2. Thriving on several parallel layers of material arranged one on top of another.
2. The thin layer of air adjacent to the earth's surface, usually considered to be less than 300 feet (91 meters) high.
3. The thin layer of air adjacent to the earth's surface, extending up to the so-called anemometer level (the base of the Ekman layer [thin top layer of the sea]); within this layer the wind distribution is determined largely by the vertical temperature gradient and the nature and contours of the underlying surface, and shearing stresses are approximately constant.
2. One of several strata or layers of the earth's atmosphere.
Temperature distribution is the most common criterion used for denoting the various shells.
2. Layers of increased ionization within the ionosphere produced by cosmic radiation; responsible for absorption and reflection of radio waves and important in connection with communications and tracking of satellites and other space vehicles.
Echo sounders are measuring instruments that send out acoustic pulses in water and measure distances in terms of the time for the echo of the pulse to return.
SONAR is an acronym for "sound navigation ranging"; ASDIC is an acronym for "antisubmarine detection investigation committee".
The name refers to the way they scatter sound waves. The layers are typically composed of krill, midwater fish, and siphonophores (species which form complex free-swimming communities composed of numerous zooids of various kinds, or organic bodies or cells having locomotion, some of which act as floats or as swimming organs, others as feeding or nutritive zooids, and others as reproductive zooids).