UACE2017 Proceedings: Coherent matched-filter reflection loss from a moving surface as a function of pulse duration and ensonified area

• Session:
  Large Time-Bandwidth acoustic signals for target detection and tracking
• Paper:
  Coherent matched-filter reflection loss from a moving surface as a function of pulse duration and ensonified area
• Author(s):
  Douglas Abraham
• Abstract:
  In many applications of active sonar the propagation paths connecting a source, object of interest, and receiver include reflection from the ocean surface. A classic result [Eckart 1963] describes the coherent surface reflection loss (SRL) of an acoustic pulse solely as a function of the Rayleigh roughness parameter by requiring a large ensonified area (LEA), in effect, where many correlation lengths of the surface contribute to the reflection and a pulse short in duration relative to the surface wave period. At the other extreme are results accounting for motion of the surface throughout the pulse's reflection by requiring a small ensonified area (SEA), in effect, where less than a correlation length of the surface contributes to the reflection. The pulse compression achieved by matched filtering broadband pulses provides the SEA in the down-range dimension and enables evaluation of SRL as a function of pulse duration (i.e., there is no restriction that the pulse be short relative to the surface-wave period). The coherent SRL for a medium-ensonified-area (MEA), the region in between the LEA and SEA assumptions where multiple correlated components of the surface contribute to the reflection, is presented in this paper. The derivation adds to the SEA model a dependence on both the ensonified area and the spatial correlation function. As expected the MEA model simplifies to the classic LEA result when the effective ensonified area is large relative to the correlation length. An example evaluation of SRL using a one-dimensional Pierson-Moskowitz wave spectrum is presented as a function of pulse duration and bandwidth to illustrate how the loss is near the LEA result for low bandwidths and tends to the SEA result as bandwidth increases.\n\nThis work was sponsored by the Office of Naval Research
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Contact details

• Contact person:
  Dr Douglas Abraham
• e-mail:
  
• Affiliation:
  CausaSci LLC
• Country:
  United States