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Ice and beyond

Climate science with CryoSat

This book looks at the reasons for launching a dedicated ice mission, and explains the technical innovations behind CryoSat's measurements of sea ice thickness and land ice topography. It also gives examples of how CryoSat has contributed to polar and climate science, and revolutionised satellite measurements of ocean currents, sea level and waves.

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Earth's gravity from space

Some insights into the achievements and legacy of ESA's gravity mission GOCE

This book looks at the reasons for launching a gravity mission, the technical innovations that allowed ESA to measure Earth's gravity field with unprecedented accuracy, and the scientific advances made possible by using GOCE data in the ocean and earth sciences.

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Introduction

Scientific achievements made possible by the ESA ice mission CryoSat

For three decades satellite data have documented the decline in Arctic sea ice, the retreat of glaciers and the loss of ice from Greenland and Antarctica. Yet many aspects of these changes remain poorly observed; for example, estimates sea and land-ice volumes are subject large uncertainties.

In 2010 the European Space Agency launched CryoSat, a mission to improve these estimates by mapping sea ice thickness and the elevation of ice sheets, particularly along their poorly observed margins.

This interactive book explores how the CryoSat mission has contributed to the polar, climate and ocean sciences. It describes key techniques of precise SAR altimetry, reviews state-of-the-art scientific achievements, and shows how data from CryoSat is helping to deliver new insights.

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For more information about the content of each chapter, select the screenshots below.

chapter 1 chapter 2 chapter 3 chapter 4 chapter 5 chapter 7
Introduction

Scientific achievements and legacy of the ESA gravity mission GOCE

Since Newton we have known that Earth's gravity varies from place to place. In 2009 the European Space Agency's Gravity field and steady-state Ocean Circulation Explorer satellite, GOCE, was launched to map these variations with unprecedented accuracy.

GOCE has brought many new insights. We now have a real opportunity to create a unified global system for mapping Earth's heights and depths - to the benefit of civil engineering, exploration, surveying, and geo-information systems. GOCE has also contributed to studies of sea level, ocean currents, polar ice sheets, plate tectonics, earthquakes and volcanism.

With examples from current research, this interactive book tells the story of the GOCE mission and the scientific discoveries made possible by GOCE data.

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For more information about the content of each chapter, select the screenshots below.

chapter 1 chapter 2 chapter 3 chapter 4 chapter 5 chapter 7

Remote and inhospitable, polar regions are among the last truly wild areas on Earth. Over the last two centuries we have gradually increased our understanding of polar environments, thanks to explorers and scientists who often risked their lives. Some thirty years ago, satellite observations brought a step-change in our ability to monitor variation and change in the Arctic and Antarctic. The data they collected have revealed some dramatic and worrying changes to polar ice.
Chapter 1 gives some of the reasons why we should be concerned, provides an overview of satellite techniques used to monitor ice, and explains why ESA decided to launch a dedicated ice mission.

Chapter 2 introduces CryoSat and the technological advances that made it so unique. This includes:
- its unique orbit, which made it possible to measure ice topography closer to the poles than ever before
- the revolutionary SIRAL altimeter, which increased the spatial resolution and accuracy of the measurements
- a sustained and on-going programme of field campaigns to improve the algorithms that convert the raw data to useful information about sea ice thickness and land ice topography.

Sea ice is an important part of the climate system. An ice cover changes the ocean's surface albedo, insulates it from heat loss, and reduces the exchange of heat and moisture between the ocean and atmosphere. Whether in the Arctic or Antarctic, sea ice is important for polar ecosystems; many plants and animals are associated with sea ice.
Chapter 3 looks at differences and similarities between the Arctic and the Antarctic, explores the forces that shape the sea ice landscape, and shows how CryoSat observations are contributing to a more detailed understanding of changes in polar sea ice.

Satellite measurements have painted a new picture of how Earth’s ice sheets are changing. As global temperatures have risen, so too have rates of snowfall, ice melting, and glacier flow. The balance between these opposing processes varies considerably on a regional scale, but satellite measurements show that Antarctica and Greenland are each losing mass overall. Chapter 4 looks at some of the changes that have occurred to the Greenland and Antarctic ice sheets, shows how satellite data have made it possible to detect where the main changes are occurring, and how CryoSat data have provided a more thorough overview of recent changes.

Although not originally intended for ocean observations, CryoSat represents a technological step-change in the measurements of wind, waves, sea level and ocean currents, which led to increased accuracy and made data available closer to the coast.
Chapter 5 explains how the ocean measurements are made, and gives examples from current research to provide better information about sea and lake surfaces and the topography of the ocean floor.

The ability to access and analyse CryoSat data with relative ease is important for future scientific work to build on the achievements described in the book.
Chapter 7 therefore gives an overview of the main data products available from CryoSat-2, and the analysis tools of the CryoSat user toolbox.

Over three centuries have passed since Newton had his 'eureka moment' while watching the fall of an apple in a Lincolnshire garden. Since then numerous scientists have worked to make gravity measurements increasingly sophisticated and accurate.
Chapter 1 looks briefly at some of this work and the reasons for launching a satellite gravity mission.

Chapter 2 introduces the GOCE satellite and the technological advances that made it so unique. This included:
- satellite to satellite tracking, which made it possible to retrieve gravitational information from GOCE's orbit;
- a revolutionary gradiometer, which 'magnified'smaller-scale gravity features and recorded them with unprecedented accuracy;
- an attitude control system and ion propulsion engine, which compensated for atmospheric drag and kept the satellite on track.

Gravity and geoid are closely related; one can be derived from the other. GOCE was launched to determine the global geoid and gravity field with best possible accuracy and spatial resolution. Chapter 3 explains what the geoid is, the mathematics behind geoid maps, and why the GOCE geoid is an improvement on earlier geoids. It also looks briefly at some of the ways in which the new geoid is used in Ocean and Earth science.

As indicated by GOCE's full name (Gravity and steady-state Ocean Circulation Explorer), ocean circulation was an important focus for the GOCE mission. Understanding the ocean's role in the climate system requires accurate measurements of current speeds. Radar altimetry gives us the actual shape of the ocean surface. Then by subtracting the shape of the geoid we can calculate current speeds from the 1-2m undulations of the sea surface topography. Chapter 5 introduces the main ocean currents, explains why they are so hard to measure and how the GOCE geoid has contributed to making current measurements from space more detailed and accurate.

The six sections of Chapter 5 give examples of how GOCE data is being used in geology and geophysics. In areas where measurements were few and scattered, GOCE has brought large improvements. This is particularly true for South America, Africa, Himalaya and Southeast Asia. The first detailed map of gravity anomalies in Antarctica became available with GOCE. Examples from this chapter includes the use of gravity anomaly maps to study plate tectonics and processes in the Earth's mantle; mapping the thickness of the Earth's crust; and the study of gravity changes caused by large Earthquakes or the melting of polar ice sheets.

Although the GOCE satellite re-entered Earth's atmosphere in November 2013, the use of its data in geophysics, geodesy, oceanography and solid Earth science has only just begun. The ability to access and analyse GOCE data with relative ease is important for future scientific work to build on the achievements described in the book. Chapter 7 therefore gives an overview of the main data products available from GOCE, and the analysis tools of the GOCE user toolbox (GUT), which has been designed and improved in collaboration with Earth and ocean scientists using GOCE data.

NOC Bilko UNESCO