Physical Oceanographic

Learn the Basics

Echogram of plume front prior to release of internal waves

Mixing layers and internal waves are of great interest to oceanographers and climatologists who use BioSonics DT-X echosounders to studies these features. Mixing layers play an important role in the transfer of energy and its effects on the physical climate. Such layers may result from turbulence generated by upwelling, winds, cooling, or processes such as evaporation or sea ice formation which result in an increase in salinity.

Areas of upwelling or where buoyant fresh water mixes with sea water are often studied to better understand the role of turbulence in mixing water of riverine and oceanic origin. Such areas of mixing produce the biochemical environment needed to fuel high biological productivity. As shown in the echogram image at right, plumes issued from river mouths can produce sharp, bore-like fronts and generates large amplitude internal waves throughout the region.

Mobile survey s can be conduct ed from virtually any size watercraft in depths as shallow as one meter. As transects are driven over the study area, the echosounder system automatically records bottom depth and sediment characteristics. The data collected is time-stamped, geo-referenced and digitally stored. Surveys are often conducted by a single operator and do not require sophisticated training.

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How It Works

Internal waves visible on the DT-X echogram

Temperature and salinity affect the density of water which in turn directly affects the speed and amount of sound energy transmitted and received by an echosounder. BioSonics DT-X echosounder is a highly sensitive scientific instrument capable of detecting very small, even particulate sized, objects in the water column. Boundaries between layers of water of different density are detectable and visible on the echogram during data collection. The internal structure of these waves can sometimes be illuminated by acoustics, if sufficient acoustic scatterers are present. Researchers use the DT-X in conjunction with other instruments to observe the position and movements of mixing layers and internal waves in the ocean to better understand this important phenomena.

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Case Studies

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