This part of IEC 62127 specifies relevant hydrophone characteristics. This standard is applicable to: - hydrophones employing piezoelectric sensor elements, designed to measure the pulsed and continuous wave ultrasonic fields generated by ultrasonic equipment; - hydrophones used for measurements made in water; - hydrophones with or without an associated pre-amplifier. IEC 62127-1, IEC 62127-2 and IEC 62127-3 are being published simultaneously. Together these cancel and replace IEC 60866:1987, IEC 61101:1991, IEC 61102:1991, IEC 61220:1993 and IEC 62092:2001.