Communication Channel Model of the Atmosphere for Optical Frequencies

In order to obtain high data rate T.V. picture transmissions from spacecrafts on planetary missions consideration has been given in the past to the use of laser communications systems. If no relay satellite is used a deep space laser communication link would involve propagation through the earths atmosphere to a ground based station. This paper gives consideration to the characteristic of the earths atmosphere as a communication channel. A channel model is given both for clear weather conditions and for inclement weather conditions. For clear weather conditions it is found that the laser atmosphere is a Quasi-Wide-Sense-Stationary correlated Scattering Channel (QWSSCS) which can be fairly accurately characterized by an array of variable gain, variable delay paths. Under inclement weather conditions the channel is characterized by a differential circuit model which is specified by the Input Delay- Spread Function. Data is compiled, for these two channel models, which describes the pertinent parameters/ such as, delay dispersion, tne amplitude distribution, amplitude power spectrum and the two dimentional spacial correlation function. It is found that for good weather conditions, pulses having widths of the order of 2 picosecond can be propagated through the whole atmosphere without appreciable distortion, whereas for inclement weather conditions one is limited to pulse widths of the order of nanoseconds