Total Column Water Vapor for Sentinel-4, 5 and 5p Towards a Climate Data Record

Gaseous water exhibits significantly greater spatiotemporal variability than other major greenhouse gases, such as carbon dioxide and methane. Consequently, satellite-based global monitoring of atmospheric water vapour is an essential methodology for elucidating its climate impacts at regional and global scales over timescales ranging from short to multidecadal. To track water vapour, total column measurements are derived from satellite observations of reflected solar radiation within the UV-VIS spectral region centred at 440 nm. This water vapour absorption band is an alternative to the conventional NIR band centred at 648 nm. The advantage of this band is that it is detectable across all European Sentinel platforms and their predecessor instruments, such as GOME on ERS-2, SCIAMACHY on Envisat and GOME-2 on MetOp-A/B/C, as well as future instruments, e.g. CO2M.
This work presents recent advancements in the application of differential optical absorption spectroscopy (DOAS) to geostationary Sentinel-4 and polar-orbiting Sentinel-5P observations. This work serves as preparatory research for future implementations with the polar-orbiting Sentinel-5 mission.
The retrieval methodology has several advantages over existing sensing techniques: (1) optimal sensitivity and coverage characteristics across both terrestrial and oceanic domains; (2) enhanced spatial resolution and temporal sampling frequency, particularly for European observations via Sentinel-4, which improves weather forecasting, scientific product development, air quality assessment and environmental policy applications; and (3) the continuous extension of long-term datasets starting with GOME-type sensors, which is crucial for regional and global climate modelling. This naturally introduces the possibility of creating a homogeneous climate data record since 1995.