OCEAN-O Flashcards
Ocean-O
Critical Depth
The depth below the Deep Sound Channel (DSC) axis at which the sound speed is the same as it is at the sonic layer depth.
Ocean-O
Mixed Layer Depth
The depth at which mixing ceases to occur. (Mar Man pg 23)
A region of relatively warm, isothermal water.
Mechanical mixing caused primarily by wave action (as a result of winds and surface storms) and by thermohaline circulation (all of the cold water sinks leaving only warm water on top).
Ocean-O
Sonic Layer Depth
The depth of maximum near-surface sound speed above the deep sound channel
Ocean-O
Sound Channel Axis
The depth of minimum sound speed within a sound channel.
Ocean-O
Thermocline
A temperature gradient in a layer of sea water where the temperature decreases continuously with depth. Usually the gradient is greater than 2.7F per 165 feet (1.5C per 50 meters) of depth
Ocean-O
Deep Cold Water Layer
The layer of water between the lower edge of the main thermocline and the ocean bottom. It is characterized by a nearly constant temperature and a positive sound-speed gradient caused by pressure
Ocean-O
Conjugate Depth
For a source below the Sonic Layer Depth (SLD), that depth below the deep sound channel axis where the sound speed equals the speed at the source depth
Ocean-O
Speed of Sound Factors
Temperature 6 ft/s every 1°F
Salinity 4 ft/s every 1 PPT
Pressure 2 ft/s every 100 feet
Ocean-O
Standard Day
Temperature 39°F
Salinity 35PPT
Pressure Sea Level
Ocean-O BT Profile (what does a BT Buoy give us)
SST - Sea Surface Temperature
MLD - Mixing Layer Depth
BLG - Below Layer Gradient
Ocean-O
Types of Propagation Loss
Absorption Spreading Spherical Cylindrical Dipolar Scattering Bottom Surface Volume Multipath Interference Diffraction
Ocean-O
Absorption
The reduction of sound intensity caused by the conversion of sound energy into heat as it passes through water
Ocean-O
Spreading
The phenomenon whereby transmitted sound intensity decreases in a constant relation to distance from the sound source
Cylindrical 3dB per distance doubled
Spherical 6dB per distance doubled
Dipolar 12 db per distance doubled
Ocean-O
Scattering
Energy losses due to the random reflection of sound. Suspended particulate matter in the water column scatters sound energy into directions other than the direction the main wave is traveling
Bottom - some of the energy with get strike the bottom and be absorbed, the reflected energy will be reduced
Surface - Reflection and scattering of sound by the surface of the sea cause loss of energy. Surface loss increases with sea state and with frequency
Volume - Sound reflecting off particles/ objects in the water
Ocean-O
Multipath Interference
Constructive and destructive interference between energy propagating in separate paths
Ocean-O
Diffraction
Diffraction concerns the wave motion beyond an obstacle that has cut off a portion of an advancing wave front
Ocean-O
Propagation Paths
Direct Path Bottom Bounce Convergence Zone Half Channel Surface Duct Sound Channel
Ocean-O
Direct Path
Bearings - YES
Aurals - YES
Doppler - YES
Single Refraction, only one change in direction. No Reflection
0-3 NM
Ocean-O
Surface Duct
Bearings - YES
Aurals - YES
Doppler - YES
The source is in the sonic layer and in a region of positive velocity gradient. The ray paths are trapped in the sonic layer due to the positive gradient refracting them upwards.
0-10 NM
Ocean-O
Half Channel
Bearings - YES
Aurals - YES
Doppler - YES
A positive velocity gradient exists from the surface to the bottom causing all the ray paths to refract upward.
0-20 NM
Ocean-O
Sound Channel
Bearings - YES
Aurals - YES
Doppler - YES
Propagation path with longest possible ranges. Sound rays refract between positive and negative gradients.
Usually too deep for buoys (more for IUSS)
0-100 NM
Ocean-O
Bottom Bounce
Bearings - NO
Aurals - YES
Doppler - ?
Erratic returns, best on smooth and hard bottoms. Good for MAC
6-12 NM
Ocean-O
Convergence Zone
Bearings - Constant
Aurals - NO
Doppler - NO
Require a depth and speed excess, a loud target and a negative over positive gradient.
22ft/s and 1200’ - 50% chance of CZ
33ft/s and 1800’ - 80% chance of CZ
18-36 NM (CZ width about 5-10% of the range)
Ocean-O
Low Frequency Cutoff
Higher frequencies cannot go into deep water
When SLD @:
100’ - <1000 HZ can go through
200’ - <300 HZ can go through
300’ - <200 HZ can go through
400’ - <100 HZ can go through
Ocean-O
When to drop another BT buoy
S - Sea State changes by 1 T - Temperature changes by 2°F A- Ambient noise changes by 2 db G - Gradient changes by 0.5°F per 100ft S - Sonic Layer Depth changes by 50ft
OceanO
Warm Eddies characteristics
- Deep SLDs
- Stronger negative gradients below the SLD
- Stronger boundary at the SLD with less leakage, resulting in better ducking of trapped frequencies within the SLD
- Poor cross-layer coupling
- Weaker CZ conditions
- Poor coupling of energy to the DSC
OceanO
Cold Eddies characteristics
- Shallower SLDs
- Weaker below layer gradient
- Poor surface ducting
- Good cross-layer coupling
- Better CZ conditions
- Better DSC coupling
OceanO
Best depth
The optimization between being below the sonic layer and close enough to the SLD to maximize the shadow zone.
Best Depth = SLD + 200ft
Signal Excess
The received signal level in excess of that required for detection
