Under-ice sonar surveys were carried out in pack-ice fields near Fletcher’s Ice Island and at two sites north of Pt. Barrow, Alaska, U.S.A. A narrow-beam scanning sonar was used to measure the location and relative back-scattering of features on the under surface of Arctic sea ice. The 48 kHz sonar had a 1.5° by 51 ° beam width. Graphic records displaying the range and relative scattering levels were assembled into sonar maps which display location and shape of under-ice features. Two distinct types of back-scattering were found: (1) very high-level back-scattering from well defined under-ice ridges and (2) very low back-scattering from areas between ridges. Higher scattering at ridges was probably due to an increase of roughness and tilting of the average plane of the scattering surface. To measure depths of features, the sonar transducer was adjusted to give a wide horizontal beam and a narrow vertical beam. Polar scans were taken at several depths of the transducer to determine depths of ridges. The tops and bottoms of features were compared and the average ratio of peak elevation to keel depth was about 1:7.

Fuller accounts of some of this work have been published elsewhere (Berkson and others, 1973; Clay and Leong, 1974; Kan and others, 1974}.

Under a long-term, bi-national, multi-disciplinary research project between the U.S. Geological Survey and various Icelandic scientific organizations, MSS imagery from the ERTS-I satellite is being used to study the varied dynamic environmental phenomena of Iceland, including its glaciers and ice caps. Initial analysis of the ERTS-I imagery has shown the importance of the repetitive imagery to:

• Record relatively short-term glaciological changes. According to measurements made on two ERTS-I images, taken 11 months apart, an outlet glacier in the north-east part of Vatnajökull, had surged 1.8 km. A combination of field observations and analysis of ERTS imagery shows a total surge in excess of 3 km which probably took place in a few months, perhaps in as little as a few weeks. Contorted moraines on another of Vatnajökull’s outlet glaciers, Skeiðararjökull, on the south-east coast, show a movement of 600 m in an 11 month period even though the snout of the glacier remained in essentially the same position.

  Several glacier-margin lakes have been observed to change in size during the year (1972-73), particularly Grjœnalón, which continued to enlarge in area each time it was imaged until its size diminished markedly after a jökulhlaup partially emptied the lake in August 1973. Seasonal changes in the size of sediment plumes along the coast, where glacial rivers debouch their sediment-laden water into the ocean, can also be observed in a time-lapse manner.

• Furnish the data necessary to revise certain glaciological features on maps, and to produce ortho-image maps of ice caps directly from ERTS imagery, at least to map scales of 1: 250 000. Sufficient ERTS-I imagery of Iceland from the late summer and early fall of 1973 now exists to map accurately, from a planimetric standpoint, 90% of that area of Iceland covered by glacial ice (previously estimated to be 11.5% of total area of Iceland). Optimum imagery (minimum snow cover, maximum exposure of glacial ice) has been obtained of Vatnajökull, Langjrikull, Hofsjökull, Myrdalsjökull, and Eyjafjallajökull or five (including the four biggest) of the seven largest ice caps in Iceland and five of the smaller (less than 50 km2) ice caps as well. On 19 August 1973 Hofsjökull had an area of 915 km- on ERTS imagery. Its area has usually been cited as 996 km2. On a 1945 Danish Geodetic Institute map (1: 500 000) the area is 981 km2; U.S. Army maps (1 : 250 000, 1969) show an area of 943 km2.

• Map subglacial volcanic and structural features. Within or at the margins of the ice caps and outlet glaciers, a number of new glaciological, structural, and volcanic features can be mapped from ERTS-I imagery, particularly at low solar illumination angles (<10°) including several probable subglacial central volcanoes, calderas, and tectonic lineaments. Some of the effects of jökulhlaups can be mapped, including subsidence cauldrons resulting from subglacial volcanic or intense geothermal activity.

This paper reviews possible uses of remote-sensing techniques to locate avalanche victims. Until recently probes and dogs were the only methods available, but recently attempts have been made to devise other methods for finding human beings in snow. Ideally such a search should be made possible for other members of the party, as the chance of survival of a victim falls rapidly with increasing time to rescue. For this all members of the party need to have something which the others can locate. The most usual proposal is an electromagnetic transmitter/receiver set. The merits of various possible frequencies are discussed. International agreement on a frequency is urgently required. Magnetic devices might be considered, but the detecting devices are too expensive or heavy to be generally carried. Search parties can of course be equipped with more sophisticated apparatus, and various possibilities are discussed for identifying metal on the victim, for identifying him by radio sounding, for locating him by mapping microwave emission, or for searching for eddy currents induced in him.

The principal elements in the Canadian national program in remote sensing are:

• The ERTS receiving station in Prince Albert,

• ERTS and airborne data processing facility in Ottawa,

• ERTS and airborne photographic reproduction facility in Ottawa,

• The airborne program,

• The remote-sensing test sites,

• The sensor development program,

• Regional and speciality interpretation centres,

• The necessary organization to manage the national program in remote sensing.

The Canada Centre for Remote Sensing (CCRS) has three operating Divisions: The Data Acquisition Division, the Data Processing Division, and Applications Division. New sensors are developed by the Centre with contracts to industry and universities. Photographic reproduction and distribution is handled by the National Air Photo Library (NAPL) of the Department of Energy, Mines and Resources.

Canada designed and constructed her own ERTS ground receiving station at Prince Albert, Saskatchewan. It was put there because of the existing 26 m diameter antenna, near the middle of the country. Data from the extreme east of Canada are not received at Prince Albert. There are plans for an east-coast station.

A quick-look display system has been incorporated into the Prince Albert station. It comprises a high-quality television display and a 70 mm camera. Prints from these negatives and microfiche copies of them (ERTSFICHE) are produced under a franchise arrangement and mailed out within two days of the satellite pass. About 70 ERTS images of Canada a day are received at Prince Albert. A tape record of the raw ERTS data is made and sent for processing to Ottawa.

This tape is handled by the Ottawa ERTS data processing facility. 70 mm monochrome images of each of the four ERTS-I multi-spectral scanner wave bands and computer-compatible tapes are produced by the facility. PDP-10 computers are also utilized for image inventory, the image analysis research of the Applications Division of CCRS, and processing airborne data.

An inventory of ERTS images is compiled in the CCRS computer as they are created together with comments on cloud cover and quality. Orders for the images are received by NAPL, checked against the computer inventory, and filled as soon as possible. The average time to filling such orders was about four weeks in December 1973, though fluctuations in service and back-log problems occur owing to occasional equipment malfunctions. An experimental regional capability of quizzing the image file is being considered. This consists of a remote terminal to the CCRS PDP-10 computer which can operate from any telephone.

The photographic products, in both colour and monochrome, maintain the full resolution of the ERTS system. NAPL also handle the reproduction and distribution of all airborne remote-sensing data from the full range of multi-spectral information present in the tapes.

CCRA has four aircraft equipped with a wide range of photographic sensors, far-infrared scanners and radiometers, and some newly developed special-purpose sensors such as a chlorophyll spectrometer, a laser fluorosensor, and a microwave scatterometer and radio-meter. These are available across Canada on a partial cost-recovery basis. Over the past three years, a series of research and development contracts to construct new equipment for clearly defined needs such as sea-ice thickness measurement, have been let by CCRS to Canadian industry and universities.

The Provinces of Ontario, British Columbia, Manitoba, and Alberta, have established their own remote-sensing centres, and Speciality centres exist at the Canada Centre for Inland Waters at Burlington for limnology, at the Department of the Environment, Ottawa for hydrology, at the Forest Management Institute, Ottawa for forestry, and at the Department of the Environment in Victoria, B.C. for oceanography.

The information content of satellite data is so high that it is not possible to display all the information in one colour print. Computer programs have been developed and special hardware systems are being acquired so as to make a statistical analysis of spectral signatures on the ERTS tapes.

The paper discusses three aspects of the interaction of a radar pulse and the medium which is being sounded, that is the glacier proper and the lower scattering surface. These aspects are:

• Radar signals attenuation during vertical sounding.

• The rale of radar signal propagation through the glacier.

• Fluctuations of radar signals during horizontal movements.

Representative samples of signal attenuation were chosen for two points in the vicinity of Mirny station in Antarctica, these samples were obtained under roughly constant temperature conditions of the ice. The scattering properties of the bedrock are shown to be the controlling factor. Histograms of attenuation for these two points are given; effective temperatures of the ice were estimated.

The measurements of the propagation velocity of electromagnetic waves were made along paths near “Molodezhnaya” station. Interesting results were obtained. The curves of the variation of the amplitude of reflected pulses were obtained for a number of short-distance paths with the radar moving horizontally, the working radar frequencies were 60, 213 and 440 MHz. Radii of autocorrelation of signal fluctuations were estimated. The fluctuation pattern along each of the paths is shown to be stable in time provided the distance is short enough. Measurement of the surface velocity of ice sheet movement by the transition of the fluctuation pattern in time seems quite promising.

An electromagnetic linearly-polarized signal transmitted through the glacier in a vertical direction, reflected from the bedrock, and received with a receiving antenna, is found to be changed into one either partially or elliptically polarized. The polarization changes are believed to be due mainly to the crystal structure of the glacier and anisotropy caused by the pressure of the upper layers.

An analysis of the polarization diagrams obtained is up to the present the main method used for studies of the reflected signal polarization. Evidently using a simple dipole a partially-polarized signal is not distinguishable from one that is elliptically polarized, nor is a nonpolarized signal distinguished from circularly polarized. However, the data recently obtained are of great importance, particularly from studies of glacier crystal structure made in deep core drilling.

Possible reasons for the polarization changes of the signal have been analysed. Results of the analyses of the polarization diagrams obtained both at individual points and along extended traverses are discussed. It has been found that the signal reflected from a considerable ice thickness is polarized in such a way that the parallel orientation of the receiving and transmitting dipoles can be disregarded. En route recordings of the signal fluctuations obtained by parallel and orthogonally polarized dipoles are shown. The results of polarization studies are important for practical purposes. For example, bedrock relief sounding carried out with crossed dipoles makes it possible to get rid of interference signals occurring due to scattering from inhomogeneous structures of the upper part of the glacier.

The inverse problem of radio-echo sounding consists in the reconstruction of subglacial relief from the known radio-echo profile, and the path, and speed of the aircraft. The present work shows that in the geometrical optical approach the solution of the inverse problem for a homogeneous, two-dimensional object (valley glacier) exists, and there is a unique solution. An algorithm for interpretation of the experimental data is suggested. It may be considered as the generalization of Harrison’s transformations for any surfaces. paths, and speed.

The direct problem of radio-echo sounding consists in the reconstruction of radio-echo profile from the known surface and subsurface relief, path, and aircraft speed. The analysis of traces in the standard radio-echo sounding mode of operation reveals the possibility of introducing a three-index trace classification {K, sign S’(o), K+} where K is the number of real roots characteristic of the equations, K+ the number of positive roots, and S’(o) the position derivative, the argument being equal to zero. The form {o, — o} is optimal for the precision of the calculation of the reflected surface coordinates, as well as for the simplicity of the interpreted picture. By a special choice of the altitude of flight, any form of any surface can be brought to {o, —o}. The decrease in beam width is equivalent to the diminution of roots of the characteristic equations. For a pencil beam the trace degenerates into a point.

The attenuation of the reflected signal depends on the glacier geometry, the dielectric parameters of the medium, the altitude and the course of the aircraft, as well as statistical characteristics of the mutual orientation of the interfaces and aerials. For the description of the energetics of radio-echo sounding, equivalent reflecting surfaces are suggested. These surfaces correspond to the Harrison’s equivalent reflecting surface. Exact formulae for the power of coherent and incoherent components of the reflected signal are obtained. Components of the full attenuation such as absorption, depolarization, and spherical divergence, are investigated with respect to refraction and focusing effects.

Experiments on radio-echo sounding of mountain glaciers have been done on Lednik Marukh (west Caucasus), Lednik Bezingy and Lednik Dzhankuat (central Caucasus), Lednik Gergety (east Caucasus), and Lednik IGAN (Polar Urals) in 1967-71 as a part of the I.H.D. programme. Radio altimeters operating at a frequency of 440 MHz with a pulse duration 0.5 μ5 and with an assumed radio-echo system performance of 130 dB were used. The apparatus was operated from the ice surface (using sledge or vehicle) and partly from a helicopter. Some measurements have been made while the apparatus was being moved continuously along longitudal and transverse profiles of the glacier. Some of the measurements have been made at separate points on the glacier. The methods of measurement and interpretation have been worked out. Data on ice thickness, subglacial topography, and internal structure of some mountain glaciers have been obtained and compared with data got using other geophysical methods and thermal drilling. There is agreement between the results.

Field experimental data show the possibility of using standard radio-echo sounding equipment of relatively low power to sound through a temperate mountain glacier. The main problem of sounding is the interpretation of echo signals, because they are a mixture of visually indiscernible echoes from the bed and from inhomogeneities in the body of the glacier. To get information about ice thickness and other things from such echo data, a method based on a statistical analysis of echo-signal fluctuations is proposed. As a main criterion the stability of echo-signal statistical characteristics is used.

Special portable equipment was designed based on this method. The equipment makes the interpretation of radio-echo sounding data simple. It eliminates distortions of echo signals because of receiver overloading by powerful impulses, automatically records the form and intensity of signals, makes its amplitudes proportional to reflection characteristics of the ice bed and inhomogeneities of the glacier body, and makes automatic statistical analysis. The thickness of a glacier, and the position of inhomogeneities within its body, are determined given more than ten radio-echo signal positions.

The method and the equipment have been used to determine thicknesses of Lednik Dzhankuat (Caucasus). Radio-echo sounding data have been compared with data obtained by other geophysical methods and thermal drilling. There is a good agreement (±10 m when the ice thickness is about 100 m).

Temperate mountain glaciers have specific peculiarities which make the interpretation of radio-echo sounding data much more difficult than for polar ice sheets. On the A or Z indicators one can observe a plurality of pulses differing in shape, amplitude, and range. Often a gap is observed on the film. The problem is to select the pulses from the bed or internal reflecting horizon and to reconstruct the subglacial relief or internal interface.

During preliminary processing, the radio-coordinates of all marks on a type A radiogram are written into a table. Then non-informative marks are eliminated and informative marks are situated on a continuous line or trace.

We put into practice three methods of interpretation: (1) an envelope method, (2) Harrison’s transformation method, (3) approximation of segments of a trace by straight lines. Harrison’s transformation method is the most general one; the others are useful for the presentation of results in a graphical form. The suggested methods are used for the interpretation of the data from a transverse profile of the valley glacier Lednik Bezengiy, Caucasus, 1970-71. Radar RW-10 with a carrier frequency of 440 MHz and overall receiver sensitivity relative to the transmitter pulse power 130 dB was used. It was revealed that the transparency of the glacier changes from year to year. The maximum ice thickness measured was 33°±15 m. Some extended interfaces in the body of the glacier were discovered. One of them, 80 m deep, coincides with seismic contrast interface and with the 0° C isotherm. Radio-echo sounding data are in agreement with gravity measurements on the same profile.

Doppler-effect laser equipment was successfully employed in Antarctica in 1969-70 to measure the rate of ice-sheet motion. The method is based on measuring differential beat frequency generated by the interaction of the direct pulse and its echo. A He-Ne laser with the wavelength of 6 328 Â was used in the 15th Soviet Antarctic Expedition. The paper gives detailed results of the measurements along with a description of the equipment used and of the observational procedures. A new modified version of the equipment was made ready for 1971-72 Antarctic season, and was used in the 18th Soviet Antarctic Expedition in the vicinity of Mirny station. New results are also discussed. Analysis of all available data makes it possible to believe that the movement of the ice sheet is irregular with occasional stops. The progressive motion of the ice sheet is accompanied by strain oscillations.

The paper gives measurements of the velocity of electromagnetic wave propagation in sea ice, the tangent loss, and the specific absorption obtained by means of coaxial-line experiments, assuming sea ice to be the dielectric. Measurements have been made at frequencies of 30, 60, 100, 200 and 400 MHz by pulses of 0.05 and 0.5 ms and video pulses of 0.02 ms at a repetition frequency of 10 kHz, with temperatures from —40° C to —10° C and salinities 17, 8.6, 4.4 and 0.56‰. Data obtained on the values of the tangent loss are in a good agreement with those obtained by Addison. The velocity has been found to be constant (170 m/ms) for radio and video pulses in the ice at any salinity value and temperatures below —22° C. At higher temperatures the velocity decreases being more pronounced with the salinity increase. Data on electrical characteristics of sea ice averaged throughout the ice thickness are presented. These measurements have been made by using long lines, frozen into the ice. Experimental radio-echo soundings of sea ice carried out at the drifting stations SP-19 and SP-21 in 1971-72 and 1972-73 by means of pulsed radar systems in the range 200-100 MHz are also discussed.

In order to make the inventory of perennial snow patches in central Japan as a part of the I.H.D. world inventory of perennial ice and snow masses, observations have been continued by the author and collaborators by taking photographs of snow patches from the air every autumn since 1968. The results obtained during the period from 1968 to 1970 were published as the Atlas of perennial snow patches in central Japan (Higuchi and Iozawa, 1971). The flight for observation in 1972 was made on 13 October, just after 5 October 1972 when the Earth resources technology satellite (ERTS-I) imagery of central Japan was obtained. Therefore it was possible to compare the ERTS imagery of perennial snow patches in central Japan with aerial photographs of them.

The perennial snow patches can be classified as (a) snow patches developed mainly from avalanching, (b) those developed mainly from snow drifting, and (c) those developed from both. The perennial snow patches in central Japan are mainly those of types (a) and (b). Since the prevailing wind direction in winter is north-west in this area, snow drifting and also avalanching of drifted snow occur at the eastern side of the mountains running southwards from the Sea of Japan. Therefore, 65% of the perennial snow patches of type (a) and 70% of those of type (b) are located at the eastern side of mountains. Fortunately, the ERTS imagery of this area was obtained at a local time when the solar azimuth was 143° so that many of the snow patches were in sunshine. Therefore, comparison of the ERTS imagery of snow patches with aircraft photographs in this case can be used as the data to discuss the limit of observation of small ice and snow masses by this satellite.

It was found from comparisons between the ERTS-I MSS imagery of band 4 (0.5 to 0.6 μm), band 5 (0.6 to 0.7 μm) and band 6 (0.7 to 0.8 μm) that the band 4 imagery was best to distinguish snow patches. Snow patches of type A were most clearly seen on the imagery. Since they are located in the valleys where avalanching occurs, the contrast between the white snow surface and the dark valley walls was quite clear. For instance, it was easy on the imagery to find four long snow patches (No. 12 701, 12 708, 12 718 and 12 720 in the Atlas) at the eastern slope of the mountain Tsurugi Dake (2 998 m above sea-level), their width being 30-50 m and their length 1 000-l 500 m. It was difficult on the imagery to distinguish snow patches of type (b) from an exposed surface, since they are not so long as those of type (a), but circular and small. However, big ones of type (b) can be found on the imagery when they are located near ridges in the sunshine. For instance, the snow patch No. 18 509 in the Atlas was seen on the imagery, its size being 200 m X 100 m. Snow patches of type (c) are few and this type seems most difficult to find on the imagery, since they located at the bottom of cirque valleys in the shadow.

An automatic snow-depth meter was constructed using an infrared beam from a gallium-arsenide photo-emission diode and an infrared detector consisting of a silicon photocell. As the field of view of both photoelectric elements is 30°, high mechanical accuracy is not required. The equipment consists of two poles of the same size, 4.8 m high and 20 cm by 20 cm wide, an operation controller, and a digital recorder. The two poles were set up on the ground facing each other at a distance of 5 m. One pole has the photo-emission diode and the other the infrared detector. In each pole, a long slit 4 cm wide and 4 m long was installed. Through one slit the infrared beam comes out and is received through the other slit. To avoid catching snow or rain in the slits, air was ejected through them.