Docstoc

Bowers_D

Document Sample
Bowers_D Powered By Docstoc
					Variation in Optical Properties along a
  turbulence gradient in shelf seas

D.G.Bowers, Caren Binding, Katherine Ellis, Sarah Jones and
                 E.G.Mitchelson-Jacob


      “The aircrew also noted changes in the
   colour of the sea…as the front was crossed”
        J.H.Simpson and J.R.Hunter (1974)
Does the size of particles
suspended in the sea depend
on the Kolmogorov Microscale?
       The Kolmogorov microscale
The turbulent energy cascade:

“Big whorls have smaller whorls
   that feed on their velocity.
   Small whorls have smaller
   whorls and so on to viscosity”

L.F.Richardson (1881-1953)


                                    A.N.Kolmogorov (1903-1987)

       λ = (υ / ε )
                3     1/ 4           = kinematic viscosity
                                     = TKE dissipation per
                                    unit mass
FLOCCULATED (and other) PARTICLES IN A DROP OF SEAWATER




      Micro-photograph, courtesy P.S.D.Smith
THE KOLMOGOROV SCALE IN THE IRISH SEA
                 KOLMOGOROV SCALE (microns)

  56.00


  55.50


  55.00


  54.50
                                                                    λ = (υ 3 / ε )1/ 4
  54.00
                                                                    TKE dissipation   W/kg
  53.50

                                                                        =cDu3/h
  53.00


  52.50


  52.00
      -7.00 -6.50 -6.00 -5.50 -5.00 -4.50 -4.00 -3.50 -3.00 -2.50
DERIVING PARTICLE SIZE FROM VISIBLE BAND REMOTE SENSING




Simultaneous
measurements of
brightness and colour
enable calculation of the
scattering cross section
per unit mass




                            SeaWiFS image courtesy RSDAS, Plymouth
SCATTERING CROSS SECTION PER UNIT MASS


 56.00
                         b* from SeaWiFS 13/09/02




 55.00
                                                          b*

                                                          Units m2/g
 54.00


                                                    Technique relies on optical
 53.00                                              properties of suspended
                                                    particles (i.e. brightness and
                                                    colour) being consistent with
                                                    mainly mineral flocs. Hence
 52.00
                                                    areas with no data.


 51.00
     -7.00   -6.00   -5.00    -4.00   -3.00
RELATION BETWEEN b* and PARTICLE SIZE




                                                  5
               Diameter D
                                                  4




                                 b* b* (m2/g)/g
                                    in m2
                                                  3


                                                  2


                                                  1


                                                  0
                                                      0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.22
                                                                            1/D
                                                                           1/D (um-1)-1
                                                                                  m
           3
     b* =                                                                                            Diameter
          Dρ p                                                                                       ( m)=50/b*


                                                                                                     (b* in m2/g)
      p   = particle density
                               Measured by Katherine Ellis north of Anglesey
THIS MEANS THAT MAPS of b* CAN BE CONVERTED to PARTICLE SIZE
  56.00                                              56.00
                          b* from SeaWiFS 13/09/02
                                                                                 size (um) 13/9/02


  55.00                                              55.00




  54.00                                              54.00




  53.00                                              53.00




  52.00                                              52.00




  51.00                                              51.00
      -7.00   -6.00   -5.00    -4.00   -3.00             -7.00   -6.00   -5.00   -4.00      -3.00

                                                       Suspended particle diameter D m
                         b* m2/g
   AND THESE can be COMPARED to the KOLMOGOROV SCALE

               KOLMOGOROV SCALE (microns)

56.00                                                             56.00                         size (um) 13/9/02



55.50


55.00
                                                                  55.00

54.50


54.00
                                                                  54.00


53.50

                                                                  53.00
53.00


52.50

                                                                  52.00
52.00
    -7.00 -6.50 -6.00 -5.50 -5.00 -4.50 -4.00 -3.50 -3.00 -2.50
                                                                      -7.00     -6.00   -5.00   -4.00      -3.00

           Kolmogorov scale m                                                 Particle diameter D m
      RELATIONSHIP between PARTICLE DIAMETER measured from
      SPACE and KOLMOGOROV SCALE




             particle diameter (microns)   250


                                           200


                                           150


                                           100


                                           50


                                            0
                                                 0   100       200    300   400    500      600
                                                           Kolmogorov Scale (microns)



                                D=76.4+0.29                 R2=0.8
                                                                                        Observations have been
=Kolmogorov scale based on =tide +wind                                                  binned into 25 micron bins
CONCLUSIONS

1) Results confirm relevance of Kolmogorov
   scale to particle size in surface waters, at
   least in most turbulent parts of Irish Sea.

2) Justifies use of satellite remote sensing for
   measuring particle size – close relation with
   Kolmogorov scale cannot be a coincidence

3) Means that remote sensing of particle size
   over whole shelf areas now possible. Will
   lead to better understanding of particle
   dynamics and more accurate measurement
   of concentration
Variation in Optical Properties along a
  turbulence gradient in shelf seas

D.G.Bowers, Caren Binding, Katherine Ellis, Sarah Jones and
                 E.G.Mitchelson-Jacob


      “The aircrew also noted changes in the
   colour of the sea…as the front was crossed”
        J.H.Simpson and J.R.Hunter (1974)

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:4
posted:8/16/2012
language:English
pages:13