Meteorology, Meteorological, History

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HISTORY OF EUMETSAT, p15.

HISTORY OF EUMETSAT, p13.

p14

spacecraft in orbit at 9° West. For a limited period another EUMETSAT satellite, positioned at 63° East, provides images of the Indian Ocean and nearby continents. The USA, Japan, China, Russia and India also have geostationary satellites keeping watch over their regions.

Geostationary satellites cannot see the poles and are confined to one region. Their distance from Earth also means that their spatial resolution is limited. Hence the value of polar orbiting satellites which are typically in a much closer orbit with an altitude of about 850 kilometres. These satellites pass over the poles. At a distance of 850 kilometres it takes a satellite 100 minutes to complete an orbit. By the time the satellite returns to the same position in its orbit, the Earth has turned so that the spacecraft is above a different spot. In this way polar orbiting satellites can pass over the whole Earth twice a day. Their strengths are two-fold. They collect global data, whereas observations from geostationary satellites are limited to the region below them. Polar orbiting satellites are also closer to the Earth, so collect more detailed data. Their weakness is that they cannot constantly monitor the same region to observe weather systems developing. In an ideal world, both types of satellite are critical and this is what EUMETSAT, with the not inconsiderable cooperation of ESA, has achieved.

At first glance it is clear to see how the idea of a constant bird's eye view of the world's weather from geostationary and polar orbit would appeal to meteorologists because of their need to have a complete and accurate description of the atmosphere for computer models. Rarely are matters so simple.

The raw information collected by satellites is a stream of values of the intensity of radiation, in particular frequency bands, returned from the atmosphere and the surface of the Earth. That is what meteorologists must turn into meaningful information about conditions on Earth. Each radiation measurement needs to be calibrated to ensure all the measurements are effectively being made against a consistent base. Every measurement needs assigning to its geographic location, and only then can the business of extracting meteorological information begin.

The process of meteorological product extraction calls on a very deep understanding of the suite of disciplines listed above as the meteorologists' scientific armament. How do radiation intensities relate to physical and chemical events in the atmosphere? How can the altitude at which these events have occurred be deduced from the data? How should an instrument be designed in order to collect the appropriate raw data to give a certain piece of meteorological information? In other words, if the main aim is sea surface temperature, or surface wind speeds, or a temperature or humidity profile throughout the atmosphere, how should the instrument be designed - that is, which frequency bands need to be monitored?

The political task facing EUMETSAT was equally hard. EUMETSAT's business is space-based meteorology - with the emphasis on meteorology, not space. Meteorologists and later, EUMETSAT itself, needed the expertise of ESA in order to develop what was in the 1970s and early 1980s a novel technology for Europe. Indeed ESA, and its predecessor ESRO, were the main driving force behind the initial development of

SEE ALSO| |

1. Mete orologists shed political shackles, a review of Declan Murphy's history of the first 25 years of EUMETSAT (2011), by Helen Gavaghan.

2. An interview in 2010 with Dr Tillman Mohr, a special advisor to the secretary general of the World Meteorological Organisation, in Science, People & Politics.

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Contents

Preface

Foreword

Introduction

Ch.1

Ch.2

Ch.3

Ch.4

Ch.5

Ch.6

Ch.7

Ch.8

The History of EUMETSAT is available in English and French from EUMETSAT©.
First printed 2001. ISBN 92-9110-040-4

Eumetsat meteorology meteorological artificial satellites
European Space Agency weather climate policy politics history