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Gordon, H. R.

Publications and source records attributed to Gordon, H. R..

29 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Diffuse reflectance of the ocean - The theory of its augmentation by chlorophyll a fluorescence at 685 nm

The radiative transfer equation is modified to include the effect of fluorescent substances and solved in the quasi-single scattering approximation for a homogeneous ocean containing fluorescent particles with wavelength independent quantum efficiency and a Gaussian shaped emission line. The results are applied to the in vivo fluorescence of chlorophyll a (in phytoplankton) in the ocean to determine if the observed quantum efficiencies are large enough to explain the enhancement of the ocean's diffuse reflectance near 685 nm in chlorophyll rich waters without resorting to anomalous dispersion. The computations indicate that the required efficiencies are sufficiently low to account completely for the enhanced reflectance. The validity of the theory is further demonstrated by deriving values for the upwelling irradiance attenuation coefficient at 685 nm which are in close agreement with the observations.

Gordon, H. R.↗
NASA NTRS1978

Some relationships between Secchi depth and inherent optical properties of natural waters

Relationships between the inherent and optical properties of the ocean (Gorden et al., 1975 and Preisendorfer, 1961) are combined with the Duntley-Preisendorfer equation to show the dependence of these properties on the depth at which a Secchi disk disappears from view. An expression relating the Secchi depth to the limiting contrast of the disk is derived in terms of the average beam attenuation coefficient, the average diffuse attenuation coefficient for downwelling irradiance, the albedo of the disk, and the reflectance functions at the Secchi depth and just below the surface. It is shown that combining Secchi depth observations with other optical properties yields significant information about the constituents of the medium.

Gordon, H. R.↗
NASA NTRS1978

Remote sensing of optical properties in continuously stratified waters

The radiative transfer equation is solved by Monte Carlo methods for natural waters in which the optical properties are distributed with depth. It is demonstrated that interpreting the reflectance of a continuously stratified ocean in terms of an equivalent homogeneous ocean yields the average of a particular combination of the water's optical properties over the dimensionless penetration depth. Although in general the dimensionless penetration depth cannot be remotely measured, a method is presented for estimating the actual penetration depth from the remote observations if the medium's absorption coefficient is known, independent of depth, and sufficiently large. The application of this to the remote measurement of the vertical distribution of suspended sediments is discussed in detail.

Gordon, H. R.↗
NASA NTRS1978

Removal of atmospheric effects from satellite imagery of the oceans

The paper analyzes the effects of atmospheric and sea surface scattering on the determination of ocean color from satellite imagery and proposes an algorithm for removing a large portion of these effects. The algorithm is based on the observations that (1) the upward radiance from the unwanted photons can be divided into effects resulting from Rayleigh scattering alone and those resulting from aerosol scattering alone, (2) the aerosol scattering phase function should be nearly independent of wavelength, and (3) the Rayleigh component can be computed without a knowledge of the sea surface roughness. The ratio of the aerosol optical thickness at the wavelength of interest to the aerosol optical thickness at 750 nm is used in the algorithm since it is assumed that the ocean is totally absorbing in a band of wavelengths around 750 nm. The calculation of this ratio from satellite measurements alone and the accuracy of the procedure are considered.

Gordon, H. R.↗
NASA NTRS1977

Albedo of the ocean-atmosphere system - Influence of sea foam

The influence of the ocean's optical properties and wind induced sea surface foam (white caps) on the short-wave albedo of the ocean-atmosphere system is studied by solving the radiative transfer equation using a Monte Carlo method. It is found that for a foam free ocean, the planetary albedo of a very clear ocean is at most 10 percent greater than that for a totally absorbing ocean. However, the introduction of a relatively small amount of sea foam on the surface can produce a considerable increase in the albedo, especially if the foam is highly reflecting. For example, it is shown that for foam which is totally reflecting (the foam albedo is 1), an increase in the wind speed from 6 to 14 m/sec would double the planetary albedo for small solar zenith angles.

Gordon, H. R.↗
NASA NTRS1976

An Experiment to Evaluate Skylab Earth Resources Sensors for Detection of the Gulf Stream

The author has identified the following significant results. An experiment to evaluate the Skylab earth resources package for observing ocean currents was performed in the Straits of Florida in January 1974. Data from the S190 photographic facility, S191 spectroradiometer and S192 multispectral scanner, were compared with surface observations. The anticyclonic edge of the Gulf Stream could be identified in the Skylab S190A and B photographs, but the cyclonic edge was obscured by clouds. The aircraft photographs were judged not useful for spectral analysis because vignetting caused the blue/green ratios to be dependent on the position in the photograph. The spectral measurement technique could not identify the anticyclonic front, but mass of Florida Bay water which was in the process of flowing into the Straits could be identified and classified. Monte Carlo simulations of the visible spectrum showed that the aerosol concentration could be estimated and a correction technique was devised.

Maul, G. A.↗
NASA NTRS1975

Remote sensing of submerged aquatic vegetation in the lower Chesapeake Bay

An experimental water penetration film and black and white near infrared film were used to study the distribution of submerged aquatic vegetation in the lower Chesapeake Bay. Detailed description of the grass beds was obtained by flying at an altitude of 5,000 feet, at low tide when wind conditions were minimal. Results show that there was a 36% reduction in the amount of submerged aquatic vegetation in the lower Chesapeake Bay from 1971 to 1974, the greatest losses occurring in the York, Piankatank and Rappahannock rivers (tabulated data is given). Recovery of some grass beds occurs primarily through seedling recruitment and subsequent vegetative growth. Cownose rays are suspected as a main factor for the decimation of some of the grass beds. Maps and photographs of the areas studied are given.

Orth, R. J.↗
NASA NTRS1975

On the use of the earth resources technology satellite /LANDSAT-1/ in optical oceanography

Observations of the Gulf Stream System in the Gulf of Mexico were obtained in synchronization with LANDSAT-1. Computer enhanced images, which are necessary to extract useful oceanic information, show that the current can be observed by color (diffuse radiance) or sea state (specular radiance) effects associated with the cyclonic boundary even in the absence of a surface thermal signature. The color effect relates to the spectral variations in the optical properties of the water and its suspended particles, and is studied by radiative transfer theory. Significant oceanic parameters identified are: the probability of forward scattering, and the ratio of scattering to total attenuation. Several spectra of upwelling diffuse light are computed as a function of the concentration of particles and yellow substance.

Maul, G. A.↗
NASA NTRS1974

Relationships between ERTS radiances and gradients across ocean fronts

A time series of the Loop Current in the Gulf of Mexico, covering an annual cycle of growth, spreading, and decay, has been obtained in synchronization with ERTS. Computer enhanced images, which are necessary to extract useful oceanic information, show that the current can be observed either by color or sea state effects associated with the cyclonic boundary. The color effect relates to the spectral variations in the optical properties of the water and its suspended particles, and is studied by radiative transfer theory. Significant oceanic parameters identified are: the probability of forward scattering, and the ratio of scattering to total attenuation.

Maul, G. A.↗