Abstract
Accuracy in free field calibration of microphones is dependent on signal to noise ratio of its enviromental circumstances, and for carrying out the calibration of microphones in the sea-water, it is necessaty that the magnitude of undersea noise be known beforehand. Measurement of the undersea noise spectrum and the amplitude in the frequency range of 5-60kc/sec at Mito-hama Bay (Numazu, Shizuoka Prefecture) was made by using ADP standard microphone. The spectrum and magnitude of surrounding noise were dependent on the time, the season, the weather, the place, etc. , and our data show that the intensity of noise was in the order of 10^<-16> watts/cm^2//cycles/sec.
