OSS has been developing since 1992 innovative approaches in relation with environmental surveillance covering both the biophysical and the socio-economic aspects. These approaches combine field surveillance techniques and spatial observation tools (remote-sensing). 
OSS has made of environmental surveillance is the spearhead of its initiatives. In line with this vision, OSS, with the support of its partners, designed, developed and implemented the ROSELT network in 1994 (Réseau d’Observatoires de Surveillance Ecologique à Long Terme) 
OSS has then launched a process aimed at supporting the creation of National Environmental Observation Mechanisms at the level of its member countries. The objective was to install sustainable monitoring systems that are perfectly integrated, at the technical and institutional levels, in national environmental information production and management systems. This process has largely contributed to the establishment of national specialized structures as the Center for Ecological and Environmental Monitoring of Niger. 
These field surveillance techniques should be completed and strengthened by spatial observation tools for the extrapolation of results and characterization of vast areas. OSS has developed thematic mapping methodologies and set up processing tools which allowed the development of maps and atlases at the national and regional scales. These activities have covered the entire zone of action of OSS through the development of base maps as the land use maps. 
The ROSELT network has been strengthened and adapted to the needs of the region’s countries in the framework of the REPSAHEL project. Implemented from 2012 to 2017, REPSAHEL allowed the installation of new observatories and the improvement of measuring tools (automatic weather stations). 
It should be noted that this network is a unique experience in the Circum-Sahara region.