Cavity RingDown Methane Sensor for Small Unmanned Aerial Systems We present the development, integration, and testing of an openpath cavity ringdown spectroscopy (CRDS) methane sensor for deployment on small unmanned aerial systems (sUAS). The openpath configuration used here (without pump or flowcell) enables a low mass (4 kg) and low power (12 W) instrument that can be readily integrated to sUAS, defined here as having allup mass of u003c25 kg. The instrument uses a compact telecom style laser at 1651 nm (nearinfrared) and a linear 2mirror highfinesse cavity. We show test results of flying the sensor on a DJI Matrice 600 hexacopter sUAS. The high sensitivity of the CRDS method allows sensitive methane detection with a precision of 10xe2x80x9330 ppb demonstrated for actual flight conditions. A controlled release setup, where known mass flows are delivered, was used to simulate pointsource methane emissions. Examples of methane plume detection from flight tests suggest that isolated plumes from sources with a mass flow as low as 0.005 gs can be detected. The sUAS sensor should have utility for emissions monitoring and quantification from natural gas infrastructure. To the best of our knowledge, it is also the first CRDS sensor directly deployed onboard an sUAS.

A WideRange and CalibrationFree Spectrometer Which Combines Wavelength Modulation and Direct Absorption Spectroscopy with Cavity Ringdown Spectroscopy A widerange, calibrationfree tunable diode laser spectrometer is established by combining wavelength modulation and direct absorption spectroscopy (WMDAS) with continuous wave cavity ringdown spectroscopy (CWCRDS). This spectrometer combines the benefits of absolute concentration measurements, wide range, and high speed, using WMDAS with enhanced noise reduction in CWCRDS. The accurate baseline ringdown time, xcfx840, is calculated by the absorption peak (measured by WMDAS) and the ringdown time containing gas absorption information (measured by CWCRDS at the center wavelength of the spectral line). The gas concentration is obtained without measuring xcfx840 in real time, thus, greatly improving the measuring speed. A WMDASCWCRDS spectrometer at 1.57 xcexbcm for CO detection was assembled for experimental validation of the multiplexing scheme over a concentration ranging from 4 ppm to 1.09% (0.1 MPa, 298 K). The measured concentration of CO at 6374.406 cmxe2x88x921 shows that the dynamic range of this tunable diode laser absorption spectrometer is extendable up to five orders of magnitude and the corresponding precision is improved. The measurement speed of this spectrometer can extend up to 10 ms, and the detection limit can reach 35 ppb within 25 s.