Evaluation of a Remote Sensing Instrument Suite to Measure Gas Columns from a Mobile Laboratory

Abstract:

An innovative suite of remote sensing instruments has been deployed in a mobile laboratory to conduct column measurements. A mobile solar tracker is simultaneously coupled to a Fourier Transform Infrared Spectrometer (FTS) and a UV-Vis Spectrometer allowing to measure ammonia (NH₃), ethane (C₂H₆), formaldehyde and nitrogen dioxide (NO₂) along the direct solar beam. The fast scanning mobile solar tracker contains a motion compensation system and imaging feedback loop making it possible to operate autonomously and to track the sun at high precision; 0.052° has been verified comparing quantitatively the column measurements of NO₂ from the UV-Vis spectrometer with measurements from the Multi Axis Differential Optical Absorption Spectrometer (MAX-DOAS), the third remote sensing instrument deployed in the mobile laboratory. The solar tracker enables direct sun observations providing high photon flux such that the FTS and UV-Vis spectrometer measure at high temporal resolution of 2 seconds. Driving the mobile lab yields high spatial resolution. The suite of remote sensing instruments aboard the mobile laboratory allows quantifying emissions applying the Solar Occultation Flux method. This method applied to the column measurements is complementary to in-situ observations in obtaining trace gas fluxes and eventually trace gas production rates from a source when driving around or upwind and downwind of that target source. This presentation characterizes the FTS by comparing it with a high resolution FTS at the National Center for Atmospheric Research, and describes the first application to measurements of NH₃ emissions from agricultural sources and C₂H₆ emissions from oil and natural gas.