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NASA NTRS1974

A feasibility study for a remote laser water turbidity meter

A technique to remotely determine the attenuation coefficient (alpha) of the water was investigated. The backscatter energy (theta = 180 deg) of a pulse laser (lambda = 440 - 660 nm) was found directly related to the water turbidity. The greatest sensitivity was found to exist at 440 nm. For waters whose turbidity was adjusted using Chesapeake Bay sediment, the sensitivity in determining alpha at 440 nm was found to be approximately 5 - 10%. A correlation was also found to exist between the water depth (time) at which the peak backscatter occurs and alpha.

Hickman, G. D.↗

NASA NTRS1974

Radiative transfer of visible radiation in turbid atmosphere

Methods are presented for solving radiative transfer problems; they include the doubling method and the closely related matrix method, iterative method, Chandrasekhar's method of discrete ordinates, and Monte Carlo method. To consider radiation transport through turbid atmosphere, an atmospheric model was developed characterizing aerosols by parameters. Intensity and polarization of radiation in turbid atmospheres is discussed, as well as lower atmospheric heating due to solar radiation absorption by aerosols.

Yamamoto, G.↗

NASA NTRS1975

Computer mapping of turbidity and circulation patterns in Saginaw Bay, Michigan from LANDSAT data

The author has identified the following significant results. LANDSAT was used as a basis for producing geometrically-corrected, color-coded imagery of turbidity and circulation patterns in Saginaw Bay, Michigan (Lake Huron). This imagery shows nine discrete categories of turbidity, as indicated by nine Secchi depths between 0.3 and 3.3 meters. The categorized imagery provided an economical basis for extrapolating water quality parameters from point samples to unsample areas. LANDSAT furnished a synoptic view of water mass boundaries that no amount of ground sampling or monitoring could provide.

Rogers, R. H.↗

NASA NTRS1975

Evaluation of the dual differential radiometer for remote sensing of sediment and chlorophyll in turbid waters

The dual differential radiometer (DDR) was tested to determine its capability for measuring suspended sediment and chlorophyll in turbid waters. Measurements were obtained from a boat dock and from a helicopter with combinations of sample and reference filters with peak transmissions at various wavelengths. Water samples were taken concurrently and were analyzed for light scattering, particle count, and total chlorophyll. Least-squares estimates of the linear relationship between DDR output and the water parameters yielded correlation coefficients of less than 0.7. Under the turbid water conditions of the present tests, the DDR did not accurately measure either suspended sediment or chlorophyll. A precise knowledge of the spectral signatures of various pollutants might enable appropriate filters to be selected for tuning the DDR to monitor a particular pollutant.

Witte, W. G.↗

NASA NTRS1976

Correlation between multispectral photography and near-surface turbidities

Four-band multispectral photography obtained from an aerial platform at an altitude of about 10,000 feet has been utilized to measure near-surface turbidity at numerous sampling sites in the Ross Barnett Reservoir, Mississippi. Correlation of the photographs with turbidity measurements has been accomplished via an empirical mathematical model which depends upon visual color recognition when the composited photographs are examined on either an I squared S model 600 or a Spectral Data model 65 color-additive viewer. The mathematical model was developed utilizing least-squares, iterative, and standard statistical methods and includes a time-dependent term related to sun angle. This model is consistent with information obtained from two overflights of the target area - July 30, 1973 and October 30, 1973 - and now is being evaluated with regard to information obtained from a third overflight on November 8, 1974.

Wertz, D. L.↗

NASA NTRS1976

Effects of multiple scattering on light pulses reflected by turbid atmospheres

Multiple scattering contributions to lidar returns from turbid atmospheres are derived by means of an analytical theory. It is assumed that scattering takes place mainly at small angles except for one event that scatters the light backward. The phase functions are approximated by the sum of Gaussian functions of the scattering angle in both the forward and backward directions. The three-dimensional radiative transfer equation is transformed to a one-dimensional problem by means of Fourier transforms. Neumann solutions to the transformed equation of radiative transfer are then found. A number of examples are presented for cloud, fog and haze models. The results are found to be in satisfactory agreement with results obtained from the Monte Carlo analysis of Kunkel (1974) and the theory of light pulses doubly scattered by turbid atmospheres which was developed by Eloranta (1972).

Weinman, J. A.↗

NASA NTRS1977

Determination of scattering functions and their effects on remote sensing of turbidity in natural waters

The development of quantitative analytical procedures for relating scattered signals, measured by a remote sensor, was considered. The applications of a Monte Carlo simulation model for radiative transfer in turbid water are discussed. The model is designed to calculate the characteristics of the backscattered signal from an illuminated body of water as a function of the turbidity level, and the spectral properties of the suspended particulates. The optical properties of the environmental waters, necessary for model applications, were derived from available experimental data and/or calculated from Mie formalism. Results of applications of the model are presented.

Ghovanlou, A. H.↗

NASA NTRS1981

Verification of reflectance models in turbid waters

Inherent optical parameters of very turbid waters were used to evaluate existing water reflectance models. Measured upwelling radiance spectra and Monte Carlo simulations of the radiative transfer equations were compared with results from models based upon two flow, quasi-single scattering, augmented isotropic scattering, and power series approximation. Each model was evaluated for three separate components of upwelling radiance: (1) direct sunlight; (2) diffuse skylight; and (3) internally reflected light. Limitations of existing water reflectance models as applied to turbid waters and possible applications to the extraction of water constituent information are discussed.

Tanis, F. J.↗

NASA NTRS1981

Comparison of reflectance with backscatter and absorption parameters for turbid waters

The relation of reflectance to backscatter and absorption parameters is investigated for waters more turbid than those of previous investigations. Experimental data are examined for river waters in which beam attenuation values range from 8.9 to 18.9 per m at 550 nm. Attenuation, absorption, backscatter, and irradiance reflectance spectral properties are presented for wavelengths between 450 and 800 nm. Comparisons of reflectance with backscatter to absorption ratio and backscatter with absorption plus backscatter ratio indicate that data for turbid waters do not fit linear or polynomial models which are presently available in the literature.

Whitlock, C. H.↗

NASA NTRS1982

Determination of turbidity patterns in Lake Chicot from LANDSAT MSS imagery

A historical analysis of all the applicable LANDSAT imagery was conducted on the turbidity patterns of Lake Chicot, located in the southeastern corner of Arkansas. By examining the seasonal and regional turbidity patterns, a record of sediment dynamics and possible disposition can be obtained. Sketches were generated from the suitable imagery, displaying different intensities of brightness observed in bands 5 and 7 of LANDSAT's multispectral scanner data. Differences in and between bands 5 and 7 indicate variances in the levels of surface sediment concentrations. High sediment loads are revealed when distinct patterns appear in the band 7 imagery. Additionally, the upwelled signal is exponential in nature and saturates in band 5 at low wavelengths for large concentrations of suspended solids.

Lecroy, S. R.↗

NASA NTRS1981

Determination of circulation and turbidity patterns in Kerr Lake from LANDSAT MSS imagery

The LANDSAT imagery was historically analyzed to determine the circulation and turbidity patterns of Kerr Lake, located on the Virginia-North Carolina border. By examining the seasonal and regional turbidity and circulation patterns, a record of sediment transport and possible disposition can be obtained. Sketches were generated, displaying different intensities of brightness observed in bands 5 and 7 of LANDSAT's multispectral scanner data. Differences in and between bands 5 and 7 indicate variances in the levels of surface sediment concentrations. High sediment loads are revealed when distinct patterns appear in the band 7 imagery. The upwelled signal is exponential in nature and saturates in band 5 at low wavelengths for large concentrations of suspended solids.

Lecroy, S. R.↗

NASA NTRS1982

Determination of turbidity patterns in Lake Chicot from LANDSAT MSS imagery

Lecroy, S. R.↗

NASA NTRS1982

Influence of dissolved organic materials on turbid water optical properties and remote-sensing reflectance

The effects of dissolved organic materials on turbid-water optical properties are assessed, by means of field measurements and laboratory simulations in which upwelled reflectance, attenuation, absorption, and backscatter spectral properties at wavelengths from 450 to 800 nm are examined in relation to water chemistry. The data show that dissolved organic materials decrease upwelled reflectance from turbid waters, and that the decrease in reflectance is a nonlinear function of concentration with the largest gradients at low carbon concentrations, depending on wavelength. Upwelled reflectance is found to be highly correlated with two backscatter-absorption parameters used in some optical models, which are nonlinear with dissolved organic material concentration change.

Witte, W. G.↗

NASA NTRS1981

Transforming ground-measured reflectances to radiances measured by various space sensors through clear and turbid atmospheres

The influence on the ratios of the ground measured reflectances in the range 0.8-1.1 microns to those in the range 0.6-0.7 microns of the intervening atmosphere and the sensor response are investigated over a typical range of remote sensing conditions. A simulation of the influences of clear and turbid atmospheres is developed, and their effects on Landsat MSS band 7 to band 5 ratios are determined for Avondale loam and stressed and unstressed vegetation. Results show that for dry loam the differences between the band 7 to band 5 ratios as determined from space and ground level measurements is 2.3% for clear and 5.6% for turbid atmospheric conditions, while for wet loams the differences are 10.4% and 29.5%. It is concluded that the effect of the atmosphere on band ratios for vegetation indicates that atmospheric conditions may delay the discrimination of stressed from unstressed vegetation by 3 to 7 days. The influence of the atmosphere is found to increase for oblique angle observations, and the path radiance and the change in path radiance are greater in the 0/180 degree azimuth than in the 90/270 azimuth.

Slater, P. N.↗

NASA NTRS1984

Turbidity very near the critical point of methanol-cyclohexane mixtures

The turbidity of a critical mixture of methanol and cyclohexane has been measured extremely close to the consolute point. The data span the reduced-temperature range between 10 to the -7th and 10 to the -3d, which is two decades closer to Tc than previous measurements. In this temperature range, the turbidity varies approximately as 1nt, as expected from the integrated form for Ornstein-Zernike scattering. A thin cell (200-micron optical path) with a very small volume (0.08 ml) was used to avoid multiple scattering. A carefully controlled temperature history was used to mix the sample and to minimize the effects of critical wetting layers. The data are consistent with a correlation-length amplitude of 3.9 plus or minus 1.0 A, in agreement with the value 3.5 A calculated from two-scale-factor universality and heat-capacity data from the literature.

Kopelman, R. B.↗

NASA NTRS1992

Application of radiative image transfer theory to the assessment of the overall OTF and contrast degradation of an image in an inhomogeneous turbulent and turbid atmosphere

A perturbation-theoretic approximation of the radiative transfer equation which neglects photon dispersion is used as a modeling basis for the propagation of the image of a self-luminous target through a turbulent atmosphere which also possesses inhomogeneously distributed turbidity along the propagation path. A contrast ratio is then introduced which provides an indicator of the relative contribution of the unscattered or coherent image component to that of the scattered or incoherent image component. Analytical expressions are then derived for the contrast ratio from the approximate form of the radiative transfer equation in the case of an inhomogeneously dispersed Joss thunderstorm rain distribution in the presence of turbulence. The case is clearly demonstrated for the need to consider a measure of the points of demarcation at which the dominant roles of the scattering processes due to turbidity and turbulence are exchanged. Such a measure can provide a performance parameter for the application of adaptive optics methods that are specific to the particular dominant scattering mechanism given the prevailing target size, total propagation length and overall propagation parameters.

Manning, Robert M.↗

NASA NTRS1996

Turbidity of a Binary Fluid Mixture: Determining Eta

A ground based (1-g) experiment is in progress that will measure the turbidity of a density-matched, binary fluid mixture extremely close to its liquid-liquid critical point. By covering the range of reduced temperatures t equivalent to (T-T(sub c)) / T(sub c) from 10(exp -8) to 10(exp -2), the turbidity measurements will allow the critical exponent eta to be determined. No experiment has precisely determined a value of the critical exponent eta, yet its value is significant to theorists in critical phenomena. Relatively simple critical phenomena, as in the liquid-liquid system studied here, serve as model systems for more complex systems near a critical point.

Jacobs, Donald T.↗

NASA NTRS2000

Time-resolved diffusion tomographic 2D and 3D imaging in highly scattering turbid media

A method for imaging objects in highly scattering turbid media. According to one embodiment of the invention, the method involves using a plurality of intersecting source/detectors sets and time-resolving equipment to generate a plurality of time-resolved intensity curves for the diffusive component of light emergent from the medium. For each of the curves, the intensities at a plurality of times are then inputted into the following inverse reconstruction algorithm to form an image of the medium: wherein W is a matrix relating output at source and detector positions r.sub.s and r.sub.d, at time t, to position r, .LAMBDA. is a regularization matrix, chosen for convenience to be diagonal, but selected in a way related to the ratio of the noise, to fluctuations in the absorption (or diffusion) X.sub.j that we are trying to determine: .LAMBDA..sub.ij =.lambda..sub.j .delta..sub.ij with .lambda..sub.j = /<.DELTA.Xj.DELTA.Xj> Y is the data collected at the detectors, and X.sup.k is the kth iterate toward the desired absorption information. An algorithm, which combines a two dimensional (2D) matrix inversion with a one-dimensional (1D) Fourier transform inversion is used to obtain images of three dimensional hidden objects in turbid scattering media.

Alfano, Robert R.↗