In SONAR (Sound Navigation and Ranging), ultrasonic waves are used. SONAR is a technique that is used to detect and locate objects underwater. Ultrasonic waves are sound waves with a frequency higher than the upper limit of human hearing, typically above 20,000 Hz.

Option 2, infrasonic waves, refers to sound waves with a frequency lower than the lower limit of human hearing, typically below 20 Hz. Infrasonic waves are not used in SONAR.

Option 3, radio waves, are electromagnetic waves that have much higher frequencies than sound waves. Radio waves are used in various applications such as communication, but they are not used in SONAR.

Option 4, audible sound waves, are sound waves that fall within the range of frequencies that humans can hear, typically between 20 Hz to 20,000 Hz. While audible sound waves can be used for communication and detection, in SONAR specifically, ultrasonic waves are utilized as they can travel long distances in water and provide accurate readings.

Hence, the correct answer is option 1, ultrasonic waves, which are used in SONAR for underwater detection and location.