Oceanography Basics Flashcards

1
Q

Describe the three layer ocean model

A

Mixed layer (isothermal)

Thermocline (transition to cold water)

Deep water (deep and cold)

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2
Q

What is the limiting ray

A

Sound ray which grazes or is tangential to a boundary layer

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3
Q

What is the critical angle ray

A

Sound ray which strikes a boundary or surface at steepest gradient

More than this (steeper) causes reflection loses

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4
Q

Shadow zones

A

Sound rays reflect away from depths at acoustic maxima. Little sound penetrates causing shadow zones

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5
Q

What are the 5 transmission paths

A

Direct path

Convergence zone

Surface duct

Bottom bounce

Sound channel

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6
Q

What are the different types of channel

A

DSC/SOFAR channel (deep/bottom)

Shallow sound channel (45-180m)

Secondary sound channel ??

Half channel ??

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7
Q

How does CZ occur

A

Sounds rays penetrate the SLD and then refract upwards

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8
Q

What are the conditions for CZ

A

Deep water (5000’ +)

Bottom velocity larger that SLD velocity

Cx of 10MS +
DE of 360m

Large Signal Excess

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9
Q

What is the annulus on CZ

A

Ring of energy around source at the surface (10% of CZ Range)

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10
Q

What is the CZ depth excess?

A

Depth at which the SOS matches and supersedes the SLD.

Depth excess needs to be 360m + for a 50% chance.

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11
Q

Give examples of CZ ranges for the North Atlantic & Med

A

NA: 25-30nm

MED: 12-17nm

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12
Q

Explain the letters in relation to CZ

A
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13
Q

Explain the letters in relation to CZ

A
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14
Q

Where does BB prevail

A

SLD less that 15m

Shallow water - lots of interference

Deep water (1000’+) - BB ranges exist similar to CZ ranges

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15
Q

Name the two types of ocean fronts

A

Semipermanent

Temporary

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16
Q

Describe semi-permanent fronts

A

Associated with water mass boundaries

Stay static for long periods of time

Example: East Icelandic Front (Iceland-FAR-NOR)

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17
Q

Temporary Fronts

A

Temp changes to ocean structure due to abnormal weather or storms

Causes wind induced currents resulting in upwelling of cold water

Example: summer snow run off - Norwegian Sea

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18
Q

Name the Effects of fronts on sound

A

Abrupt changes is SVP

Higher AN (bio and fishing)

Errors in bearings (refracts to cold)

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19
Q

What are eddies and what effect do they have acoustically

A

Circular current flows that form on either sides for ocean currents

Up to 100nm in diameter

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20
Q

What are the 2 types of vertical ocean currents

A

Sinking of surface water

Upwelling

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21
Q

Describe upwelling and it’s Aco properties

A

In costal areas wind blows surface water seaward allowing cold water to rise in its place

High AN due to rich water - Bio/Fishing
Reduction in surface temp

22
Q

Describe sinking of surface water and its acoustic properties

A

Occurs at front boundaries where the denser cold water sinks

Causes currents, rip-tides, trapped debris

23
Q

Name the three types of bottom and their properties

A

Rock - smooth rocky bottoms are best reflectors but are rare and often covered in sediment (600m thick in Atlantic)

Sand - exploitable for BB when flat

Mud/Silt - poor reflector due to smaller particles. <300hz can be refracted

24
Q

Explain the continental shelf

A

Continental shelf - Smooth sand or mud
Shallow gentle decrease to 600’
High AN, good BB

Contains areas of continental borderland:
Irregular areas of shelf containing peaks and valleys (poor Aco properties)

25
Q

3 types of bottom typography

A

Shelf

Slope

Deep ocean basin

26
Q

Explain the areas to continental Slope (3)

A

Slope - sharp decrease from shallow to deep. Steep, jagged Rock

Rise - base of slope, begins to flatten

Sea fans - deposits of sediment at the mouth of submarine canyons

Sub canyon - ancient valleys cut into the rise. Subs hide due to scattering

27
Q

Explain the deep ocean basin

A

Deep regions between slopes

28
Q

Describe the 4 areas of deep ocean basin

A

Abyssal plain - deep layer of sediment/mud, smooth, BB

Trenches - very deep canyons in ocean floor

Ridge - underwater mountains, barriers to sound (mid-Atlantic/reykjanes)

Seamounts - isolated mountains

29
Q

Explain the two types of seamount & Atolls

A

Guyot - flat topped

Pinnacles - jagged

Atoll - ring of reef islands

30
Q

SPL

A

Sound pressure level

31
Q

Name the two types of transmission losses

A

Spreading - distribution of energy as it moves from source

Attenuation

32
Q

Name the 3 types of spreading and their dB losses

A

Spherical - unbounded - 6dB

Cylindrical - sound channel - 3dB

Dipolar - source at SLD break - 12dB

33
Q

What are the Types of attenuation loss

A

Absorption

Scattering

Leakage and boundary effects

34
Q

Describe absorption

A

Energy converted to heat through molecular action

Salinity up, temp down, frequency up = more loss

35
Q

What are the 4 types of scattering

A

Volume - bio

Bottom - sediment

Deep Scattering Layer - bio

Surface - wave action, wind.

36
Q

What is the DSL

A

Deep scattering layer - daily migration of plankton and bio causing higher volume scattering

200m night 900m day

37
Q

Describe leakage and boundary effects

A

Low frequencies can leak out of channels due to diffraction and scattering.

Deeper and higher frequencies mean more ducting chance

38
Q

Describe the active equation

A

SE = SL - 2PL - AN - RD + TS

39
Q

Describe the passive equation

A

SE = SL - AN - RD - (DI) - PL

40
Q

Describe passive FOM equation

A

FOM = SL - AN - RD - (DI)

41
Q

Types of AN and frequencies (5)

A

Shipping - low freq (<500)

Seismic - low

Sea state - 500hz +

Bio - various

Precipitation - 10000hz

42
Q

Describe the 5 layer ocean model

A

Mixed layer

Seasonal thermocline - temporary where temp decrease

Transient thermocline - mixing affect, short term (hours)

Perm thermocline

Deep water

43
Q

Describe upslope transmission

A

A source in deeper water may send sound rays into shallower water

Causes more reflection loss at boundaries causing less detectable sound

44
Q

Describe down slope enhancement

A

Source in shallow water may reflect sound down slope til the water is deep enough for refraction into channels

Larger range, more detection

45
Q

Describe the Diurnal effect

A

The heating and cooling of the surface layer by the sun

Means daily or during the day

Heating causes more shadow zones/transient channels

46
Q

What is the MLD

A

Depth at greatest temperature

Captures heat and effects bio/plankton depth (AN)

47
Q

Rarefaction

A

Pressure decrease point in a medium

48
Q

Describe half channels

A

Sound rays refract upwards (if a + BLG exists)

49
Q

Describe Compression

A

Pressure increase at a point in a medium caused by sound energy

50
Q

Factors effecting SOS

A

Salinity 2 ft/s per 1/1000 increase

Pressure 4ft/s per 100ft depth increase

Temperature 6-8ft/s per F increase