"received" in the sense that observing the monitor indicated the presence of a slow-scan pic- 

 ture, most of the pictures suffered from distortion and were severely degraded below labor- 

 atory quality (see fig. 4). The primary source of distortion was loss or displacement of hori- 

 zontal lines. This effect has been seen previously in both the CUTLINK experiments (Ref. 3) 

 and amateur radio transmission (Ref. 7). Both of these references attribute line loss or dis- 

 placement to multipath arrivals that affect the line sync signal. In our experiments the severity 

 of line sync problems varied widely. In a few worst-case examples, half the lines were missing, 

 resulting in a picture highly compressed in the vertical direction. In the best pictures (e.g., 

 fig. 8b) only a single line displacement occurred out of 120 transmitted lines. The LOFAR- 

 GRAM analysis of the next section also shows the effects of multipath on the received power 

 spectrum. 



Commenting on his CUTLINK results, Mr. Guthals of Ball Brothers Research Corp- 

 oration noted that in their slow-scan images "distortion was displayed in the form of ghost 

 images, waviness, line sync irregularities and granulation" (Ref. 3). It is interesting to note 

 that aside from "waviness," all these effects were noted during our experiments. Next to line 

 sync irregularities, graininess was the most persistent distortion observed in our pictures. 

 Graininess is generally attributed to a low signal-to-noise ratio. The LOFARGRAM analysis 

 below indicates that in our case the "noise" is probably signal multipafhs. Just as in photo- 

 graphy, the effect of graininess is to lower resolution. Unlike line sync irregularities, which 

 produce an abrupt and total loss of information (as far as the eye is concerned), graininess 

 causes a gradual deterioration as the signal-to-noise ratio degrades. Ghost images, also caused 

 by multipath in time synchronization with the main signal, were barely in evidence in some 

 of the pictures and proved the least objectionable of the various distortions. 



Figures 5a, 5b, and 5c are SUBSAT pictures received aboard Box L during the second 

 transmission of the third pass while DOLPHIN was at one-half test depth. Figure 5a, the gray 

 scale, shows almost no sync problems but is considerably more grainy than the original (see 

 fig. 4a) as are 5b and 5c. The girl, fig. 5b, shows numerous line sync problems due to an 

 early sync trigger. Indeed, in the line tear near the middle of the picture the actual sync 

 pulse appears as a block line segment about one-quarter the way across the screen. Early 

 sync triggers are the major line sync irregularities in figs. 5a and 5b, though some jitter due to 

 late sync triggering is evident upon close inspection. 



(a) Gray scale (b) Girl (c) Test pattern 



Figure 5. Pictures from DOLPHIN at one-half test depth. 



14 



