A TRUE AIRSPEED INDICATOR BASED ON DOPPLER SHIFTED MOLECULAR LASER BACKSCATTER

AN INVESTIGATION OF TWO METHODS OF USING DOPPLER SHIFTED MOLECULAR BACKSCATTER TO MEASURE AN AIRCRAFT'S TRUE AIRSPEED IS PROPOSED. BECAUSE AEROSOL BACKSCATTER AT HIGH ALTITUDE IS SO SMALL, ITS USEFULNESS IN MEASURING AIRSPEED IS SERIOUSLY DOUBTFUL. QUANTUM-LINE RESONANT (NON-RAYLEIGH) MOLECULAR BACKSCATTER ON THE OTHER HAND IS SEVERAL ORDERS OF MAGNITUDE STRONGER. THE FIRST METHOD WE PROPOSE WOULD USE GAS CORRELATION SPECTROSCOPY TO DETECT A SMALL DOPPLER SHIFT IN A BROAD CO2 EMISSION LINE. THIS METHOD DOES NOT REQUIRE SPATIAL OR TEMPORAL COHERENCE BETWEEN THE EMITTED LIGHT AND RECEIVED SIGNAL. THE SECOND METHOD WE PROPOSE FOR MEASURING MOLECULAR DOPPLER SHIFT IS TO COUNT ZERO CROSSINGS IN A RETURN SIGNAL AFTER IT HAS BEEN HETERODYNED WITH A REFERENCE LASER BEAM. THIS METHOD HAS THE POTENTIAL FOR MAKING VERY ACCURATE AIRCRAFT TRUE AIRSPEED MEASUREMENTS. THE PROPOSED EFFORT WILL INVESTIGATE THE RELATIVE ADVANTAGES OF THESE TWO TECHNIQUES. THIS INVESTIGATION WILL CONSIDER THE REALISTIC INTERFERENCES FROM FOG, CLOUD AND OTHER WEATHER-RELATED EFFECTS. A PRELIMINARY PHASE II PROOF-OF-FEASIBILITY HARDWARE DESIGN WILL BE COMPLETED FOR THE SUPERIOU TECHNIQUE.