Search

In April-May 1998 sea ice conditions in the Barents and Kara Seas were studied from synchronous RADARSAT, ERS and "Okean" radar images. SAR images were transmitted in quasi-real time onboard nuclear icebreaker "Sovetsky Soyuz" and signatures of the main sea ice types and features were retrieved and compared with subsatellite observations. RADARSAT and ERS signatures of first-year ice are rather similar, whereas for gray and new ice they can be different. Analysis of synchronous RADARSAT and "Okean" images proved, that large-scale ice features can be identified from both images, whereas navigationally important small-scale features-only from SAR.

Coincident ship based X-, C-, and L-band scatterometer data and measurements of physical ice and snow properties were collected during ERS-1 synthetic aperture radar (SAR) overflights in the Barents Sea in March of 1992. One aspect of this Seasonal Ice Zone Experiment (SIZEX) concentrated on the marginal ice zone (MIZ), where a variety of sea ice types and open ocean conditions were encountered. A specific objective of SIZEX was to determine which MIZ ice types can be clearly discerned using ERS-1 SAR C-band imagery. First- and second-order statistics were generated to characterize ERS-1 ice signature. Comparing these statistics for each ice type, reveals that many of the ice types observed in the MIZ have comparable tones, as indicated by their means (i.e., multiyear and pancakes). However, the use of the SAR image texture may be used in conjunction with the tonal properties to successfully discern the various ice types and open water (all wind regimes) found in the MIZ. >

We have studied hypervelocity impacts at 5 km s−1 of 1 mm diameter projectiles on two types of ice: H2O and CO2. We compare crater morphology for the resulting impact craters and find that the craters are smaller in the CO2 ice than in H2O ice. However the crater shape, as expressed by the ratio depth/diameter, is indistinguishable between the two types of ice. Further, we have investigated the dependence of crater size and shape on projectile density. We find that for densities of 2750 to 7850 kg m−3, the ratio depth/diameter does not have the strong dependence on density suggested elsewhere in the literature. This is true for both types of ice. We thus suggest that whilst the crater size may depend strongly on ice type, the shape does not and is also almost independent of projectile density.

During a field expedition with the Russian nuclear icebreaker "Sovetsky Soyuz" to the Laptev Sea in September 1997, RADARSAT ScanSAR images were used to investigate late summer ice conditions and support ice navigation. The predominant ice types were first year and newly formed ice, primarily nilas. The in situ observations made from the icebreaker and its helicopter were used to validate the ScanSAR observations and assess the capability of RADARSAT data to discriminate open water, first year and new ice. Also SSM/I and ERS SAR were compared with the ScanSAR data. To observe first year ice at concentrations above 10% seemed to be straight forward, while nilas was difficult to discriminate from open water during low wind conditions. Use of RADARSAT ScanSAR data represents a significant improvement in ice monitoring and navigation in the Northern Sea Route.

This paper describes a minor part of the work done in connection with a preliminary investigation of a neural network’s capability to classify ice types. It includes a short review of earlier used techniques, implementation of different neural networks and results from various experiments with these networks. The estimation of ice type concentrations from Synthetic Aperture Radar (SAR) images has been investigated for several years, see e.g. [9]. The classification estimation has been performed by training a Bayesian Maximum Likelihood Classifier (BMLC) [8] with a classification rate about 80%. The neural networks considered are all of the feed-forward type. For training, different learning algorithms and error functions are used. Both pruning and construction algorithms are used to get an optimal architecture. Experiments showed that almost any kind of neural network, using a Standard Back-Propagation (Std_BP) learning algorithm for minimising the Mean Square Error (MSE), is able to perform better than the BMLC. The reason is that the neural network is able to use a larger training set than the BMLC.

ERS-1 Synthetic Aperture Radar (SAR) imagery from the Alaska SAR facility is available to operational ice analysts at the Joint Ice Center. Analyst can use the imagery directly through manual interpretation. One such use would be to provide information on ice conditions for a field expedition. In addition, analysts can run automated algorithms which produce estimates of ice type and ice motion from SAR images. Such automated analysis will become increasingly important if SAR is to be used to improve climatologies of ice characteristics and to improve the performance of dynamic ice models. Here the ice classification and ice motion algorithms developed by the Jet Propulsion Laboratory for ERS-1 SAR imagery are evaluated and results presented. Remote sensing, Synthetic aperture radar, Sea ice.

Different mechanisms in various ice-structure interaction scenarios are described. Only bottom-founded structures are considered, and the aim is to give insight for ice forces design starting from the physical background. The effect of structural shape and size at the water-line, type of foundation, structural rigidity, mass and damping are related to ice type, properties, thickness, integrity and velocity, as well as to other environmental effects to result in typical ice-structure interaction modes. Ice failure can be visco-plastic yielding, crushing, shearing, bending or splitting. Structural response can be static or dynamic. Also the ice can exhibit dynamic response. A coupling of the dynamic response of the structure with the ice failure process may develop. After ice failure has occurred, the clearing mechanisms of broken ice are again dependent both on the structure and the ice.

We quantitatively assess seasonal changes in community structure and habitat selection among seabirds in the Scotia-Weddell Confluence region, Antarctica. Additionally, we discuss the biological and physical factors underlying the patterns. Data were derived from strip-transects on closely-coordinated multidisciplinary cruises that characterized the physics and biology during spring 1983, autumn 1986 and winter 1988. We describe for the first time ever for the Southern Ocean seasonal changes in seabird communities in terms of composition, using cluster analysis, as well as relative density and diversity among species. Sea-surface temperature, distance to the pack ice edge and ice type, all physical characteristics of habitat, were the most important environmental variables that affected assemblage composition

This paper presents an overview of recent remote-sensing techniques as applied to geophysical studies of floating ice. The current increase in scientific interest in floating ice has occurred during a time of rapid evolution of both remote-sensing platforms and sensors. Mesoscale and macroscale studies of floating ice are discussed under three sensor categories: visual, passive microwave, and active microwave. The specific studies that are reviewed primarily investigate ice drift and deformation, and ice type and ice roughness identification and distribution.

The development of strong preferred c-axis alignments in sea ice has been a subject of debate since its initial discovery in 1959. Although numerous theories have been proposed for its development, none has been able to account for all of its field characteristics.A detailed field investigation was carried out at Pond Inlet, N.W.T., to describe further the occurrence and structure of this ice type. Data collected over the winter of 1983–84 suggest two possible mechanisms of development. The first involves the selective growth of crystals during the formation of the initial ice skim, while the second requires the solid-state rotation of slip planes during constrained plastic deformation.

The rigidity modulus is determined for simply supported, circular ice plates 0.5 and 1.22 m in diameter. Measurements for the 0.5 m diameter plates were made at −10 °C and for the 1.22 m plates in the range of −7 to −37 °C. The elastic moduli and Poisson's ratio, calculated from the rigidity modulus, are in the range of 6.0–12.0 GPa and 0.29–0.60 respectively, depending on ice type, temperature, and grain size. The plate characteristic lengths calculated from the measured values of the elastic moduli are compared with characteristic lengths determined from field measurements of the deflection of ice covers under load. Key words: ice, ice cover, rigidity modulus, elastic modulus, Poisson's ratio.

A geologic interpretation of a 1:500 000 scale mosaic of optically correlated Seasat SAR imagery showed that 14 of the 17 major units mapped by the Geological Survey of Iceland could be recognized although it was not possible to close all the radar geologic boundaries. Interactive work with computer correlated imagery produced no additional information significant to mapping at that scale. Comparison with Landsat revealed that the radar produced more data on ice type, alluvial categories and upon lineaments but the overall interpretative value of Landsat was clearly the better of the two. The results of local co-registering Landsat and Seasat were interesting but did not cause any modification of the regional interpretation

A computer simulation program which depicts the behaviour and distribution of oil spilled in or under sea ice has been developed. The program combines mathematical models developed in previous studies to describe the motion of oil in/under landfast, first-year and multi-year ice. By inputting or estimating such key parameters as oil type, spill type, spill duration, flow rate, ice type, relative under ice current speed and direction, under ice roughness and distinct ice features, a time series of “maps” is generated showing the distribution of the spilled oil. At present, the simulation does not include the movement of oil contaminated ice but future development plans include incorporation of the program into a Beaufort Sea ice motion model. The program is a tool which can be used to assist on - scene commanders during spill response and to plan counter-measures for oil spills in/under sea ice.

Measurements of the ultrasonic absorption of water have been made up to pressures of 2000 kg/cm2. The data show that both the shear and compressional losses decrease as the pressure is raised. Comparison of these results with the values predicted by Hall's theory of sound absorption in water shows that the theory must be modified to be in agreement with the experimental data. The modification consists of assuming that the open or ice type of packing is associated with the higher free‐energy state. If this modification is made, the observed data is in excellent agreement with theory. This result leads to the conclusion that even at 0°C less than 30 percent of the molecules in water are arranged in the ice type of packing. The results also indicate that the free‐energy difference between the two states of packing in water is temperature dependent.