Measurement

1
Chapter 2??????????

• Measurement
• World-wide distributions and their characters
• Stratification - ??
• Water Mass - ??
• Sound and Optics

2
Basic ideas for the temperature measurement

• Expansion of liquid or a metal
• Differential expansion of two metals
• Vapor pressure of a liquid
• Thermocouples (????)
• Change in electrical resistance.
• Infrared radiation from the sea surface

3
Expansion of liquid or a metal

• Mercury thermometers
• Min-max thermometers
• Reversing thermometers
• Precision is around 0.01oC
• Linearity in the expansion coefficient of the
  liquid
• The constancy of bulb volume
• The uniformity of capillary bore
• The exposure of thermometer stem to temperatures
  other than the bulb temperature.
• Two types of errors Offset and parallax
  (??)errors.

Left Protected and unprotected reversing
thermometers is set position, before reversal.
Right The constricted part of the capillary in
set and reversed positions. From von Arx (1962).
4
????a. Nansen bottle
5
Mechanical bathythermograph (MBT) Expandable
bathythermograph (XBT)

• MBT
• Measure the depth and temperature.
• Only used in the depths less than 300m, slow
  speed, low accuracy, easy deformation, and shift
  due to spring problem.
• Using oF instead of oC (accuracy could reach
  0.1oF).
• XBT
• Using the electrical resistance of materials
  recording the temperature.
• Recording the upper ocean temperature when the
  ship was underway.
• The material could cooper, platinum, nickel, and
  semi-conductor. The latter type made sensor
  called as thermistors.
• The thermistors of XBT is widely used in
  oceanography.
• Depth measurement using the elapsed time of
  freely falling.
• Accuracy is 0.1oC.
• The depth measurement could be a source of error
  of recorded temperature.

6
Salinity/conductivity-temperature-depth
profilersCTD

• STD/CTD system uses a platinum resistance
  thermometer.
• It connects with ship using cable. Modern CTDs
  have accuracies of 0.002oC over a range of 3 to
  32oC, and stability 0.001oC/month.
• The response time of the platinum thermometer is
  typically 250ms.
• Need in-situ calibration.

7
In-situ CTD profiling from monitor
8
Sea surface temperature

• Buckets
• Injection temperature (has to consider heating
  effect)
• Above methods cannot record the true SST
• Direct measurement of true SST is quite
  difficult.
• Satellite-sensed sea surface temperature
  (radiation temperature)
• Estimated from long-wave sea-surface radiation
  using infrared sensors.
• Measured on global temperature a nearly synoptic
  scale.
• Cloud is problem. Composite T is usually made.
• Accuracy could be a problem
• ITOS was earliest (1970)
• AVHRR is most popular today, resolution is 1x1km,
  accuracy is improved (0.5-1.0oC).

9
Dynamic response of temperature sensors

• Sensor response to temperature change has a time
  lag.
• The lag depends upon the material of sensor.
• Heat transfer equation is
• The solution, if T is function of t only, is
• e-folding time scale.
• There have a number ways to define the e-folding
  scale for example, e-1 or e-petc.
• Large temperature gradient needs to soak the
  sensor for a little bit long time.

10
?? Salinity (Non-dimension)

• ??
• The total amount of solid material in grams
  contained in one kilogram of seawater when all
  the carbonate has been converted to oxide, all
  the bromine and iodine replaced by chlorine and
  all the organic material oxidized.
• ????
• ?The total amount of dissolved material in
  sea-water?
• ????-??????????????
• Unit. parts per thousand
• ??
• ???
• ???(Titration)
• ????????? salinity1.80655chlorinity
• Chlorinity/salinity relation varied with
  era
• Accuracy could reach 0.002
• Potential error end-point for titration

11

• ???(calibration)
• ???????,??????????????,???psu(practical salinity
  unit)?
• Seawater conductivity depends on the ion content
  of the water and is therefore directly
  proportional to the salt content.
• Avoid depended on chlorinity but now depends upon
  the standard water.
• Quick and profile sampling
• Accuracy could reach 0.005psu
• Mismatch of response times of T and S could be a
  big problem.
• Sensor shifted is another problem.
• Small problems sensor heats the water, pressure
  impact.
• Nonconductive methods
• Some dissolved material may not cause any
  conductivity.

12
??Pressure

• Unit decibar (dabr)
• ?????(hydrostatic pressure),????????????
• ?????????????
• Calibration is needed, in general.
• ??????????????????????????
• ??1026kg/m3,g9.8m/s2,z1m,
• ? p1.005x104kg/m2s21.005 dbar/m ? 1m0.995dbar
• ???????bar,??10m?????????
• ????,??????????,??????
• ?????XBT,???(???)??free fall speed???,???????????
• ?????????????????????

13
?? Density

• ???????,????????????
• ???????non-linear relationship
• ??
• meaning we cant just add each effect
  individually instead need addition of 7 terms
• Or, in partial differential equation(PDE)form
• higher order terms
• where the higher order terms are nonlinear

14

• Since the sea water density varies from 1021 to
  1070 kg/m3 ,it is generally expressed as
• ss.t.p.density-1000
• ssalinity, ttemperature, Ppressure
• It is referred to as the in-situ value.
• If the pressure effect is ignored, thenss.t.p st
  . It represents the in-situ density when the
  water pressure is neglected(but he atmospheric
  pressure is remained).
• So, thest is function of temperature and
  salinity. Their relationships are also
  non-linear. Generally speaking, T increases
  density decreases(except below the temperature of
  maximum density)S increases density increases.
  Salinity decreases the temperatures of density
  maximum and freezing point of seawater. The
  former one has larger decreasing rate than the
  latter one. Both temperatute are equal at
  1.33oC at a salinity of s24.5 psu?
• Density is also significantly affected by the
  pressure? The density ignored the effect of
  pressure is called ass?potential density, where
  ? is the potential water temperature at surface.

15
Sea water temperature vertical distribution

• ??????,??????????,?????
• Conductivity?????
• Turbulence mixing???????????????
• ???
• ??????????????,????,?????
• Conductivity??
• ???
• ????????
• ????,???(???)?,????????????,?????????
• ???????????,??????????????
• ???????????(thermocline),?????????????,???????main
  thermocline,????sub-thermocline?Thermocline?physi
  cal oceanography????????,???????/?????????
• ?????,?????in situ temperature??,????????,????????
  ?????????0.05-0.1oC/1000m,???????
• ?????,Oceanographer??potential temperature??in
  situ temperature,potential temperature is defined
  as The temperature of water sample that is
  adiabatically to the surface is called the
  potential temperature ???????
• ?????????????20? at surface, 8? at 500m, 5? at
  1000m, 2? at 4000m,????????????????????,?2??

16

• Sea surface temperature (SST)
• ?????,?????
• ????????????
• ?????????,??????film?
• SST?????????????????,?????non-linear?
• ??SST????,?????????????????
• Mixing layer???
• ????????,????????????,???????????????,??????0-200m
  ?
• ????????????,mixing layer??
• ????????,mixing layer???
• Thermocline???
• ??the depth has the largest temperature
  gradient???????????
• ????10-1000m(???????????)
• ????????????,?????????,???????,?????????,???(????)
  ???????,???????,????????
• ???????interface????interface?,??????????,?????
• ??Thermocline ? Tropical Ocean??, ? Polar Regions
  ???
• ??????thermocline?

17
Sea surface temperature horizontal distribution

• SST?????????,?????????,???????
• ?????????30?,????????SST???30??
• ?????-2??
• ??????????????????Warm pool,????????,????????,??co
  ld tongue?
• ???,?sub-tropic?SST??????????,???????
• ????SST????,???????,???????????

18

• ????????????????,?????????????????
• ??????????????,????????????/????,?????????,???????
  ????????????????,??sub-tropic grye???
• ??????????????
• ????????????????????????
• ????????,??-2-22oC

19

• ????????,???????-1-4oC,????????13oC?
• ??????????????
• ?????????????,????????????,?????????????,?????????
  ?????????
• ??????,??????,???????mode water??????

20
Sea temperature variation in time

• ??3????,??????????,??11????,?11?????10?????????
• ????,?????????,??????semi-diurnal, diurnal,
  Intra- seasonal (days to months), annual,
  inter-annual, etc.
• ???????(?25m)??????????,?annual
  ????????????,??????????
• subsurface????????????,????????/?????????,??SCS1?s
  ubsurface????????
• subsurface???????surface?,????thermocline???SCS2?7
  5-100m ??????
• ????????????????,??????10????????10oC????

21
Salinity vertical distribution

• ????????????,????????,????????,??????3.6109??????
  ??????????????????,???????,???????????????????????
  ,??????????? ????????,??????????/????????
• 75????????34.5-35psu?
• ??????????34.72psu
• ?????,salinity???????????
• ??????????halocline?
• ???????????????,??????
• ??????salinity?,???????34psu
• ?????salinity????????200m?,??????35psu,??????salin
  ity???,???600m?,??????34.2psu?
• salinity????,????,????34.4-34.7???

22
Sea surface Salinity horizontal distribution

• ??????????????/????,?????????????,???????????????
  ?,??????SSS????????????
• ?SSS???
• Precipitation
• Evaporation
• Soil moisture
• Atmospheric water vapor
• Sea ice extent
• ???????????33?37 psu North Atlantic(35.5)gtSouth
  Atlantic and South Pacific(35.2)gtNorth
  Pacific(34.2)????????????????Mediterranean(39),
  Red Sea (41)
• ??????,salinity????,??????salinity?????
• ??????,???????????????

23

• ?????????????????????????????,?????????????
• ???salinity????????,?????????,????????????,?????,?
  ?????
• ???????salinity?????????,???????(??25o??)??????sub
  -tropic gyre???
• ????????,???????,???????????
• ???????????2000???????,?????????,????,????????????
  ?

24
Water density distribution

• ???????,???????,????
• ??????????
• ??????????,????????????
• Vertical distribution
• ???????
• density?mixing layer????uniform,????????(Pycnoclin
  e),???thermocline?????,??????sub-pycnocline?
• ???????,??????????,?potential density???uniform?
• Horizontal distribution
• Surfaceincrease from the equator to 50 to 60
  and then slightly decreases to the poles.
• SubsurfaceT dominates the density variation in
  upper 100m.
• ??????(isopycnic surface)?????????
• Deep waterdistribution is generally uniform
• Temporal variation
• ?????,???????????? ?

25
C. Stratification ??

• Stratification ???????????,???????,??????,?????,??
  ???????????/????????????,???????????,?/????(mixing
  )?????????????,?????mixing????????????????????????
  ???,??stratification?stratification???????,???????
  ???
• Stratification ???/?????????,??????????????,??????
  ??????????????????
• ?stratification?(??),???????homogeneous
  ocean,????inhomogeneous ocean??stratified
  ocean??stable???,??????(neutral)?unstable????
• Unstable ??????????,????????,??????,????????,?????
  ??????????,?stratified ocean?,??????overshot,?????
  ??????,???????????,??????????????,????????,??????B
  runt-Vaisiala Frequency ?buoyancy frequency
  (N),??????????motion in the stratified
  ocean???????
• Stability??????????stratified????The stability is
  proportional to (1/?)( ??/?z) ??buoyancy
  frequency ???? proportional to (1/?)( ??/?z) ?

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D. Water Mass????

• ??water mass ????????????????????
• Water mass ??????????????
• ????????????????????????,????????,???????????/????
  ???????????????????????,??????????????
• ???????????????????????????,????????,???????????,?
  ??????
• ??????,??????????????,???????,????????????????,???
  ???????,???????Mistral wind ????,??????,??????2000
  ??? homogenous water mass, ????????38.4????12.8??
  ??????????,?Strait of Gilbratar?????????????,?????
  ?36.5????11?????????????????100??????,???????????,
  ???????????????????
• ?????????,??????????,????????
• ?????????????,??????????North Pacific
  Intermediate water (NPIW)??,??South
  Ocean??????North Pacific Ocean?????????
• ???(T-S Diagram) A T-S diagram is a graph
  showing the relationship between temperature and
  salinity as observed. ??,???????????????,?????????
  ?????????????,?????????T-S Diagram
  ????????????,???st .(?????????)??????T-S Diagram
  ???
• ????????
• ????????????
• ?????????
• ???????????
• ????????????????????????,?T-S Diagram
  ????,?????????????????????

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E. Sound and Optics

• The ocean is relatively opaque to all forms of
  electromagnetic radiation, form very long radio
  waves to the short ultraviolet.
  ???1??????100m???????,???????????,????????????????
  ?,????????????????????????????????????????????????
  ?????????,??????,????????,?????????
• ????????
• Echo sounder?????????????????,????????,????(?????
  )????,??????????,???????????(???),????????????????
  ????????????,????,????????????,????,??????
• ???????????????,???????????????,???????
• Acoustic Doppler Current Profiler
  ???????????????????????????????????plankton(????)?
  
• Inverted Echo Sounder??????????????
• ?????????

28

• Some definitions used in underwater sound
  Intensity
• ??????????,???????????,???????(above the normal
  hydrostatic pressure)???????????
• I
• ??????10-3N/m3?105 N/m3(??????)
• Sound level and decibel
• ???????????,?sound level?
• SL101og(I/I ref)201og(P/pref)101ogI
• SL ???decibel?????????,???????
• Frequency????????15,000-18,000Hz(1cycle/s)?20-50H
  z
• ????????1500m/s?
• ?????????????????????,???????????
• c14494.6T-0.55T20.0003T3 (1.39-0.012T)(S-35)
  0.017Z
• T?????S?psu?Z???(decibar)?c???(m/s)?
• ?????,??????????????,????????,????????,???????????
  ?,???????
• ???????(?????)??????????????,????deep sound
  channel?,?sound ray ????????,???????channel???????
  ???,??????,??????????????????????????????2000m,typ
  ical????700m?

29

• Transmission loss
• ??????????,?????????homogenous?,??????????????????
  
• ???????,?????????????,?transmission loss
  ?????????,???????????,??????transmission loss?
• ?????????,???????????,????????,?transmission loss
  ????????
• ???sound channel??sound ray ?????????(?ray????/???
  /????????),?transmission loss ??????,????????,????
  
• ????(Attenuation)
• Attenuation????????(absorption)???(scatter)???,???
  ???????,?????????????????????
• ????????????????????,???????????????????
• ????????Beers Law???
• -jI
• I
• j?????,???????
• j?2
• ????????,??????????????,??????,????????,???,??????
  ???
• The additional attenuation loss in the salt water
  is related to an ionic relaxation phenomenon in
  the MgSO4 salts and boric B(OH)3.

30

• Refraction and Reflection
• Since the velocity of sound is not a constant in
  the ocean, sound rays follow curved paths.
• Snells low
• Critical angle
• For angles less than critical angle, no sound
  energy can be refracted into the higher-velocity
  layer.
• The thermocline complicates the problem of
  transmitting sound energy in the surface layer.
• The percentage of sound energy reflected back
  into the ocean from the surface or the ocean
  bottom depends on the angle the sound ray makes
  with the interface and the difference in the
  acoustic impedance of the two media.
• ??????
• ???????????????????????????????,??????????????,???
  ?????????????,??????????????????????????,?????????
  ??????,???????,???????
• ????????????acoustic propagation?reflection???????
  ??

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Underwater Optics

• The ocean is nearly opaque to electromagnetic
  radiation, except for a narrow hand centered in
  the optical wavelengths.
• Attenuation includes scattering and absorption.
• Absorption is primarily the transfer of radiant
  energy into heat.
• Both absorption and scattering are wavelength
  dependent.
• Refraction causes distortion in underwater
  photography and vision of diver.
• To one looking up, the objects in the air are
  higher in the sky than they usually are. To one
  looking down, the objects in the water are closer
  and larger than they are.
• Wave action can cause deviation on the order of
  15?in the expected direction of maximum
  radiation.
• ??????????,????????,??????????????????????????????
  ???????????/????????????????????plankton?????/????
  ,???????plankton?

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return
34
On the left is a plot off sound speed as a
function of depth. On the right are the paths
followed by sound waves as they travel away from
a sound source located at a depth of 1000 m, on
the sound channel axis. Only rays that do not hit
the ocean surface or seafloor are shown. Adapted
from Figure 2.3 in Munk et al., 1995.
35
??????????
Kuperman and Lynch, 2004
????(??)
????
??
??
??????????-????(?-????),??????,???????????,???????
?????(???????)
Depth (m)
??????
return