A compact QCL spectrometer for mobile, high-precision methane sensing aboard drones

Abstract

<jats:p>Abstract. A compact and lightweight mid-IR laser absorption spectrometer has been developed as mobile sensing platform for high-precision atmospheric methane measurements aboard small, unmanned aerial vehicles (UAVs). The instrument leverages on two recent innovations: a novel segmented circular multipass cell (SC-MPC) design and a power efficient, low-noise, intermittent continuous-wave (icw) laser driving approach. A system-on-chip hardware control and data acquisition system enables energy-efficient and fully autonomous operation. The integrated spectrometer weighs 2.1 kg (including battery) and consumes 18 W of electrical power, making it ideally suited for airborne monitoring applications. Under stable laboratory conditions, the device achieves a precision (1σ) of 1.1 ppb within 1 s and 0.1 ppb CH4 at 100 s averaging time. Detailed investigations were performed to identify and quantify the effects of various environmental factors, such as sudden changes in pressure, temperature, and mechanical vibrations, which commonly influence UAV mounted sensors. The instrument was also deployed in two feasibility field-studies: an artificial methane release experiment as well as a study on vertical profiles in the planetary boundary layer. In both cases, the spectrometer demonstrated its airborne capability of capturing subtle and/or sudden changes in atmospheric CH4 mole fractions and providing real-time data at 1 s time resolution. </jats:p>

Compact and Lightweight Mid-IR Laser Spectrometer for Balloon-borne Water Vapor Measurements in the UTLS

“…This enables a compact setup, increases the mechanical stability, and reduces the optical path outside the sampling volume. These features are of general importance for mobile laser spectrometers, as illustrated by Tuzson et al (2020) for drone based methane detection.…”

“…This partly open source hardware features a field programmable gate array (FPGA) and a microcontroller unit (MCU) running a GNU/Linux operating system. The FPGA on Red Pitaya has been reconfigured to provide the functionalities for high-resolution absorption spectroscopy (Liu et al, 2018;Tuzson et al, 2020).…”

1/f Noise Characteristics of Waveguide-Integrated PbTe MIR Detectors and Impact on Limit of Detection

“…PbTe films have successfully been used in waveguide-integrated detectors for on-chip gas sensors [11,12], important for applications in industry, environment and homeland security. The well-known trend of Internet of Things (IoT) and the newer Internet of Everything (IoE) are expected to boost their use and lead to integrated, compact, low power consumption and connected solutions [13].…”

Cavity Ring-Down Methane Sensor for Small Unmanned Aerial Systems

“…Other recent sensors combine low mass (<~5 kg), low power (<~30 W), and high sensitivity (<~0.1 ppm), making them better suited to sUAS deployment [17][18][19][20][21][22]. Zondlo and collaborators have demonstrated compact laser sensors (meeting these specifications) based on wavelength modulation spectroscopy (WMS) with Herriot cells for use on both fixed-wing and hexacopter sUAS [17,18].…”

“…Another group reports a compact laser sensor integrated to a fixed wing sUAS though noise in the flight-data called for detection thresholds in the 0.3-1 ppm range [20,21]. The sensor we present herein uses a different spectroscopy technique but is most similar, in broad attributes, to this class of (point-measurement) laser absorption sensors (i.e., [17][18][19][20][21][22]). Similar laser techniques can be applied, also in compact packages, in backscatter configurations where the beam is directed out of the sUAS sensor to a hard target from which scattered light is collected (with a detector on the sensor).…”