How well can MethaneSAT detect and quantify pastoral agricultural emissions?

MethaneSAT is a joint American and New Zealand satellite mission, which involves partnership between the Environmental Defense Fund (EDF), MethaneSAT LLC and New Zealand government. MethaneSAT’s primary mission is to detect and quantify methane (CH₄) emissions from both point and area sources from the global oil and gas production industry in support of emissions reductions. MethaneSAT will target specific 200 km x 200 km regions and map CH₄ within those regions at 100 m x 400 m resolution with unprecedented precision. The Aotearoa New Zealand team’s aim is to develop and test the ability of the satellite to detect agricultural CH₄ emissions. New Zealand is an ideal place to develop this capability due to its large CH₄ emissions, 85% of which are from agricultural sources. We will present results of modelled atmospheric CH₄ concentrations for agricultural targets in New Zealand, emission estimates from the agricultural targets and CH₄ measurements collected during a shakedown field campaign, in preparation for the MethaneSAT launch in 2024.

We use 1.5 km spatial resolution, New Zealand specific bottom-up CH₄ fluxes and the Numerical Atmospheric dispersion Modelling Environment (NAME III), driven by meteorological input from the New Zealand Convective Scale Model (NZCSM, 1.5 km spatial resolution) Numerical Weather Prediction (NWP) model to create modelled agricultural XCH₄ (column averaged) enhancements. The MethaneSAT-like targets are created for different scenarios to assess the changes in the XCH₄ enhancements relative to meteorological conditions and bottom-up fluxes. We use the modelled agricultural XCH₄ fields to test operational methods that are being developed for Level 4 products (i.e., emissions) in an Observing System Simulation Experiments (OSSE) framework and adapt them for diffuse agricultural sources. We will present results of modelled XCH₄ scans for the main agricultural targets across New Zealand and the application of the MethaneSAT Level 4 methods (i.e., Geostatistical Inversion Framework, Divergence Integral Method) for agricultural sources.

The 2023 New Zealand MethaneSAT pre-launch shakedown field campaign took place over ten days in Waikato, a region with New Zealand’s strongest agricultural CH₄ emissions. The campaign involved the deployment of two EM27/SUN portable spectrometers and in situ CH₄ samplers. One EM27/SUN was at a fixed location for the duration of the campaign, while the second instrument was positioned up or downwind to measure enhancements of XCH₄. Four remote sites were used, with measurements collected on multiple occasions and under different meteorological conditions. Typical XCH₄ enhancements of between 3 and 8 ppb were observed while side-by-side measurements with the two spectrometers yielded a minimum detection limit of 0.3 ppb. Ground based and airborne in situ measurements were also collected to provide additional context to the measured enhancements. The measured XCH₄ enhancements aligned with agricultural XCH₄ estimates from the modelling framework.