CHARM-F: A New Airborne Lidar for the Measurement of Methane and Carbon Dioxide – a Demonstrator for MERLIN

Abstract

CHARM-F is a new four-wavelengths lidar for simultaneous soundings of atmospheric CO2 and CH4. It is designed for the use onboard the German research aircraft HALO. Due to the high technological conformity, it also serves as a demonstrator for MERLIN, the French-German satellite mission carrying a methane lidar. MERLIN’s Preliminary Design Review was successfully passed recently. The launch is planned for 2020. Due to HALO’s maximum flight altitude of 15 km and special features of the airborne lidar, such as a relatively large laser ground spot, the resulting data are similar to those obtained by a spaceborne system. Both, the CHARM-F and the MERLIN lidars are designed in the IPDA (integrated path differential absorption) configuration using short double pulses, which gives column averaged gas mixing ratios between the system and ground. A first CHARM-F measurement campaign on HALO was performed in spring 2015. The focus of the flights was on the completion of the airworthiness certification, technical tests and the collection of first data. The campaign was very successful and a valuable dataset was obtained. First results will be presented. One main application of the data is the support of the retrieval algorithm development for MERLIN. Further goals are to study general measurement sensitivities and system design details. Since the IPDA lidar methodology is still a new approach, there is need to improve the knowledge about details in the system design and in performance questions. The assessment of the instrument performance is supported by another instrument, which was onboard during the flight campaign: a cavity ring down spectrometer, providing in-situ data of carbon dioxide, methane and water vapor with high accuracy and precision. This configuration is ideal for validating the lidar data. For the near future, more detailed characterizations of CHARM-F are planned, the continuation of the support of MERLIN, as well as the preparation of the scientific aircraft campaign CoMet (2017).