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Mini-DOAS measurements during the HALO Southtrac mission in fall 2019

Subject Area Atmospheric Science
Term from 2019 to 2022
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 423217792
 
Final Report Year 2022

Final Report Abstract

Within the framework of the SPP-1294 phase II, the novel mini-DOAS (Differential Optical Absorption Spectroscopy) instrument was successfully deployed and operated on the HALO aircraft the SouthTRAC mission in fall 2019. Re-occurring data transmission problems of the aircraft’s Basis HALO Measurement and Sensor System (Bahamas) to correctly submit on-line data to our instrument in real-time (i.e., the clock, and the aircraft’s location and attitude data, all of which are necessary to command the instrument and in particular limb receiving telescopes and to identify the measured data) led us to a refinement of the mini-DOAS instrument in summer 2019. Thereby a new ARINC (Aeronautical Radio Incorporated) input port was added to our electronics and directly connected to aircrafts avionics, from which the relevant data of the aircraft (e.g., the GPS clock, 3-D location, and attitude) could directly be received and processed in real-time. This novel complementary data connection, in addition to earlier refinements, improved the operational availability of the HALO instrument to nearly 100% (from previously 90 – 95%). To this end, the instrument successfully collected data in about 686 flight hours, corresponding to 122,592 (UV) and 483,837 (visible) skylight limb spectra during the previous mission. Significant progress has been made within the present project to develop suitable retrieval methods, tools and software to infer absolute concentrations from the remotely sensed quantities (i.e., mostly slant column amounts of the targeted species) from the air-borne UV/vis/nearIR limb measurements under all skies. These include (a) a versatile radiative transfer Monte Carlo model (McArtim) with which Jacobian (and Hesse) matrices can be calculated, (b) a novel Mie scattering code based on Green's dyadic technique (GDT) matrix approach with which the light scattering of irregular shaped solid small particles (c.f. cirrus ice particles) can be calculated to a high accuracy, and (c) an inversion code and scaling method to infer absolute concentrations at flight level of the targeted species from the limb measurements. To date 70% to 80% of the measured limb and ~20% of the nadir data have been finally processed and the retrieved concentrations of the targeted gases (O3, O4, SO2, NO2, HONO, BrO, IO, OClO, CH2O, C2H2O2 and CH3H4O2*) are stored on the HALO data base ( https://halo-db.pa.op.dlr.de/data_source/65 ). A small fraction (25% - 33%) of the processed data could already be interpreted and partly disseminated in the peer reviewed literature. The processed data within the present project will also contribute to the WMO/UNEP (2022) assessment of stratospheric ozone. For her PhD study Dr. Rotermund also received the ‘Umweltpreis der Viktor und Sigrid Dulger Stiftung‘ for the year 2020. The preliminary work mostly conducted within bachelor and master thesis as well as those arising from the past PhD studies provide strong evidence that the mini-DOAS data set collected during the 11 HALO missions since 2012 to which we contributed contain much more valuable scientific information to be exploited.

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