outfall pipeline extending 1.5 km offshore from Newcastle into water of depth 
24 m are under consideration. The HDWB is concerned with monitoring the 
marine environment near the existing outfalls and assessing the likely 
effects on benthic communities from this proposed new pipeline. 
Photography has been selected as the best method of non-destructively 
monitoring marine growth at several locations on the ocean floor. Depths of 
up to 30 m restrict divers, using self contained breathing apparatus, to a 
very short period at each test site. At these depths, for periods longer 
than 20 minutes, a diver will require a stage decompression before surfacing, 
which greatly reduces his effective working day. The selected sites have 
strong currents which are useful for good dispersal of effluent but which 
make the diver's task extremely difficult: the weight and bulk of the 
camera, flash unit and surrounding frame must therefore be minimised. 
An image splitting attachment which fits neatly onto the front of a 
single Nikonos III camera was constructed so that stereoscopic measurements 
could be made to determine linear and volumetric growth rates of marine 
organisms. A frame in the form of a truncated pyramid was incorporated in 
the design (see figure 1). Bolts in each study area positively locate the 
base of the frame before each exposure. Numerical control is provided by 
plastic coated surveying tapes glued to the rectangular base of the rig. . The 
rig can be easily dismantled and stowed on board the 6 m half-cabin boat used 
by the scuba divers. 
The resulting stereoscopic half-frame images have a relative ¢ tilt of 
approximately 35° and appear as if they have been taken by cameras separated 
by 155 mm with a flying height of 1 metre (see figure 2). Stereoscopic 
viewing of the images presents no problems but the tilts preclude the use of 
mechanical analogue plotters or simple parallax bar techniques. The use of 
computerized algorithms employing the collinearity equations have produced 
results of test models with standard errors of + 1 to 2 mm in planimetry and 
+ 5 mm in height (Done and Fryer, 198la). Similar results have been obtained 
using the SD-4 second-order analytical plotter (Qasco, 1980). Lens distor- 
tions were not applied in these tests. Calibration tests of the Nikkor 28 mm 
lens have indicated maximum radial distortions of 20 microns, so the correc- | 
tion of the image data for these distortions should improve the standard ) 
error of the results. 
Coral Ecology 
Macrobenthic ecology is a science in which abundance, size and spatial | 
168 |