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Principles of Satellite Observation

Principles of Satellite Observation

Satellite Observation: A Key Lever for Sustainable Water Management

Why Satellites?
In the face of growing pressures on water resources, such as climate change, increased demand, and natural hazards, it is essential to improve our knowledge in order to manage better. Earth observation by satellite provides unprecedented access to large-scale hydrological data, often impossible to obtain solely through ground-based measurements.

Complementarity Between Ground and Satellite Observations
Traditionally, hydrological measurements (hydrometry) rely on ground stations that record key parameters such as river discharge, water level, or soil moisture. These data are crucial for:

  • Flood forecasting and risk management,
  • Designing hydraulic infrastructure,
  • Ecological monitoring of rivers and wetlands,
  • Regulatory control of water withdrawals.

However, such measurements are often complex to implement, costly, and very localized.
That’s where satellites come in, to enhance, expand, and densify hydrological data.

What Satellites Measure: The Scope of Space Hydrology
Thanks to technologies like satellite altimetry (which measures water surface height using radar), satellites can:

  • Monitor changes in the levels of lakes, rivers, and reservoirs,
  • Estimate river discharge,
  • Observe snow cover, soil moisture, and vegetation dynamics,
  • Analyze water quality: suspended matter, chlorophyll, temperature, sediment fluxes, etc.


SWOT and TRISHNA: Two Satellites Serving Water Management

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SWOT – Surface Water and Ocean Topography
Developed jointly by CNES (France) and NASA (USA), SWOT is a satellite mission launched in 2022 that aims to map, for the first time at high resolution, the water heights and discharges of rivers, lakes, and coastal zones worldwide.

TRISHNA – Thermal infraRed Imaging Satellite for High-resolution Natural resource Assessment
Planned for launch in 2027, this Franco-Indian satellite (CNES–ISRO) will specialize in measuring evapotranspiration and surface temperature. It is especially useful for:

  • Monitoring water stress in irrigated crops,
  • Estimating evaporation from water bodies,
  • Fine-scale modeling of water balance at the field level.

TRISHNA will complement SWOT by providing thermal data, which are essential for more sustainable agricultural water management.