Space

Tunisia's Earth Observation Systems

In the area of Earth observation, Tunisia has focused increased efforts on the operational applications of space technology. Meteorology and remote sensing are the main fields of application of Earth observation techniques.

Two key elements in the contribution of satellites to meteorology are global coverage of both hemispheres and continuity of observation. Previously, meteorological data could be gathered only by radiosounding using too few ground stations unevenly spread over the surface of the planet. Deserts, polar regions, oceans and tropical zones did not have any stations for measuring meteorological parameters. The data were partial and lacked continuity.

With geostationary and polar-orbiting meteorological satellites the field of vision has been extended; observations have become regular and their quality has increased; the information gathered is rapidly disseminated and instantly processed on powerful computers; and meteorological satellites provide daytime images of cloud cover. In addition, the development of radiometers capable of measuring infra-red rays has made it possible to detect cloud presence at night and on-board sounders have made it possible to determine air temperature and humidity by satellite.

Three types of meteorological satellite are used for gathering meteorological data: polar-orbiting satellites equipped with radiosondes; geostationary satellites, which transmit images of the Earth at regular intervals; data-gathering satellites, which broadcast the information received by a number of meteorological stations attached to balloons. These satellites make it possible to carry out meteorological monitoring on a planetary scale (the World Weather Watch programme, consisting of five geostationary satellites and two polar-orbiting satellites of the United States of America).

As regard the experience of the National Meteorological Institute (INM) in the operation of meteorological satellites, in order to improve the quality of weather forecasting and to develop its activities at the regional and local levels, INM has over the last five years equipped itself with stations handling the following data:

The main purposes for which these stations are used are: general weather forecasting; aeronautical protection; very short-term prevention; rainfall estimation; sea-surface temperature readings; and vegetation index readings. INM also uses an ONT channel to disseminate meteorological data and parameters, via EUTELSAT, to the regions in the interior of the country.

In addition to the data gathered by the meteorological stations and transmitted across the national territory, INM uses images from the Meteosat satellites and those of the National Oceanic and Atmospheric Administration (NOAA) of the United States for the following purposes: immediate forecasting for the country (1-6 hours); estimating rainfall in regions lacking land-based facilities for measuring precipitation; estimating global solar rays reaching the ground; calculating the vegetation index; and measuring the sea-surface temperature. INM operates a station for receiving and processing images from the Meteosat geostationary satellite and a station for receiving and processing images from the NOAA polar-orbiting satellites.

Remote sensing is an operational application on which efforts have been concentrated with a view to its expansion and utilization in development projects. As stated previously, Tunisia is one of the pioneer countries in this field. For example, alongside the ARZOTU experiment, three national seminars on remote sensing were organized between 1975 and 1982. At a seminar held in 1984 to discuss the issue of remote sensing for Tunisia, it was possible to evaluate and reorient efforts. In particular, it was recommended that a national body be set up with responsibility for coordinating national activities in this field. That recommendation was implemented in 1988 with the establishment of the National Remote Sensing Centre, which has helped to foster the emergence of other users of this technology, who have in turn contributed to the expansion of the applications.

Details of the main users are set out below:

(a) The National Engineering School of Tunis, with its space information system and remote-sensing laboratory (LTSIRS), is highly active in the areas of training and research and development in new satellite image-processing technologies. River basins, coastal zones, mining and the environment are some of the subjects studied at this laboratory;

(b) The Institute for Arid Regions, a research and development centre operating under the administration of SERST, has a geographical information and remote-sensing laboratory that uses remote sensing in thematic studies on desertification and natural resource management. The Institute has also acquired considerable experience in the training of users of remote-sensing technology in Tunisia, the Arab world and Africa since 1981. Its efforts received international acclaim in 1986, when the International Society for Photogrammetry and Remote Sensing honoured Tunisia with the Dolezal award, in recognition of the Institute's work in desertification mapping and monitoring in Africa;

(c) The National Agency for the Protection of the Environment and the Agency for Coastal Protection and Development, which are attached to the Ministry of the Environment and Regional Planning, are two of Tunisia's most active bodies in the field of the environment and are hence major users of remote-sensing technology.