Assessing water quality from sky now possible

Lake Chad basin benefits from…

Lake Chad is an exceptional reservoir of fresh water that not only supports more than 45 million people in Africa but also represents an important biodiversity niche. If the variability of its size and especially the reduction of more than 90% of its surface are well documented, the monitoring of the quality of its water has only been the subject of rare studies since the pioneering research of ORSTOM^? in the 60s and 70s. In fact, the complexity of this ecosystem, made up of hundreds of lagoons, and recent security problems rule out any possibility of using conventional means of measurement with permanent equipment or regular water samples.

The lack of information was a major obstacle to establishing a diagnosis on the degradation of this unique ecosystem. The new data produced will therefore be essential for the development of policies and management priorities for the protection of water quality and ecosystems as well as for the implementation of the Sustainable Development Goals in the region.

Satellite monitoring of parameters

Data production is based on open source algorithms developed by French research institutes led by the IRD research team based at UMR GET. These algorithms use images from earth observation satellites including the Sentinel-2 satellites launched in 2015 and 2017 by the European Space Agency. The main parameters available for the main lake, the many lagoons and the rivers draining the region are:

• the concentrations of suspended solids,
• turbidity,
• an indicator of the presence of dissolved organic matter,
• the concentration of chlorophyll-a,
• an algae toxicity indicator (HAB),
• the variability of flooded surfaces,
• the level of the lake,
• the surface temperature of the water.

Focus on IRD contribution

IRD researchers were involved in all stages of spatial data processing, from data validation to training portal users.

“This portal constitutes a real scientific breakthrough and for development because it provides for the first time, in free access, information on the water quality of the lakes and rivers of the Lake Chad basin and with unprecedented precision. The data will be thus useful for researchers and government institutions as well as for civil society actors “explains Jean-Michel Martinez, Research Director at IRD.

Today, the IRD contributes to the development of innovative techniques for the exploitation of spatial data in order to provide information on the water quality of rivers, lakes and estuaries in the South. These works consider theoretical developments on the modeling of the optical properties of water, the creation of data processing software, their dissemination to partners in the South as well as the transfer of technologies through cooperation programs such as that of the World Portal. Unesco and the one with the Brazilian Water Agency on the Hidrosat program .

Cross-border cooperation

The realization of this project is an excellent example of cooperation between research institutes, a private company, as well as international and regional governmental organizations.

List of contributors:

• The IRD; the National Center for Space Studies (CNES); the French Biodiversity Office (OFB); the National Research Institute on Agriculture, Food and the Environment (INRAE); the French Institute for Scientific Research (CNRS).
• Magellium, a French company specializing in digital image processing and analysis.
• Experts from the Lake Chad Basin Commission (LCBC) contributed to the collection and analysis of in situ measurements of the water quality of the Lake Chad basin. These measurements were used to calibrate and validate the data produced by the algorithms.
• Unesco’s water science division, which coordinated the efforts of all partners.

Next step

The use of the Unesco portal for water monitoring on Lake Chad is a first step in the deployment of this innovative tool. A new phase is already in development in the Rio de la Plata basin with UNESCO and the Intergovernmental Coordinating Committee of the Countries of the La Plata Basin (CIC Plata) formed by institutions from the five countries that share this basin: Brazil, Bolivia , Paraguay, Uruguay and Argentina.

This post was initially shared by IRD.