LEARNING OBJECTIVES Identify applications, limitations, and assumptions of the RAY program, Interpret the RAY program output.

The RAY program may be used to understand how sound propagates through a specific environment by tracing and displaying the paths of individual sound rays. The rays to be traced maybe specified by the user or selected by the module.

The RAY program graphically displays the interaction between the environment and the sound energy propagating through it. Its function is to display regions of a water column for a given set of environmental parameters (that is, sound speed profile and bottom topography [insonify regions]). Likewise, it can be used to easily display those regions of the water column that are not insonified due to shadow zones and bathymetric blockage. The RAY program serves as a modifier of flat bottom omnidirectional propagation-loss output by depicting the ranges/bearings from the source location where bottom effects may impact the propagation-loss curve. For a skilled interpreter, a finely detailed ray diagram can also point out possible locations for convergence zones (CZs) and shadow zones.

The restrictions as well as the principles taken for granted in using the RAY program areas follows:

Figure 8-2.-Example output of a search location density map.

Table 8-3.-Example Output of a Search Recommendation - Level I

. The RAY program uses a single sound speed profile, generated by the Sound Speed Profile (SSP) program. Thus, sound speeds used-in this program are a function of depth, but not range.

. In output displays, horizontal and vertical plotting scales are often different, resulting in an apparent difference between the angle of incidence and the angle of reflection with respect to a locally sloping bottom.

. A positive ray is downgoing; a negative ray is upgoing.

. If the source is located at the surface (that is, source depth of zero), the operator should not select any negative (upgoing) rays.

. The module traces only outgoing rays. If the angle of reflection from a sloping bottom is +89.9, then the ray is terminated.

. Computed ray diagrams are very sensitive to the users selection of launch angles and source depth, as well as bathymetry and sound speed,

. The RAY program uses the sound speed profile to calculate ray paths. If variable bottom depths, either automatically retrieved or manually supplied, exceed the deepest depth of that sound speed profile, the Raytrace module extrapolates the sound speed profile to the deepest variable bottom depth provided

. Because of computational limitations a 0 ray cannot be traced Whenever a 0 ray is requested or expected on the output diagram, a +0.01 ray and a -0.01 ray will be traced.

. Because temperature and salinity are relatively stable below 2500 m, sound speed profiles reaching 2500 m are accurately extrapolated. Extrapolations of sound speed profiles that do not extend to 2500 m, however, are suspect. Computed ray paths that descend to depths where extrapolated sound speeds are suspect should be used with caution.

The principle means of detection used in antisubmarine warfare (ASW) employs acoustic energy, Water, a poor medium for the transmission of electromagnetic (EM) energy, is an excellent conductor of acoustic energy or sound. Sound is a wave phenomenon, consisting of alternate compression and refraction of the medium. The speed of sound, or speed at which the acoustic waves advance through the medium, depend on certain characteristics of the medium. Properties of seawater that affect sound speed are salinity, temperature, and pressure. Output from this program is classified and should be labeled as required.

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