new NEMO version. In the polar regions, NEMO-LIM3 compares better with observations, while NEMO-LIM2 deviates more, producing too much ice in the Arctic, for example. Differences between NEMO-LIM2 and NEMO-LIM3 do not change in simulations even when the freshwater adjustments are turned off. In the extra-polar regions, the oceanographic conditions of the two NEMO-LIM versions remain relatively similar, although they slowly drift apart over decades. A simplified NEMO-LIM3 configuration, having a virtual, single-category sea-ice thickness distribution, produced sea ice with a skill sufficient for ocean-ice hindcasts that target oceanographic studies. We conclude that NEMO3.6 is ready to be used as a stand-alone ocean-ice model and as a component of coupled atmosphere-ocean models.


Sign in / Sign up

Export Citation Format

Share Document