||An altimeter and echo sounder. This instrument is designed to measure distance to the seabed, but it can also be used in other underwater applications where distances need to be measured and monitored. The device is designed to be mounted on ships, boats, ROV, etc. Some of the applications include ROV and AUV Altitude, Heading and Attitude, Scour Monitoring, Hydro-graphic Survey, Touchdown Monitoring, Wave Height Measurement, Under Ice Measurement, Equipment Deployment, Motion Reference, Underwater Positioning. In addition to Altitude, the ISA500 provides Heading, Pitch and Roll as well as Temperature. Heading, Pitch and Roll readings are provided a MEMS (Micro-Electro-Mechanical System) sensor located within the unit. Temperature is measured by a sensor, which sits against the ISA500 end cap. The ISA500 falls into a category of a sonar, as it relies on underwater acoustics in ranging purposes. It operates by transmitting an acoustic pulse into the water, which travels until it comes into contact with the seabed. Upon contact with the seabed, part of the pulse is absorbed, and part is reflected back to the transmitter, which records the time between transmitted and reflected signal. Knowing the speed of sound in water and the time between transmitted and received (reflected) signal, once can calculate the distance. The key characteristics of ISA500 include: ranging capabilities (1-120+ m) with 1 mm resolution; heading, pitch and roll; temperature. Optional configurations include: depth rating of 1000m, 6000m or 11000m; housed in a compact titanium or lightweight acetal housing; available in forward looking and right angle housing configurations; Pitch, Roll and Heading (AHRS). Range: 0.1m to 120m (1mm resolution); Heading accuracy: +/- 1deg (0.1deg resolution); Pitch (+/- 90deg) and Roll (+/- 180deg): Accuracy 0.2deg (0.1deg resolution); Beam angle: 6deg conical at 500kHz.