John E. Tyler

Optical Properties of Clear Natural Water

This paper reports spectroradiometric data obtained with a highly developed double monochromator at three depths and above the surface, at Crater Lake, Oregon. These data have been used to calculate spectral values of the diffuse-attenuation coefficient, and the underwater-reflectance function of Crater Lake water, which is a natural analog of distilled water. The data have also been used to calculate the spectral and total energy available for visibility or photosynthesis and the radiant power absorbed per unit volume, all at a number of depths to 600 m. The data and calculations are reported at 5-nm intervals in the wavelength region 350 nm to 700 nm.

Transmission of Solar Radiation into Natural Waters

Physical and biological measurements in aquatic environments are becoming more accurate and precise as instruments and experimental techniques improve. These improved measurements go hand in hand with an increasingly quantitative description of the relationship between solar radiation, the optical properties of natural waters, and aquatic photoprocesses (e.g., Bannister, 1974; Kiefer and Austin, 1974; Morel and Smith, 1974; Patten, 1968). As man becomes increasingly aware of his own, often adverse, impact upon the aquatic environment, the techniques of optical oceanography assume greater importance as a means for the rapid and accurate assessment of this environment (e.g., Gibbs, 1974; Jerlov and Steemann Nielsen, 1974; Smith et al., 1973; Clark et al., 1969). It is timely, therefore, to formulate a consistent set of fundamental radiometric quantities, units, and nomenclature that will have consistent applicability to limnology and oceanography, as well as to photochemistry and photobiology.

Predicted Optical Properties for Clear Natural Water

This paper presents the results of an effort to predict the optical properties of a clean-water type as a function of wavelength. The prediction is based on extensive experimental spectral values for the irradiance-attenuation coefficient and the irradiance reflectance for clean, naturally occurring water, together with an analytical expression for the shape of the asymptotic radiance distribution and a synthesized table of spectral values for the total scattering coefficient based on recent experimental data obtained by Morel in the Mediterranean Sea. The values predicted for the total attenuation coefficient are found to compare favorably with recent data for the total attenuation coefficient obtained at several wavelengths by Austin, in the Sargasso Sea. Other optical properties predicted herein are found to be consistent with experimental values recently reported in the literature.

Spectroradiometric Characteristics of Natural Light Under Water

This paper presents spectroradiometric data on the natural radiant flux occurring underwater at three locations in the Gulf of California, in Pacific coastal water near San Diego, and in the plankton-rich water of San Vicente Reservoir (San Diego County). Spectral radiance and irradiance have been measured, and it is shown that under certain circumstances spectral data for these two radiometric quantities are directly proportional. The data have been used to calculate spectral values of the attenuation coefficient and of the reflection function. The various spectra correlate qualitatively with apparent chlorophyll concentration and water color.

An Oceanographic Radiance Distribution Camera System

An oceanographic optical instrument has been designed and constructed to record the radiance distribution of natural radiant energy underwater. The instrument contains two cameras placed back-to-back, each equipped with a fisheye (180 degrees field of view) lens and is fabricated so that film can be exposed by remote control. The instrument is designed to operate at depths up to 100 m. Values of underwater radiance can be obtained from the exposed films by means of photographic photometry. Radiance distributions obtained in natural waters will provide basic information needed for the study and solution of several problems in optical oceanography. First, the radiance distribution is an important input for the study of the interaction of electromagnetic radiation with the sea. From the distribution of radiance in the natural light fields in the ocean, many of the important optical properties which relate to radiative transfer processes in the ocean can be calculated. Second, from these optical properties one can compute the magnitude of the deterioration of image contrast of submerged objects and thus furnish information for the study and solution of underwater visibility problems, which include problems in underwater television and photography. Finally, since radiant energy is critical to the beginning of the marine food chain through photosynthetic plankton, radiance distribution measurements will provide information of fundamental importance to the problem of primary productivity in natural waters.

In Situ Spectroscopy in Ocean and Lake Waters

In situ experimental measurements over the wavelength range 400–700 nm have been made in Crater Lake and in Pacific coastal water to reveal their inherent absorption spectra. The measurements are reported as the ratio of the radiance observed in a horizontal direction underwater to the irradiance falling on the surface of the water and, as such, are independent of the spectral properties of the source of flux as well as those of the detector. The instrument used is discussed briefly and a short theoretical analysis is given to illustrate the effect of changes in absorption and scattering on the ratios obtained.

A survey of experimental hydrologic optics

This paper describes current experimental methods and instrumentations used to measure the constructs of radiative transfer in the sea as specified by theory. Experimental data are presented to illustrate the salient properties of the underwater light fields and to show the application of radiative transfer theory to the determination of some of the optical properties of natural waters. Applications of the theory to practical problems in biological and physical oceanography are discussed briefly.

A Scattering Meter for Deep Water

The deep water scattering meter was developed for the purpose of studying the scattering properties of ocean water. By means of a straightforward calibration, data taken with this instrument can be readily expressed as absolute values of the volume scattering function.

Ocean analysis by means of Beer's law.

A method for applying Beers law to the analysis of ocean or lake water is described. The method makes use of measurements of daylight irradiance for studying the quantum efficiency of in situ photosynthesis by phytoplankton populations. Alternatively, the method can make use of in situ beam transmittance measurements for monochromatic studies of ocean contaminants.