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Contents:
Sound: A POW’s Weapon 91
By Commander Everett Alvarez, Jr.,
U. S. Navy
Landsat: A Routine Problem-Solving Tool for Naval Officers 94 By Bruce H. Needham
Sound: A POW’s Weapon
By Commander Everett Alvarez, Jr.,
U. S. Navy, First American Prisoner of War in the Vietnam War
Have you ever asked yourself what would happen if you were thrust into a situation where you were deprived of the ability to employ all your senses? To survive, you would have to adjust.
And adjust is just what the prisoners of war who were detained in the prison camps in North Vietnam did. Although we did not physically lose our senses, we were deprived of the normal functions of our senses.
Almost immediately after capture, we aviators who had been shot down and apprehended by the North Vietnamese were confined in almost unimaginable conditions.
“Bodies built for movement were confined to closet-like boxes, active minds were forced to be idle within the numbing nothingness of four walls in a dingy little cell . . . ”'
Many of us lived in cells seven feet by seven feet. All through the day there was no light—save whatever daylight could filter through small ventilation ducts near the ceiling about 18 feet above the floor. The concrete walls were barren. The concrete floors were almost always moist. Most cells had two, two- foot-wide concrete slab beds on either side. This left a narrow aisle about two- 1 Robinson Risner. The Passing of the Night, Random House, 1973, introduction.
and-a-half-feet-wide and seven-feet- long in which to walk. The entrance to the cell was blocked by a heavy steel reinforced door. If a person was fortunate, his door would have a crack or a termite-eaten pinhole in it through which he might be able to peek out, or through which a small ray of daylight might penetrate into the cell.
Most of us were issued a straw mat, a mosquito net, a water jug, a metal cup, one blanket, a set of prison striped pajamas, and two pairs of shorts. These were all our earthly possessions. Each cell was furnished with a “Bo” (small wooden bucket which served a combined, purpose as our commode, our sink, and our stool).
For the first few years that the North Vietnamese had American prisoners, the Viets would allow the prisoners out of their cells for just five to ten minutes a day to wash, rinse our clothing, and dump the Bo’s. (If a prisoner was being punished or under maximum security for some reason, he would not be allowed these “privileges.”) Except for the times that the prisoners were taken to interrogation, they never ventured more than a few feet from their cells, and then only for the reasons stated above.
For almost all of our waking moments, there was nothing to see. There was very little to touch or feel. And most of us who spent a very long period of time in solitary confinement—I personally knew individuals who lived in isolation for one, two, three, and even four years—may just as well have lost the ability to talk. We had no one with whom to speak.
As a consequence, and out of necessity, we had to adapt ourselves to a new manner of living. We depended primarily on sound. In our new existence, hearing was now our primary sensor. We came to know our new immediate world through its sounds. As time passed and as the weeks rolled by—turning into months, then years—the sounds we lived with and learned to know so well became our only real world.
From the time the gongs would ring in the early morning, until they rang again at night marking the end of another day, familiar noises filled the long hours signifying the passing events of the daily routines.
We learned to tell by the particular way the turnkey (guard) rattled his key ring who was on duty for that day. We knew by the manner in which he handled his keys and the rate at which he opened the cell doors if he was being hurried, or if he was in no particular hurry. We could sense anything unusual that was happening, or if the turnkey was just in the area conducting his routine chores, and if he was in a pleasant or sour mood.
We could tell by the particular creaking noises the doors made as they were
being swung open whose cell it was. The shuffling noises as the rubber sandals scraped along the concrete floors gave us the clue as to who was out of his cell washing himself or dumping his Bo.
We learned to recognize each prisoner’s peculiar cough, or the manner in which he cleared his throat, or wheezed, or sniffed his nose. We also learned to recognize each of the guards by their guttural commands, their individual vocal characteristics, and the peculiar tones of their voices.
We also learned to keep an open ear for danger signs—the swishing of a guard’s ammo belt against his trousers, or the pat of his gun butt against his leg—especially when we were engaged in some covert activity, such as communicating. As we quietly pressed our ears against a crack in the door or lay on the floor with our ears against a rat hole at the bottom of the door, these same noises indicated if the guard was equipped with an AK-45 semi-automatic rifle or an old World War II model carbine.
Our sense of hearing became so sophisticated that we knew when a guard was in our area making his rounds, if he was daydreaming, or if he was unusually alert or wary. His pace indicated his intentions, and whether he had seen something or discovered something out of the ordinary. We could even tell by the combinations of many noises that he generated where he was looking and at what he was looking. Unbeknownst to the guards, we had them under constant sensory observation the entire time they were in the area of the cell-blocks.
There were also the friendly sounds— the small, incidental, relatively unimportant noises, such as the rats scurrying throughout the cell-blocks at night in their search for food, the chirping of a bird somewhere outside, the rustle of a stiff breeze through the leaves of a tree beyond the courtyard wall, the rushing of the water in the drains or gutters after an afternoon rain storm, and the sounds of the food carriers bringing the daily rations into the cell blocks—which gave us a feeling of comfort in an odd sort of way. For, in this limited world in which we lived, certain sounds indicated that everything was “normal,” as far as life for a POW in North Vietnam could be.
And then there were the other
sounds—the unfriendly ones. These were the sounds that generated fear and represented real danger—sounds that brought an empty feeling in the pits of our stomachs and made us break out in cold sweats. The shuffle of more than one pair of guard’s feet marching into our area meant someone was being taken to quiz (interrogation). If it happened at night, it was especially disturbing because that meant the urgency on the part of the captors was great. We all learned to know that awesome, terrible feeling so well as each of us expectantly wondered: “Are they coming for me?”
As a cell door creaked open, there was a sense of relief knowing it wasn’t me they were after and a feeling of gratitude at being spared one more time was mixed with a deep sorrow for the other man who was being taken out. While each incident generated the same flash of feelings, we were always left wondering what our tormentors sought and how long our fellow prisoner would be gone. (During certain periods of our captivity, men who were taken out for interrogation never did return to their cells. Some of them made their way to the United States in 1974 in coffins—the North Vietnamese having listed them as having died in captivity on the dates they were taken to interrogation.)
The reason the North Vietnamese imposed these harsh conditions is obvious: to maintain complete control. Since they held a relatively small number of American POWs (less than 350) for the eight- and-half years, the Viets had both the time and facilities to handle us in the manner best suited for their purposes. Our captors isolated us because they wanted to discourage any unified feelings, any united efforts of resistance as a group. Through complete isolation there was a:
”... psychological impact and transformation that took place which would make the PW’s more susceptible to exploitation . . ,”2
”... there is the realization that one is at the mercy of his captors, that the captor has complete physical control over him, that all moral values, pro-
3 Leonard C. Eastman. “A Comparison of Prisoner of War Treatment,” a paper prepared for Naval Postgraduate School, February, 1974, p. 4.
tective laws and avenues of recourse
or evading the situation have been removed from his environment . . ,”3
The affects of sensory deprivations soon became obvious to most of us. Many of us began to react in different ways. Some went into states of prolonged depression; some could not eat; and others suffered from nightmares and hallucinations. I experienced a combination of several of these affects.
In fact, we suffered from everything from fear of losing our sanity to the world’s worst cases of “cabin fever.” Furthermore, we recognized what was happening to us, both physically and mentally. Besides the dangers of losing our physical and mental balance, we could see that these conditions caused us to be affected to a greater degree by propaganda.
What was probably the greatest realization on the part of the POWs in North Vietnam was the necessity to combat the enemy propaganda in every way possible. We realized that we had to remain united in our efforts to resist their propaganda and indoctrination attempts if we were to enjoy “success.” We understood that every man needed the feeling of belonging, merely as a matter of survival alone.
It soon became obvious that if we were to survive, and if we were to maintain any degree of sanity for a prolonged period of time, we would have to communicate—and communicate we did. Regardless of the risks involved, the dangers present, and the threats of punishment by the officers and guards of the camps, we communicated every chance we had. No prisoner would pass up an opportunity to “talk” to another prisoner who was in solitary, even if just to pass the time of day. All day, and well into the night, the lines of communication were used. Often it was nothing more than idle chatter, but it did wonders for our morale. And morale was such a key factor. In order to keep one’s spirits high, to keep from losing hope, and to give each other comforting thoughts, it was vitally important to be
5 Edgar H. Schein. "Reaction Patterns to Severe Chronic Stress in American Army Prisoners of War of the Chinese," Journal of Social Issues, 1957,
P- 22.
able to communicate with the men in the other cells.
Because of the strictness of the camp regulations forbidding communication with men outside of our own cells, we had to create covert means by which to talk to our buddies. Basically, these new means evolved on the use of any mode of generating sound that we could possibly get away with.
The most common method was by tapping on the brick and mortar walls of the cells. We soon discovered these walls to be excellent conductors of sound. A light tap with the fingernail could be heard clearly by the man on the opposite side of the wall if he pressed his ear to the wall. And, there was little danger of the noise being heard outside the cell-block by a roving guard. Soon a complete alphabet was devised utilizing the tapping sound (similar to Morse code). Before long message traffic was flowing continually from one end of a cell-block to another; then later, from cell-block to cell-block and from building to building.
As time progressed, the men were gradually let out of their cells more often to do odd tasks such as sweeping the courtyards, weeding the yards, planting small gardens, etc. Whenever the opportunity presented itself during the performance of these odd jobs, we almost always sent code, be it by the noise the brooms made when swept against the concrete yards, by the striking action of a hand sickle cutting weeds, or by the noise of a hoe striking the ground. It even developed to the point that some men sent messages to others by the noises made by shaking out their blankets or by snapping their towels or wet clothing when they washed them out.
This is not to say that the efforts of communicating were always successful. There were countless times that the individuals were caught and punished. But it wasn’t long before we were right back at it. No matter how hard the North Vietnamese tried to stop us from communicating, they were never successful for very long.
One example of the ingenuity the POWs displayed is shown in the method of communication developed in a couple of maximum security-type camps. These cells were separated by doublewalls— i.e., a void space between the two walls to prevent communication by tapping, and staffed by a double complement of guards.
In these camps, the means of sending code developed through the use of the "natural” and sometimes guttural noises a person made, such as a cough, a clearing of the throat, a sneeze, a belch, a burp, a blowing of the nose, and, for a couple of prisoners who had the latent talent to do so at will, the passing of gas. Each of these sounds, or any combination of them, represented a letter of the alphabet. These noises were conducted quite easily through the silent, echoing passageways of the cell- block. Of course, it would take a very long time to transmit even the shortest of messages. Sometimes, depending on the conditions, it would take a complete afternoon to send out one sentence. But we had nothing else to do, so it also was a good way to pass time.
I heard of one individual living in one of these camps that would feign sleep for a couple of hours each day during the siesta hours and through his snoring managed to send complete transmissions, telling how everyone was and what was going on in his cell-block. These transmissions were readily received by the men living in two other cell-blocks. (This was a method the North Vietnamese never caught on to. As soon as conditions permitted, it was dropped because of the difficulty and time needed.)
The transition from the normal way of life to one of deprivation was difficult indeed. To recognize the routes which one could take to be able to cope with the situation was challenging.’And what was a wonderment to most of us was the manner in which we could exist in this new way of life—the countless joys we received over some exchanges that were transmitted through the walls; the sorrow we all felt to hear some depressing news that came from a message sent from somewhere beyond the walls; and the numerous times our spirits were bolstered by a few well-coined phrases tapped out by a friend who somehow knew how-we felt at the time.
Prisoners got to know each other extremely well by communicating through brick walls. Each of us knew of the other’s boyhood, his background, his experiences, his wife and children, his dreams, and his ambitions. All this was passed over long periods of time, even though any two men, who lived next to each other, probably never saw one another.
Nevertheless, most of us developed visual impressions of what each person looked like, strictly from the "conversations” we had. Most of the time, years went by before we finally had the chance to actually see a fellow prisoner—and most of the time our impressions were completely wrong.
Imagine the situation years later, after our return home, at a function or reunion of some sort, as two individuals were being introduced:
“You’re Jim Black? Hi! . . . I’m Tom!! I lived next to you for two years in the Zoo!”
“Tom! . . . No kidding!! You don’t look at all like you sounded.”
Landsat: A Routine Problem-Solving Tool for Naval Officers
By Bruce H. Needham, Earth Science Analyst/Oceanographer, General Electric Company, Space Division
Landsat-1, formerly named the Earth Resources Technology Satellite (ERTS-i), which was launched from Vandenburg Air Force Base, California on 23 July 1972, has been lauded by scientists, engineers, and government officials for the past four years for its ability to identify potential energy and mineral resources, identify specific crops and predict productivity, detect pollution, sediment, and land use changes. But little mention has been made of Landsat-1 as a problem-solving tool of interest to professional naval officers.
The advent of Landsat-1 has afforded us the opportunity to completely survey the world’s oceans in a short time and in a common format. Landsat-1 was placed into a 496 nautical mile (900 km)-high circular, polar orbit. Although its physical dimensions are small (weight: 2,100 pounds, height: 10 feet, diameter: 5 feet), its payload is large. Landsat-1 is equipped with two separate but compatible sensor systems consisting of three return beam vidicon (RBV) cameras and a multispectral scanner subsystem (MSS) which image the earth’s surface in spectral bands ranging from wavelengths of .475 to 1.1 micrometers (from blue-green to near infrared).
The Landsat-1 system’s prime advantages are:
► Synoptic coverage: An area 100 X 100 nautical miles (185 X 185 km) is imaged every 25 seconds.
► Repetitive coverage: The same scene is reimaged every 18 days, thereby affording complete world coverage between 81° North and 81° South latitudes with a 14% image sidelap at the equator and an 85% sidelap at 80° latitude.
^ Sun-synchronous orbit: Images are obtained at the same local time every day with a constant sun-angle.
► High resolution: Items smaller than one acre (79 X 56 meters) are discernible.
► Data collection system (DCS): DCS provides the capability for Landsat-1 to collect, transmit, and disseminate data from remotely located earth-based sensors called data collection platforms (DCPs) anywhere in the world.
Landsat, as the following examples illustrate, can be of practical use to the professional naval officer, primarily in the areas of shallow water depth detection {bathymetry') and sea and lake ice monitoring.
There are about 130,000 km. of coastline on earth. These coastal waters are relatively shallow and have the greatest density of shipping. The history of navigation and shipping is filled with examples of ship losses due to collisions with uncharted shoals or with shoals whose positions were only known approximately. An estimate of the average losses for U. S. shipping over a six-year period given in Table 1 shows losses running about $90 million per year. On a worldwide basis, U. S. shipping is about 10% of the total for commercial ships of 100 or more gross tonnage so the estimated world loss is about one billion dollars. The number of vessels involved and the primary causes of the U. S. ship casualties are given in Table II. At least one loss category (Depth of Water Less Than Expected) is directly attributed to inaccurate depth information.
Some charts presently in use contain data based on survey records from the early 19th century when the simplest techniques (subject to a wide variety of errors) were used for depth sounding. The chart makers were forced to use such labels as "position approximate” and "existence doubtful” in reference to some reported soundings. The same shoal may have been reported by two different ships with inaccurate geographical coordinates. Location information is one of the most frequent sources for ambiguity on shipping charts.
In 1965, the Fourth Session of the International Oceanographic Committee identified as a major problem the need for updating navigational charts to remove doubtful hydrographic data, and the International Hydrographic Office in Monaco called upon coastal countries to improve and update their navigational charts. Many countries, however, lack the technical and financial resources to update this data. If only surface ships are used tor hydrographic surveys, a long, slow, and costly process is involved, with the limitations of the sampling procedures affecting the accuracy of the work.
The use of Landsat-1 for remote bathymetry has several advantages over conventional ship survey techniques. First, the coverage is continuous, providing a two-dimensional image rather than a series of points or transections. This means that all shoals are much more likely to be detected, and their geographic locations can easily be detei- mined by reference to land areas within the image. Second, Landsat’s coverage is repetitive, so that changes due to construction and shifting sand bars can be assessed. Finally, because remote bathymetry is less expensive per unit area than conventional methods, areas can be charted which were previously uncharted because of economic constraints.
Three investigations, funded by NASA, in the Landsat-1 program have provided tangible evidence of significant errors in presently used hydrographic charts and the ability to manipulate Landsat-1 data to derive both qualitative and quantitative information of shallow water depths using remote sensing.
Table II Number of Vessels Involved in U. S. Commercial Ship Casualties (Primary Causes)
Table I Estimated U. S. Losses Through U. S. Commercial Ship Casualties (in millions of dollars)
| 1966 | 1967 | 1968 | 1969 | 1970 | 1971 |
Vessel | 95.139 | 53.080 | 63.206 | 68.267 | 69.214 | 78.961 |
Cargo | 7.454 | 9.801 | 5.186 | 10.269 | 17.360 | 6.629 |
Property | 3.131 | 12.262 | 12.676 | 7.926 | 10.629 | 8.911 |
Total | 105.724 | 75.143 | 81.068 | 86.462 | 97.263 | 94.511 |
♦ This table has been constructed using fiscal year figures in the following issues of the Proceedings of the Marine Safety Council: December, 1966; November, 1968; December, 1969; December, 1970; and December, 1971.
The first investigation, led by R. S. Williams of the U. S. Geological Survey, aptly illustrates the inaccuracies of hydrographic charts when compared to Land- sat imagery, which is both geographically and geometrically accurate. Coastal features which are imaged by Landsat include the coastline at different times in the tidal cycle, harbors, lakes and ponds, marshes (wetlands), and beach and dune areas; submarine features include tidal flats, shoals, dredged and natural channels, and bars. Comparison with conventional maps at 1:1,000,000 and 1:250,000 scales show many inaccuracies between the Landsat imagery and the two map scales. These discrepancies are caused by cartographic generalization from large scale maps and, in some instances, actual changes in landform. The photos (page 96) of the Cape Cod area compare three Land- sat-1 images of the same area in bands 4, 5, and 7 (see Table III) with a 1:1,000,000 scale map (IMW, NK-19, Boston, North America, 1969; compiled by the Army Map Service in 1955 from 1:250,000 maps [1947], 1:506,880 maps [1939], and USC&GS charts [1947 & 1949]).
The Landsat imagery can be used to increase the accuracy of these maps, portray additional environmental information, and provide the capability for frequent updating of maps at such scales. Because of the spectral characteristics of the four MSS bands (water acts as an optical filter, progressively absorbing radiant energy at longer wavelengths, until almost complete absorption occurs in the near infrared), maximum clear water transmission is found in the green Landsat MSS band 4 (see Table III).
D. S. Ross of International Imaging Systems (I2S) has developed an algorithm which utilizes photographic and electronic density contouring of Landsat-1 images to estimate water depth in the Great Bahama Bank in steps of water depth less than two meters, five to ten meters, and ten to about 20 meters.
The third and most promising investigation is being conducted by F. C. Polcyn of the Environmental Research Institute of Michigan (ERIM). Concentrating on the clear waters of the Little Bahama Bank, Polcyn has developed three numerical techniques for the calcu-
1967 | 1968 | 1969 | 1970 | 1971 |
551 | 984 | 1193 | 1300 | 1325 |
386 | 307 | 124 | 22 | 10 |
177 | 50 | 32 | 31 | 22 |
202 | 446 | 253 | 274 | 370 |
34 | 70 | 46 | 57 | 19 |
31 | 34 | 57 | 3 | 4 |
63 | 110 | 76 | 54 | 50 |
376 | 540 | 610 | 5lQ | 524 |
323 | 135 | 133 | 86 | 81 |
157 | 97 | 151 | 172 | 151 |
105 | 34 | 63 | 30 | 14 |
947 | 1142 | 1333 | 1304 | 1435 |
23 | 62 | 112 | 220 | 147 |
3030 | 4001 | 4183 | 4063 | 4152 |
rather than just "Calculated Risk.”
Wavelength Estimated Maximum Water
AI55 Band Associated Color (micrometer) Depth Penetration
4 | blue-green | .5- .6 | up to 17 meters |
5 | orange | .6- .7 | less than 2 meters |
6 | red | .7- .8 | less than 20 centimeters |
7 | near infrared | .8-1.1 | surface only |
Table III Water Depth Penetration of MSS Bands in Clear Water
Primary Cause 1966
Personnel Fault | 550 |
Calculated Risk* | 257 |
Restricted Maneuvering |
|
Room | 210 |
Storms/Adverse Weather | 374 |
Unusual Currents | 50 |
Sheer, Suction, |
|
Bank Cushion | 36 |
Depth of Water Less |
|
Than Expected | 100 |
Failure of Equipment | 311 |
Unseaworthy/Lack of . |
|
Maintenance | 340 |
Floating Debris/ |
|
Submerged Object | 153 |
Inadequate Tug |
|
Assistance | 137 |
Fault on Part of Other |
|
Vessel or Person | 746 |
Unknown (Insufficient |
|
Information) | ’ 29 |
Total | 3293 |
* Before 1969, "Error in Judgment/Calculated
lation of water depth on the basis of the intensity of the bottom reflected solar radiation while negating the adverse effects of sun-glint and differing bottom reflectance properties over a large area. Bottom features as deep as nine meters (approximately 34 feet) have been detected on Landsat images. Absolute depth calculations for water depth to 4.5 meters (15 feet) have been demonstrated for the Little Bahama Bank with accuracies of ±0.25 meters. Accuracies of remote sensing techniques applied to bathymetry are on the order of 10-20% to depths of 4.5 meters, whereas the accuracies of modern ship survey techniques are on the order of 2-3%. Costs
for processing Landsat data to produce depth charts are estimated to be on the order of $1.50 per square mile.
A recent joint NASA/Cousteau Society experiment conducted in August-Sep- tember 1975 provided additional support for the use of Landsat data for bathymetric information. The first phase of the experiment consisted of providing near-to-real-time analysis of Landsat data to ships at sea. The Cousteau Society’s ship Calypso was on station in the Bahama Islands at the time of overpass of Landsat. Imagery obtained from Landsat at approximately 1030 local time was digitally processed on the General Electric Company’s IMAGE
100 multispectral image analyser. Radiance values obtained from the imagery were correlated with in situ depth and positional data from the Calypso, and these results were transmitted back to the Calypso within 18 hours via satellite. The second phase consisted of the collection of precise sea truth data (measurements of bottom reflectance, water transparency and positional information) and digital analysis of the Landsat imagery. Using this sea truth data, initial results indicate that the Landsat imagery (with bands 4 and 5 operating at a high gain mode—three times normal gain) can be used to obtain bathymetric information to depths of 22 meters. These results were verified to accuracies within 10% of measured values. This experiment utilized the expertise of scientists and engineers from NASA, the Cousteau Society, GE, and ERIM in addition to 13 satellites, including six U. S. Navy navigational satellites.
By these examples it is evident that the use of multispectral, remotely sensed data obtained by Landsat can be effectively utilized to produce accurate, low cost depth charts on a worldwide basis. Once used to update the navigational charts of the world, this process can be repeated at selected intervals (especially after major storms) to identify changing conditions. These updates could be distributed expediently in the form of "Notices to Mariners.”
In recent years, the economic development of Arctic Alaska has become of particular national interest. Economic development will require an increased understanding of the region’s natural character and the processes which operate to maintain or change that character. Ice probably has the greatest effect on these processes. Despite the importance of adequate ice information, the harsh polar environment and the remoteness of the area have required the use of slow and costly methods for acquiring such data. It appears that satellite-borne, remote sensors will play a vital role in bridging this barrier.
More than eight Landsat investigators have dealt with sea and lake ice, ranging from the mapping of ice boundaries, the location of navigable leads, the monitoring of the movements of ice floes, even
to the detection of Antarctic icebergs suitable for collection for use as fresh water sources and for abatement of thermal pollution.
The results of analyses of three Arctic areas and the Great Lakes indicate that sea and lake ice is detectable in all four MSS bands and can be distinguished from clouds through interpretive keys. Pictured below is a Landsat-1 MSS band 5 image of the Eastern Beaufort Sea, taken on 26 September 1972, showing ice and clouds. Overall, MSS bands 4 and 5 appear to be better for mapping ice boundaries, whereas band 7 provides valuable information on the ice type (age) and ice surface features. Ice features as small as the "small floe” (20 to 100 meters across) can be detected, and ice concentrations mapped from Landsat-1 imagery are in good agreement with the limited amount of correlative data (aircraft and ground observations) to date.
Multispectral analysis is also useful for distinguishing ice floes from surrounding brash ice and ice cakes and for detecting puddling on the ice surface as opposed to cracks or fractures through the ice. In areas of nearly solid ice cover, greater detail is evident in band 7, primarily because the difference in reflectance between ice floes, brash ice, and cracks and openings is greater. Also reflectance variations within some ice floes may be associated with hummocks, ridges, or refrozen cracks.
An extensive U. S. Geological Service field survey conducted off the northern coast of Alaska from mid-July to mid-September 1972 illustrated the advantage of synoptic coverage in these remote ice covered areas. The researchers did not have access to Landsat-1 data until after the field work was completed. After examination of the Land- sat imagery, it was revealed that certain critical regions, which from the ground appeared inaccessible to the research vessels, could in fact have been reached.
Landsat imagery’s large 70-80% side- lap, in Arctic regions, permits time-lapse studies of ice movements for periods up to four days. A high incidence of cloud- free conditions assures the frequent repetitive coverage required to monitor such movements and the opening and closing of leads from the time of maximum ice extent through the spring breakup.
The combined interaction of these advantages shows great potential for the use of Landsat imagery to detect navigable leads in sea and lake ice, thus reducing costs and increasing safety in ship transits. The Canadian Ice Forecasting Central was so impressed by Landsat-1 coverage of sea ice areas that it replaced its April ice survey flights in the Eastern Arctic Ocean and Beaufort Sea in 1973 at a considerable savings.
Obviously, Landsat is an instrument whose full potential has not yet been tapped. With present state-of-the-art technology, Landsat data may be processed either photographically or digitally to obtain results of significant value to the professional naval officer. Landsat may be used to produce reliable, low cost navigational charts on a global basis and to develop applicable "Notices to Mariners” when required. Landsat data may also be functionally utilized to closely monitor sea and lake ice conditions and to relay the location of navigable leads to ships in transit.
With the successful launch of Land- sat-2 on 22 January 1975, we will continue to have access to this data gathering platform for years to come. Landsat-2 was placed in an identical sun-synchronous, polar orbit as Landsat-1 with the exception of being 180° out of phase. This affords us the added advantage of coverage every nine days vice the previous 18 days. A third satellite in this series, Landsat-C, is planned for launch in 1978 and will carry a thermal infrared sensor in addition to those listed in Table III.