8.0 GENERAL

Over the past two and one-half decades, the acquisition of scientific data by diving has become widespread, and has resulted in many new and highly significant discoveries in the marine sciences. In many of today's detailed studies of the marine environment, the use of scuba is the only means by which valid observations and measurements can be made. Using specialized equipment and techniques to take advantage of this new tool, the diving scientist has selectively sampled, recorded, photographed, and made field observations that are as significant to marine research as those made by his "dry-land" colleagues, or those who must remotely probe the sea from its surface.

New approaches needed to solve unanswered questions have been provided by placing scientists in the environment they want to measure and observe. This intimate contact has shown that in some research, such as observations of fish behavior, ecological surveys and benthic inventories, the entire study can be done using diving techniques. In many cases, the studies cannot be made by means other than diving. In other studies, diving investigations may only be needed to supplement commonly used remote sensing methods or surface ship surveys. Regardless of the project or the role that diving plays in a study, it is obvious from the published record in scientific journals, that marine research, utilizing diving as a scientific tool, has been of considerable importance in developing an understanding of the ocean, its organisms, and the processes that govern its existence.

The purpose of this section is to present examples of procedures that have been used in diver-oriented science projects. The methods should serve as guidelines and should not be construed as being the only way a survey, study, or set of observations can be conducted. There are definite limitations as to what a scientist can do, utilizing scuba as a tool.

As in all scientific research, the investigator should use the most efficient and least expensive means to obtain data. Scuba is only one way to do the job.

Unlike the "dry-land" scientist, the diving scientist or technician, unless saturated, must usually work against time measured in minutes versus hours. For 10 minutes working time, on the bottom at 50 meters, he must decompress for 2 minutes. If bottom working time is extended to 40 minutes, decompression time on ascent is 82 minutes. Longer periods of work, therefore, may increase decompression times to periods double the work time. It can be readily seen that the economics of scientific diving projects depend almost entirely on how efficiently and fast scientists can perform their tasks.

Maximum efficiency under water requires good tools and rugged instruments that can be set up rapidly. In most instances, these instruments and tools are made by individual scientists to meet the specific needs of their experimentation. Almost no standardization exists for scientific equipment and methods. Through necessity, scientists who dive must not only be proficient in their discipline, but be a diver, inventor, and mechanic. A resistance to sea sickness helps immeasurably.

8.1 SURVEYING AND RECORDING PROCEDURES

To systematically and accurately study any region, it is necessary to precisely plot the location of obtained data on a base map. This is especially important if there is need to return to the same location several times during a study. The scale of the base map will depend on the detail of the study and the size of the area to be investigated. In geological mapping of the seafloor, a scale of 1-inch equals 200 yards is adequate for reconnaissance

surveys; in archeological or some biological studies, a much more detailed base map, with a scale of 1-inch equals 30 feet, may be required. In general, if existing charts do not contain the proper scale or sounding density, it may be necessary to construct a bottom bathymetric map prior to diving, utilizing echosounder survey techniques. Gross features can be delineated, and more efficient utilization of bottom time can be planned, if the diver has a good bathymetric map of the study area. If published topographic charts are inadequate, the sounding plotted on original survey boat sheets of a region (made by the Coast and Geodetic Survey now the National Ocean Survey) can be contoured and will usually provide an adequate bathymetric control for a diver survey of a region. If the survey plan requires bottom traverses, it will be necessary to provide some means of locating the position of the diver's samples and observations on the base chart.

The great majority of diving is carried out in near-shore waters where surface markers, fixed by divers over strategic points in the working site, may be surveyed from the shore using well-established land techniques including the theodolite, plane table, and alidade, or from the sea, using bearings from a magnetic compass, or preferably, measuring horizontal angles between known points with a sextant (Shepard 1973). With the exception of the compass, these methods allow one to establish the locations of a number of major features in the working area to an accuracy of 3 feet or better. If buoys are used for location, particular care is needed to ensure that the surface floats used during the initial survey lie directly over the weights anchoring them to the selected underwater features; the best plan is to wait for a calm day at slack tide. The seabed markers remaining after the floats have been cut away should be clearly labeled and coated with fluorescent paint to enhance their visibility.

Having established a basic grid on the seafloor, fixed relative to permanent features on the shore, the diver now proceeds to record the position of individual features within the working area relative to the grid.

8.1.1 Underwater Surveying

With the exception of long distance visual triangulation, many of the methods used in land surevin. be used under water. A review of a

standard college text on "Surveying" will provide the scientist with much of the basic information needed to conduct such a survey. Woods and Lythgoe (1971) give an excellent description and review of methods that have been used under various diving conditions. A special consideration for diving surveys is that most distances must be measured by a calibrated line or a metal surveyor's tape. If long distances are required, these lines must be on reels or severe fouling and tangling will occur. In clear waters, optical instruments can and have been used to measure both distance (range finder) and angles between objects for triangulation. Warton describes his successful use of a standard surveyor's theodolite in the Mediterranean. He prevented corrosion by dismantling his instrument each night and soaking the component parts in kerosene (Woods and Lythgoe 1971).

Small transistorized echosounders, encased in underwater housings, have also been used to measure distances between acoustic or natural reflectors on the seafloor. This method is extremely useful in turbid waters of harbors, or in the measuring of distances across the heads of near-shore submarine canyons. The echosounder pointed up at the surface also gives an accurate depth reading. If a compass is incorporated into this package and a narrow-beamed sound source is used, bearing angles can also be measured.

The first step in surveying any area is to establish a horizontal and vertical control network of accurately located stations (bench marks) in the region to be mapped. Horizontal control is the framework on which a map of features (topography, biology, or geology) are to be constructed. Its purpose is to provide a means of locating the detail that makes up the map. Vertical control gives the relief of the region and may be obtained by stadia distance and vertical angles or by spirit leveling. Rough measurements can be made by comparing differences in depth using a diver's depth gauge, but these can be inaccurate if the reference point is the irregular sea surface.

The detail to appear on the finished map is located from the control networks (bench marks) by measurement of distance and angles to the features which are to appear on the finished map. On some surveys, the control is located first and the detail is located as a separate operation after the control survey has been completed. On other surveys, the control and the detail are located at

the same time. The former method is preferable if long-term observations in an area are contemplated, such as a region around a permanently established habitat. The latter is preferable if reconnaissance studies are being made in remote regions or in areas that will not require reestablishment of stations.

8.1.2 Underwater Photogrammetry

The science and art of obtaining reliable measurements from photography "photogrammetry" while not as advanced under water as on land, is a tool that is being utilized with increasing frequency. Limited visibility is one of the major drawbacks in its application.

Photographs with appropriate scales in the field of view can be useful in measuring objects on the sea floor, and recording changes with time. Subtle changes are often recorded on sequentially obtained exposures of the same area or station that would be missed by relying on a diver's memory alone. Whenever possible, photographs should be taken of environmental features described in sea floor studies. These photographs are useful in conveying word pictures and dimensions to persons who do not dive and who lack a "common vocabulary" with persons who work under water.

Photographic transects are useful in showing variations over an area or with depth. Unfortunately very little "true" photogrammetry has been accomplished to date because of the technical difficulties in producing corrected lenses, maintaining altitude and constant depth, and high relative relief of many bottom features. To date, a system capable of obtaining accurate photogrammetric pictures equivalent to those obtained on land does not exist. Mertens (1970) discusses the problems of underwater photogrammetry and outlines several systems used in simple measurements from photographs. Woods and Lythgoe (1971) have presented a number of photogrammetric methods for measuring microoceanographic features, archeological sites, and seafloor features. The fundamental optics of underwater photographic measurements are well described in McNeil (1972) and would be valuable to anyone wishing to develop an underwater photogrammetric system for sea floor mapping.

Discussions of underwater photography methods and equipment used by diving scientists are given in Section 7.3.

8.1.3 Bottom Survey Methods

In most instances, the diver's position on the bottom can be determined by locating the surfacetending boat over the bubbles and shooting angles on shore stations previously located on the base map. A three-arm protractor is an extremely valuable tool to plot the position of the diver on the base map. A simple means for the diver to request a location from the surface tender is to send a small buoy to the surface. An inexpensive buoy can be made by cutting a broom handle into 1-inch lengths. A small balloon can also be used. If a sample is to be retrieved, the buoy can be wrapped with a light line to which a sample sack is attached. A diver can easily carry four to six of these small buoys and continue bottom traverses after each sample station without having to take the time to surface. Each sample station should be recorded by the divers on a writing slate along with the time of its retrieval for correlating with the times their position was determined and plotted by the surface tender. Field notes should also be correlated with time for later location on the base map of the survey area.

It is more efficient in nonsaturation diving surveys for the traverse to start in deep water and move toward shallower areas. If several divers are involved, it will often be necessary to change partners after the first dive to utilize the maximum bottom time available to the group. For instance, diver "A" starts with diver "B" on the first dive of the day to 150 feet for 5 minutes. Diver "A" then dives to 150 feet with diver "C" for 5 minutes on another outer traverse line. The group would then move into shallower water and divers "B" and "C" would dive together utilizing the repetitive dive tables to determine their maximum no-decompression time for the next dive (See Appendix D). Utilizing this method, a team of three men can easily make up to nine dives per day, if cold water is not a restriction to the survey work. For long traverseswimming with hard work, it is usually not practical to spend over 3 hours total per day under water. Presurvey planning is required if efficient utilization of bottom time is to be expected. For practical purposes, a maximum depth of 150 feet has been determined as the point where traverse surveying becomes too time-consuming and inefficient to be considered a useful nonsaturation diving tool. Useful deeper dives can and should be made, especially in regions of steep slope. These dives,

however, should be for special purposes and not for routine and systematic surveys.

8.1.4 Diver Towing

In many traverses across the bottom, a diver may wish to be towed, either to conserve energy or to cover a greater distance for the same expenditure of bottom time. Several methods have been used for towing a diver. One simple, inexpensive, and practical method of towing is to attach a tow bar or grapnel at the end of a long parachute shroud line (breaking strength 800 lbs.). The divers hold on to the tow bar or grapnel, and use their bodies to plane up or down as they are towed at about 1 to 2 knots.

Another towing method uses the aquaplane (Figure 8-1). The simplest version is a board, which, when tilted downwards or sideways, provides a dynamic thrust to counter the corresponding pull on the towing cable. The addition of a broomhandle seat and proper balancing of the towing points permit one-handed control of the flight path. With this aquaplane, which can be made in a few hours from materials available in the field, a diver may be towed at speeds of two or three knots by a small boat, the maximum speed being limited by the hydrodynamic forces that tend to tear off the diver's mask.

As in the swimming traverse, a diver keys ob

servation to time. At the same time, a surface attendant "shoots in" surface locations as the tow boat or escort boat moves along the traverse with horizontal sextant angles marking locations versus time. Later, the position of the diver at times of recorded observations can be determined by subtracting the length of the tow line from the position of the surface boat at the time of the observation. Practical experience has shown that tows of about 15 minutes will usually obtain as much information as a diver can record prior to returning to the surface for interrogation and recording of data.

In areas where entanglement is not a problem, it may be necessary at times for divers to drop off a tow line during traverses to investigate objects of interest. The tow sled can be improved by adding a trailing line of 30 to 40 feet. This will permit the diver who drops off the sled to grasp the line and return to the sled. Hand signals can also be sent along the tow line to instruct the boat to speed up, slow down, or stop. Divers should carry flares (smoke and light) on long traverses in rough water or in areas of strong current. The scope of the tow line may be up to 10 to 1, and in deep water this could place a diver far behind the tow boat. In such cases, a safety boat may be used to follow behind the towed divers to assist in the event that they become separated from the tow line.

If after the divers drop off a tow, their bubbles cannot be seen from the tow boat, there is the