OCEAN-O

Question 1

Ocean-O

Critical Depth

Answer 1

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.

Question 2

Ocean-O

Mixed Layer Depth

Answer 2

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).

Question 3

Ocean-O

Sonic Layer Depth

Answer 3

The depth of maximum near-surface sound speed above the deep sound channel

Question 4

Ocean-O

Sound Channel Axis

Answer 4

The depth of minimum sound speed within a sound channel.

Question 5

Ocean-O

Thermocline

Answer 5

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

Question 6

Ocean-O

Deep Cold Water Layer

Answer 6

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

Question 7

Ocean-O

Conjugate Depth

Answer 7

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

Question 8

Ocean-O

Speed of Sound Factors

Answer 8

Temperature 6 ft/s every 1°F

Salinity 4 ft/s every 1 PPT

Pressure 2 ft/s every 100 feet

Question 9

Ocean-O

Standard Day

Answer 9

Temperature 39°F
Salinity 35PPT
Pressure Sea Level

Question 10

Ocean-O
BT Profile (what does a BT Buoy give us)

Answer 10

SST - Sea Surface Temperature
MLD - Mixing Layer Depth
BLG - Below Layer Gradient

Question 11

Ocean-O

Types of Propagation Loss

Answer 11

Absorption
Spreading
Spherical
Cylindrical
Dipolar
Scattering
Bottom
Surface
Volume
Multipath Interference
Diffraction

Question 12

Ocean-O

Absorption

Answer 12

The reduction of sound intensity caused by the conversion of sound energy into heat as it passes through water

Question 13

Ocean-O

Spreading

Answer 13

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

Question 14

Ocean-O

Scattering

Answer 14

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

Question 15

Ocean-O

Multipath Interference

Answer 15

Constructive and destructive interference between energy propagating in separate paths

Question 16

Ocean-O

Diffraction

Answer 16

Diffraction concerns the wave motion beyond an obstacle that has cut off a portion of an advancing wave front

Question 17

Ocean-O

Propagation Paths

Answer 17

Direct Path
Bottom Bounce
Convergence Zone
Half Channel
Surface Duct
Sound Channel

Question 18

Ocean-O

Direct Path

Answer 18

Bearings - YES
Aurals - YES
Doppler - YES
Single Refraction, only one change in direction. No Reflection

0-3 NM

Question 19

Ocean-O

Surface Duct

Answer 19

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

Question 20

Ocean-O

Half Channel

Answer 20

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

Question 21

Ocean-O

Sound Channel

Answer 21

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

Question 22

Ocean-O

Bottom Bounce

Answer 22

Bearings - NO
Aurals - YES
Doppler - ?

Erratic returns, best on smooth and hard bottoms. Good for MAC

6-12 NM

Question 23

Ocean-O

Convergence Zone

Answer 23

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)

Question 24

Ocean-O

Low Frequency Cutoff

Answer 24

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

Question 25

Ocean-O

When to drop another BT buoy

Answer 25

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

Question 26

OceanO

Warm Eddies characteristics

Answer 26

• 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

Question 27

OceanO

Cold Eddies characteristics

Answer 27

• Shallower SLDs
• Weaker below layer gradient
• Poor surface ducting
• Good cross-layer coupling
• Better CZ conditions
• Better DSC coupling

Question 28

OceanO

Best depth

Answer 28

The optimization between being below the sonic layer and close enough to the SLD to maximize the shadow zone.

Best Depth = SLD + 200ft

Question 29

Signal Excess

Answer 29

The received signal level in excess of that required for detection