Abstract

A submarine nephelometer has been built for use in measuring the volume scattering function of natural waters. Theory and construction details of the optical system are given, including pertinent data for the photodetector used. The instrument is capable of measuring volume scattering function between angles of 20° and 170° in typical coastal waters. Results of preliminary tests with the instrument are given.

© 1958 Optical Society of America

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References

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  1. For photometric symbols see, Committee on Colorimetry, J. Opt. Soc. Am. 34, 245–266 (1944).
  2. J. M. Waldram, Trans. Illum. Eng. Soc. (London) 10, 147–188 (1945); W. E. K. Middleton, Vision through the Atmosphere (University of Toronto Press, Toronto, 1952), pp. 201–202.
  3. This is an important feature since some of the calibration procedures are much more easily accomplished in air.
  4. B. S. Pritchard and H. R. Blackwell, , Vision Research Laboratories, July (1957); Engineering Research Institute, University of Michigan, Ann Arbor, Michigan.
  5. Nonuniform flux distribution in the light beam, or nonuniform sensitivity in the beam of detectivity could be very troublesome in the determination of volume-scattering function since calibration procedures and computations are all based on uniform-flux and sensitivity distributions. The present instrument is not perfect in these respects but is tolerable.
  6. Monroe H. Sweet, J. Soc. Motion Picture and Television Engrs. 54, 35–62 (1950).
  7. The measuring head of optical instruments is here considered to be made up of a collector which is designed to accept light in accordance with some preconceived definition (e.g., radiance or irradiance), and a detector which may include the optical filter in the system. These components are joined by a “coupling” which must be designed to assure proper and constant sampling of the radiant flux for all lighting conditions that will be met in making measurements with the instrument. An important property of this coupling is its efficiency represented here by the symbol C.
  8. This device removes air from the water as well as particulate matter larger than 2 μ.

1950 (1)

Monroe H. Sweet, J. Soc. Motion Picture and Television Engrs. 54, 35–62 (1950).

1945 (1)

J. M. Waldram, Trans. Illum. Eng. Soc. (London) 10, 147–188 (1945); W. E. K. Middleton, Vision through the Atmosphere (University of Toronto Press, Toronto, 1952), pp. 201–202.

1944 (1)

Blackwell, H. R.

B. S. Pritchard and H. R. Blackwell, , Vision Research Laboratories, July (1957); Engineering Research Institute, University of Michigan, Ann Arbor, Michigan.

Pritchard, B. S.

B. S. Pritchard and H. R. Blackwell, , Vision Research Laboratories, July (1957); Engineering Research Institute, University of Michigan, Ann Arbor, Michigan.

Sweet, Monroe H.

Monroe H. Sweet, J. Soc. Motion Picture and Television Engrs. 54, 35–62 (1950).

Waldram, J. M.

J. M. Waldram, Trans. Illum. Eng. Soc. (London) 10, 147–188 (1945); W. E. K. Middleton, Vision through the Atmosphere (University of Toronto Press, Toronto, 1952), pp. 201–202.

J. Opt. Soc. Am. (1)

J. Soc. Motion Picture and Television Engrs. (1)

Monroe H. Sweet, J. Soc. Motion Picture and Television Engrs. 54, 35–62 (1950).

Trans. Illum. Eng. Soc. (London) (1)

J. M. Waldram, Trans. Illum. Eng. Soc. (London) 10, 147–188 (1945); W. E. K. Middleton, Vision through the Atmosphere (University of Toronto Press, Toronto, 1952), pp. 201–202.

Other (5)

This is an important feature since some of the calibration procedures are much more easily accomplished in air.

B. S. Pritchard and H. R. Blackwell, , Vision Research Laboratories, July (1957); Engineering Research Institute, University of Michigan, Ann Arbor, Michigan.

Nonuniform flux distribution in the light beam, or nonuniform sensitivity in the beam of detectivity could be very troublesome in the determination of volume-scattering function since calibration procedures and computations are all based on uniform-flux and sensitivity distributions. The present instrument is not perfect in these respects but is tolerable.

The measuring head of optical instruments is here considered to be made up of a collector which is designed to accept light in accordance with some preconceived definition (e.g., radiance or irradiance), and a detector which may include the optical filter in the system. These components are joined by a “coupling” which must be designed to assure proper and constant sampling of the radiant flux for all lighting conditions that will be met in making measurements with the instrument. An important property of this coupling is its efficiency represented here by the symbol C.

This device removes air from the water as well as particulate matter larger than 2 μ.

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Figures (5)

Fig. 1
Fig. 1

Details of the optical system of the nephelometer. P1 is the axis of rotation of the Waldram stop and P2 is the axis of rotation of the scanning system. The sample volume is made independent of θ by the operation of the Waldram stop.

Fig. 2
Fig. 2

Scanning system of nephelometer showing volume calibration attachment in place on the scanning arm. The light source is at the left (not shown).

Fig. 3
Fig. 3

Plot of sample volume vs angular setting of scanning arm. The variability is believed to be caused by systematic errors which do not have physical significance. For this paper volume corrections were based on the “best straight line” which is shown.

Fig. 4
Fig. 4

The scanning arm, here represented as dA1, is shown below the volume with its axis vertical (instead of horizontal as in previous figures).

Fig. 5
Fig. 5

These tests were run to study the operating characteristics of the instrument in water of high and low-scattering properties. For these tests it was unnecessary to evaluate the constant of Eq. (8) (in brackets). By evaluating this constant, this figure would give values of the volume scattering coefficient for this particular sample, for a 60-mμ spectral band centered at 480 mμ.

Equations (9)

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σ ( θ ) = d J ( θ ) H d v ,
Reading = k R A H ,
V = χ 1 χ 2 k 1 A d x ,
σ ( θ ) = d J ( θ ) H d v ,
J ( θ ) = d p 1 d ω = C R θ e α r 2 d A 1 / r 2 2 .
H = d p 0 d A 0 = C R 0 e - α r 1 d A 1 × d A 2 d A 0 ,
σ ( 90 ° ) = R 90 R 0 · e α ( r 1 + r 2 ) [ r 2 2 d A 0 d A 1 d A 2 χ ] .
σ ( 90 ) R 90 × R θ = σ ( θ ) .
σ ( θ ) = R θ e α ( r 1 + r 2 ) [ r 2 2 d A 0 d A 1 d A 2 χ R 0 ] .