gives the unattenuated beam distribution as a reference. It also allows for 

 checking of the dissector sweep settings and is a critical check of cleanliness 

 of the windows. The instrument is deployed into the water. Whilst at the sur- 

 face, the windows are swabbed to make sure that they are fully wetted. The 

 instrument is then lowered to the required depth using marks on the cable as 

 depth indicators. During the operating period the signals are recording and 

 water samples taken. After the experiment was completed the instrument was 

 retrieved and replaced on its deck support. The windows are cleaned with fresh 

 water and a second on-deck calibration taken. 



The instrimient was set at 24-ft total length for the waters off St. John, V.I. 

 A 46-ft Chris Craft houseboat was used for deployment of the instrument, and is 

 shown in Fig. 3. The measurements were made in shallow waters generally, i.e., 

 50-ft depth. Francis Bay, north of St. John, was the site of most of the 

 measurements. It provided a sheltered location for initial operation of the 

 instrument. Later readings were taken in Lameshur Bay, site of the TEKTITE 

 habitat. Considerable data were obtained with the bulk of the data being in 

 three sequences of measurements: 



1. Time Sequence, Francis Bay . A 5 -minute period of data was taken each 

 hour from 1800 hrs to 2400 hrs, with the instrument on the surface. 



2. Depth Sequence, Francis Bay . Readings were taken with the instrument 

 lowered in 10-ft depth steps. 



3. Continuous Sequence, Lameshur Bay . A continuous sequence of data for 

 a 15-minute period was taken with the instrument on the surface. 



The boat was anchored for operation of the instrument. Because of the large 

 forward "sail area" of the houseboat, the principal anchor was deployed from 

 the stern. This reduced swing to about + 15° and a light bow anchor reduced 

 this to a much smaller quantity. Some swing of the boat over the submerged 

 instrument was unavoidable but no difficulty in handling was encountered. 



RESULTS 



The scattering data has been transferred from magnetic tape to 8 channel chart 

 and an initial analysis of the results started. 



The dissector data is shown in Fig. 5. From this can be determined a first 

 evaluation of the small angle scattering (from the scattering extrapolated to 

 zero) and of the attenuation length. 



It is, of course, possible to examine this in terms of variation of the center 

 beam and the scattering with time. The peak of the attenuated light is remark- 

 ably steady and the scattering also shows little timewise variation. 



Some of the reduced data for the depth sequence is shown in Fig. 6. The vari- 

 ation of attenuation length and scattering with depth can be observed. 



Since an accurate calibration of the instrument is not yet available, the 

 resulting volume scattering function cannot yet be shown. Estimates have been 

 made using a nominal calibration only and these indicate that the small angle 

 scattering is on the high side of the band of values as determined by other 

 experimenters. 



VII-38 



