Half a century of satellite remote sensing of sea-surface temperature

Sea-surface temperature (SST) was one of the first ocean variables to be studied from earth observation satellites. Pioneering images from infrared scanning radiometers revealed the complexity of the surface temperature fields, but these were derived from radiance measurements at orbital heights and included the effects of the intervening atmosphere. Corrections for the effects of the atmosphere to make quantitative estimates of the SST became possible when radiometers with multiple infrared channels were deployed in 1979. At the same time, imaging microwave radiometers with SST capabilities were also flown. Since then, SST has been derived from infrared and microwave radiometers on polar orbiting satellites and from infrared radiometers on geostationary spacecraft. As the performances of satellite radiometers and SST retrieval algorithms improved, accurate, global, high resolution, frequently sampled SST fields became fundamental to many research and operational activities. Here we provide an overview of the physics of the derivation of SST and the history of the development of satellite instruments over half a century. As demonstrated accuracies increased, they stimulated scientific research into the oceans, the coupled ocean-atmosphere system and the climate. We provide brief overviews of the development of some applications, including the feasibility of generating Climate Data Records. We summarize the important role of the Group for High Resolution SST (GHRSST) in providing a forum for scientists and operational practitioners to discuss problems and results, and to help coordinate activities world-wide, including alignment of data formatting and protocols and research. The challenges of burgeoning data volumes, data distribution and analysis have benefited from simultaneous progress in computing power, high capacity storage, and communications over the Internet, so we summarize the development and current capabilities of data archives. We conclude with an outlook of developments anticipated in the next decade or so

Influence of the oceanic cool skin layer on global air–sea CO2 flux estimates

The global oceans are a major sink for atmospheric CO2, but the magnitude of this sink is still under question since there are many uncertainties inherent in determining global CO2 fluxes across the air–sea interface. The sign and magnitude of the air–sea fluxes show significant regional and seasonal variation. The gas transfer variables necessary to determine air–sea CO2 fluxes are temperature dependent and studies of global CO2 fluxes commonly rely on measurements of the sub-surface oceanic mixed layer temperature, rather than the cooler skin temperature for these calculations. This surface skin temperature is, on average, about 0.2K cooler than that of the mixed layer, leading to underestimates of oceanic CO2 uptake when the mixed layer temperature is used for calculations. This study explores the impact, upon both the global annual mean, and as seasonal global distributions, of replacing a mixed layer temperature measurement with a skin temperature measurement to improve global estimates of air–sea CO2 exchange, making use of extensive satellite and in situ measurements. Resulting estimates show, contrary to previous studies, that the contribution of the cool skin is relatively minor on a global scale, suggesting that calculations can confidently continue to move forward in refining estimates and monitoring air–sea CO2 exchange from remotely sensed parameters, providing better resolution both in time and space in future studies. •We improve estimates of global CO2 fluxes by replacing Tdepth with SSTskin.•We utilize improved parameterizations of the SSTskin–Tdepth temperature difference.•We use more realistic probabilistic representation of the global wind field.•Satellite derived temperature can be confidently used over ship based observations