| SPORE No. 68 - April 1997 |
With the launch of the first American civil observation satellite in 1972, remote sensing became a practical technology: with the development of Geographic Information Systems (GIS), this space technology is providing significant support to development. Whether the data are used for map making, forecasting harvests, surveying land degradation or identifying agricultural potential, nothing escapes the satellite's eye.
The picture resolution that can be obtained from observation satellites 800km up in the sky has improved from 80m to five or six metres since 1972. Every house and tree can now be identified from the images which the Spot satellite sends back to Earth. At the even greater distance of 36,000km from the Earth's surface, geo-stationary weather satellites are capable of a much wider angle of vision and can produce images which cover practically all of the Sahel, for example. More than 20 of these satellites are in permanent operation above us, taking pictures from the visible to the infrared range of the spectrum. The most recent satellites produce microwave or radar images which can give a view of the ground even through heavy cloud. These images yield a wealth of information, which can be used not only for cartography but also for analysing biophysical features in the environment.
Methods of interpreting the information have also gained in precision, thanks to the work of a small number of specialist institutions. The International Institute for Aerospace Survey and Earth Sciences in the Netherlands (known since 1950 as the International Training Centre for Aerial Survey) has acquired a reputation for excellence in the processing and interpretation of geographical information, in particular for natural resource management and for identifying appropriate development policies. However, with the exception of measurements which can be made directly from space, such as air humidity, the interpretation of satellite information must be backed up by ground observations. Systematic ground level verification of satellite image interpretation is an essential part of any programme and the cost of this ground work can be more than the cost of purchasing the corresponding satellite image.
Information technology has made it possible to assemble and process, with a computer hardly more powerful than a standard PC, an amazing amount or varied information on any particular region and to use this data in the form of superimposable thematic maps. These Geographic Information Systems make it easy to correlate the biophysical characteristics of a region (for example, topography, soil type and structure, water resources, natural and other vegetation cover) with socio-economic variables, such as the type of cultivation, communication networks or population density.
Food security from space
Pictures from the NOAA weather satellite are being used by P4AS (le Projet pilote de prevision des productions agricoles au Sahel) in an ambitious project to monitor crop production and predict harvests throughout the Sahel. The satellite images are processed at a station in Niamey, Niger and are complemented by ground observations. Using this data, CILSS is able to make forecasts of the likely harvest in time to arrange humanitarian aid, if necessary, and supplies from regions which have a surplus to those that are likely to be in deficit.
Satellite images can provide answers to very complex questions and can, for example, provide a country-wide assessment of natural resources degradation within a time scale which, without such images, would be an impossible task. A multi-disciplinary team from the Institut National des Sols de LomÃ© and from ORSTOM, undertook an exhaustive study of this type in Togo during 1994. The work, which is applicable to any region with rainfall between 800mm and 1200mm from Sudan to Senegal, is based on a small number of Landsat and Spot images. These were purchased for less than 150,000FF and were confirmed by ground surveys which required the team to travel over 35,000km in different regions of the country. The use of topographical and other classical maps, and the interpretation of historical data, completed the GIS. The three areas of Togo that were revealed to be severely degraded cover no more than 5% of the total surface area. Although this analysis of the situation was reassuring, the study also showed that intensified clearing of vegetation from the beginning of the 1990s, after 25 years of a strictlyenforced protection policy, would lead to accelerating land degradation over the next ten years and that more detailed surveillance at provincial level would be useful.
Cape Verde has also developed a GIS to optimize development of the island of Santiago and improve agricultural productivity from its resources. The database, set up by the Institut de Recherche Agricole Cap Verdien (INIDA) with the support of the Institut de Recherche du Portugal (IICT) and the Cartographie et d'Information GÃ©ographique service of CIRAD, collates inventories of the island's natural resources: climate and rainfall; topography; morphology; and plant biodiversity. The addition of new 'layers' of information is envisaged, for example, for demography and urbanization. The system is, however, already in operation, notably for planning distribution networks for electricity and water throughout the island and for the development of small water catchment areas. GIS will be a powerful tool in future, both for development and for the management of natural resources. •