Journal ArticleDOI
Heterodyne detection through rain, snow, and turbid media: effective receiver size at optical through millimeter wavelengths.
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TLDR
The influence of forward scattering on heterodyne receiver performance is investigated, taking into account turbulence and it is shown that the SNR is improved when the ratio of the scattering particulate size to turbulence coherence diameter decreases.Abstract:
Both scattering and turbulence can effect the spatial coherence of short wavelength signals propagating through the open atmosphere. In this paper, the influence of forward scattering on heterodyne receiver performance is investigated, taking into account turbulence. It is shown that the effect of forward scattering is to reduce the effective heterodyne receiver area through spatial coherence degradation. A common approach to scattering as an attenuation phenomenon is not always valid. Generally, this approach underestimates the SNR. The accuracy of the attenuation approach depends on the ratio R of the actual receiver diameter to the scattering particle diameter. If R > 100, scattering is essentially large angle and the typical treatment of scattering as an attenuation effect is indeed justified. However, for small R, forward scattering is primarily small angle, field coherence is noticeably affected by forward scattering, and the attenuation approach is not valid. Further, it is shown that the SNR is improved when the ratio of the scattering particulate size to turbulence coherence diameter decreases. From the practical point of view, the most important result of this study is that small receivers use their area more effectively than large receivers. Thus, an array of several small receivers may perform better than one large receiver with the same total area. The treatment here is particularly relevant for coherent detection through clouds, fog, precipitation, and turbid media in general, including liquid media.read more
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References
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Journal ArticleDOI
The relation of raindrop-size to intensity
J. Otis Laws,Donald A. Parsons +1 more
TL;DR: The applicability of such results to conditions of natural rainfall has been thrown in doubt as discussed by the authors, and the results have been found to be affected by the drop-size and velocity of the artificial rains applied.
Journal ArticleDOI
Optical heterodyne detection of an atmospherically distorted signal wave front
TL;DR: In this article, the effect of atmospheric distortion on the performance of an optical heterodyne detection system is examined theoretically and an exact expression relating the distortion to the detector signal-to-noise ratio is derived.
Journal ArticleDOI
Atmospheric degradation of electrooptical system performance
TL;DR: The total atmospheric mutual coherence function is introduced as a tool for analyzing the dependence of the performance of several types of EO systems as the combined effect of molecules, turbulence, and aerosols.
Journal ArticleDOI
Computed transmission through rain at microwave and visible frequencies
TL;DR: This paper presents tables which contain the Mie scattering coefficient, absorption coefficient, extinction coefficient, equivalent medium index of refraction and phase delay for rains conforming to the Laws and Parsons drop-size distribution for microwave frequencies of interest in common carrier radio relay systems.
Journal ArticleDOI
Limitation on image resolution imposed by a random medium
TL;DR: It is shown that at a large optical distance where the total coherent intensity is negligibly small compared with the total incoherent intensity, it is still possible to form the Airy disk due to the coherent intensity.