Passive Sonar Identification System for Underwater Lift Bags and Flags

Abstract

The invention is a system that enables passive sonar identification of underwater items by making use of lift bags and/or flags, having distinctive sequences of bands of sonar-signal-reflecting materials, wherein the lift items are partially inflated so as to present a predictable orientation with respect to the floor of a body of water and its surface.

What is claimed is: 
     
         1 . A system comprising:
 a lift device;   said lift device resting on floor of a body of water is partially inflated and pointed essentially toward surface of said body of water;   said lift device has one or more bands of sonar-signal-reflective material such that when said lift device is pointed essentially toward said surface said one or more bands comprise bands that are essentially horizontal as viewed from a side; and   said one or more bands, where more than one, are essentially parallel to one another and essentially vertically displaced from one another.   
     
     
         2 . A system as in  claim 1  further comprising:
 said one or more bands of sonar-signal-reflective material, when impinged upon by an incident sonar signal, will reflect said incident sonar signal as a reflected sonar signal; and 
 said reflected sonar signal, compared with said incident sonar signal, will differ in signal characteristics because of said one or more bands of sonar-signal-reflective material. 
 
     
     
         3 . A system as in  claim 2  further comprising:
 at least one of said one or more bands has a width, W; and 
 at least one of said one or more bands has a width,  2 W. 
 
     
     
         4 . A system as in  claim 3  further comprising:
 said at least one of said one or more bands with said width W represents a binary  1 ; and 
 said at least one of said one or more bands with said width  2 W represents a binary  0 . 
 
     
     
         5 . A system as in  claim 3  further comprising:
 said at least one of said one or more bands with said width W represents a binary  0 ; and 
 said at least one of said one or more bands with said width  2 W represents a binary  1 . 
 
     
     
         6 . A claim as in  claim 1  further comprising:
 said one or more bands, where more than one, may be made of different materials such that the reflection coefficients of the bands are different.