4. THE SWEDISH NATIONAL DEFENCE RESEARCH INSTITUTE (FOA) 
FOA is the principal authority for defence research in Sweden, and the In- 
stitute has built up a considerable fund of know-how over the decades and its 
resources are very extensive, In recent years it has been increasingly active in 
the civil field, and technical advances it has made in the submarine/diving area 
are now being made available to industries and institutions, both Swedish and 
foreign, active in the offshore oil and natural gas market. 
The Swedish Board for Technical Development has supported FOA projects of 
potential interest to the offshore sector, as a result of the present trend of 
increased Swedish efforts to find new resources, such as oil, gas, sand, gravel 
and minerals. Directly related to submarine technology are activities such as 
hydroacoustics and hydrooptics. Much of the knowledge in seismography gathered 
at FOA over the years is expected to be of great value in seismic detection of 
potential natural resources. 
Underwater imaging has been a part of FOA's research program since 1970. 
Underwater operations in the Baltic are serioulsy hampered by poor visibility, 
ecpecially near the bottom, i.e. in the region where most underwater work has 
to be done. In the Kattegat, at the west coast of Sweden, the visibility condi- 
tions are more favourable. Further, in severe winters, for instance in 1981-82, 
large areas of the Baltic and the Kattegat are ice-covered. 
Tests have been carried out on laser scanning and range-gating systems with 
the aim of improving visibility. Work has also centred on a range of TV equip- 
ment, light sources, and illumination geometries. 
In the field of hydroacoustic imaging, FOA is developing methods and equip- 
ment to facilitate observation and work also in turbid and ice-covered waters. 
Insonification of the target area is carried out in the ultrasonic frequency 
range, 0.5 - 3 MHz, and the elctronic conversion of the reflected signals pro- 
duces a picture perceptible to the human eye. An acoustic lens may be used for 
image generation or the camera may be lensless. In the latter case use is made 
of holographic recording. 
Underwater activity as a rule requires very accurate navigational means for 
position-finding, implying cooperation of units located both at the surface and 
below. The use of submarine vehicles for searching, bottom mapping, etc., makes 
particularly high demands on accurate position-finding equipment. The require- 
ment for an absolute position accuracy of a few metres can be met where it is 
possible to arrange bottom-fixed navigation facilities. 
Tests have been carried out on the use of short laser pulses for the meas- 
urement of water depth, with both ships and helicopters being used as carriers 
of the laser equipment. The results have confirmed that a laser system, tailored 
to this type of application, is of value for the mapping of bottom topography in 
shallow waters, for instance in several littoral areas in the Baltic as well as 
in the Kattegat. Maximum depth penetration of more than 30 metres was obtained 
from experiments performed with a CCRS-Mk-II lidar (laser infrared radar, com- 
mercially available from Optech Inc.) installed in a helicopter. Mapping of an 
area close to a large shipping route demonstrated good agreement between sonar 
and laser profiles. A scanning system is recommended for hydrographic charting 
purposes. 
For the testing of equipment, instrumentation, and techniques used in the 
fields of hydroacoustics, hydrooptics and navigation, FOA has developed a remote- 
controlled underwater vehicle designated FOA-SUB. The max.operating depth of the 
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