Note: The FCDR should be stabilised, which means it should be harmonised or otherwise improved so as to maximise observational stability. Harmonisation is the recalibration of the sensor observations, using a stated reference and/or overlaps with other sensors in the series. The purpose of the recalibration is to bring consistency between sensors given the known (best estimate) differences in instrument characteristics (e.g., spectral response functions) between sensors. A harmonised (or otherwise stabilised) FCDR should enable more stable CDRs to be derived. The word stabilised in the definition should be considered to encompass this technical definition.  Other approaches may be valid such as homogenisation.