The DLR QCL/ICL spectrometer is based on cutting-edge quantum cascade and interband cascade laser technology. It allows for airborne in-situ observation of important greenhouse and other trace gases in the Earth’s lower atmosphere. In its current configuration the instrument is capable of measuring ultra-low concentrations of methane (CH4), ethane (C2H6), carbon dioxide (CO2), carbon monoxide (CO) and nitrous oxide (N2O) at ppb-scale sensitivity (e.g. it can detect a single particle out of 1000 million particles) at up to 3 measurements per second. To this end, a downstream vacuum pump pulls sample air from outside of the aircraft into a measurement cavity. Inside the cavity, a wavelength-modulated laser is reflected approx. 400x between two gold coated mirrors. Thereby the gases to be quantified absorb a wavelength-dependent part of the laser light, proportional to its concentration in the cavity.
DLR’s QCLS instrument: central measurement module (left), and (right) configuration with peripherals in an aircraft rack (Figures: CC-BY4.0 J. Kostinek, DLR)
The instrument was first deployed in late summer 2017 during the ACT-America field campaign aboard a NASA C-130 aircraft, where it provided valuable information on ethane concentrations above the Eastern and Central U.S.. For the CoMet mission in summer 2018 it was deployed aboard the DLR Cessna 208B for quantifying methane emissions from the Upper Silesian coal basin – one of Europe’s emission hot spots. Currently, the DLR QCLS is being adapted to add several isotopes to the portfolio of measureable species.
NASA’s C130 research aircraft, where the DLR-QCLS was first deployed (Photo: CC-BY4.0 J. Kostinek, DLR)