Abstract

We have built a new fisheye camera radiometer to measure the in-water spectral upwelling radiance distribution. This instrument measures the radiance distribution at six wavelengths and obtains a complete suite of measurements (6 spectral data images with associated dark images) in approximately 2 minutes (in clear water). This instrument is much smaller than previous instruments (0.3 m in diameter and 0.3 m long), decreasing the instrument self-shading. It also has improved performance resulting from enhanced sensor sensitivity and a more subtle lens rolloff effect. We describe the instrument, its characterization, and show data examples from both clear and turbid water.

© 2005 Optical Society of America

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References

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    [CrossRef]
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    [CrossRef]

Appl. Opt. (3)

Bull. Scripps Inst. Oceanogr. (1)

J. E. Tyler, �??Radiance distribution as a function of depth in an underwater environment,�?? Bull. Scripps Inst. Oceanogr. 7, 363-41 (1960).

J. Atmosph. and Ocean. Techn. (1)

K. J. Voss and G. Zibordi, �??Radiometric and geometric calibration of a spectral electro-optic "fisheye' camera radiance distribution system,�?? J. Atmosph. and Ocean. Techn. 6, 652-662 (1989).
[CrossRef]

J. Geophys. Res. (1)

E. Aas and N. K. Hojerslev, �??Analysis of underwater radiance distribution observations: apparent optical properties and analytical functions describing the angular radiance distributions,�?? J. Geophys. Res. 104, 8015 �?? 8024 (1999).
[CrossRef]

J. Opt. Soc. Am. (1)

Limnol. Oceanogr. (3)

K. J. Voss, C. D. Mobley, L. K. Sundman, J. Ivey, and C. Mazell, �??The spectral upwelling radiance distribution in optically shallow waters,�?? Limnol. Oceanogr. 48, 364 �?? 373 (2003).
[CrossRef]

K. J. Voss and A. Morel, �??Bidirectional reflectance function for oceanic waters with varying chlorophyll concentrations: measurements versus predictions,�?? Limnol. Oceanogr. 50, 698 �?? 705 (2005).
[CrossRef]

G. Zibordi and J.-F. Berthon, �??Relationships between the Q-factor and seawater optical properties in a coastal region,�?? Limnol. Oceanogr. 46, 1130-1140 (2001).
[CrossRef]

Ocean Optics XV (1)

J. P. Doyle and K. J. Voss, �??3D Instrument Self-Shading effects on in-water multi-directional radiance measurements,�?? presented at Ocean Optics XV, Monaco, 16-20 Oct. 2000.

Oceanologia (1)

J. Piskozub, �??Effect of ship shadow on in-water irradiance measurements,�?? Oceanologia 46, 103-112 (2004).

Opt. Eng. (1)

K. J. Voss, �??Electro-optic camera system for measurement of the underwater radiance distribution,�?? Opt. Eng. 28, 241-247 (1989).

Proc. SPIE (1)

K. J. Voss and A. L. Chapin, �??Next generation in-water radiance distribution camera system,�?? in Ocean Optics XI, G. D. Gilbert, eds., Proc. SPIE 1750, 384 �?? 387 (1992).

Transport Theory and Statistical Physics (1)

W. S. Helliwell, G. N. Sullivan, B. Macdonald, and K. J. Voss, �??A finite-difference discrete-ordinate solution to the three dimensional radiative transfer equation,�?? Transport Theory and Statistical Physics 19, 333-356 (1990).
[CrossRef]

Other (1)

F. L. Pedrotti and L. S. Pedrotti, Introduction to Optics (Prentice Hall, New Jersey, 1993).

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Figures (8)

Fig. 1.
Fig. 1.

Picture of NuRADS system (fore ground) with the older RADS-II system (background). The new system is significantly more compact than the older system.

Fig. 3.
Fig. 3.

Dark noise data for the instrument. Left Fig. shows that the average pixel count of the dark/readout noise is approximately 2675 counts, and only increases when the integration time is greater than 2 seconds. Right Fig. shows that the standard deviation in the individual pixel averages is on the order of 4 counts.

Fig. 4.
Fig. 4.

An example angular calibration. A small source is imaged by the camera, and a series of images is obtained as the camera is rotated. For each image, the source location in the image is determined and correlated with the rotation angle. The line is a linear least squares fit to the data.

Fig. 5.
Fig. 5.

Angular calibration history for one of the NuRADS camera systems. In this graph the open circles represent K for in-water calibrations while the filled circles represent K for in-air calibrations. The error bars represent the error in determining K from the calibration data.

Fig. 6.
Fig. 6.

Rolloff functions for NuRADS (blue crosses) and for RADS-II (red crosses). As can be seen, the rolloff for the NuRADS system is much less severe than for the RADS-II system. At 80°, the rolloff is only 0.9 versus 0.2 for the older system.

Fig. 7.
Fig. 7.

Calibration history of one of the NuRADS camera systems. As can be seen the absolute calibration is fairly stable over the instruments history.

Fig. 8.
Fig. 8.

Upwelling radiance distribution images in clear water. Solar zenith angle is 38 degrees in air. Nadir angles are linearly related to the radius from the center. The center of each image is the nadir, the edge of the circle is the horizon (90 deg nadir angle). At very large nadir angles, in the lower wavelengths, the ship shadow or hull is evident and is labeled in one of the graphs At the reddest wavelength the direct instrument self-shadow is quite evident and is labeled in the graph.

Fig. 9.
Fig. 9.

Upwelling radiance distribution images in turbid, coastal water. Solar zenith angle is 33 degrees in air. Figure geometry is the same as Fig. 8.

Tables (3)

Tables Icon

Table 1. Spectral characteristics of the current NuRADS configuration.

Tables Icon

Table 2. Qu, µu, and Lu for the clear water radiance distributions. The last column [Qu(MAG)] is Qu predicted by Morel et al.[15].

Tables Icon

Table 3. Qu, µu, and Lu for the turbid water radiance distributions.

Equations (6)

Equations on this page are rendered with MathJax. Learn more.

θ = K r
d Ω = K ( π 180 ) sin ( θ ) r d A .
Lwater = Lair e cr n 2 Twater air .
M = Lwater # air ( # water Lair )
μ u = E u E O u
Q u = E u L u .

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