SeNtInel 5P validaTion by Comet HALO

Kurzfassung

The goal of the proposed activity is the validation of the methane column of S5P using aircraft measurements. The airborne platform foreseen is the German research aircraft HALO. A dedicated HALO science mission that is focused on the measurement of methane (and carbon dioxide), dubbed CoMet, has been evaluated by the scientific steering committee of HALO and is now scheduled for the 1st half of 2017. In order to maximize gain, the team proposes to make use of the gathered data from this campaign. For CoMet the aircraft will be equipped with a unique payload consisting of a suite of the most sophisticated instruments currently available to measure atmospheric carbon dioxide and methane. Remote sensing instruments, both active and passive, will be complemented by in-situ sensors to obtain maximum synergy. Therefore, this approach can to a significant extent make use of resources already planned to answer the long-term validation needs (phase E2) of S5P. Concerning active remote sensing, the Integrated Path Differential Absorption (IPDA) lidar technique using hard target reflection from the Earth’s surface in the near IR (1.64 µm) has been identified in the last few years to measure the column averaged dry air mixing ratio of CH4 (and CO2) and high accuracy and low bias. As a passive remote sensing instrument, the MAMAP2D airborne spectrometer system capable of direct and quantitative remote column-averaged measurements of atmospheric CH4 (and CO2) complements the payload. This instrument measures reflected and scattered solar radiation in the short wave infrared (SWIR) and near-infrared (NIR) parts of the electro-magnetic spectrum. In order to validate the remote sensing instruments and provide the best possible greenhouse gas profile information, the most sophisticated in-situ instruments to measure CH4 (and CO2) currently available based on cavity-ringdown spectrometry (CRDS) will complement the core payload. Also part of this in-situ package is a flask sampler which will collect air samples for subsequent laboratory analysis and thus provide supplemental information on isotopic composition and other tracers correlated with the emission of GHGs. The above listed instruments are complemented by mini-DOAS which is capable of providing another independent method to measure the greenhouse gases and the aircraft’s basis measurements system. The latter will provide precise and quality-assured data of temperature, pressure, and humidity as well as aircraft position and attitude which are required to retrieve the dry-air columnar information. The CoMet mission will take place in the European air space. Due to HALO’s long range capability, gradients can be precisely captured up to sub-continental scales. It is planned to fly over TCCON sites to validate the TCCON CH4 column against the columns retrieved from aircraft. The flight strategy also foresees flights along forecasted CH4 gradients and over methane hotspots like hard coal mining areas. For S5P validation there is much prospect to synchronize the scientific flights with overflight from S5P. Currently a total of 40-60 flight hours are planned. There is hope that additional funding for flight hours specially dedicated to underfly the satellite can be allocated on the basis of this proposal. It should be mentioned that one of the overarching goals of CoMet is to answer the question whether this payload is an adequate tool to validate future greenhouse gas satellites (e.g. MERLIN, CarbonSat) that will provide even a better accuracy than S5P. One of the CoMet components is to provide important remote sensing and in-situ data information for the inverse modelling approach for regional budgeting of methane fluxes. The S5P validation effort will equally benefit from this activity. For further information on CoMet, a White Paper is available on request.