CoMet 3.0 Tropics: HALO returns to Oberpfaffenhofen from Brazil following a successful measurement campaign

In these areas, due to the persistent dampness, hardly any oxygen reaches the soil. The microorganisms living there therefore break down dead plants without oxygen, producing methane (CH₄) in the process. This process is particularly efficient at high tropical temperatures. Wetlands are thus the Earth’s largest natural source of methane and represent the greatest uncertainty in global methane budgets.

Scientific leadership of the campaign was provided by the DLR Institute of Atmospheric Physics and the Brazilian Instituto Nacional de Pesquisas Espaciais (INPE, National Institute for Space Research). Also involved were the HALO partners from the Universities of Bremen and Heidelberg, as well as the Max-Planck-Institut für Biogeochemie in Jena. The campaign was further supported by the DLR Facility for Flight Experiments. In total, around 120 researchers from institutions in both countries were involved. In addition to Brazil, Bolivia also granted permission for measurement flights in its airspace.

Campaign highlights

The measurement flights carried out speak for themselves. During three flights over the Pantanal – one of the world’s largest inland wetlands, roughly half the size of Germany – the temporal evolution of greenhouse gas emissions at the start of the dry season was recorded. Four flights took place over Bolivian territory – a first for HALO – including two flights that detected exceptionally high concentrations of methane over the wetlands of the Llanos de Moxos. In addition, there were overflights of the Balbina Reservoir and the 325-metre-high ATTO(Amazon Tall Tower Observatory) measurement tower, a German-Brazilian project in the Brazilian rainforest, where continuous measurements of meteorological, chemical and biological data, as well as greenhouse gas concentrations, have been taking place since 2015.

Further measurements were taken over the Amazon, its delta region and the Mamirauá wetlands. Here, too, surprisingly high methane concentrations were measured in the boundary layer close to the ground. Near Santarém, on the Amazon, there is a European Space Agency (ESA) supersite (i.e. a comprehensively instrumented measurement site), which was flown over a total of three times.  The measurement programme was supplemented by overflights of pristine rainforest and by flying through several plumes of smoke from forest fires. Forest fires are also a significant source of greenhouse gases in the atmosphere. Overall, this resulted in an invaluable dataset for science, derived from both the remote-sensing and in-situ instruments on board HALO.

Reference data for satellite missions and climate models

A key objective of the campaign was to validate existing satellite missions and prepare for future ones aimed at monitoring greenhouse gases. These include the Franco-German climate mission MERLIN, the Copernicus Sentinel Expansion mission CO2M, Sentinel-5, and, amongst others, the Japanese greenhouse gas satellites GOSAT-2 and GOSAT-GW. Airborne measurements provide spatially high-resolution reference data for this purpose, particularly in the tropics, where ground-based and satellite-based observations are limited due to difficult-to-access terrain and heavy cloud cover. At the same time, the campaign aims to help distinguish methane emissions from natural sources (such as tropical wetlands) from those from anthropogenic sources (such as agriculture, waste management, energy production and forest fires), and to reduce the uncertainty in global methane estimates. The data will be analysed using regional inverse models as well as climate-chemistry models and will ultimately contribute to reporting (MRV) under the United Nations Framework Convention on Climate Change.

The unique CoMet payload was deployed on board HALO for this purpose. This included the CHARM-F lidar and an imaging spectrometer (MAMAP2D) for measuring the greenhouse gases CO₂ and CH₄ between the aircraft and the ground.  Both serve as airborne demonstrators for future satellite instruments. In addition, in-situ instruments were used to measure trace gases and atmospheric concentrations of CO₂, CH₄, CO and N₂O. In addition, a further remote-sensing instrument was used to measure NO₂, HONO and HCHO, alongside HALO’s upgraded baseline instrumentation and meteorological dropsondes. Individual flight segments were specifically routed over ground-based measuring stations such as ATTO and the Santarém Supersite, in order to link the aircraft measurements with long-term time series on the ground.

Collaboration