Earth Observation and remote sensing are often used interchangeably and in many conversations – and who doesn’t have conversations about this sort of thing?! – that causes no problem. However, they do not mean the same thing.

The simplest distinction we can give you is that:

Remote sensing is the technology and process of collecting information from a distance.

Earth Observation is the application of remote sensing capabilities to understand the Earth.

What is remote sensing?

Remote sensing means gathering information about an object, area or phenomenon without making direct physical contact with it.

Instead of taking a sample or placing an instrument directly on the thing being measured, a remote-sensing system detects energy reflected or emitted by it. That information can then be processed to reveal characteristics that may not be visible to the human eye.

Remote-sensing instruments include:

• Optical cameras
• Multispectral and hyperspectral sensors
• Thermal infrared sensors
• Radar and Synthetic aperture radar (SAR) technology
• LiDAR sensors
• Microwave radiometers

These instruments can be carried by satellites, aircraft, drones, vehicles or fixed installations. Remote sensing is therefore not limited to space, nor is it necessarily concerned with the Earth. Similar principles are used in medical imaging, industrial inspection, astronomy and planetary exploration.

Remote sensing describes how the information is collected.

What is Earth Observation?

Earth Observation, usually shortened to EO, is the collection and analysis of information about the Earth’s surface, oceans and atmosphere.

EO frequently uses satellites, but it can also incorporate measurements collected from aircraft, drones, ground-based instruments and in-situ sensors. It may combine these observations with mapping, modelling, artificial intelligence and other datasets to produce useful information.

Earth Observation can be used to:

• Monitor crops, forests and natural habitats
• Measure changes in land use
• Detect floods, fires, oil spills and other hazards
• Track air pollution and atmospheric conditions
• Monitor coastlines, oceans and inland waters
• Assess infrastructure movement and ground subsidence
• Support defence, security and emergency response
• Understand climate change and its effects

EO therefore describes what is being observed and why.

Is satellite imagery the same as Earth Observation?

Satellite imagery is one important form of Earth Observation, but EO is much broader than pictures taken from space.

Many EO satellites collect measurements that do not resemble conventional photographs. Radar satellites can operate through cloud and at night. Thermal sensors detect emitted heat. Hyperspectral instruments identify materials by measuring their spectral signatures. Other satellites measure atmospheric gases, sea-surface height, soil moisture or changes in the Earth’s gravitational field.

The resulting data often require significant processing before they become usable information. An EO product might be a map of flood extent, a crop-health indicator, an estimate of methane emissions or an alert showing that a bridge or railway line has moved by a few millimetres.

The real value of Earth Observation is therefore not simply the image. It is the evidence and insight extracted from the observation.

Where do the two terms overlap?

Most Earth Observation depends on remote-sensing technology, so there is substantial overlap between the two fields.

A satellite using radar to measure ground movement is performing remote sensing and producing Earth Observation data. A drone surveying a coastal cliff is doing the same. A temperature probe placed directly into the soil, however, contributes to Earth observation in the broadest sense but is not a remote-sensing instrument because it takes a measurement through physical contact.

The boundaries are not absolute and different organisations use the terminology in slightly different ways. In the space and geospatial sectors, “Earth Observation” often refers particularly to satellite-derived data and services. “Remote sensing” is more likely to describe the underlying scientific and technical discipline, regardless of the platform carrying the sensor.

A useful way to remember the difference

Remote sensing is the means; Earth Observation is the purpose.

Remote sensing provides the instruments and techniques needed to collect measurements from a distance. Earth Observation turns those measurements into knowledge about our planet—and, increasingly, into information that helps governments, businesses and communities make better decisions.