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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Ozone abundances in the lower mesosphere deduced from backscattered solar radiances

Backscatter ultraviolet data obtained by the Explorer E satellite imply very large ozone column abundances above 56 km in the tropics during mid-day. The number of molecules in a vertical column decays by a factor of 2-3 after the solar zenith angle exceeds 75 deg in the evening. An increase of similar magnitude occurs after sunrise. Such behavior implies the presence of a greater source of odd oxygen than is included in current photochemical theories. Ozone profiles deduced between altitudes of 50 and 62 km when the solar zenith angle exceeds 80 deg are in reasonable agreement with past rocket results.

Frederick, J. E.↗
NASA NTRS1977

An empirical model for ocean radar backscatter and its application in inversion routine to eliminate wind speed and direction effects

Several regression models were tested to explain the wind direction dependence of the 1975 JONSWAP (Joint North Sea Wave Project) scatterometer data. The models consider the radar backscatter as a harmonic function of wind direction. The constant term accounts for the major effect of wind speed and the sinusoidal terms for the effects of direction. The fundamental accounts for the difference in upwind and downwind returns, while the second harmonic explains the upwind-crosswind difference. It is shown that a second harmonic model appears to adequately explain the angular variation. A simple inversion technique, which uses two orthogonal scattering measurements, is also described which eliminates the effect of wind speed and direction. Vertical polarization was shown to be more effective in determining both wind speed and direction than horizontal polarization.

Dome, G. J.↗
NASA NTRS1978

Ozone profiles and chemical loss rates in the tropical stratosphere deduced from backscatter ultraviolet measurements

Analysis of data obtained by the backscatter ultraviolet (BUV) experiment on the Atmosphere Explorer E satellite has provided equatorial ozone mixing ratio profiles for equinox and solstice conditions. The combination of these results with a pure oxygen chemical model yields the rate of odd oxygen loss due to the sum of the odd hydrogen, nitrogen, and chlorine cycles. Use of recent mid-latitude stratospheric measurements of HO(x), NO(x), and ClO(x) with the BUV data provides an independent calculation of the catalytic loss. Below 45 km the agreement between the two sets of loss rates is satisfactory. At higher altitudes the odd hydrogen cycle provides far more O(x) loss than can be tolerated by the BUV measurements if the photodissociation of O2 is the only source and has the currently accepted magnitude. The results suggest either a tropical HO(x) concentration smaller than is now believed or the presence of a very large source of odd oxygen in the upper stratosphere and lower mesosphere.

Frederick, J. E.↗
NASA NTRS1978

On the relationship of radar backscatter to wind speed and fetch

The physics of the interaction of electromagnetic waves with the ocean surface has been an active area of research for a number of years. This paper contains the results of satellite and aircraft experiments to investigate the ability of active microwave radars to infer surface wind speeds remotely. Data obtained from the recent National Aeronautics and Space Administration (NASA) Skylab experiment are compared with surface wind speeds measured by low-flying aircraft and ships-of-opportunity and found to give useful estimates of the ocean wind field. Also investigated was the influence of varying wave height on radar measurements of wind speed by measuring the backscattering cross-section for constant wind speed but variable wave conditions. It is found that this effect is of little importance.

Ross, D.↗
NASA NTRS1978

Backscattering from a Gaussian-distributed perfectly conducting rough surface

The original intent of the reported investigation was to find a solution to the composite surface scattering problem which provided for a continuous transition between the near-specular physical optics and wide-angle tilted plane Bragg solutions. The employed approach is based on analytical techniques rather than physical considerations. The analysis employs a perturbation technique developed by Burrows (1967, 1968, 1973), which because of its simplicity, is the key to the entire solution. The analysis is restricted to the case of backscattering from a perfectly conducting surface. General expressions are presented for the scattering from a Gaussian perfectly conducting surface characterized by an anisotropic spectrum and possessing many scales of roughness. The accuracy of the result is dependent upon the large-scale structure having large height excursions and small curvature.

Brown, G. S.↗
NASA NTRS1978

Remote sensing of sea state by analysis of backscattered microwave phase fluctuations

The relative phase of a normally incident microwave signal scattered off the sea surface is a random function of space and time. The statistics of these random phase fluctuations contain information about the wave-height statistics. This study demonstrates that the wave-height spectra can be deduced directly in terms of the spectra of the phase fluctuations without recourse to inversion techniques even when surface roughness exceeds many wavelengths of the incident signal. In the particular case of a nadir-directed satellite-mounted microwave source operating in the backscatter mode, the wave-height and phase spatial spectra are proportional with a constant proportionality of (2k0) squared, where k0 is the wavenumber of the scattered signal.

Clifford, S. F.↗
NASA NTRS1978

An investigation of the observability of ocean-surface parameters using GEOS-3 backscatter data

The degree to which ocean surface roughness can be synoptically observed through use of the information extracted from the GEOS-3 backscattered waveform data was evaluated. Algorithms are given for use in estimating the radar sensed waveheight distribution or ocean-surface impulse response. Other factors discussed include comparisons between theoretical and experimental radar cross section values, sea state bias effects, spatial variability of significant waveheight data, and sensor-related considerations.

Miller, L. S.↗
NASA NTRS1978

Seasonal and interannual variations in total ozone revealed by the Nimbus-4 backscattered ultraviolet experiment

The first two years of Backscattered Ultraviolet (BUV) ozone data from the Nimbus-4 spacecraft were reprocessed. The seasonal variations of total ozone for the period April 1970 to April 1972 are described using daily zonal means to 10 deg latitude zones and a time-latitude cross section. In addition, the BUV data are compared with analyzed Dobson data and with IRIS data also obtained from the Nimbus-4 spacecraft. A harmonic analysis was performed on the daily zonal means. Amplitudes, days of peaks, and percentage of variance were computed for annual and semi-annual waves and for higher harmonics of an annual period for the two years. Asymmetries are found in the annual waves in the two hemispheres, with a subtle interannual difference which may be due to changes in the general circulation. A significant semi-annual component is detected in the tropics for the first year, which appears to result from influences of the annual waves in the two hemispheres.

Hilsenrath, E.↗
NASA NTRS1978

The modulation of the radar backscattering cross section by long ocean waves

The modulation transfer function which relates the backscattered microwave power to the long ocean wave field was measured in the North Sea during JONSWAP 75. Results from this tower experiment with an X-band scatterometer are presented and compared with the two-scale wave model (relaxation-time model).

Alpers, W.↗
NASA NTRS1979

Comparison of backscatter ultraviolet /BUV/ and ground-based total ozone fields for December 1970

For the period December 1970, comparison is made between the monthly average analyses (mapped fields) of the backscatter ultraviolet (BUV) total ozone data and the ground-based observations. In particular, significant differences of over 50 Dobson units are noted over the region of the North Atlantic Ocean with the BUV of greater magnitude than the ground-based data. As part of the overall verification program, both analyses are compared against the 100 mb height fields. The results indicate that the BUV analysis in the region of question is the more consistent of the two.

Miller, A. J.↗
NASA NTRS1979

Microwave backscatter dependence on surface roughness, soil moisture, and soil texture. II - Vegetation-covered soil

Results are presented for an experimental investigation to determine the relationship between radar backscatter coefficient (sigma) and soil moisture for vegetation-covered soil. These results extend a previous report which showed the experimental relationship between sigma and soil moisture for bare soil. It is shown that the highest correlation between sigma and soil moisture is 0.92 for the combined response of four crop types measured at 4.25 GHz, 10 deg incidence angle, and HH polarization. Radar look direction, relative to the crop row direction, is shown to have an insignificant effect on soil-moisture estimation if the radar frequency is higher than 4 GHz. The dependence on soil type can be minimized by expressing soil moisture in units of percent of field capacity. The possibility of using a single radar for measuring soil moisture for both bare and vegetated fields is demonstrated with a linear estimation algorithm having an experimental correlation coefficinet of 0.8.

Ulaby, F. T.↗
NASA NTRS1980

Electromagnetic backscattering from a random distribution of lossy dielectric scatterers

Electromagnetic backscattering from a sparse distribution of discrete lossy dielectric scatterers occupying a region 5 was studied. The scatterers are assumed to have random position and orientation. Scattered fields are calculated by first finding the mean field and then by using it to define an equivalent medium within the volume 5. The scatterers are then viewed as being embedded in the equivalent medium; the distorted Born approximation is then used to find the scattered fields. This technique represents an improvement over the standard Born approximation since it takes into account the attenuation of the incident and scattered waves in the equivalent medium. The method is used to model a leaf canopy when the leaves are modeled by lossy dielectric discs.

Lang, R. H.↗
NASA NTRS1979

Seasonal and interannual variations in total ozone revealed by the Nimbus 4 backscattered ultraviolet experiment

The first 2 years of backscattered ultraviolet (BUV) ozone data from the Nimbus 4 spacecraft have been processed to a more refined level. The seasonal variations of total ozone for the period April 1970 to April 1972 are described using daily means for 10 deg latitude zones and a time-latitude cross section. In addition, the BUV data are compared with analyzed Dobson data and with infrared interferometer spectrometer data also obtained from the Nimbus 4 spacecraft. A harmonic analysis was performed on the daily zonal means. Amplitudes, days of peak ozone values, and percentage of variance have been computed for the annual and semiannual waves and for higher harmonics of an annual period for the 2 years. Asymmetries are found in the annual waves in the two hemispheres, with a subtle interannual difference which may be due to changes in the general circulation. A significant semiannual component is detected in the tropics for the first year. This component appears to result from influences of the annual waves in the two hemispheres. A search for shorter periods using the harmonic analysis revealed no periodicity whose amplitude was higher than the noise level.

Hilsenrath, E.↗
NASA NTRS1980

Absorption coefficients of ozone for the backscatter UV experiment

Band-averaged absorption coefficients for the wavelength channels of the backscatter ultraviolet (BUV) experiment computed with the laboratory ozone absorption measurements are presented. The coefficients ranged from plus or minus 11 to plus or minus 4% about the range midpoint for the major ozone-determining channels on the BUV; these percentage uncertainties in the band absorption coefficients lead to similar uncertainties in the absolute values of derived total ozone because of their reciprocal relationship. Derived total-ozone ratios of the BUV A:B pairs, the Dobson (1963) AD:CD double pairs; and the BUV B:Dobson AD are estimated for the different sets of coefficients based on the ratios experimentally observed in the BUV and Dobson data. It is shown that the Inn and Tanaka (1959) measurements produce the most consistent results, and band-averaged coefficients for the BUV-profiling wavelengths are computed.

Klenk, K. F.↗
NASA NTRS1981

Ozone profiling from backscattered UV radiance measurements A new procedure

This paper presents a data analysis technique that has been developed to support a stratospheric ozone measurement and profiling program. The data consist of solar backscattered UV radiation monitored by a spacecraft. The output consists of ozone mixing ratio profiles complete with error bars throughout the atmosphere. The technique is based upon principles of nonlinear optimal estimation. It provides a number of desirable features that have not been available together in any previously constructed technique for the problem. Iteration on both radiation measurements and total ozone measurements is among these features.

Whitney, C. K.↗
NASA NTRS1981

Absolute tracer dye concentration using airborne laser-induced water Raman backscatter

The use of simultaneous airborne-laser-induced dye fluorescence and water Raman backscatter to measure the absolute concentration of an ocean-dispersed tracer dye is discussed. Theoretical considerations of the calculation of dye concentration by the numerical comparison of airborne laser-induced fluorescence spectra with laboratory spectra for known dye concentrations using the 3400/cm OH-stretch water Raman scatter as a calibration signal are presented which show that minimum errors are obtained and no data concerning water mass transmission properties are required when the laser wavelength is chosen to yield a Raman signal near the dye emission band. Results of field experiments conducted with an airborne conical scan lidar over a site in New York Bight into which rhodamine dye had been injected in a study of oil spill dispersion are then indicated which resulted in a contour map of dye concentrations, with a minimum detectable dye concentration of approximately 2 ppb by weight.

Hoge, F. E.↗