1-11 Introduction

The VEGETATION Programme is developed jointly by France, the European Commission, Belgium, Italy and Sweden. The satellite component of the programme will be launched in March 1998 onboard Spot 4 & 5 and will deliver measurements which were specifically tailored to monitor land surfaces' parameters with a frequency of about once a day on a global basis and a medium spatial resolution of one kilometre. Its original features and its situation onboard Spot 4 & 5 will allow users to have access to:

robust and simple multitemporal measurements of the solar reflection domain radiative properties of land areas,
a continuous and global monitoring of the continental areas either through the centralised archiving and processing facility, or, for local or regional studies, using local receiving stations,
long term data sets with accurate calibration and positionning, continuity and consistency through the renewal of the system on further satellites,
multiscale approaches of surface parameters and processes using simultaneous measurements acquired through the VEGETATION instrument and the High Resolution instruments of the SPOT series.

1-12 Overall objectives

The overall objectives of the "VEGETATION" system are to provide accurate measurements of basic characteristics of vegetation canopies on an operational basis,

either for scientific studies involving both regional and global scales experiments over long time periods (for example development of models of the biosphere dynamics interacting with climate models),

or for systems designed to monitor important vegetation resources, like crops, pastures and forests.

The "VEGETATION" system, consisting of a satellite-borne sensor and of its associated ground segment, provide long term basic measurements adapted to biosphere studies. Opportunities for scale integration are provided by the combination with the main SPOT instruments (HRVIR) which allow high spatial resolution for detailed modelling activities or multilevel sampling procedures. Availability of data to different types of users is facilitated through the centralisation of reception and archiving global data sets

1-13 Overall system organisation

As presented in the following diagram, the VEGETATION Image Ground Segment is based on a main centralised architecture. It comprises the following subsytems :

The Principal Receiving Station located in Kiruna/ Sweden. It receives the world-mode images telemetry (many periods of visibility per day). It corresponds to the images of terrestrial areas at full resolution, as stored onboard the Spot 4 & 5 solid state memory. This telemetry is transmitted in X band.

The Programming and Control Center located in Toulouse/ France. It sends the commands to the Spot 4 & 5 satellite, through an up-links S-band station

The Image Quality Monitoring Center, located in Toulouse/ France, which has a dual role:

  • Monitors the VEGETATION image quality and provides relevant parameters (such as the calibration coefficients) to the processing center;
  • Monitors the performances and functioning of the L band transmission through an L-band reference station located as well in Toulouse.

The Processing and Archiving Image Center, located in Mol/ Belgium, hosted by the VITO Center. It is the main operational entity of the Ground segment, which ensures the following missions:

  • Manages the world-wide archive;
  • Processes all global mode VEGETATION data;
  • Processes user orders;
  • Distributes VEGETATION image products;
  • Offers a catalog service on Internet;
  • Is interfaced to the distribution organisation and ensures related accounting and invoicing activities.

The Distribution Organisation shared between the 4 distributors Spot Image, CLEO, SSC (Swedish Space Corporation) and Telespazio. It is the commercial interface with all users and has a direct link with the Processing center.

This main centralised architecture is the operational body that will deliver the products, described in this document, with the nominal performances specified.

A secondary network of distribution is possible throughout Regional Receiving Stations that can acquired the direct telemetry in L-band. The declared L-band stations will have access to required calibration data and orbital parameters, necessary to perform local pre-processing.

The nominal performances described in this document do not apply to the products that would be generated by these Regional Receiving Stations.

    Fig. 1.1: Overall system structure.

1-14 Mission objectives

Surface parameters mapping :

This is the basic requirement, especially for climate and meteorological studies where boundary conditions have to be prescribed as in the case of General Circulation Models or forecasting models. Factors such as albedo, surface roughness, resistances to heat exchanges (sensible and latent) are important variables for these models and they can be either determined directly from the measurements or inferred from identification of land cover. The seasonal and long-term variations of such variables are related to vegetation dynamics. The capability to identify, through these variations, physical characteristics of land cover is a key to accurate prescription of these variables. Scales addressed in GCM or forecasting models (typically about 100 km) require that land cover and its variability is determined with a sampling of about 8 to 10 km : the basic spatial resolution needed for identification of land cover and its variability is 1 km.

Agricultural, pastoral and forest production:

Since the beginning of the land surface satellite remote sensing era (1972), important projects (for example LACIE, AGRISTARS for USDA, MARS for ECC, TREES for JRC/ESA...) have been set up to develop methodologies and strategies to use remote sensing data either for mapping of land use in anthropogenized or natural ecosystems or for estimation of production potential. Their specific objective was to determine the evolution of productions. This objective had to be adapted to the management of crop production for agricultural exporting countries, to the monitoring of pastoral resources and their dependence from meteorological evolution, to the evaluation of possible global impacts of deforestation and more generally to the need for information related to political or social orientations and decisions.

Terrestrial biosphere monitoring and modelisation :

The contribution of the continental biosphere to the biogeochemical cycles (exchanges of carbon and other trace gases) and to water and energy exchanges is one of the objectives of the development of global models. Interaction with human activities is also one of the main points to be studied, because the effect of human pressure on the biosphere might be one of the means by which man is acting on climate in the long term. Biosphere processes and land cover characterisation are the basis for quantification : estimations of land cover variables as well as the dynamics of these variables have to be made in order to obtain a good understanding of these processes upon which models may be built. Predictions of impact of climate change on the biosphere and of interactions of the biosphere with the climate (either due to natural factors or to human pressure) can only be inferred from quantification and formalisation of the mechanisms by which vegetation cover and ecosystems are functioning. Multilevel series of models have to be developed and linked, ranging from ground studies, local parameterisation and exchange models to regional or global dynamics and interaction models. Remote sensing of the vegetation as shown above offers a unique tool for these developments, providing the specification of the systems be adapted to each particular need.

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