The AN/SSQ-57B Low Frequency Analysis and Recording (LOFAR) sonobuoy is an A-size, expendable, non-repairable, calibrated sonobuoy. It uses the AN/SSQ-41B platform, substituting a calibrated hydrophone for frequencies in the 10Hz to 20,000Hz range. The LOFAR sonobuoy provides omnidirectional passive acoustic signature data to the monitoring unit(s). The sonobuoy is calibrated and can be used to accurately measure ambient noise, and through post event analysis, provides Sound Pressure Level (SPL) measurements.The LOFAR sonobuoy is an expendable, omnidirectional passive sonar unit. It consists of an omnidirectional hydrophone that descends through the bottom of the sonobuoy canister to a pre-selected depth. The LOFAR operates from one of 31 RF channels preset during manufacturing. The buoy can also be provided with EFS/99 RF channel capability. There is a selectable operating life of one, three, or eight hours and selectable operating depth of 90 or 400 feet. The LOFAR, upon self-activation, operates in a passive mode at the preset life and depth. Upon reception of acoustic signals, the subsurface unit converts the pressure waves into amplified electronic signals. These signals are then sent to the surface unit where they are applied to an FM carrier for VHF transmission. The monitoring platform receives the signal for recording, processing, and analysis. The AN/SSQ-57M is a moored version of the AN/SSQ-57A and utilizes the same omnidirectional hydrophone system. This low cost, expendable, air-deployable, passive sonobuoy has a twelve hour battery operating system and is capable of being anchored in water depths from 25 to 120 meters in salinity down to zero percent. Operating life can be set for 1, 4 or 12 hours.