How do you personally and professionally relate to water and/or space technologies?
Personally, I was always connected with natural environments and would often visit mountain streams and waterfalls. My professional experiences with both water and space technologies started in 2004 when I worked at the Amazonian Manatee Project in a nature reserve in Amazonas, Brazil. Then, in 2006 I became a water resources specialist at the Brazilian National Water and Sanitation Agency (ANA), where I first worked with a focus on the impacts of aquaculture projects on the water quality of reservoirs. Since 2009, I’ve been studying and working on the application of space technologies to the monitoring of water-related variables in rivers and reservoirs.
Can you tell us more about your current project, HidroSat?
HidroSat is an ongoing project executed in partnership between ANA and IRD, the French National Research Institute for Sustainable Development. The project aims at turning remote sensing of water-related variables into an operational monitoring program, capable of providing ANA, its institutional partners, and the general public with temporally and spatially comprehensive monitoring data. The variables of major interest are water level, discharge, sediment concentration, sediment discharge, turbidity, and chlorophyll-a concentration.
What other tasks involving remote sensing are addressed by water and sanitation agencies?
Water and sanitation agencies usually apply remote sensing techniques to complement field data on rivers, lakes, and reservoirs. In general, such data complementation will fill spatial and temporal gaps in institutional databases and thus support specific studies and analyses, including hydrologic modelling, impact evaluation, trend analysis and change detection.
What capacity building needs in the field of water quality monitoring do you see among staff of governmental agencies in Latin America?
In general, there is a need for more comprehensive training programs on methods for sampling and analysis of water quality. Those programs should focus on quality control and quality assurance of the water quality data, which is a common issue.
As for remote water quality monitoring, techniques of satellite image processing and in situ acquisition of data on water optical properties still require capacity-building efforts from governmental agencies, which is one of the motivations of the HidroSat project.
What's the essential elements of hydrologic monitoring networks? How can space technology be used to this end?
The essence of such a network is to capture the temporal dynamics of hydrological phenomena in a spatially defined geographical area. The spatial extension and operational costs of such a network will depend on its monitoring goals. Some goals require long-term time series over enormous regions, whereas others require intensive but short time series in small areas.
When designing a network, it is therefore crucial to have well-established goals. In the case of governmental networks, because they generally are regional or national and fulfill a variety of societal demands, they must be capable of producing long-term time series with high sampling frequencies for hundreds or thousands of monitoring stations. Unsurprisingly, the resulting costs of operation and maintenance become very high. Hopefully, they can be minimized by the combination of ground and satellite-based monitoring. This is an important way space technologies can be useful.
In your article "Long-Term Series of leaves - Concentration in Brazilian Semiarid Lakes from Modis Imagery", you mentioned that not all lakes can benefit from MODIS-based monitoring. What are the requirements for using MODIS-based monitoring? What kind of lakes are suitable for MODIS-based monitoring? And what other space-based datasets could we use to overcome limitations?
Even though the spatial resolution of MODIS bands 1 and 2 (red and near-infrared) is 250 m, it is 500 m for bands 3-7 (blue, green and mid-infrared bands). And this is the best-case scenario when a target is at nadir. Under high zenith angles, the effective resolution is much coarser. So, MODIS imagery will be applicable only to large water bodies, in general lakes and reservoirs or wide rivers as the Amazonian ones. Anyway, if the monitoring goal is limited to water turbidity or water clarity, then it is possible to use only the first two bands, which facilitates monitoring rivers not necessarily as wide as those we see in the Amazon. As a rule-of-thumb, we look for river reaches and lake/reservoir zones at least three-pixel wide – 750 m if only bands 1-2 are considered. The two MODIS sensors onboard of Aqua and Terra satellites have produced an incredible global archive of daily images since the year 2000. But they will be out of operation soon. Currently, VIIRS (Visible Infrared Imaging Radiometer Suite, aboard the satellites Suomi NPP and NOAA-20) and OLCI (Ocean and Land Colour Instrument, aboard the satellites Sentinel-3 A and B) sensors can provide daily images, with low spatial resolution, whereas MSI(MultiSpectral Instrument, aboard the satellites Sentinel-2 A and B) can provide images with 5-day intervals and a spatial resolution of 10 m for some bands. Thanks to this combination of good spatial and temporal resolutions, MSI probably has the best potential for hydrologic monitoring among the optical sensors onboard of international missions with freely accessible data.
In the study mentioned in the previous question, why did you focus on the semi-arid region? What are the impacts of climate on Chlorophyll-a (assessment)? Do you have any advice for Chlorophyll-a assessment in other climate zones?
In the Brazilian semi-arid region, rivers are intermittent as a rule. That means water is only flowing during the wet season. The population in the region depends on water in public reservoirs, which is stored not only for water supply but also for other uses, such as aquaculture and irrigation. The considerable potential for conflicts among water users gets worse during the frequent droughts in the region, when the reservoirs will be severely deplenished. Water quality issues during droughts worsen the already critical situation. The occurrence of high chlorophyll-a concentrations is of concern because it indicates high phytoplankton biomass, a condition that elevates public health risks and hinders drinking water treatment. For satellite-based chlorophyll monitoring, in general, my advice is that the sensors included in the monitoring program could, alone or in combination, provide frequent images (weekly or better) and at least two bands positioned in the red-near-infrared spectral region, to retrieve reflectance in the chlorophyll absorption maximum (660 – 680 nm) and a close wavelength with minimal chlorophyll absorption (700 nm). MSI/Sentinel-2 and OLCI/Sentinel-3 are good candidate sensors for the job.
Why is Chlorophyll-a assessment or other water quality parameters’ monitoring infrequent or absent in many lakes? What are the challenges involved?
That is a common scenario in developing countries. Water quality monitoring is expensive and requires specialized techniques. Under budget constraints, monitoring programmes are suspended or downgraded, becoming unable to provide enough data to support governmental needs. In a huge country like Brazil, there is an additional challenge of integrating the interests and efforts of different federal and state agencies.
What do you think are the main water problems faced in Brazil? What can be done to solve them?
Unfortunately, Brazil has low sanitation coverage, especially regarding sewerage, which reaches only about half of the population. This is, in my opinion, the most concerning water-related issue to be faced. In 2020, a new law was approved, creating the Basic Sanitation Legal Framework. It aims to facilitate private investments in sanitation services. Since then, ANA has become responsible for defining directives and standards for the sector (before that law, ANA was not involved in sanitation, except for regulating its water consumption and effluent impacts in federal rivers and lakes). This new sanitation framework is currently our greatest hope for a gradual, but consistent improvement of sanitation coverage.
Can you give us some examples of unresolved but worth exploring issues regarding the application of remote sensing for water resources management?
The development of universal algorithms for remote water quality monitoring, applicable to most rivers and lakes in the world, is something that has been pursued and would bring expressive advances to governments and academic institutions. Some satellite products developed and offered by space agencies go in that direction, but their internalization in operational monitoring programs without further validation and adaptation is not reliable. The great difficulty in getting universal algorithms comes from the exceptional complexity of the interactions between light and constituents in water. Just to mention one specific example: phytoplankton monitoring. These organisms are incredibly variable in terms of shape, size, physiology, ecological strategies, and pigment composition. Their optical properties, therefore, can also be widely variable. A satellite product capable of monitoring phytoplankton biomass globally is necessarily a complex one, whose successful development will depend on the integration of many national datasets and on the collaboration of many international research groups.
What do you need to innovate?
In the context of our ongoing project, an important innovation would be the development of a web platform where users could interactively define areas of interest and retrieve spatial and temporal information coming from both ground and satellite monitoring. Such a platform is still beyond our capabilities in what concerns to budget and IT infrastructure. But it is only a temporary obstacle, hopefully.
Bringing the question to a personal scope, innovation for me, is the result of perseverance in seeking new solutions to old problems. Knowledge, open-mindedness, and collaboration are all important, of course, but perseverance is the key.
What is your favourite aggregate state of water?
Liquid, undoubtedly.
