3. EQUIPMENT AND INSTRUMENTS 



77 



Lament Geological Observatory of Columbia 

 University, the Times Facsimile Corporation 

 of New York, and the Western Electric Co. 

 under sponsorship of the U..S. Navy. Develop- 

 ment was prompted by the need for precision 

 depth recordings in the ocean deeps on an 

 expanded scale. It is used by the Coast and 

 Geodetic Survey on major ships in depths 

 where soundings cannot be recorded on the 

 expanded scale of the EDO-185. The PDR 

 equipment is not designed to be portable. 



A typical installation (Fig. 25) consists 

 of the Mark V recorder wired to utilize the 

 transmitter, receiver, and transducer of the 

 AN/UQN (Navy designation) series of depth 

 recorders manufactured by the EDO corpora- 

 tion of College Point, New York. A service 

 manual and instructions for installation are 

 furnished with each equipment. 



The combination of the PDR with AN/ 

 UQN depth recorder gives a sonic sounding 

 system which will provide nearly continuous 

 records of the ocean depths. The PDR 

 equipment is used to supplant the recorder 

 unit of the sonar sounding equipment and 

 provides a sounding record with a scale ex- 

 pansion and an accuracy beyond the capa- 

 bility of conventional sonar sounding equip- 

 ment. 



The scale of the MK V recorder is 18.85 

 inches equals 400 fathoms or about 1 milli- 

 meter equals 1 fathom. The estimated in- 

 strument accuracy is at least one part in 

 3000 exclusive of vagaries of propagation 

 and bottom reflection of sound in sea water. 

 The equipment will operate in any depth of 



Figure 25. — Precision Depth Recorder. 



water, being limited only by the power capa- 

 bilities and signal/noise ratio of the sonar 

 sounding set installation. 



To provide precision display of the results 

 from the sonar sounding equipment, the 

 PDR has some important features not found 

 in conventional equipment. A high precision 

 tuning fork controls the slip free drive of 

 the Facsimile-type Recorder. Under ordinary 

 operating conditions this provides a timing 

 function better than one part in 1,000,000. 

 The velocity of 800 fathoms/second is used 

 for conversion of time measurements to 

 depth. 



A second feature is programmed gating. 

 When operating conditions are most favor- 

 able the PDR will trigger the sonar equip- 

 ment and record the results at the rate of 60 

 operations (pings) per minute. This mode 

 of operation is known as HDR (High Den- 

 sity Recording). HDR usually works well 

 in relatively shallow depths up to 1,500 fath- 

 oms where the return echoes are strong. 

 However, at greater depths where the echoes 

 are weaker, difficulty may be experienced 

 with HDR because the outgoing ping and 

 reverberation may use up the portion of the 

 recording paper where the return echo would 

 be recorded. In another case it may be 

 found that the deep sea scattering layer tends 

 to obscure the record of the bottom echoes. 

 Also noisy sea conditions, poor bottom re- 

 flectivity, and possibly a detuned sonar re- 

 ceiver tend to give a low signal/noise ratio 

 which makes it difficult to identify sound- 

 ings. For such operating conditions the PDR 

 provides programmed gating which permits 

 the transmitter and recorder to operate in 

 a preset sequence arranged to minimize the 

 noise on the record and at the same time 

 give a maximum density of sampling. 



A third feature of the PDR is that depth 

 and time intervals are written on the graphic 

 record simultaneously with the soundings. 

 The four-hundred fathoms of record is di- 

 vided into twenty-fathom intervals and these 

 so-called twenty-fathom markers are broken 

 by time intervals. On Navy equipment the 

 time interval is usually three minutes 

 while the Coast and Geodetic Survey pre- 



