Introduction

At the start of 2005, there are 68 satellites operating (annex A) and providing important data about the Earth and its environment, helping us to develop our understanding of the basic Earth System and of human influences on it. These data cover measurements of a very wide range of geophysical parameters, spanning the whole spectrum of the environment including atmosphere, land, oceans, and ice and snow. This section considers some of the key observations contributed by EO satellites, as indicated in the table.

This list is not comprehensive, but does include many key measurements of interest to the main user groups of Earth observation satellite data, and describes a significant part of the capability of current and planned instruments.

The CEOS/WMO Database contains considerably more detail on the expected performance of the various CEOS agency missions and on the specifications of the requirements for certain applications and users. For example, the CEOS/WMO Database provides information on more than 120 different geophysical measurements. See below for contact details for access to the CEOS/WMO Database.

This section identifies the satellite instruments which primarily contribute data for any particular measurement from the list above and indicates the plans for future provision of that measurement over the next 15 years. Measurement continuity is a key requirement in many areas, for example in providing confidence to sustain public and commercial investment in operational applications of Earth observation data. It is also of paramount importance for the generation of long term datasets required for global environmental programmes and for climate change studies. This section identifies the prospects for achieving that continuity given the programmes and plans that exist in 2005 – whether it may be provided by a single series of satellites dedicated to a particular measurement, or whether users of that measurement must look to various satellite missions planned by different agencies world-wide to satisfy their information requirements.

The need for this continuity, and to ensure that the measurements by different agencies from different countries can be inter-compared and calibrated requires a significant degree of coordination in mission planning and data provision. Harmonisation and maximum cost-effectiveness for the total set of space-based observation programmes is the objective of CEOS. Harmonisation of the space-based and in-situ observational resources is the aim of IGOS (see annex B). The IGOS Partnership provides a forum for establishing the performance and timing necessary from CEOS agency missions in order to satisfy the information requirements of the IGOS Themes, and of international programmes such as the Global Climate Observing System (GCOS), Global Ocean Observing System (GOOS), the Global Terrestrial Observing System (GTOS), the World Climate Research Programme (WCRP), and the International Geosphere-Biosphere Programme (IGBP).

Overview

Current areas of strength of the Earth observation satellites providing data today include:

• Atmospheric chemistry measurements, including of ozone, are being provided by instruments on NASA’s Aura and Terra missions and by ESA’s Envisat;
• Atmospheric humidity and temperature profiles are routinely provided for operational meteorology by the NOAA and DMSP series polar orbiting satellites and by a number of meteorological geostationary satellites;
• Atmospheric winds (through cloud tracking), cloud amount and tropical precipitation estimates are provided for most of the globe by the geostationary meteorological satellite series Meteosat, GOES, GMS, FY-2, and INSAT/Kalapana;
• Multi-purpose imagery for both land and sea is being collected by both high resolution optical and synthetic aperture radar (SAR) instruments for use in environmental, public, and commercial applications. Optical sensors include AVHRR on the NOAA polar orbiters and those on Terra, SPOT, Landsat, and IRS series. SAR sensors include those on the ERS/Envisat and RADARSAT series. Future missions and increasing spatial resolution will ensure improved data collection and application opportunities;
• Sea surface temperature information is being generated by data from existing meteorological satellites and from instruments on the Aqua/Terra and the ERS/Envisat series. Future plans should provide continuity. Satellites are now also making consistent and continuous measurements of other important oceanographic parameters such as ocean topography, ocean currents, and sea surface winds – such as from QuikSCAT, Jason-1, and Envisat;
• Sea ice and ice sheet extent are being measured by a range of missions (including ICESat) and continuity is planned (eg by Cryosat, ALOS, and Terrasar-X).

Future missions will feature a new generation of technology and techniques to enable Earth observation satellites to extend their contribution, including:

• a significant increase in information about the chemistry and dynamics of the atmosphere, including: long term global measurements of concentrations of ozone and many other trace and greenhouse gases; information on the role of clouds in climate change; the ability to better map cloud cover and precipitation - including over the oceans; measurements of 3-D atmospheric winds without the need for cloud tracking; global aerosol distributions; and extended coverage of atmospheric measurements into the troposphere to allow improved pollution monitoring. Just as significantly, existing measurement capabilities for many key parameters, such as atmospheric humidity and temperature, will have greatly improved accuracy and spatial resolution. A variety of novel instruments will be used - such as cloud and rain radars, and lidar instruments proposed for future missions;
• Improved repeat coverage, resolution, and accuracy of many oceanographic measurements, including ocean surface winds, and ocean colour and biology;
• New capabilities for determination of soil moisture and ocean salinity – starting with ESA’s SMOS mission;
• New information on global land surface processes, through use of increased number of spectral bands, and multi-directional and polarisational capabilities of future imaging sensors;
• Estimates of global biomass and carbon stocks, and estimates of mass balance of the polar ice sheets and their contributions to global sea level change – from innovative new lidar systems;
• Improved measurements of global ocean currents, based on data from altimeters and gravity field instruments – such as GRACE and GOCE.

We can expect the exact plans to change as space agency programmes evolve to keep pace with accepted scientific and political priorities for information on the Earth System – including the influence of the processes initiated by the Ad-hoc Group on Earth Observations (GEO - discussed in detail in Part I of this document).


Measurement timelines

For each measurement category listed in section 7.1, a brief discussion is given below of the significance of that measurement, together with an indication of the present and future measurement capabilities of satellite observations. This description is supported by two timeline diagrams spanning the period 2005-2020, indicating the instruments contributing to that measurement and the missions on which they are expected to fly.
The first timeline shows missions that are either:

• Current: where at least the prototype has been launched, and financing is approved for the whole series; or
• Approved: where financing is available for the whole series, the prototype is fully defined, the development is in phase C/D.

The second shows missions which are not yet approved - rather they are:

• Planned: financing is available up to the end of phase B, financing of the full series is being considered; or
• Considered: conceptual studies and phase A have been completed, financing of phase B is in preparation.