Detecting exactly information from pulse position modulation (PPM) is difficult in shallow water channels because of the high noise level there. This paper reports results of analyses of some statistical characteristics of shallow water channel noise and its adverse effect on detecting PPM information; and proposes some efficient countermeasures (the method of statistical decision, use of pulse width discriminator and digital selective-frequency filter) to overcome noise interference. The results have been applied to PPM detection systems and proved to be efficient, and are of reference value for other models of signal detection. Detecting exactly information from pulse position modulation (PPM) is difficult in shallow water channels because of high noise level there. This paper reports results of analyzes of some statistical characteristics of shallow water channel noise and its adverse effect on detecting PPM information; some efficient countermeasures (the method of statistical decision, use of pulse width discriminator and digital selective-frequency filter) to overcome noise interference. The results have been applied to PPM detection systems and proved to be efficient, and are of reference value for other models of signal detection.