Accession Number:



LIRA: A Model for Predicting the Performance of Low-Frequency Active-Sonar Systems for Intermediate Surveillance Ranges.

Descriptive Note:

Final rept. Dec 76-May 79,

Corporate Author:


Personal Author(s):

Report Date:


Pagination or Media Count:



LIRA is a computer model developed to predict the performance of active-sonar systems for intermediate-range surveillance. The program provides a series of outputs as a function of target range. Propagation loss incoherent and largest arrival, reverberation level, and signal excess are provided in both printed and plotted forms. Other printed outputs are two-way travel time to the target, angle of largest ray arrival at the source, signal level at the output of the beamformer, signal-to-noise ratio, and probability of detection. Reverberation plots show surface, bottom, and volume components as well as total reverberation and competing noise level. Source and receiver are not required to be at the same depth. Target ranges may extend from 1 yd to 1000 kyd a maximum of 500 target ranges are allowed per run. Source frequency is allowed to be between 25 Hz and 25 kHz. Pulse length may be between .0001 and 100 s. The sound-speed profile is represented by curvilinear segments to eliminate false caustics. The sound-speed profile is assumed to be constant with range and the ocean bottom horizontal. The propagation loss models are ray theory supplemented with caustic corrections derived by Brekhovskikh, and empirical equations based on the AMOS data and corrected for low frequencies using normal mode theory. Beam patterns for both transmitter and receiver are incorporated into propagation loss. The Hall-Watson model is used for absorption loss. Surface backscattering strength is a combination of the Chapman-Harris equations, Eckarts equations, and Richters data. Bottom backscattering strength is derived from Lamberts law and Schmidts data. Volume backscattering strength is represented as the column strength.

Subject Categories:

  • Computer Programming and Software
  • Acoustic Detection and Detectors

Distribution Statement: