Maneuvering, or changing course, disturbs the array and complicates analysis of the sampled data stream. These periods of instability are closely tested during sea trials and known by the crew's officers and enlisted sonar experts. Modern systems compensate by constantly self-measuring the relative positions of the array, element to element, reporting back data that can be automatically corrected for curvatures by computers as part of the beamforming math processing. A ship must also limit its overall top speed while a towed array is deployed. Hydrodynamic drag increases as a square function of velocity, and could tear the cable or damage its mooring hardware. Furthermore, a minimum speed may have to be established depending on the buoyancy of the towed array (military arrays are ballasted to sink, geophysics arrays are supposed to be neutrally buoyant at about 10m). The array could also be damaged by contact with the seafloor or if the vessel operates astern propulsion, or can even be damaged if it bends too tightly. See also Aperture synthesis Phased array FFT Spectrum analyzer Synthetic aperture sonar Towed pinger locator References External links Towed Hydrophone Arrays (OSC) Surveillance Sonar Submarines Multidimensional signal processing