Stratospheric-trace-gas-profile retrievals from balloon-borne limb imaging of mid-infrared emission spectra

<p>The Limb Imaging Fourier Transform Spectrometer Experiment (LIFE) instrument is a balloon-borne prototype of a satellite instrument designed to take vertical images of atmospheric limb emission spectra in the 700–1400 <span class="inline-formula">cm</span><span class="inline-formula">⁻¹</span> wavenumber range from the upper-troposphere–lower-stratosphere (UTLS) altitude region of the atmosphere. The prototype builds on the success of past and existing instruments while reducing the complexity of the imaging design. This paper details the results of a demonstration flight on a stabilized stratospheric balloon gondola from Timmins, Canada, in August 2019. Retrievals of vertical trace gas profiles for the important greenhouse gases <span class="inline-formula">H₂O</span>, <span class="inline-formula">O₃</span>, <span class="inline-formula">CH₄</span>, and <span class="inline-formula">N₂O</span>, as well as <span class="inline-formula">HNO₃</span>, are performed using an optimal estimation approach and the SASKTRAN radiative transfer model. The retrieved profiles are compared to approximately coincident observations made by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) solar occultation and Microwave Limb Sounder (MLS) instruments. An evaluation of the LIFE measurements is performed, and areas of improvement are identified. This work increases the overall technical readiness of the approach for future balloon, aircraft, and space applications.</p>