(a) SEACLIFF. (b) MAXINE D. 



Figure 8. Live camera video from SEACLIFF at 2000 feet. 



exhibits only one line sync problem plus very slight granulation and ghosting. Comparison 

 with the locally recorded frame, fig. 8a, shows that very little visual information has been 

 lost. Fig. 8b represents the highest quality acoustically transmitted picture observed during 

 the SEACLIFF or DOLPHIN experiments. 



3.2 LOFARGR AM ANALYSIS 



All cassette tapes of received video during both experiments, as well as the tapes of 

 live camera video were subjected to LOFARGRAM analysis. Both problems with the hard- 

 ware, such as excessive tape recorder flutter, and problems with acoustic propagation can 

 often be detected by such an analysis. 



Figure 9a is a LOFARGRAM of Procedure D, the GREY SCALE transmission by 

 SEACLIFF from a 1000-ft depth. This figure is the analysis of the locally recorded signal 

 aboard SEACLIFF, i.e., the video prior to entering the acoustic path. 



Since GREY SCALE is a sync pulse (1200 Hz) plus four other discrete frequencies, 

 it might be expected that the LOFARGRAM would consist of the five discrete lines corres- 

 ponding to these frequencies. What is actually observed is five frequency bands; each band 

 is split into equally spaced components modulated by an envelope function which decays 

 outwards from the center of each band. A little thought reveals that the splitting is due to 

 the analysis of a series of identical slow-scan lines, i.e., the splitting occurs at the line rate of 

 1 5 Hz. The envelope function is a (sinc)^ function having a width inversely dependent on the 

 duration of the individual frequency burst. Note the envelope of the 5-msec sync tone is 

 much wider than that associated with any of the 16-msec GREY SCALE tones. 



Figure 9b is a LOFARGRAM of the same transmission represented in fig. 9a but 

 as received and recorded aboard the MAXINE D. Figure 9b shows obvious amplitude varia- 

 tion throughout in the form of many white, nearly horizontal interference bands, which are 

 best seen by viewing the figure edge-on from the side. These interference regions are char- 

 acteristic of "selective fading," which is caused by destructive multipath interference. Al- 

 though the selective fading was most evident in fig. 9b, because of the simple and repetitive 

 nature of its video content, it was noted on most of the DOLPHIN and SEACLIFF LOFAR- 

 GRAMS, indicating that multipath effects were a main factor in degrading picture quality. 



16 



