17 - Sound Propagation Paths Flashcards
Sound in an Isovelocity Gradient
Long Ranges, straight line rays
Sound Propagation in a Negative Gradient
- Temp decrease with depth
- Sound bends down
- Shadow zones formed
Sound Propagation in a Positive Gradient
- Sound bends up
- Possible shadow zones
- Temp increase with depth
Layer Depth Phenomenon
(Positive over Negative)
- Critical ray defines sonic layer boundary
- Critical ray splits up and down, creates Shadow Zone (SZ)
Sonic layer depth = depth of highest sound velocity
What is Sound Channeling?
Negative over Positive
- Creates Sound Channel
- Sound horizontally channeled great distances
Sound does not escape
What are the Sound Propagation Paths?
6 Paths
- Direct Path
- Surface Duct
- Half-Channel
- Sound Channel
- Convergence Zone (CZ)
- Bottom Bounce (BB)
Characteristics of a Direct Path
- Simplest propagation path
- Direct contact
- Close ranges
Characteristics of a Surface Duct
- Positive velocity gradient at the surface refracts sound back toward the surface
- ## Both the source and receiver must be in the sonic layer
Only ray paths trapped are considered Surface Duct
Characteristics of a Half-Channel
- Isothermal water causes positive velocity gradient from surface to bottom
- No shadow zones, and longest direct path ranges
Like a Surface Duct all the way to the bottom due to SVP gradient and shallow water
Characteristics of a Sound Channel
- Longest range transmission path available
- Only loss is absorption
- Negative / Positive gradient
Characteristics of the Convergence Zone (CZ)
- Need depth excess
- Reflects and refracts toward bottom again, can have multiple CZs
Amount of depth excess determines zone width
Characterisitics of a Bottom Bounce (BB)
- Beam bounces back towards surface
- Needs a relatively smooth, hard bottom
Bottom Dependent
Shallow areas can result in too much noise
