Laser "firefly" clustering: A new concept in atmospheric probing

Profiling the chemical and particulate composition of the atmosphere is of growing importance as awareness of the role of pollution monitoring increases and deliberate contamination by hostile elements becomes a sad reality. Low cost, flexible, safe and mobile solutions are sought. In this letter, we propose an innovative concept of distributed probes in which miniature, low power lasers are deployed in situ at the altitude of interest. We term these laser transmitters "fireflies". The emitted light is at eye safety levels and is modulated by orthogonally coded signals, which make it possible to distinguish between the transmitters. The light is scattered by the aerosols and molecules in the locality of the firefly and received on the ground. Analysis of the received signals makes it possible to obtain a spatial map of the atmospheric constituents without having to perform mechanical scanning. It is shown that signal-to-noise ratios (SNRs) of above 10 dB can be achieved when using more than 1700 fireflies at an altitude of 1 km for a midlatitude summer clear night scenario. At half the altitude, 350 fireflies suffice to achieve the same SNR for the same environment.