About Earth Observation and Satellite Imagery

Image of a remote sensing satellite over Earth

Image of a remote sensing
satellite over Earth
© Geoscience Australia

What is satellite remote sensing?

Satellite remote sensing involves gathering information from sensors mounted on orbiting satellites to capture features on the Earth's surface. There are two types of sensor systems known as 'active' and 'passive'.

An 'active' system propagates its own electro-magnetic radiation, and measures (as digital numbers), the intensity of the return signal. Synthetic Aperture Radar (SAR) is an example of an active system.

A 'passive' system generally consists of an array of small sensors or detectors, which record (as digital numbers), the amount of electro-magnetic radiation reflected and/or emitted from the Earth's surface. A multi-spectral scanner is an example of a passive system.

The digital data acquired by satellites is transmitted to ground stations and can be used to reconstitute an image of the Earth's surface. When processed, satellite images may resemble an aerial photograph taken from a very high altitude, but in fact there are some very important differences which enable much more information to be determined about the areas of interest.

These differences include:

  • acquisition of infra-red reflectances enable better identification and assessment of features
  • images are acquired on a regular basis enabling access to current and archived data
  • images can be produced in photographic or digital form
  • cheap and user friendly software is now available to view and analyse digital imagery on PCs.

Why do we use satellite remote sensing?

Data acquired by Earth observation satellites provide a number of benefits for studying the Earth's surface, including:

  • continuous acquisition of data
  • regular revisit capabilities (resulting in up-to-date information)
  • broad regional coverage
  • good spectral resolution (including infra-red bands)
  • good spatial resolution
  • ability to manipulate/enhance digital data
  • ability to combine satellite digital data with other digital data
  • cost effective data
  • map-accurate data
  • possibility of stereo viewing
  • large archive of historical data.

How is data provided to the end-user?

Data is provided as digital data products which can be viewed and manipulated on a variety of software systems.

How is data used?

Satellite data is used to provide timely and detailed information about the Earth's surface, especially in relation to the management of our renewable and non-renewable resources.

Some examples of satellite data usage are:

  • assessment and monitoring of vegetation types and their status
  • soil surveys
  • mineral exploration
  • map making and revision
  • production of thematic maps
  • water resources planning and monitoring
  • urban planning
  • agricultural property management planning
  • crop yield assessment
  • natural disaster assessment.

Why don't images look like photographs?

Understanding Artificial Colour in Satellite Imagery

This application allows you to change the colour value associated with different spectoral bands using the Tweed Heads region as a case study. This explains the difference between an image and a photograph.

Topic contact: earth.observation@ga.gov.au Last updated: October 27, 2011