African water and equatorial space weather focus of inaugural Alcantara workshop

'Ground-truth' check on African reservoir
27 February 2014

Researchers from three continents gathered at ESA’s technical heart in the Netherlands for the inaugural Alcantara initative workshop – fostering cooperation between research groups in Europe and those beyond, to jointly tackle key knowledge gaps in space research.

“Named for Spain’s ancient Roman bridge, Alcantara was initiated by ESA’s General Studies Programme in 2012 to foster links between leading academic institutions inside and outside Europe to study areas of mutual benefit,” explained Andres Galvez, head of ESA’s future-oriented GSP.

Alcantara partnerships take place within existing ESA programmes – two in the first phase. One is the Agency’s long-running TIGER initiative, supporting African countries in applying Earth observation technology to water management.

The second being ESA’s Monitor programme, seeking to understand  how space weather in the vicinity of the equator – far stronger and less predictable than anywhere else in the world – affects satnav performance.

Tiger initative

So Alcantara’s initial subjects of interest are found on opposing segments of the atmosphere – firstly, applying Earth observation to African water, and secondly, charting the ionosphere, the electrically active outer shell of Earth’s atmosphere.

However, as participants of the 20 February workshop, hosted at ESA’s ESTEC technical centre, talked together, these seemingly disparate fields turn out to have various factors in common.

Most of all, new opportunities are set to open in both: ESA’s Sentinel satellites – the first being launched in April – will soon make an unprecedented quality and quantity of Earth observation data products available to anyone with the technical skills to use them.

Stormy ionosphere

And the mid-decade completion of ESA’s Galileo satellite navigation constellation, along with Chinese and Indian systems joining the already operational US and Russian constellations, will enable a rain of satnav signals for precision applications, but specially disruptive space weather conditions will need to be compensated for before these benefits extend to equatorial regions.

Participants speak

Nick van de Giesen of the Delft University of Technology spoke on behalf of his partner, Frank Annor of Ghana’s Kwame Nkrumah University of Science and Technology, who had his boots in water, ‘ground-truthing’ the small reservoirs their team is studying across the West African Sahel.

“Nobody knows for sure how many of these locally-made and maintained reservoirs there are,” Dr van di Giesen commented. “But they are important to store water into the dry season in areas where there are no natural lakes. They are variously used for irrigation, household water, recreation and cattle.”

Seasonal radar satellite survey of African reservoir

The team relied on optical imagery from multiple satellites during dry season, harnessing cloud-piercing radar imagery to fill in details during wet season.

The team are not just counting the mapping the reservoirs, but applying area to depth algorithms to estimate their volume over time, and by extent their evaporation rate.

“Often the assumption is that small reservoirs a few hectares in area are inefficient because of high evaporation, but we’ve made a robust estimate of a low evaporation rate, on the order of 2 mm per day. Next we’re trying to understand why that is.”

Water hyacinths trapping fishing boats

Elijah Cheruiyot of Kenya’s University of Nairobi discussed his own partnering with TU Delft, applying Earth observation to early warning of aquatic vegetation over Lake Victoria, Africa’s largest lake.

“Initial blooms of water hyacinths dry away to host other species, until there’s a whole forest on the water,” he said. “These infestations can obstruct navigation, fishing and hydroelectric power generation – as well as proving harmful to human health, encouraging mosquito breeding.”

Their work involves developing an early-warning algorithm based on spectral detection using medium-resolution satellite images able to cover the entire 68 800 sq km lake.

Regions of strong ionospheric activity at low geomagnetic latitudes

“The potential seems to be there for continuous observation in a simpler, more affordable way,” Mr Cheruiyot concluded.

Other water projects included assessing the irrigation requirements of crops in Morocco and hydraulic modelling in Egypt and Tanzania.

Looking skywards, joint teams shared the stormy state of the ionosphere across Africa, South East Asia and South America, with perturbations made worse as the ‘total electron count’ rises due to solar activity – the 11-year Solar Cycle being currently at its peak.

Crests of electron density over South American equator

Lucilla Alfonsa of Italy’s National Institute of Geophysics and Volcanology discussed the Monitoring Ionosphere Over South America project, working with regional partners across the continent to maintain satnav monitors to build up a 3D record of ionospheric perturbation.

“The picture is made more complex still by the South Atlantic Anomaly – a hole in Earth’s magnetic field that has claimed the functionality of various low-orbiting satellites – having gradually moved westwards so it is actually over the continent itself,” she observed.

Lack of the latest equipment and limits to data sharing from national regulations had presented problems, but the interest was there on the ground – although truly remote regions had yet to be covered fully. 

Alcantara workshop

Improved models and mitigation techniques for ionospheric effects in equatorial regions also offered benefits in terms in water and crop management, the workshop agreed – improving the quality of satellite radar imagery, for instance, and enabling the use of precision agriculture guided by satnav coordinates.

Note for editors

For a list of all studies and participating entities please see

For the full agenda of the meeting and names of speakers see

Delegates of the African Geophysical Society also were present at the symposium as they participated in one of the studies: Dr Babatunde Rabiu of the Nigerian Space Agency  and Dr Olivier Obrou from Ivory Coast’s University of Cocody are Society President and Treasurer.

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