This Volume collects a series of key-note lectures delivered at the fourth "Oceans from Space" Symposium, held in Venice, Italy, in 2010. The revisited postscript in the title identifies it as the ideal follow-up of the legendary Oceanography from Space, edited by J.F.R. Gower and published in 1980, following the very first edition of "Oceans from Space." This series of conferences, which are held every 10 years only, is designed as a periodical state-of-the-art review of satellite oceanography, providing both an outline of current research, as well as a forum to debate topical issues. The "Oceans from Space" Venice 2010 lectures, authored by a unique group of prominent scientists, address virtually every facet of oceanographic remote sensing. All salient marine applications of passive and active techniques are covered in the present collection. The main results already achieved, or soon to come, demonstrate the potential of Earth Observations to help explore the dynamical and bio-geo-chemical features of the World's Oceans. V. BARALE graduated in Physics in 1977, from the University of Milan, and then received both his M.S., in 1982, and Ph.D., in 1986, at the Scripps Institution of Oceanography, from the University of California at San Diego. Since 1990 he has been with the Joint Research Centre of the European Commission. His research focuses on the ecological assessment of marginal and enclosed (European) seas, using optical remote sensing. J.F.R. GOWER received his Ph.D. in Radio Astronomy in 1966 at the University of Cambridge, England, after graduating in Natural Sciences from the same University in 1962. He moved to Canada and joined the University of British Columbia in 1967. Since 1971 he has been at the Institute of Ocean Sciences, where he worked on optical, SAR and altimeter satellite data. He originated the "Oceans from Space" Conference series. L. ALBEROTANZA graduated in Geology in 1969 at the University of Padova. His career developed at the Consiglio Nazionale delle Ricerche (CNR), in Venice, where he has done research on optical remote sensing of marine, coastal and lagoon areas. He has been Director of the Venice CNR Institute, Professor at the University of Venice, and is now President of the Venice City Council Tidal Forecasting and Early Warning Centre.

The enclosed and marginal seas surrounding the European continent exhibit a wide spectrum of environmental traits, ranging from sub-polar to sub-tropical climates, from shallow continental shelves to deep oceanic basins, from pristine marine reserves to regions impacted by countless economic and recreational activities. Understanding the inner workings of these seas a" aiming to reconcile the conflicting needs of protecting their ecological balance and exploiting their natural resources a" requires adequate observation systems, integrating both in situ and remote sensing techniques. This volume reviews the current potential of Earth Observations, while devoting particular attention to applications dealing with the issues, peculiarities and special challenges posed by the European Seas. The assessment of surface parameters by means of passive techniques a" which measure reflected visible and near-infrared sunlight, or surface emissions in the thermal infrared or microwave spectral regions a" is addressed. Active techniques a" which use transmitted impulses of visible or microwave radiation, for a subsequent evaluation of the signal returned by the water surface a" are covered as well. An in-depth analysis of the specific merits and drawbacks of each spectral region, and of both passive and active techniques, provides clues to help compose the unique mosaic of dynamical and bio-geo-chemical features of the European Seas.

The African Seas include marginal basins of two major oceans, the Atlantic and the Indian, a miniature ocean, the Mediterranean Sea, and an infant ocean, the Red Sea. Understanding the wide spectrum of environmental features and processes of such a varied collection of marine and coastal regions requires that in situ observation systems be integrated and actually guided, by the application of orbital remote sensing techniques. This volume reviews the current potential of Earth Observations to help in the exploration of the marginal seas around Africa, by virtue of both passive and active techniques, working in several spectral ranges - i.e. measuring either reflected visible and near-infrared sunlight, as well as surface emissions in the thermal infrared and microwave spectral regions, or again the surface reflection of transmitted lidar or radar impulses of visible or microwave radiation. The in-depth evaluation of the advantages offered by each technique and spectral region and in particular by the development of advanced multi-technique systems, contributes to the assessment of the abundant natural resources that the Seas of Africa have to offer, of those in dear need of being - sustainably - exploited and of others that should be protected and maintained in their still pristine conditions.

To all those sailors / Who dreamed before us / Of another way to sail the oceans. The dedication of this Volume is meant to recall, and honour, the bold pioneers of ocean exploration, ancient as well as modern. As a marine scientist, dealing with the oceans through the complex tools, ?lters and mechanisms of contemporary research, I have always wondered what it was like, in centuries past, to look at that vast ho- zon with the naked eye, not knowing what was ahead, and yet to sail on. I have tried to imagine what ancient sailors felt, when "the unknown swirls around and engulfs the mind", as a forgotten author simply described the brave, perhaps reckless, act of facing such a hostile, menacing and yet fascinating adventure. Innovation has always been the key element, I think, for their success: another way, a better way, a more effective, safer and worthier way was the proper answer to the challenge. The map of our world has been changed time and again, from the geographical as well as the social, economic and scienti?c points of view, by the new discoveries of those sailors. One of the positive qualities of human beings is without doubt the inborn desire to expand their horizons, to see what lies beyond, to learn and understand.

Optical remote sensing is of invaluable help in understanding the marine environment and its biogeochemical and physical processes. The Coastal Zone Color Scanner (CZCS), which operated on board the Nimbus-7 satellite from late 1978 to early 1986, has been the main source of ocean colour data. Much work has been devoted to CZCS data processing and analysis techniques throughout the 1980s. After a decade of experience, the Productivity of the Global Ocean (PGO) Activity - which was established in the framework of the International Space Year 1992 (ISY '92) by SAFISY, the Space Agency Forum of ISY - sponsored a workshop aimed at providing a reference in ocean colour science and at promoting the full exploitation of the CZCS historical data in the field of biological oceanography. The present volume comprises a series of state-of-the-art contributions on theory, applications and future perspectives of ocean colour. After an introduction on the historical perspective of ocean colour, a number of articles are devoted to the CZCS theoretical background, on radiative transfer and in-water topics, as well as on calibration, atmospheric correction and pigment concentration retrieval algorithms developed for the CZCS. Further, a review is given of major applications of CZCS data around the world, carried out in the past decade. The following part of the book is centered on the application of ocean colour to the assessment of marine biological information, with particular regard to plankton biomass, primary productivity and the coupling of physical/biological models. The links between global oceanic production and climate dynamics are also addressed. Finally, the last section is devoted to future approaches and goals of ocean colour science, and to planned sensors and systems. The book is required reading for those involved in ocean colour and related disciplines, providing an overview of the current status in this field as well as stimulating the debate on new ideas and developments for upcoming ocean colour missions.

Here is a review of the current potential of Earth Observations that devotes particular attention to the challenges posed by the European Seas. The assessment of surface parameters by means of passive techniques - which measure reflected visible and near-infrared sunlight, or surface emissions in the thermal infrared or microwave spectral regions - is addressed. Active techniques - which use transmitted impulses of visible or microwave radiation - are covered as well.