





D 

 ^^^■DEPRESSION 



D 







" ' g ^s^^ 





1 



— — _____ 







A 

 t 







DIRECTION 01 



7 TOW FISH MO VEMENT C 



> 











C 











: 



50' 



D 



15m 



• 



"*— £ 





^—PROJECTING 

 TARGET 





D 









Figure 4. Sample side-scan sonar record (sonograph) 



usually used for highlighting an interesting feature or for referencing 

 position. The distance of a target perpendicular to the line of travel can be 

 calculated once the height of the towfish above the bottom is known (Figure 5) 

 by simple trigonometry (i.e., the Pythogorean theorem). The height of a 

 target can be calculated using similar triangles (Figure 6). Several brands 

 of side-scan sonar systems have microprocessor functions available (either 

 built into the recorder or as an accessory component) which will adjust the 

 towfish signal to print a sonograph corrected for slant range. More recent 

 electronic advances allow incorporating vessel speed and/or positioning 

 stations into the data processing, allowing printing of a sonograph with true 

 bottom distances in both directions (Mazel 1984). 



13. The sonograph image is of varying shades with each shade a function 



11 



