The DELTIC Spectrum Analyzer 



DEL TIC is a new data-processing technique 

 for the analysis of CTFM sonar returns. The 

 DELTIC equipment performs frequency analy- 

 sis by a sampling procedure and presents an 

 output which is equivalent to the 100 -channel 

 filter bank analyzer typically used in CTFM 

 sonar equipment. The DELTIC technique is 

 particularly advantageous for low-frequency, 

 high-resolution analysis in real time. The 

 analyzer has an interesting and useful feature 

 of storage and repeated analysis of data, either 

 automatically or by operator selection. 



The conventional 100 -channel, multifilter 

 analyzer is generally designed with detectors 

 and envelope filters following each of the 100 

 filters. The purpose of the envelope filters is 

 to improve the signal-to-reverberation ratio 

 normally encountered in sonar equipment. The 

 tinne constants involved in the envelope net- 

 work depend on the scan rate of the sonar 

 hydrophone as it passes a point reflector. 

 Envelope filtering should not be used in 

 searching for potential fish target signatures 

 because no restriction should be placed upon 

 the naturalness of the processed target signals 

 and the fish motion with respect to the scanning 

 rate of the sonar set. To eliminate such re- 

 strictions a multichannel analyzer without 

 envelope filters would be required, and, there- 

 fore, no provision could be made for minimizing 

 the unwanted reverberation. A multichannel 

 analyzer without envelope filtering would pass 

 a considerable degree of background noise or 

 reverberation that would be presented on the 

 visual display and degrade the presentation. 



The DELTIC spectrum analyzer operates on 

 a totally different principle and can cope with 

 the variations in time responses expected for 

 the fish-type targets. The mechanism of the 



reduction of the reverberation in such an 

 analyzer is considerably different from that 

 used in the conventional multichannel filter 

 analyzer and the equipment therefore can be 

 used to examine fish-type spectra signatures 

 without compromising perfornnance. The 

 DELTIC equipment operates with a wider fre- 

 quency or range gate than that used for ultimate 

 analysis to sense the level of background 

 reverberation and apply appropriate compen- 

 sation to the analysis capability of the DELTIC. 

 The DELTIC also provides a "holding" feature 

 by which interesting data can be retained, as 

 desired, for repeated display. In addition, the 

 DELTIC analyzer has been designed to be 

 directly interchangeable with the conventional 

 100 -channel, multifilter analyzer in Straza 

 sonar systems. This arrangement pernnits a 

 system to be used interchangeably as a sonar 

 or as a Doppler analyzer. 



Kay Vibralyzer and DELTIC 



The Kay vibralyzer was used for the analysis 

 of selected portions of the CTFM data where 

 permanent records were needed. It was the 

 permanent output of the Kay vibralyzer that 

 first provided measurable proof of the surface 

 and bottom reflections which were indicated 

 in the DELTIC display. 



About 5 minutes are required for the analysis 

 of 20 seconds of taped information. This 

 relation indicates the tremendous amount of 

 time required for analyzing test recordings; 

 therefore, a technique had to be found which 

 could be used for searching rapidly to isolate 

 portions of the tape for later analysis with the 

 Kay vibralyzer. The DELTIC was used for the 

 search, and excerpt tapes were then produced 

 for fine analysis and permanent record with 

 the vibralyzer. Figure 7 indicates a typical 



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Figure 7. — Sample output from Kay vibralyzer showing double return from SCUBA diver at Mission Bay 



Yacht Club site. 



11 



