1. INTRODUCTION AND BACKGROUND 

 1.1 SCOPE OF REPORT 



This report presents the results of two separate experiments conducted in fiscal year 1977 

 designed to investigate the feasibility of reception and transmission of 7200-baud slow-scan video 

 using an underwater acoustic link. These experiments were primarily motivated by an existing 

 need for U. S. Navy manned submersibles to transmit video information, in real or near-real 

 time, to their surface support ships. Other motivating factors included the future need for 

 video information from unmanned, untethered submersibles as well as from potential remote 

 undersea observation sites. These requirements, coupled with the recent availability of com- 

 paratively inexpensive off-the-shelf scan converters and microprocessors, seemed to demand 

 a further look into the feasibility and practicality of acoustic slow-scan television. 



The remainder of this section will concern itself with a review of past slow-scan work 

 pertinent to the present experiments. In Section 2 the present experimental equipment will 

 be detailed and our two experiments will be summarized. The results of these experiments 

 will be discussed in Section 3. Conclusions based on these experiments and recommendations 

 for future experiments appear in Section 4. 



1 .2 PRIOR ACOUSTIC SLOW-SCAN TELEVISION EFFORTS 



During the last two decades there has been considerable progress in transmitting video 

 and other data via reduced-bandwidth formats. Most of this work has been directed towards 

 electromagnetic transmissions over hard-wired or radio frequency links. However in 1967 the 

 Ball Brothers Research Corporation of Boulder, Colorado, began a study of the advantages 

 to be gained from a cableless underwater television system. This study led to their develop- 

 ment of the "CUTLINK" acoustic slow-scan television system (Ref. 1), the first cableless 

 system to transmit television pictures in near-real time from ocean depths to the surface (Ref. 

 2). The characteristics of the CUTLINK system are displayed in Table 1. 



TABLE 1. CUTLINK CHARACTERISTICS. 



Design Depth 



20,000 ft 



Raster and frame transmission time 



80 lines, 10 sec/frame 





200 lines, 57 sec/frame 





500 lines, 342 sec/frame 



Illumination 



200 W-sec 



Modulation Methods 



Analog FM, A modulation, PCM 



Carrier Frequency 



14.5 kHz 



Receiver Bandwidth 



3 kHz 



Digital Bit Rate 



2.5 K bits/sec 



Transducer Beamwidth 



70 deg at 3 dB down 



CUTLINK was designed to telemeter acoustic television signals over nearly vertical 

 paths from abyssal depths (<20,000 ft) to a surface platform. Telemetry was centered at 

 14.5 kHz with a nominal bandwidth of 3 kHz and either analog FM, delta modulation, or 



