Earth Under Surveillance: Observation Satellites

The Era of Space Surveillance

Since the advent of the space age, satellites for Earth observation have allowed monitoring of our planet with unprecedented precision. These instruments provide data on climate, oceans, forests, as well as urban and agricultural areas. Their observations are essential for disaster management, deforestation monitoring, and the study of climate change.

Main Types of Observation Satellites

Observation satellites are mainly divided into three categories:

• Optical satellites: capture images in the visible and near-infrared spectrum.
• Radar satellites: use microwave signals to obtain images even through clouds or at night.
• Altimetric satellites: measure ocean and land surface topography using instruments like Synthetic Aperture Radar (SAR).

Scientific and Environmental Applications

These satellites provide crucial data for:

• Monitoring natural disasters such as floods, fires, or earthquakes.
• Studying the evolution of glaciers and polar ice caps.
• Monitoring urbanization and land-use changes.
• Climate modeling and weather forecasting.
• Monitoring air quality and greenhouse gas emissions.
• Observing oceans, currents, and sea surface temperatures.
• Tracking deforestation and forest regeneration.
• Managing water resources, including groundwater.
• Monitoring crops and food security.
• Assessing the environmental impact of mining and industrial activities.
• Mapping coastal areas and preventing coastal erosion.
• Detecting and monitoring volcanic and geological phenomena.
• Urban planning and analyzing population growth.
• Protecting biodiversity through monitoring natural habitats.
• Validating and improving global climate models.

Examples of Iconic Satellites

Some satellites have become benchmarks for Earth observation:

• Copernicus Sentinel-2: for vegetation and soil monitoring.
• Terra and Aqua: NASA missions for studying the atmosphere and oceans.
• Envisat: ESA mission for global environmental observation.

Comparison Table of Satellites

Source: ESA - Observing the Earth, NASA Earthdata, and Wikipedia – Gaofen.

How Many Observation Satellites Are Orbiting in 2025?

In 2025, approximately 11,700 active satellites orbit the Earth, most in LEO below 2,000 km altitude. These satellites perform a variety of missions, including telecommunications, navigation, Earth observation, scientific research, and defense.

Among this total, around 1,000 satellites are specifically dedicated to Earth observation. This category includes civil, military, and commercial satellites such as the Pléiades Neo, CO3D, NISAR, FLEX, TRISHNA, Sentinel-6B constellations, as well as satellites from Planet Labs, ICEYE, and other private operators.

The total number of observation satellites is constantly increasing. Future projects aim to deploy new constellations to improve coverage and observation frequency. In 2025, these satellites represent approximately 8% of the total of active satellites in low Earth orbit.

Note:
The exact number of Earth observation satellites is actually an estimate, not an absolute figure, due to satellites whose information is not publicly disclosed, notably those of China, Russia, or certain military programs.