## Upwelling radiance distribution camera system, NURADS

Optics Express, Vol. 13, Issue 11, pp. 4250-4262 (2005)

http://dx.doi.org/10.1364/OPEX.13.004250

Acrobat PDF (3346 KB)

### 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

## 1. Introduction

1. A. Morel and B. Gentili, “Diffuse reflectance of oceanic waters. III. Implication of bidirectionality for the remote-sensing problem,” Appl. Opt. **35**, 4850–4862 (1996). [CrossRef] [PubMed]

3. 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]

3. 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]

4. K. Miyamoto, “Fish Eye Lens,” J. Opt. Soc. Am. **54**, 1060–1061 (1964). [CrossRef]

5. R. C. Smith, R. W. Austin, and J. E. Tyler, “An oceanographic radiance distribution camera system,” Appl. Opt. **9**, 2015–2022 (1970). [CrossRef] [PubMed]

8. 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]

9. 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]

11. 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]

## 2. Fundamental NURADS instrument description

## 3. Characterization and calibration

12. 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]

### 3.2 Camera linearity

5. R. C. Smith, R. W. Austin, and J. E. Tyler, “An oceanographic radiance distribution camera system,” Appl. Opt. **9**, 2015–2022 (1970). [CrossRef] [PubMed]

### 3.3 Angular calibration

*r*is the radial distance, in pixels, from the center of the image, and

*K*(in degrees/pixel) is a calibration constant found through calibration.

*K*in both air and water. If they are the same, then the instrument is set up properly. Before and after each deployment we do the angular calibration to help determine if any changes have happened in the optics. A typical example is shown below in Fig. 4, for an in-water calibration. The

*K*derived from this graph was 0.469±0.004. The r

^{2}for this regression was 0.9995.

*θ*(in radians) is

*θ=K(π/180) r*, then

*dθ=K(π/180) dr*.

*dA*) is given by

*dA=rdϕ dr*, and solid angle is defined by

*dΩ=sin θ dθ dϕ*. Thus

*dΩ*represented by each pixel (

*dA*) is:

^{-5}sr, while at 70 degrees each pixel represents 5×10

^{-5}sr.

### 3.4 Immersion calibration

^{2}) effect between air (inside the instrument) and water (outside). With the fisheye system, and the hemispherical dome window, there is another effect that offsets this n

^{2}refraction effect. In essence the apparent aperture size of the system varies whether it is in-water or in-air. Hence, we must do a calibration to determine the immersion factor. The calibration is done in the following manner. The instrument is placed, dry, in a barrel and a reflectance plaque is suspended above this barrel at 45 degrees to the vertical. The plaque is illuminated by a 1000W FEL lamp. Images of the plaque are obtained as the water level in the tank is raised above the level of the dome window. Several measurements are made with different water levels, with the window submerged, to determine the water attenuation. The average of a 20×20 pixel area, centered on the plaque, is obtained at each measurement point. The attenuation coefficient of the water is determined from the measurements at the different water levels, and is used to correct for attenuation effects. The apparent radiance that the plaque should have at the front of the camera window is

*Lwater*and

*Lair*, when in water and air respectively. This can be calculated by compensating for the air-water interface effects, and water attenuation as:

^{-cr}is the attenuation from the surface of the water to the front of the dome window,

*n*is the index of refraction of water, and

*Twater-air*is the Fresnel transmission through the air-water interface.)

*Lwater*and

*Lair*, along with the pixel averages when the window was dry (#

*air*) vs. wet (#

*water*) are used to determine the immersion correction,

*M*.

### 3.5 Camera lens rolloff

### 3.6 Spectral calibration

### 3.7 Polarization Sensitivity

## 4. Sample data

### 4.1 clear water case

^{3}.

_{u}) and Q

_{u}:

_{u}is the upwelling irradiance, Eo

_{u}is the upwelling scalar irradiance, and L

_{u}is the nadir upwelling radiance. For an isotropic radiance distribution, Q

_{u}would be equal to π and µ

_{u}would be equal to 0.5. Table 2 shows Q

_{u}and µ

_{u}calculated from the images shown. As can be seen Q

_{u}is slightly higher than π, as reflected in the images by the brightening in radiance towards the horizon. µ

_{u}is slightly less than 0.5. The variation in these factors reflects the variation in the pure water absorption, with Q

_{u}increasing towards the longer, red, more absorbed wavelengths. The last column is the Q

_{u}predicted by the model of Morel et al.[15

15. A. Morel, D. Antoine, and B. Gentili, “Bidirectional reflectance of oceanic waters: accounting for Raman emission and varying particle scattering phase function,” Appl. Opt. **41**, 6289–6306 (2002). [CrossRef] [PubMed]

_{u}is somewhat smaller than the model prediction, except at 616 nm. At 616 nm, instrument self-shadow is obvious in the measurement and may be decreasing Lu more than E

_{u}. In all cases though the two values are within 10% of each other.

_{u}decreases from the blue to the red reflecting the obvious blue color of the water.

### 4.2 Turbid water case

^{3}.

_{u}and µ

_{u}factors shown in Table 3. The spectral variation of the parameters, and the underlying radiance distribution, reflects the influence of dissolved organic material in these turbid waters, case 2 waters. In particular, the increased absorption at the lower wavelengths causes Q

_{u}to be higher, and µ

_{u}to be lower than in the clear water case. As the wavelength increases, total absorption decreases, and Q

_{u}decreases.

_{u}increases. It can be seen that, as expected in this turbid coastal water, the maximum upwelling nadir radiance is in the green, with little light coming out at the blue wavelengths.

_{u}’s are within the range shown in [16

16. 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]

16. 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]

## 5. Conclusion

_{u}, and we are working on a model of Q

_{u}in turbid water. In addition, since the radiance distribution is fundamentally dependent on the backscattering phase function of the water, this data can be used to test models of the in-water light field and constrain this phase function.

## Acknowledgments

## References and Links

1. | A. Morel and B. Gentili, “Diffuse reflectance of oceanic waters. III. Implication of bidirectionality for the remote-sensing problem,” Appl. Opt. |

2. | J. E. Tyler, “Radiance distribution as a function of depth in an underwater environment,” Bull. Scripps Inst. Oceanogr. |

3. | 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. |

4. | K. Miyamoto, “Fish Eye Lens,” J. Opt. Soc. Am. |

5. | R. C. Smith, R. W. Austin, and J. E. Tyler, “An oceanographic radiance distribution camera system,” Appl. Opt. |

6. | K. J. Voss, “Electro-optic camera system for measurement of the underwater radiance distribution,” Opt. Eng. |

7. | K. J. Voss and A. L. Chapin
, “Next generation in-water radiance distribution camera system,” in |

8. | 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. |

9. | K. J. Voss and A. Morel, “Bidirectional reflectance function for oceanic waters with varying chlorophyll concentrations: measurements versus predictions,” Limnol. Oceanogr. |

10. | 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. |

11. | 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 |

12. | 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. |

13. | F. L. Pedrotti and L. S. Pedrotti, |

14. | J. Piskozub, “Effect of ship shadow on in-water irradiance measurements,” Oceanologia |

15. | A. Morel, D. Antoine, and B. Gentili, “Bidirectional reflectance of oceanic waters: accounting for Raman emission and varying particle scattering phase function,” Appl. Opt. |

16. | G. Zibordi and J.-F. Berthon, “Relationships between the Q-factor and seawater optical properties in a coastal region,” Limnol. Oceanogr. |

**OCIS Codes**

(010.4450) Atmospheric and oceanic optics : Oceanic optics

(120.5630) Instrumentation, measurement, and metrology : Radiometry

**ToC Category:**

Research Papers

**History**

Original Manuscript: May 3, 2005

Revised Manuscript: May 17, 2005

Published: May 30, 2005

**Citation**

Kenneth Voss and Albert Chapin, "Upwelling radiance distribution camera system, NURADS," Opt. Express **13**, 4250-4262 (2005)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-13-11-4250

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### References

- A. Morel and B. Gentili, �??Diffuse reflectance of oceanic waters. III. Implication of bidirectionality for the remote-sensing problem,�?? Appl. Opt. 35, 4850-4862 (1996). [CrossRef] [PubMed]
- J. E. Tyler, �??Radiance distribution as a function of depth in an underwater environment,�?? Bull. Scripps Inst. Oceanogr. 7, 363-41 (1960).
- 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]
- K. Miyamoto, �??Fish Eye Lens,�?? J. Opt. Soc. Am. 54, 1060- 1061 (1964) [CrossRef]
- R. C. Smith, R. W. Austin and J. E. Tyler, �??An oceanographic radiance distribution camera system,�?? Appl. Opt. 9, 2015-2022 (1970). [CrossRef] [PubMed]
- K. J. Voss, �??Electro-optic camera system for measurement of the underwater radiance distribution,�?? Opt. Eng. 28, 241-247 (1989).
- 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).
- 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]
- 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.
- 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]
- 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]
- F. L. Pedrotti and L. S. Pedrotti, Introduction to Optics (Prentice Hall, New Jersey, 1993).
- J. Piskozub, �??Effect of ship shadow on in-water irradiance measurements,�?? Oceanologia 46, 103-112 (2004).
- A. Morel, D. Antoine, and B. Gentili, �??Bidirectional reflectance of oceanic waters: accounting for Raman emission and varying particle scattering phase function,�?? Appl. Opt. 41, 6289 �?? 6306 (2002). [CrossRef] [PubMed]
- 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]

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