NIWA is developing the capability to utilize satellite measurements of greenhouse gases to retrieve their surface sources, within a regional framework. One component of the retrieval is the modelling of the trace gas distribution given an estimated or a priori distribution of surface emissions (the 'forward model').

An example of this technique is the retrieval of methane sources from the New Zealand region. This is a particularly interesting example as New Zealand has a large ruminant livestock population, thus methane is an important component of New Zealand's greenhouse gas inventory. Further, New Zealand is a relatively isolated source, aiding the retrieval.

The transport of methane within the atmosphere is simulated using the New Zealand Limited Area Model (NZLAM), a detailed regional model which takes meteorological input from the NZLAM variational (VAR) assimilation suite. No methane chemistry is included in the model due to the long lifetime of tropospheric methane relative to the residence time of air within the model domain.

Results from the model are studied to determine the predicted total and partial column enhancements due to the estimated source, measured relative to the background methane field. The dynamical residence time is quantified. The time averaged spatial distributions of the column enhancements and the sensitivity of the column enhancements to the emission distribution have also been investigated. The results will be discussed in relation to the predicted accuracy of satellite instruments designed to measure methane.