Abstract

Techniques are presented for the estimation of the optical attenuation coefficient and a backscatter parameter that is proportional to the optical backscatter coefficient from data collected from a laser-based airborne hydrographic system. The validity of two such techniques is discussed in light of substantial amounts of data that have been collected using the WRELADS airborne depth sounder. The data collected demonstrate a number of different functional relationships linking attenuation to backscatter in adjacent bodies of water. It also demonstrates the capability of using such airborne techniques for detection, mapping, and monitoring of unusual turbidity features within the ocean.

© 1986 Optical Society of America

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References

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  1. M. F. Penny et al., “Airborne Laser Hydrography in Australia” 25, 2046 (1986).
  2. Moniteq Ltd., “Determination of Parameters of Significance for Accuracy Optimization of a Scanning Lidar Bathymeter,” Final Report, Canadian Hydrographic Service Contract, Concord, Ontario (1983).
  3. G. C. Guenther, R. W. L. Thomas, “Effects of Propagation-Induced Pulse Stretching in Airborne Laser Hydraphy,” Proc. Soc. Photo-Opt. Instrum. Eng.Ocean Optics 7, 287 (1984).
    [CrossRef]
  4. D. M. Phillips, R. H. Abbot, M. F. Penny, “Remote Sensing of Sea Water Turbidity with an Airborne Laser System,” J. Phys. D 17, 1749 (1984).
    [CrossRef]
  5. N. G. Jerlov, Marine Optics (Elsevier, Amsterdam, 1976), 231 pp.
  6. R. W. Preisendorfer, Hydrologic Optics, Vol. 1 (U.S. Department of Commerce NOAA, Washington, D.C., 1976), 218 pp.
  7. H. R. Gordon, R. C. Smith, J. R. V. Zaneveld, “Introduction to Ocean Optics,” Proc. Soc. Photo-Opt. Instrum. Eng. 15Ocean Optics 6, (1979).
  8. H. R. Gordon, “Interpretation of Airborne Oceanic Lidar: Effects of Multiple Scattering,” Appl. Opt. 21, 2996 (1982).
    [CrossRef] [PubMed]
  9. D. M. Phillips, B. W. Koerber, “A Theoretical Study of an Airborne Laser Technique for Determining Sea Water Turbidity,” Aust. J. Phys. 37, 75 (1984).
  10. B. Billard, P. J. Wilsen, “Sea Surface and Depth Detection in the WRELADS Airborne Depth Sounder,” Appl. Opt. 25, 2059 (1986).
    [CrossRef] [PubMed]
  11. B. Billard, “Estimation of a Mean Sea Surface Reference in the WRELADS Airborne Depth Sounder,” Appl. Opt. 25, 2067 (1986).
    [CrossRef] [PubMed]
  12. F. A. Graybill, An Introduction to Linear Statistical Models, Vol 1 (McGraw-Hill, New York, 1961).
  13. J. D. Klett, “Stable Analytic Inversion Solution for Processing Lidar Returns,” Appl. Opt. 20, 211 (1981).
    [CrossRef] [PubMed]
  14. J. G. Shannon, “Correlation of Beam and Diffuse Attenuation Coefficients Measured in Selected Ocean Waters,” Proc. Soc. Photo-Opt. Instrum. Eng.Ocean Optics 3, (1975).
  15. J. T. O. Kirk, “Monte Carlo Study of the Nature of the Underwater Light Field in, and the Relationships between Optical Properties of, Turbid Yellow Waters,” Aust. J. Mar. Freshwater Res. 32, 517 (1981).
    [CrossRef]
  16. D. M. Phillips, M. L. Scholz, “Measured Distribution of Water Turbidity in Gulf St. Vincent,” Aust J. Mar. Freshwater Res. 33, 723 (1982).
    [CrossRef]

1986 (2)

1984 (3)

G. C. Guenther, R. W. L. Thomas, “Effects of Propagation-Induced Pulse Stretching in Airborne Laser Hydraphy,” Proc. Soc. Photo-Opt. Instrum. Eng.Ocean Optics 7, 287 (1984).
[CrossRef]

D. M. Phillips, R. H. Abbot, M. F. Penny, “Remote Sensing of Sea Water Turbidity with an Airborne Laser System,” J. Phys. D 17, 1749 (1984).
[CrossRef]

D. M. Phillips, B. W. Koerber, “A Theoretical Study of an Airborne Laser Technique for Determining Sea Water Turbidity,” Aust. J. Phys. 37, 75 (1984).

1982 (2)

H. R. Gordon, “Interpretation of Airborne Oceanic Lidar: Effects of Multiple Scattering,” Appl. Opt. 21, 2996 (1982).
[CrossRef] [PubMed]

D. M. Phillips, M. L. Scholz, “Measured Distribution of Water Turbidity in Gulf St. Vincent,” Aust J. Mar. Freshwater Res. 33, 723 (1982).
[CrossRef]

1981 (2)

J. T. O. Kirk, “Monte Carlo Study of the Nature of the Underwater Light Field in, and the Relationships between Optical Properties of, Turbid Yellow Waters,” Aust. J. Mar. Freshwater Res. 32, 517 (1981).
[CrossRef]

J. D. Klett, “Stable Analytic Inversion Solution for Processing Lidar Returns,” Appl. Opt. 20, 211 (1981).
[CrossRef] [PubMed]

1979 (1)

H. R. Gordon, R. C. Smith, J. R. V. Zaneveld, “Introduction to Ocean Optics,” Proc. Soc. Photo-Opt. Instrum. Eng. 15Ocean Optics 6, (1979).

1975 (1)

J. G. Shannon, “Correlation of Beam and Diffuse Attenuation Coefficients Measured in Selected Ocean Waters,” Proc. Soc. Photo-Opt. Instrum. Eng.Ocean Optics 3, (1975).

Abbot, R. H.

D. M. Phillips, R. H. Abbot, M. F. Penny, “Remote Sensing of Sea Water Turbidity with an Airborne Laser System,” J. Phys. D 17, 1749 (1984).
[CrossRef]

Billard, B.

Gordon, H. R.

H. R. Gordon, “Interpretation of Airborne Oceanic Lidar: Effects of Multiple Scattering,” Appl. Opt. 21, 2996 (1982).
[CrossRef] [PubMed]

H. R. Gordon, R. C. Smith, J. R. V. Zaneveld, “Introduction to Ocean Optics,” Proc. Soc. Photo-Opt. Instrum. Eng. 15Ocean Optics 6, (1979).

Graybill, F. A.

F. A. Graybill, An Introduction to Linear Statistical Models, Vol 1 (McGraw-Hill, New York, 1961).

Guenther, G. C.

G. C. Guenther, R. W. L. Thomas, “Effects of Propagation-Induced Pulse Stretching in Airborne Laser Hydraphy,” Proc. Soc. Photo-Opt. Instrum. Eng.Ocean Optics 7, 287 (1984).
[CrossRef]

Jerlov, N. G.

N. G. Jerlov, Marine Optics (Elsevier, Amsterdam, 1976), 231 pp.

Kirk, J. T. O.

J. T. O. Kirk, “Monte Carlo Study of the Nature of the Underwater Light Field in, and the Relationships between Optical Properties of, Turbid Yellow Waters,” Aust. J. Mar. Freshwater Res. 32, 517 (1981).
[CrossRef]

Klett, J. D.

Koerber, B. W.

D. M. Phillips, B. W. Koerber, “A Theoretical Study of an Airborne Laser Technique for Determining Sea Water Turbidity,” Aust. J. Phys. 37, 75 (1984).

Penny, M. F.

D. M. Phillips, R. H. Abbot, M. F. Penny, “Remote Sensing of Sea Water Turbidity with an Airborne Laser System,” J. Phys. D 17, 1749 (1984).
[CrossRef]

M. F. Penny et al., “Airborne Laser Hydrography in Australia” 25, 2046 (1986).

Phillips, D. M.

D. M. Phillips, R. H. Abbot, M. F. Penny, “Remote Sensing of Sea Water Turbidity with an Airborne Laser System,” J. Phys. D 17, 1749 (1984).
[CrossRef]

D. M. Phillips, B. W. Koerber, “A Theoretical Study of an Airborne Laser Technique for Determining Sea Water Turbidity,” Aust. J. Phys. 37, 75 (1984).

D. M. Phillips, M. L. Scholz, “Measured Distribution of Water Turbidity in Gulf St. Vincent,” Aust J. Mar. Freshwater Res. 33, 723 (1982).
[CrossRef]

Preisendorfer, R. W.

R. W. Preisendorfer, Hydrologic Optics, Vol. 1 (U.S. Department of Commerce NOAA, Washington, D.C., 1976), 218 pp.

Scholz, M. L.

D. M. Phillips, M. L. Scholz, “Measured Distribution of Water Turbidity in Gulf St. Vincent,” Aust J. Mar. Freshwater Res. 33, 723 (1982).
[CrossRef]

Shannon, J. G.

J. G. Shannon, “Correlation of Beam and Diffuse Attenuation Coefficients Measured in Selected Ocean Waters,” Proc. Soc. Photo-Opt. Instrum. Eng.Ocean Optics 3, (1975).

Smith, R. C.

H. R. Gordon, R. C. Smith, J. R. V. Zaneveld, “Introduction to Ocean Optics,” Proc. Soc. Photo-Opt. Instrum. Eng. 15Ocean Optics 6, (1979).

Thomas, R. W. L.

G. C. Guenther, R. W. L. Thomas, “Effects of Propagation-Induced Pulse Stretching in Airborne Laser Hydraphy,” Proc. Soc. Photo-Opt. Instrum. Eng.Ocean Optics 7, 287 (1984).
[CrossRef]

Wilsen, P. J.

Zaneveld, J. R. V.

H. R. Gordon, R. C. Smith, J. R. V. Zaneveld, “Introduction to Ocean Optics,” Proc. Soc. Photo-Opt. Instrum. Eng. 15Ocean Optics 6, (1979).

Appl. Opt. (4)

Aust J. Mar. Freshwater Res. (1)

D. M. Phillips, M. L. Scholz, “Measured Distribution of Water Turbidity in Gulf St. Vincent,” Aust J. Mar. Freshwater Res. 33, 723 (1982).
[CrossRef]

Aust. J. Mar. Freshwater Res. (1)

J. T. O. Kirk, “Monte Carlo Study of the Nature of the Underwater Light Field in, and the Relationships between Optical Properties of, Turbid Yellow Waters,” Aust. J. Mar. Freshwater Res. 32, 517 (1981).
[CrossRef]

Aust. J. Phys. (1)

D. M. Phillips, B. W. Koerber, “A Theoretical Study of an Airborne Laser Technique for Determining Sea Water Turbidity,” Aust. J. Phys. 37, 75 (1984).

J. Phys. D (1)

D. M. Phillips, R. H. Abbot, M. F. Penny, “Remote Sensing of Sea Water Turbidity with an Airborne Laser System,” J. Phys. D 17, 1749 (1984).
[CrossRef]

Ocean Optics (3)

G. C. Guenther, R. W. L. Thomas, “Effects of Propagation-Induced Pulse Stretching in Airborne Laser Hydraphy,” Proc. Soc. Photo-Opt. Instrum. Eng.Ocean Optics 7, 287 (1984).
[CrossRef]

H. R. Gordon, R. C. Smith, J. R. V. Zaneveld, “Introduction to Ocean Optics,” Proc. Soc. Photo-Opt. Instrum. Eng. 15Ocean Optics 6, (1979).

J. G. Shannon, “Correlation of Beam and Diffuse Attenuation Coefficients Measured in Selected Ocean Waters,” Proc. Soc. Photo-Opt. Instrum. Eng.Ocean Optics 3, (1975).

Other (5)

F. A. Graybill, An Introduction to Linear Statistical Models, Vol 1 (McGraw-Hill, New York, 1961).

N. G. Jerlov, Marine Optics (Elsevier, Amsterdam, 1976), 231 pp.

R. W. Preisendorfer, Hydrologic Optics, Vol. 1 (U.S. Department of Commerce NOAA, Washington, D.C., 1976), 218 pp.

M. F. Penny et al., “Airborne Laser Hydrography in Australia” 25, 2046 (1986).

Moniteq Ltd., “Determination of Parameters of Significance for Accuracy Optimization of a Scanning Lidar Bathymeter,” Final Report, Canadian Hydrographic Service Contract, Concord, Ontario (1983).

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Figures (13)

Fig. 1
Fig. 1

Characteristic waveforms as recorded by WRELADS showing the backscatter envelopes (a) in the presence of a sea surface reflection and (b) when no sea surface reflection was detected.

Fig. 2
Fig. 2

Scatter diagram of attenuation k plotted against backscatter B for 60 s of data collected from mid-Gulf of St. Vincent near Adelaide. k has units of m−1. B is related to bb, but the constant of proportionality is unknown. (a) Plot for all 2520 points having accuracy of 15% or better; (b) reduction of scatter when all seven spots at the same scan angle in each 2-s frame of data are averaged.

Fig. 3
Fig. 3

Scatter diagram of attenuation k plotted against backscatter B for sections of data collected from different flights over the Gulf of St. Vincent. The data are averaged by frame: (a) for 50 s covering a localized mid-Gulf peak in turbidity; (b) for two sections of 6 s and 1 min from the same pass (the smaller section being inshore nearer to Port Adelaide); and (c) for 5 min covering a mid-Gulf section.

Fig. 4
Fig. 4

Possible alternative interpretations of a two-stage decay backscatter envelope. The received signal (a) may be assumed to arise from either a changing k with sea depth (b) or a changing B with sea depth (c).

Fig. 5
Fig. 5

Received waveform and its interpretation when there was a vertical gradient of turbidity with depth. The received signal (a) and the estimated attenuation coefficient k (b) are plotted against sea depth.

Fig. 6
Fig. 6

Sea depth profile along a test area running southwest from a point 5 km north of Garden Island in Western Australia. The locations of the ten sections from which the data collected are presented in Fig. 7 are indicated by number. The sections are contiguous except for a 1.5-km gap close to Carnac Island.

Fig. 7
Fig. 7

Scatter diagrams of attenuation against backscatter for the ten sections of data whose locations are indicated in Fig. 6. The data were collected in a single pass and divided into segments of 20, 10, 12, 16, 10, 14, 16, 38, 110, and 154 s, respectively. Data from section 9 were thinned by using alternative half cycles only. Data from section 10 were cut by one-third by using the outermost spots only. The composite of all sections is presented in (b).

Fig. 8
Fig. 8

Waveform recorded near Carnac Island where two layers of water with markedly different turbidity characteristics are present in the one vertical column of water.

Fig. 9
Fig. 9

Scatter diagram of attenuation against backscatter for 500 s of data collected in a single pass over the Gulf of St. Vincent from mid-Gulf (30–35-m depth) to inshore (6-m depth). The plotted points represent data that have been averaged by a 2-s frame as described for Fig. 2(b).

Fig. 10
Fig. 10

Profiles of backscatter B and attenuation k for a single 500-s (35-km) pass over the Gulf of St. Vincent. Only data from spot 1 (starboard extreme spot) are plotted.

Fig. 11
Fig. 11

Comparison of two backscatter profiles demonstrating the repeatability of data. The solid curve is as for Fig. 10(a). The broken line represents data collected 20 min later. The aircraft tracks for both passes were coincident within 20 m.

Fig. 12
Fig. 12

Expanded backscatter profile for an 80-s portion of the data presented in Fig. 10 but with the profile for the port extreme spot 13 (broken curve) included for comparison. The cross-track separation of spots 1 and 13 is 250 m.

Fig. 13
Fig. 13

Comparison of the backscattear profile of Fig. 10 with that recorded in a similar flight on the following day (broken curve). The day-to-day scaling of backscatter is not necessarily exact.

Equations (5)

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b f = 2 π 0 π / 2 β ( θ ) sin θ d θ , b b = 2 π π / 2 π β ( θ ) sin θ d θ ,
d P ( r ) / d r = T 2 A P 0 β ( π ) exp ( - 2 k r ) / n 2 ( H + r ) 2 ,
P ( r ) = B exp ( - 2 k r ) .
B = const k n ,
k ( r ) = f ( r ) / [ 1 / k m + ( 2 / n ) r r m f ( r ) d r ] ,

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