## 6 Conclusions and Outlook
\begin{table}
\begin{tabular}{p{85.4 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Element** & **Readiness** & **Comments** \\ \hline RTM and Intercomparison & 3/5 & Inter-comparisons of retrieval algorithms are recommended for quantifying cross-mission biases as well as for better assessing the discrepancies due to inconsistent variable definition (e.g., green Vs. total fAPAR) [IDN-25]. \\ \hline FRM and supersites & 3/5 & FRM4 VEG and CEOS-LPV supersites are the essential first step. Yet, there is a need to move towards sustained operations of permanent FRM sites [IDN-21]. In the Copernicus domain, there is a lack of an integrated solution to support Cal/Val needs of current and future missions [IDN-19, IDN-20]. \\ \hline Protocols & 3/5 & Community-endorsed protocols have recently been published by CEOS-LPV for key ECVs, e.g., LST, Albedo, Soil moisture. However, there is a lack of protocols for SR, fAPAR and phenology [IDN-22] and a need to update and maintain protocols to keep pace with science and technological evolutions [IDN-23]. This is currently on-going work within CEOS-LPV. \\ \hline Networks & 2/5 & A large number of regional and continental networks are currently available. However, the majority of them were not primarily designed for Cal/Val purposes. There is a need to embed Cal/Val practices across these networks and work towards harmonisation [IDN-15, IDN-16, IDN-17]. The MM concept, as in GAIA-CLIM, can facilitate network interoperability. Though, some gaps remain in terms of geographical coverage [IDN-13, IDN-14], and there is a need to ensure sustainability in the long-term [IDN-18]. \\ \hline Ad-hoc campaigns & 3/5 & There is a deluge of Cal/Val data acquired as part of ad-hoc campaigns and new devices are being tested, in particular UAV-based. Yet, the accuracy of these new methods needs to be properly assessed [IDN-24]. \\ \hline Database and Tools & 2/5 & There is an urgent need to upgrade and secure maintenance of the OLIVE tool [175] and update the used reference database [IDN-27, IDN-28]. Overall, there is an urgent need to enhance the discoverability and accessibility of Cal/Val data following FAIR guiding principles [IDN-26] and of a dedicated cloud-based platform for land Cal/Val [IDN-29]. \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Readiness level for L2 bio-geophysical data with references to needs identified in Table 4.  
The general approach to Cal/Val was finally presented, which is based on a set of building blocks. The application of this framework and the detailed recommendations gathered during past Cal/Val Workshops will allow to shape ESA Cal/Val strategy for land in the coming years, addressing the gaps with an integrated solution. The longer-term objective is to pave the way for enhanced interoperability among current and future ESA/Copernicus land imaging sensors for the benefit of land applications. The concept, methodology and design originate from [PERSON] and [PERSON]. The writing of the paper was led by [PERSON] All authors contributed in the writing and revision, specifically for their relevant area of expertise and responsibility. [PERSON] is the Head of the ESA Sensor Performance, Products and Algorithm Section (SPPA), [PERSON] and [PERSON] are the ESA Data Quality and Cal/Val managers respectively of the S2 and S3 missions, [PERSON] is the ESA S2 Mission Manager, [PERSON] is leading the IDEAS-QA4 EO Cal/Val framework and oversees the Proba-V Data Quality and Cal/Val activities, [PERSON] and [PERSON] support the Cal/Val activities of S2 and S3 missions, [PERSON] contributes to the CHIME mission science and Cal/Val requirements definition, [PERSON] coordinates the ACIX and CMIX activities. All authors have read and agreed on the published version of the manuscript. The writing and editing of this overview paper was carried out as part of the ESA-funded Quality Assurance for Earth Observation (IDEAS-QA4 EO) framework contract.