Abstract
Sea surface temperature is an essential variable for oceanography, meteorology, and climatology. In situ and satellite observations are used together in creating products that meet the requirements for both near-real-time and retrospective, consistent data sets. In situ measurements, particularly those of drifting buoys and moorings, are used to validate satellite sea surface temperature retrievals, and in some cases are also used to define those retrievals. The validation strategy should have clear objectives and be designed accordingly. A checklist of eight aspects to consider in designing a validation strategy is discussed, the question of independence being particularly crucial. Validation can and should assess both the retrieval characteristics and the uncertainty model attributed to the retrieval. The other usage of in situ data is in blending with satellite information to create higher level products, such as gap-filled analyses of sea surface temperature. While daily analyses are typical, the scope for capturing subdaily variability is discussed. For product validation, particularly of blended analyses, we emphasize the value of producers reserving an agreed set of in situ data; this is to help drive real reductions in product uncertainty to meet the more stringent emerging requirements for sea surface temperature observation in the context of coupled weather and climate models.