It can be thought of as a laser radar. The Doppler effect was discovered in 1842 by an Austrian Physicist named Christian Doppler. By comparing the incoming and outgoing laser pulses, you can determine the magnitude of the Doppler shift, and convert this into a velocity number.
Molecules are very small when compared to aerosols.
Aerosols actually help improve the accuracy of the velocity measurements. In addition, aerosols deteriorate the temperature and density measurements since they do not behave as air molecules. For this reason, it is critical to separate the aerosol signal from the molecular signal, and analyze each separately. Then a very high degree of accuracy can be obtained for all measurements including velocity, temperature, density, and pressure. A Fabry-Perot etalon is an optical filtering device.