By means of the ground-based, airborne and satellite GHG emissions will be analysed. The impact of GHG emissions depends on various sources with different locations, magnitudes, timing, and composition. Bottom-up methods based on process-based or bookkeeping models for natural and anthropogenic fluxes, on a combination of activity data and emission factors (in the case of inventories) are often considered the best way to account for all of these sources and their attributes together.

Opportunities to conduct observation-based assessments are crucial to assess both top-down atmospheric inversions, bottom-up inventories and evaluate model performance. Such assessments are difficult to achieve purely from the ground since surface measurements.

Atmospheric inversions can help for the quality control of national GHG inventory reports. IPCC encourages Parties to verify reported emissions against independent source of information, to promote transparency and align emissions reporting with real-world conditions. However, their accuracy also depends on the surface in-situ network density (very little to no station in tropics).

GHG budgets that use both top-down and bottom-up methodologies are complementary because to some extent, the difference between the two approaches can be used to quantify uncertainties, which can then be used to identify sectoral emission sources or sinks for further detailed observation and understanding.

There is a strong potential to develop atmospheric inversions with higher spatial resolution for quality control of inventories and it requires more accurate spatial maps of emissions from inventories (priors). The airborne observations can make a unique and valuable contribution to observation-based emissions assessments.