Cloud top pressure retrievals from Sentinel 3 OLCI as a proxy for the future PACE OCI

The Ocean Colour Instrument (OCI) on the future NASA Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission will extend and improve on various surface and atmospheric data records available from current and historical satellite missions. Previous passive spaceborne sensors have, in most cases, used thermal infrared techniques to retrieve cloud altitude. OCI will lack these bands, although will sample O2 absorption features that are sensitive to aerosol/cloud altitude. In advance of the launch of the PACE observatory (in 2023-2024) it is desirable to have a data processing stream in place and tested with real satellite measurements from some suitable proxy. We have therefore developed a cloud top pressure retrieval based on measurements from the Ocean and Land Colour Instrument (OLCI) flying on the Sentinel 3 satellites, which has similar spatial resolution and measurement capabilities in the O2 A-band to OCI. In this presentation we illustrate the status of and plans for this algorithm, using simulated OCI measurements and real OLCI data, the latter validated against ground-based observations of cloud top height.