The center seat of the boat was removed, a 
6-inch by 34-inch hole was cut athwartships in 
the bottom, anda like-size section of auto safety- 
glass window was installed. The area adjacent to 
the window was painted dull black to minimize 
stray reflections. An electric trolling motor, 
powered by two 6-volt auto batteries, propelled 
the boat. Two crewmen were used to maneuver 
the craft and operate the system. 
High voltage for the photomultiplier was 
obtained from the control box cathode ray tube 
power supply. The control box and battery (two 
l2-volt auto batteries in series) were installed in 
the bow along with a 400-cycle inverter. 
The window, which extended the full width of 
the boat bottom, was wide enough to accomimedate 
the 3-inch wide scanning aperture and to provide 
an approximately 80° lateral field of view after 
refraction at the air-water interface, 
EXPERIMENTS 
Roosevelt Lake, a small artificial lake near 
State College, Pennsylvania, was chosen as the 
site at which photography with the water-borne 
equipment would be tried. The bottom of this 
lake slopes gently from the beach to a maximum 
depth of about 12 feet. 
Two targets were prepared for the tests, 
The first was a one-foot square sheet of aluminum 
painted to prodace a black and white checker- 
board comprising four 6-inch squares; the second 
target was a pair of 6-inch by 18-inch aluminum 
strips set in the form of a cross, One strip was 
painted black, the other white. These targets 
were placed near each other on the lake bottom 
and their position marked by a buoy, 
Both natural light and artificial light photo- 
graphs were planned, but time limitations pree 
vented the latter. The water was relatively 
clean, enabling the bottom to be seen through the 
glass window. A coating of moss and silt signifi- 
cantly reduced the reflectivity and contrast of 
the bottom, resulting in very low contrast objects. 
This bottom situation, probably representative 
of the worst conditions to be encountered, points 
up the need for contrast-increasing devices 
including side lighting. Under conditions of 
little or no silt, considerably better results are 
naturally expected. 
It was possibly to vary the speed of the 
pram in six steps from less than 1/2 knot to 
about 3 knots. A maximum of about 2 knots was 
used during the photographic runs because 
higher speeds caused lapping under the bow, 
producing an accumulation of air bubbles under 
the blass window, Since the recording film speed 
must be matched to the boat's velocity in relation 
to depth, the maximum available film speed of 
one foot per minute dictated a boat speed of one 
foot per second when the depth was seven feet, 
the depth at which the targets were planted, 
Future models of a system could accomm.date 
considerably greater velocities. 
275 
Figure 4 shows a photograph which was 
taken with this gear, The angular size of the 
scanning spot was three milliradians, The left- 
hand side of the upper photo shows some tree 
branches or, perhaps a tree stump. The boat- 
shaped object in the center appears to be a sunken 
canoe. The checkered target appears at the 
center-right, and the cross in the upper right 
corner. It is noted that the whites of the targets 
are extremely bright while the blacks are not 
immediately evident, This is a consequence of 
the poor reflectivity and the presence of some 
scattering particles in the water respectively. 
The uniform lateral striations are spontaneous 
variations of the electronic level at very low 
frequencies, More recent developments have 
minimized these lines, The day on which this 
run was made was very cloudy with intermittant 
drizzle, The second photo was made ona sunny 
day. The shadow of the boat is evident as a 
black stripe down the photo, Bottom objects, 
such as tree stumps and a silt-covered plank 
are evident with better contrast. Surface wave 
patterns caused occasional light patterns, In 
the left portion, the checkered target is evident 
despite the boat's shadow. 
CONCLUSIONS 
Acceptably identifiable photographs of targets 
ona shallow lake bottom have been obtained 
using a scanning-type system, These results 
are encouraging, and further work is required 
to illustrate the ultimate worth of the system for 
oceanographic research, 
In order to simulate the lighting conditions 
which are found at the ocean floor, a series of 
photos should be taken at night using artificial 
illumination, Figure 5 shows one possible 
mounting configuration of these lights, which 
would be encased in a watertight container and 
immersed in the water, 
A high intensity beam spot which would scan 
along with the camera so as to coincide with the 
look spot of this equipment is another possibility. 
This configuration permits either an increase in 
brightness or a decrease in power requirements 
or both over the system utilizing fixed lights. 
The scanning beam source would be as much 
displaced from the scanner aperture as physically 
feasible. 
Although intense scattering from the beam 
would find its way into the instantaneous field of 
view of the scanner aperture, the contrast- 
enhancing capabilities of the electronic process- 
ing system permit the large steady component of 
the signal due to backscattering to be cancelled, 
Moreover, the volume of water directly illumi- 
nated by the light beam would be relatively small 
since it is necessary to provide light flux for 
only a small picture element at any given instant, 
This reduces the amount of cross-scattered light 
