The Fine Resolution Explorer for Salinity Carbon and Hydrology (FReSCH) is a new mission
concept that was submitted to the 12th call of the Earth Explorers program in September 2023.
After the evaluation results published in April 2024, FReSCH was not selected to start a Phase 0
study but was labeled as a “commended mission” by the ESA Advisory Committee for Earth
Observation (ACEO). A number of remarks and recommendations were done by ACEO mainly
related to three points: (i) link of Mission Goal, Mission Objectives and Science Questions, (ii)
impact of land-sea contamination and auxiliary datasets’ uncertainties/availability to retrieve sea
surface salinity close the the coast and to land-ice interfaces, (iii) impact of uncertainties and
availability of input data to estimate the surface partial pressure of CO2.
The goal of this proposal in response to “FReSCH Pre-phase 0 Science Requirement
Consolidation” is to consolidate the scientific preparation of FReSCH taking into account ACEO’s
comments. It is structured in one management and three technical packages. The latter are
devoted to addressing the recommendations mentioned above. The first one will review the
FReSCH mission goals and objectives and will formulate specific science questions to be tackled
by FReSCH. This will be done using as reference the new ESA Earth Observation science strategy
published in 2024. The work will be done by the consortium members with the support of an
advisory board to ensure that a wide range of expertises is available. The second technical work
package is devoted to do a finer analysis of the impact of sea surface temperature and wind speed
data (uncertainties/availability) into fine resolution sea surface salinity retrievals close to the coast.
Synergies with other sensors such as Sentinel 3 and CIMR will be discussed. The land sea
contamination effect known from SMOS will be revisited with a two-fold innovative approach in
order to quantify the effect for an instrument such as FReSCH. The last technical package will
provide a literature review of physical and statistical methods to estimate pCO2 and a sensitivity
study of the most promising one to estimate pCO2 from space remote sensing observations. The
goal is to address the impact of the uncertainties in the input data into the pCO2 estimations to
assess the final error of the estimations close to the coast. The effect of missing input data for instance due to cloud coverage will also be discussed. Finally, a roadmap with plans for an optimal
campaign to acquire valuable data for pCO2 estimation from space will be discussed.