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Measurement

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Basic ideas for the temperature measurement. Expansion of liquid or a metal ... ?????,??????????,???????Mistral wind ????,??????,??????2000 ??? homogenous water ... – PowerPoint PPT presentation

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Title: 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) ?

26
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
    ????,?????????????????????

27
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???????
    ??

31
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?

32
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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)
??????
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