A compact, fast-response synchronous measurement of temperature for UAV applications

We report a compact, portable, low power tunable diode laser based sensor for a fast, non-intrusive measurement of temperature on airborne-based vehicles. The proposed sensor design avoids common problems in existing sensors such as adiabatic compression of the ambient airstream, thermal inertia of the sensing element, and impinging cloud particles. These effects are quite common in the conventional temperature sensors used in most aerial vehicles for ambient temperature measurements. The molecular oxygen transitions are measured using a 765 nm wavelength range vertical cavity surface emitting laser in the spectral region of two closely spaced oxygen transitions, centered at 13069.95 cm ^-1 and 13068.07 cm^-1 respectively, according to HITRAN database. Another advantage of the proposed sensor design is that it can simultaneously detect additional trace gas species along with in-situ temperature measurements. For example, in this design we detect carbon dioxide concentration using a 2000 nm wavelength laser. The two laser beams are co-aligned and coupled into a single 20 cm multipass cell. The absorption signal (from both carbon-dioxide and oxygen) was detected simultaneously on a 2 micron photodetector. Second harmonic (Nf, N=2) detection, using wavelength modulation spectroscopy was employed to enhance the sensitivity of measurements. The sensor can readily be miniaturized and consumes less than 2 W of power, ideal for use of unmanned aerial systems and other airborne platforms.