Communications satellites have helped minimize the risk by greatly reducing the time spent at periscope depth to exchange data. Radar is an acronym for radio detection and ranging. A radar system transmits a radio beam, then detects and measures the echo when the beam bounces off an object. This provides information about both the target's direction and range. Like periscopes and radio antennas, however, radar masts protruding above the water provide vital information at the expense of increased risk of detection.
Submarines generally use radar only on the surface when leaving or entering port.
A sound signature is the unique, repetitive noise created by every ship's rotating machinery, such as engines, propellers, and pumps. Submarine sonar technicians analyze and record these signatures for the sound library. This device above the sonar console continuously measures and displays the depth, temperature, and salinity of the surrounding seawater to compute the speed of sound in the ocean. These data are essential to the interpretation of incoming sonar data and the avoidance of detection by active or passive sonar. A similar recorder is located in the attack center.