Observing the Earth from space: a global vision

Imagine being able to peer down at Earth from space, like a benevolent giant. This is what satellites allow us to do, offering us a large-scale overview both fresh and salt water resources. Thanks to them, for continental hydrology, we can observe:

• Extent of water surfaces : lakes, rivers, wetlands…
• Water level variations : floods, droughts, intermittents…
• Water quality : turbidity, presence of pollutants, etc.
• Flows

Satellites thus offer global geographic coverage, making it possible to monitor large regions, including remote or difficult to access areas. They are excellent observers of natural phenomena (floods, droughts, etc.) on a large scale, both spatial and temporal.

Return to Earth for a precise measurement

However, observation from space is not enough. Satellite observations are frequent but limited by revisit periods. Thus, satellite passages can be separated by several days.

To refine our knowledge and validate spatial data, it is essential to return to Earth. This is where the in situ data, collected by sensors and ground stations.

These highly precise field measurements allow us to:

• Measuring parameters not observable by satellite: ocean salinity, surface speed and river flow, etc.
• Capturing local and sudden variations like floods.
• Provide continuous, fine-scale monitoring, essential for resource management and decision-making in the event of an emergency.
• Calibrate and validate satellites to ensure the reliability of their data.

A marriage of data for better understanding

It is by combining spatial and in situ data that we get the most out of these two approaches. Their complementarity is a major asset for continental hydrological observation and monitoring. By combining the extensive coverage of satellites with the precision and continuity of in-situ measurements, we obtain more complete and precise vision water resources and hydrological processes. Water cycle modeling becomes more reliable and makes it possible to best predictions. Finally, new decision-making tools serving resilient water management can emerge for civil protection, agriculture, energy, tourism, etc.

vorteX-io, a major player in Cal/Val satellites

The calibration and validation of satellites (also called Cal/Val) is an essential step, which ensures the accuracy and reliability of the collected data, in order to meet the scientific and operational requirements for which they are intended.

Calibration aims to characterize and correct errors in measurements which may arise in particular from environmental conditions, the aging of the instrument or even data processing algorithms. Validation consists of assessing the accuracy and reliability of spatial data by comparing them to independent references. This is where in situ measurements come in!

You will have understood, Cal/Val is of capital importance for ensuring the quality and correct interpretation of data and thus support scientific research and the development of new products and services. vorteX-io plays an essential role in this domain. Thanks to our expertise in collecting in situ hydrological data in real time, we contribute to the Cal/Val phases of large missions or projects, in close collaboration with space agencies and experts in charge of Cal/Val.

Among them are SWOT (Surface Water and Ocean Topography), St3TART (Sentinel-3 Topography mission Assessment through Reference Techniques) and St3TART Follow On.

• The SWOT mission

SWOT, a Franco-American mission operated jointly by the National Center for Space Studies (CNES) and the National Aeronautics and Space Administration (NASA), aims to measure the level of continental surface waters (lakes, reservoirs and rivers) and their widths, and also estimate the flow of the main rivers. It would also enable us to determine the level of the oceans and seas. 90% of the planet’s water surfaces are scrutinized by SWOT to better understand the water cycle, better control this resource and improve climate models.

In 2022, vorteX-io deployed around twenty micro-stations and conducted 4 drone campaigns with its altimeter VTX-1 on two sections of the Garonne: one between the north of Toulouse and the confluence with the Tarn, the other between Aiguillon (Lot-et-Garonne) and La Réole (Gironde). During a collaboration with the University of Caen, data was also collected on these two sections with a LiDAR on board an aircraft, then reprocessed by vorteX-io. Through these deployments, we were able to collect 300,000 water height measurements, which were compared with those measured by the SWOT satellite .

• The St3TART and St3TART Follow On projects

The project St3TART is funded by the European Union and operated by the European Space Agency (ESA). It aims to define what exactly is a reference measurement, in order to validate satellite measurements on three new types of surfaces being studied: inland waters (lakes, reservoirs, rivers, estuaries, etc.), sea ​​ice and land ice (ice caps, mountain glaciers). As an extension, the project St3TART Follow On intends to operationally produce these reference measurements, in support of the validation activities of the Sentinel-3 satellites of the Copernicus Sentinel-3 Surface Topography Mission (STM).

In this context and among the numerous campaigns carried out, a specific campaign was realized on the Canal du Midi , near the town of Trèbes in the south of France. This site was chosen because the Canal du Midi has a controlled water surface height and an ideal geometry (the channel is perpendicular to the Sentinel-3 track): a perfect site to evaluate the best possible performances that can be achieved by Sentinel-3! In May 2022, a vorteX-io micro-station was therefore installed on a bridge crossing the Canal du Midi, just under the passage of the satellite. The precise water heights collected by the station could be used to operationally calculate a reference measurement and compare it to Sentinel-3 data.

The comparison results obtained demonstrated the excellent performance of Sentinel-3 on this site, in accordance with the mission requirements.

The surroundings of the French town of Marmande, located on the Garonne in Lot-et-Garonne, had been identified as another ideal site for Cal/Val project activities, thanks to the favorable orientation and location of a Sentinel-3A ground trace, and the location of a nearby Sentinel-3A crossover point. The site is also flown over by a Sentinel-6 track, which is of great interest for cross comparisons between several missions. Several in-situ instruments provide water levels along the river (Vigicrues and vorteX-io micro-stations) making it possible to refine local comparisons with satellite altimeter measurements.

In addition, on February 8, 2022, a drone equipped with the altimeter VTX-1, with an embedded LiDAR and camera, was deployed by vorteX-io to measure the height of surface water on a section of approximately 20 km along the Garonne. Overflights of the Vigicrues station in Marmande were also carried out for comparison. These measurements were used to determine the slope of the river, identify local specificities (waterfalls, ponds, etc.) and ensure accurate calibration and validation satellite altimetry over rivers.

The campaign took place during a period of low water level, which is quite common for this river. Two other campaigns were therefore carried out to estimate the slope of the river and its characteristics under different water level and flow conditions, in June 2022 and March 2023. The data collected during these flights also served for the Cal/Val of the SWOT satellite.

Hydrological observation: a crucial issue for the future

Thanks to its technical skills and advanced technologies, vorteX-io actively contributes to the advancement of space remote sensing capabilities. As water challenges increase with climate change, complementarity of spatial and in situ data is becoming more essential than ever. For water stakeholders (scientists, managers, public authorities, etc.), this integrated approach represents a powerful tool to better understand the water cycle and its evolution, predict natural disasters and adapt our resource management systems accordingly.

The objective of this exciting environmental research and development project is to develop innovative methods for remotly measuring the water quality of rivers and hydrological networks.
We are very pleased to announce that future micro-stations in the vorteX-io network will be equipped with unprecedented features that allow them to remotely and in real-time measure two essential parameters for water quality:
– surface temperature
– turbidity

Stream temperature measurement

Among the various metrics measured in the field of water quality, water temperature is one of the most important. It is indeed a key factor in the habitat and metabolism of aquatic species and thus in the biodiversity of wetlands in general. Some aquatic organisms have specific temperature requirements for reproduction and even survival. As such, an increase in temperature can directly affect their growth and development and, by extension, weaken entire sections of the food chain in these fragile ecosystems.

Water temperature also has a significant impact on the amount of dissolved gas in the water. In general, the higher the temperature of the water, the less able it is to dissolve gases. A watercourse can thus undergo a drastic decrease in the dissolved oxygen content in its waters, which can have harmful consequences on the aquatic fauna and flora.

Moreover, water temperature is an important variable for both agriculture and industry, and even in the energy sector.

In this regard, power/nuclear plants, for example, use large quantities of water to cool their equipment. The temperature of the incoming water and the temperature of the discharged one are therefore a major factor in this process and can have a significant impact in terms of nuclear safety.

Close monitoring of temperature variations in rivers and lakes also allows the detection of potential sources of pollution.

Finally, on a larger scale, this metric is one of the key indicators for assessing the impacts of climate change on continental aquatic ecosystems.

Turbidity measurement

The turbidity of a liquid refers to the presence of undissolved matter in suspension that affects its transparency.

In a watercourse, suspended particles can be either of natural origin (sediments, algae, organic matter, etc.) or of anthropogenic origin (chemical pollutants, waste, etc.). That’s why an increase in turbidity can be an important indicator of water quality degradation.

The amount of suspended matter in water can have a direct impact on human health as high levels of turbidity can be associated with health risks, such as waterborne diseases. Turbidity measurement allows the detection of human health risks related to the consumption ofpotentially contaminated water (bacteria, viruses, parasites and toxic chemicals).

Furthermore, episodes of flooding and drought have a direct influence on the turbidity levels of a watercourse. During a flood, high flows bring with them large amounts of sediment, organic matter and soil from the riverbed, banks and submerged lands.
On the other hand, in the case of an acute drought episode, especially during heat waves, when water evaporates due to heat, the suspended matter particles become concentrated in the small remaining amount of water. In some cases, turbidity can then rise exponentially.

Turbidity is an important parameter for many applications, especially for drinking water treatment and industrial and municipal effluent monitoring. By measuring turbidity, fluctuations in water quality can be detected early and action taken to protect the environment and human health.

In the coming weeks, and still within the framework of the contract that binds us to the Adour-Garonne Water Agency, a second series of tests will be carried out to measure turbidity by remote sensing as well. This will be the second metric measured by the future versions of our micro-stations.

Water agencies and water quality measurement in France

In France, the measurement of water quality in rivers is mainly carried out by the 6 water agencies, which are public institutions in charge of water resource management.

The water agencies oversee the water quality measurement network, which includes:
–field measurements
– automated measuring stations

© www.lesagencesdeleau.fr

During field measurements, water samples are manually collected and then analyzed in a laboratory.

Automated measuring stations are equipped with sensors that continuously measure parameters such as temperature, turbidity, pH, etc.
The data is then automatically transmitted to the water agencies.

These water quality data are used to assess the condition of streams, track trends, identify areas at risk, and guide actions to protect and restore aquatic environments.

Unfortunately, although essential, measuring the water quality of rivers requires a lot of human time for manual sampling and is extremely costly in terms of automated sampling equipment.

It should be noted that while submerged devices (probes, stations) are highly effective, they are also by definition particularly exposed to the vagaries of watercourses. Flood events, severe weather, impacts caused by driftwood, ice, etc. are all causes of failures and drift in the quality of the data collected.

This is why thescale of the human and financial resources required to ensure their maintenance weighs heavily on the budget of the french water agencies in charge of these measures.
The cost of the equipment, its installation and maintenance can largely explain why the number of sensors currently deployed on the French territory does not exceed 800.

The vorteX-io approach: remote sensing

In contrast to these immersed sensors, vorteX-io’s idea is to develop its network of hydrological micro-stations, mainly installed on bridges spanning rivers, towards new functionalities.

In addition to the measurements already carried out (water height, surface velocity, image/video capture), the vorteX-io micro-stations will soon be able to measure the surface temperature as well as the turbidity of the water.
As micro-stations are located several meters above the water, they are by definition sheltered from the hazards suffered by submerged collectors. As the measurements are made at a distance from the water, it is called remote sensing.

Another major advantage of vorteX-io micro-stations is their low cost, as they require virtually no maintenance. Actually, thanks to their unique design, directly inherited from the space domain, their vital constants are automatically monitored, remotely and in real time. Once installed, no human intervention is required and their operation is fully automated.
The internal battery is powered by a solar panel. This energy autonomy ensures their long-term internal operation, that of the embedded measuring instruments, but also thetransmission of telemetry and the reception of commands, firmware updates, etc.

The advantages of being located away from the water are numerous, but the downside is that this method excludes the possibility of taking water samples.
Chemical measurements (pH, conductivity, dissolved oxygen, nutrients, metals, bacteria, pesticides, etc.) will therefore remain the prerogative of underwater instruments.

How to measure water quality without being immersed?

Remote sensing of water surface temperature is performed in the thermal infrared range using the sensors embedded in the new version of the vorteX-io micro-station (v.2.1).

The validation of the “vorteX-io measure” in real conditions has been taking place since the beginning of 2023 on the Girou, a small river in Haute-Garonne (in the Southwest of France). The site corresponds to the necessary validation criteria since it was already equipped with operational submerged probes, dedicated to temperature measurement and used by the Adour-Garonne Water Agency. It was the ideal place to compare the measurements made by the two devices.

Remote measurements are more complex than those made with immersed instruments. Thus, one of the problems to be solved in order to obtain reliable measurements with thermal imaging cameras, lies in the fact thatit is necessary to take into account only the water surface. To avoid that the calculations are distorted by the temperature of possible emergent objects (banks, floating obstacles, bridge and other fixed structures …), a “software mask” must be applied to keep only the parts of the image that correspond to the water.

By applying to the images a Deep Learning algorithm specially developed by our R&D team, and applied to the optical images, we can concentrate the measurements only on the water surface.
An average calculation is then applied to obtain accurate results.

The images below detail the process of creating the “software water masks” used in the surface temperature calculations.

Conclusion

The results obtained regarding water temperature measurements are already very encouraging. R&D is still underway for the automatic measurement of turbidity by remote sensing and we will present the results shortly.

These innovations will allow for the real-time measurement of surface temperature and turbidity of watercourses at a lower cost and at a scale previously unimaginable.

Already at the forefront of hydrological measurements in terms of quantitative data on rivers, vorteX-io is now preparing to complete the scope of its offer by adding the qualitative dimension. These innovations are part of our goal to create the first hydrological database at the European scale, which can be consulted via Maelstrom®our platform dedicated to hydrology.

Protection of wetland biodiversity, monitoring potential sources of pollution, better management of water resources (consumption and sanitation), evaluation of the impacts of climate change on hydrological systems and ecosystems: the issues related to water quality data are numerous and increasingly relevant.

The summer of 2022 proved to be exceptionally hot, one of the most scorching ever recorded by national weather records from various countries. In Western Europe, France, the United Kingdom, Spain, and Portugal experienced intense heat episodes with temperatures reaching 40°C on several occasions with varying durations. This is nothing new, one might say, as summer is regularly the scene of extreme heatwaves, whether in Europe, the United States, India, Australia, Brazil, etc. Indeed. But the intensity and frequency of these suffocating peaks is rapidly increasing, as records from meteorologists around the world attest. The World Meteorological Organization (WMO), a specialized agency of the United Nations, reported that July 2022 was one of the hottest months on record globally.

These periods of intense droughts are also particularly sensitive regarding the risk of fires, particularly forest fires. No debate on this point, every summer brings its sad procession of forests ravaged by fire and 2022 has unfortunately distinguished itself on this front. Even though the media largely covered the dramatic news on a daily basis, there are however other ecological risks, largely less known and also linked to periods of heatwaves and droughts.

Huge networks at risk

These risks concern the fast and catastrophic degradation, in terms of quality and quantity, of lakes, rivers, and all aquatic environments and wetlands. These complex ecosystems are experiencing much the same fate on territories extending to the scale of entire countries and even beyond.

When extremely high temperatures extend over long periods of time and are compounded by a severe lack of rainfall, water levels drop and at the same time water temperature rises. Almost all natural aquatic environments thus end up in a situation of stress, even fragility and danger. Due to the interplay of watersheds and the interconnection of waterways, this situation can quickly spread and extend to huge territories.
Especially since the risks threatening natural aquatic environments can accumulate and aggravate each other.

Excessive fish mortality rate

The first victims of these extreme climate periods are usually the fish populations in the hydrological systems we are talking about.
The decrease in the water volume in rivers causes a forced concentration of fish fauna, a major stress factor for fish, especially for fish larvae, which are more fragile and easily exposed to their predators. The drop in water level is usually combined with a rise in temperature, increasing the risk exponentially.

As with all other gases, the amount of dissolved oxygen in water is closely related to the temperature of the water. The solubility of oxygen in wetland water decreases when the temperature increases. 20°C water temperature is already synonymous with significant stress for most common fish species in our watercourses. When the water reaches 23°C, the situation becomes critical, and beyond 25°C,their very lives are in danger.

Eutrophication of environments and alteration of water quality

The scarcity or even disappearance of rainfalls combined with evaporation due to heat are directly responsible for the appearance of another risk. The eutrophication of aquatic environments is a pollution phenomenon, the origin of which can be natural or due to human activity, caused by the excessive concentration of nutrients certain algae can assimilate. Matter in excess leads to the proliferation of certain species of aquatic plants, phytoplankton and aerobic bacteria, which causes a disequilibrium in the environment due to the overconsumption of oxygen it causes. This alteration of water quality can cause an impoverishment, then literally death by asphyxiation of an aquatic ecosystem. Heat and droughts considerably increase this eutrophication phenomenon in the environment, since when flows decrease significantly, the water concentration in nitrogen, carbon, nitrates, and phosphates accelerates proportionally. It is therefore a major risk in terms of ecology and biodiversity of aquatic environments and wetlands.

Bank erosion

Banks of lakes and watercourses are the buffer zone between aquatic and terrestrial environments. This transitional situation makes banks extremely rich environments in terms of biodiversity, but also particularly fragile because it is subject to strong constraints throughout the annual cycles. The constant variations of humidity-flooding-drought, temperature, and flow, put a strain on these sensitive areas and expose them ongoing erosion.

If it seems obvious that flooding episodes are particularly violent for the banks of natural aquatic environments, one could however easily underestimate the impact that periods of drought and heatwaves have on them.
The bank soil constitutes a most favorable support for the establishment and development of numerous plant species, the riparian woodland. This flora provides important functions of shading and water filtering, favoring the natural regulation of temperature and the water quality of aquatic environments, reducing the risk of eutrophication. When heatwaves and droughst reach dramatic levels, like those of the summer of 2022, many riparian woodland plants dry out and eventually die, no longer providing their regulatory function. Their root system loses strength and then disappears, and with it its soil stabilization function, seriously accentuating the risk of erosion caused by future floods, rainfall runoff and human activities. The repeated swelling/contraction cycles of the banks due to alternating periods of flooding and droughts also play an important role in the fragility of this sensitive transition area.

Monitoring tools and the role of prevention in drought risk management

Throughout the history of humanity climatic hazards have of course always been part of the cyclical risks borne by each civilization, and the 21st century is no exception to this law. Each passing season brings with it its share of chaotic episodes. We are bearing the brunt of the effects of global, rapid, and increasingly brutal climate change. But there is no point in giving in to sterile catastrophism, on the contrary, there is still time to act, with the aim of preventing, anticipating, and minimizing the effects of climate change, particularly the risks of water-related natural disasters. Science allows us to better understand the water cycles, locally as well as globally.
Oceanography, hydrology, and fluviology allow us to better understand nature and how to palliate its instabilities, at least partially.

The means of knowledge and technologies at the disposal of our modern societies are numerous and more and more efficient. Hydraulic structures, reasoned management of water resources, ecology of natural environments, progress in Earth observation space missions dedicated to hydrology, the development of monitoring networks (via in-situ hydrological stations and intelligent and communicating field sensors) are powerful tools at our disposal to measure, understand and finally act. We must also add to this “arsenal” the constant progress of predictive computer models and hydrological applications. The development of Artificial Intelligence has greatly contributed to this progress.
In addition to these technical tools, we can also be legitimately confident in the change that is taking place (somewhat forcibly, it must be said) in the way we perceive our relationship with the planet. Realizing a little more each day how much we are an integral part of nature and how much we are intimately dependent on it can only push us to change our paradigm. Quickly.