To achieve this, a characterisation of each sensor's performance will first be made, including an analysis of the best available retrieval algorithms. Data-merging methods starting from both radiance and derived bulk properties (such as surface chlorophyll concentration) will be tested. The final choice of which merging algorithm to implement will be made following an algorithm intercomparison and trade-off analysis. A thorough validation of the final products against in-situ measurements will be performed following well defined protocols, such as those developed and demonstrated under the SIMBIOS programme. To show the potential for supporting operational oceanography, the data merging system developed will be used to provide a demonstration global NRT ocean colour service based on ENVISAT/MERIS and AQUA/MODIS.