The purpose of this document is to advance and define requirements for the eLTER RI to be able to serve validation processes of the major Earth Observation (EO) data providers. The document describe the general requirements for in-situ data and identified current eLTER Standard Observations (SOs) that are mostly needed in the calibration and validation processes of the main EO data providers. The docume give a view to the current validation protocols and tools used in the cal/val processes as well as described a framework to evaluate the maturity of in-situ observations for EO validation. Finally, key steps for the eLTER RI required to develop research infrastructure activities to be able serve these validation processes are identified