. Basic methods for the calibration of sonar equipment. 42 TESTING TECHNIQUE SURFACE. SO that BOTTOM Figure 3. Geometry of leHection iiUerleience in calibra- tion tests. with the result that R - = y.(f.„j,a„() 2/1 (f 2/7 Vrf' + 4/7 0' A 2/7 Vd' + 4/7- _ (12) The term Z> is the diameter of the piston, A the wave length, and ,/i(.v) the Bessel function of imit order. For a line source of length L suspended vertically, m in T— sin ^ j sin e (13) Rr i„ {1^. 2/7 V " \ A ' \/d- + 4/7-'/ 2/7 \/d- + 4/7- (14) Since the sicie lobes for a circular piston and for a line are of minor importanc
. Basic methods for the calibration of sonar equipment. 42 TESTING TECHNIQUE SURFACE. SO that BOTTOM Figure 3. Geometry of leHection iiUerleience in calibra- tion tests. with the result that R - = y.(f.„j,a„() 2/1 (f 2/7 Vrf' + 4/7 0' A 2/7 Vd' + 4/7- _ (12) The term Z> is the diameter of the piston, A the wave length, and ,/i(.v) the Bessel function of imit order. For a line source of length L suspended vertically, m in T— sin ^ j sin e (13) Rr i„ {1^. 2/7 V " \ A ' \/d- + 4/7-'/ 2/7 \/d- + 4/7- (14) Since the sicie lobes for a circular piston and for a line are of minor importance in the consideration of reflections, R^, R,,, and R, may be given approxi- mately (provided h /d is not too large) by the expres- sions (10) (15) (16) The reflected intensity reaching the receiver versus the intensity of the direct wave is then given in db by where a = 1 for a pressure-gradient receiver, a = %(7rD/A)- for a circular piston, and a = y^lnL/X)- for a line. This ecjuation is plotted in Figure 4. It is seen that, for reducing the effect of reflections, a piston is more satisfactory than a line whose length is equal to the diameter of the piston. At low fre- quencies, however, where A becomes large, both a line ? ° >- ^^^ ^^ ^ Z 2 ^ ^ ^, \ V »- -5 0 LU N ^ ^ \ \ X "X s > >- \ \\ \ N s v\ t -10 i/i z UJ 1— V \ V N \ ^ \ V. Q UJ G -15 ^ ^ ^ 1 \ ^ > ^SP 1 Q 2 0 3 0 .4 0 5 0 6 0 7 2 3 h d Figure 4. Surface reflected intensity versus direct intensity for directional sources, h = depth, d = testing distance. For dipole source o = 1; for circular piston source a = V4 (^D/\y, D = diameter of piston, x = wave length; for line .source suspended vertically. = 1/3 (-^L/X)-, L = length of Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original United States. Office of Scientific R
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