Buoys and floats are designed to float on the surface of a body of water, or are supported below the water’s surface to mark a location. They are used in marine navigation, boat mooring, nautical communications, and weather observation applications. Buoys and floats were made traditionally from iron, but are now available in plastic materials such as polyethylene. Products that can be fitted with marine lanterns may carry specifications such as lantern focal height. Buoy shape, size, height, color, configuration, and markings are additional parameters to consider. According to international maritime standards, green buoys have odd numbers and red buoys have even numbers. There are several types of buoys and floats used for meteorological observation. Weather buoys are designed to measure air temperature, barometric pressure, and wind speed and direction. Typically, these buoys and floats report data via satellite phone networks and radio links. Unlike moored buoys, which remain anchored in place, these drifting buoys are allowed to float in ocean currents while their position is determined by satellite. By contrast, tsunami buoys are fixed-location devices that are designed to detect sudden changes in underwater sea pressure, which may signal a tsunami. Waverider buoys measure the movement of the water’s surface as a wave train, which is then analyzed to determine wave height and wave direction. Profiling buoys and floats that measure buoyancy, temperature and salinity are also available. Some buoys and floats are used for mooring and marking applications. Navigation buoys are used in harbors, bays, channels, rivers, and inland waterways to designate speed and direction. Dedicated mooring buoys are designed to attach to mooring cables and chains from ships, boats, and offshore vessels. Shot buoys mark the location of scuba divers and help to promote boat safety. Divers also use subsea decompression buoys to mark their underwater positions during decompression stops. Fairway buoys mark the entrance to a channel or nearby landfall while wreck buoys indicate the location of an unseen hazard or a disabled boat or ship. Spar buoys are tall, thin devices that float upright in the water. Specialized buoys and floats include target buoys and military communications buoys. As their name suggests, target buoys are used to similar a target such as a boat during military exercises. Sonobuoys are used by anti-submarine warfare (ASW) aircraft to detect submarines with sonar, a technique that sends out an acoustic pulse and measures distances in terms of the time for the echo of the pulse to return.