Peter O. Minott

Measurements of Turbulence Profiles in the Troposphere

Temperature structure coefficients were measured with balloon-borne temperature sensors. Data converted to refractive-index-structure coefficients are reported. These extend knowledge of this coefficient to the upper troposphere. The results are discussed with reference to possible meteorological origins for turbulence.

Scintillation in an earth-to-space propagation path.

Results of an experiment to measure the scintillation at a satellite from a ground-based laser transmitter are presented. The GEOS-II satellite in a nearly circular orbit of 1250 km was illuminated by a ground-based laser tracking station using a 4880-A continuous-wave argon laser. A detector aboard the satellite measured the incident light and telemetered the data to recording equipment on the ground. Log-amplitude variance, probability distributions, and scintillation frequency distributions are derived from the data. The probability distribution is shown to be log-normal. Log-amplitude variance and normalized power spectral density are shown to be within the limits measured for stellar scintillation.

Wavelength Dependence of Laser-Beam Scintillation*

An experiment has been performed to confirm the proportionality between log-amplitude variance and the 7/6 power of wavenumber predicted by Tatarski for horizontal propagation from a spherical-wave transmitter to a point detector. The validity of this proportionality was tested for two wavelengths: 0.632 and 10.6 μ. Beams from a helium-neon and a CO2 laser were simultaneously transmitted over a folded 1.2-km horizontal path and were detected with a photomultiplier and a gold-doped germanium detector. The primary scintillation statistic, log-amplitude variance, was evaluated for each wavelength with a digital computer and the ratio of variances at 0.632 and 10.6 μ was found to be in close agreement with predictions. Power spectral density, autocorrelation, and cumulative probability density were also evaluated for each wavelength. Scintillation statistics at 10.6 μ were found to be log normal, as in the visible.

Solar disk sextant

In this paper we present the conceptual design of an instrument, called the solar disk sextant, to be used in space to measure the shape and the size of the sun and their variations. The instrumental parameters required to produce sufficient sensitivity to address the problems of solar oblateness, solar pulsations, and global size changes of climatic importance are given.

Active alignment method for postlaunch coalignment of laser beam combiner systems

A laser transmitter for high bandwidth geosynchronous satellite communications is described. High optical power is achieved by combining semiconductor laser diodes. An active alignment scheme is proposed for achieving the +/- 20 microrad post launch multiple laser angular co-alignment requirement.

Tracking and Delay Relay Satellite System (TDRSS)-LIGHT: a space communications architecture

There is a growing interest in applying the resources of the Tracking and Data Relay Satellite System (TDRSS) as the primary support capability for future small satellite users. This interest is based on a variety of benefits offered by the TDRSS, and not available with globally-distributed space-ground links. An architecture based on an optical augmentation to the current TDRSS space network is discussed, including a candidate design for the user and relay terminals.

Determination of Atmospheric Structure Function by Using a Single Coherent Detector

The wave structure function associated with atmospheric turbulence is important in the effective design of telescopes for coherent optical receivers. This paper describes a method of measurement of the wave structure function by employing an already existing optical receiver. The aperture of this receivers telescope is masked by an opaque screen with two small holes. It is then shown that when the incident beam obeys Gaussian statistics, the receivers A.M. output can be simply related to the wave structure function of the incident beam.

Source Altitude for Experiments to Simulate Space-to-Earth Laser Propagation

The bias in scintillation measurements caused by the proximity of a spherical-wave source to the turbulence region of the atmosphere is predicted, and the laser-source altitude required for meaningful experiments simulating space-to-earth laser propagation is estimated. It is concluded that the source should be located at two or more times the maximum altitude of the tropopause to ensure that all measurements are not biased by more than 25%. Thus the vehicle used for experiments of this type should be capable of reaching a minimum altitude of 32 km.