. Basic methods for the calibration of sonar equipment. 24 TYPES OF ACOUSTIC MEASUREMENTS 40° 320'. 150° 160' 170' ItiO' I'JO' â JOO' 210 210° 200' 190' 180* 170° 160° 150* FiCL'RF 6. Direclivitv index 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 Research and Development. National Defense Research Committee. Washington, D. C.

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