Aerosol and cloud backscatter at 1.06, 1.54, and 0.53 mum by airborne hard-target-calibrated Nd:YAG /methane Raman lidar.

A lidar instrument was developed to make simultaneous measurements at three distinct wavelengths in the visible and near infrared at 0.532, 1.064, and 1.54 mum with high cross-sectional calibration accuracy. Aerosol and cloud backscatter cross sections were acquired during November and December 1989 and May and June 1990 by the NASA DC-8 aircraft as part of the Global Backscatter Experiment. The instrument, methodology, and measurement results are described. A Nd:YAG laser produced 1.064- and 0.532-mum energy. The 1.54-mum transmitted pulse was generated by Raman-shifted downconversion of the 1.064-mum pulse through a Raman cell pressured with methane gas. The lidar could be pointed in the nadir or zenith direction from the aircraft. A hard-target-based calibration procedure was used to obtain the ratio of the system calibration between the three wavelengths, and the absolute calibration was referenced to the 0.532-mum lidar molecular backscatter cross section for the clearest scattering regions. From the relative wavelength calibration, the aerosol backscatter cross sections at the longer wavelengths are resolved for values as small as 1% of the molecular cross section. Backscatter measurement accuracies are better than 10(-9) (m sr)(-1) at 1.064 and 1.54 mum. Results from the Pacific Ocean region of the multiwavelength backscatter dependence are presented. Results show extensive structure and variation for the aerosol cross sections. The range of observed aerosol cross section is over 4 orders of magnitude, from less than 10(-9) (m sr)(-1) to greater than 10(-5) (m sr)(-1).

Optical system design and integration of the Mars Observer Laser Altimeter.

The Mars Observer Laser Altimeter, developed for flight on the Mars Observer spacecraft payload in September 1992, is designed to measure the topography of the Martian surface over a 2-year period from a 400-km mapping orbit. A 40 mJ pulse diode-pumped laser together with a 0.5-m-diameter beryllium telescope and a silicon avalanche photodiode are the principal optical subassemblies of this active remote-sensing instrument. Optical design rationale and measured optical performances during assembly and integration are presented.

Dual-wavelength correlation measurements with an airborne pulsed carbon dioxide lidar system.

Dual-wavelength correlation data are presented for ground-level and airborne measurements of topographic and ocean backscatter near the 9.5-microm wavelength. Data were acquired with a pulsed carbon dioxide, dual-laser, dualwavelength lidar system. The best system performance gave a dual-wavelength uncorrelated noise component of 2.8% and 9% standard deviation for ground-based and airborne data, respectively. This sets one limit on lidar measurement accuracy with a single pulse pair.

Continuous wave lidar measurement of atmospheric visibility.

The technique of measurement of phase shift with a modulated cw lidar system for the purpose of atmospheric visibility assessment was evaluated both theoretically and experimentally. A closed form solution for prediction of phase shift as a function of visibility and modulation frequency was developed. Data obtained with a bistatic cw lidar configuration were compared with predictions. Results indicate the expected trends with equipment parameters and call for more extensive experiments.

Corrections for atmospheric refractivity in satellite laser ranging.

The range correction calculated from ground-level meteorological measurements is shown to consist of a series of terms. The zeroth order term of this series corresponds to the correction obtained under the assumption of a spherically symmetric refractivity profile. The higher order terms arise due to departures from the spherical-symmetry assumption. The range correction is also shown to have residual errors, and an analytic expression for these errors is derived. Pertinent surface data are analyzed to obtain the magnitudes of the higher order corrections and the residual errors.

Scintillation statistics caused by atmospheric turbulence and speckle in satellite laser ranging.

We study the statistics of scintillation at the ground-based receiver for the earth-space-earth retroreflector configuration of satellite laser ranging. These statistics are governed by the joint effects of atmospheric turbulence and speckle produced by the retroreflector array. An expression for the probability density function of scintillation is obtained and evaluated numerically. Comparison of the normalized variance of scintillation calculated by using this function shows good agreement with results obtained by other methods.

Scintillation statistics measured in an earth-space-earth retroreflector link.

An experiment is described for the measurement of scintillation in a vertical path from an earth-based laser transmitter to the GEOS-III satellite and back to an earth-based receiver telescope. Measurements of the normalized variance, probability density function, and power spectral density of scintillation are presented. These results are discussed in terms of recent analytical results.

Laser beam scintillation beyond the turbulent atmosphere: a numerical computation.

The extended Huygens-Fresnel formulation for propagation through turbulence is used to examine scintillation of a finite laser beam. The method is demonstrated analytically for propagation beyond a weak Gaussian phase screen. A numerical integration technique is used to extend the results to a more realistic turbulence model. Results are compared with existing Gaussian beam propagation theory.

Comparison of vertical profile turbulence structure with stellar observations.

Vertical profiles of microthermal turbulence structure have been obtained from balloon flights to altitudes near 25 km above mean sea level. Comparison of the observed turbulence structure with meteorological data and simultaneously acquired stellar scintillation data has been successful. For this comparisonintegrals over the observed turbulence structure were computed as required by theory. Turbulence and wind velocity data were also employed to predict successfully stellar irradiance spectra.

Fourier spectrum of a chopped bivariate normal intensity distribution.

Theoretical and experimental results are presented for chopping or mechanically modulating a bivarate normal intensity distribution. This distribution is a useful approximation in many optical situations. The present analysis is an extension of that due to McQuistan and Julich. The chopped intensity distribution is expanded in a Fourier series with the coefficients calculated numerically by computer. Coefficients are determined for various beam to chopper width ratios and for several levels of approximation to the intensity distribution. Experimental verification is provided by spectral analysis of the detected signal from a chopped laser beam.