EARTH OBSERVATION
Earth Observation (EO) satellites help us to monitor and protect our environment, manage our resources, respond to global humanitarian disasters and enable sustainable development.
They provide essential information on a vast number of areas, including; ocean salinity, ice thickness, crop health and air quality.
EO satellites can be divided into two types based on how they capture imagery; passive and active.
HOW EO SATELLITES WORK
EO satellites can be divided into two types based on how they capture imagery; passive and active.
PASSIVE EO SATELLITES
Passive satellites detect radiation reflected off the Earth’s surface, such as visible light and infrared. In general, passive satellites are not able to work through clouds.
Approximate max resolution: 50cm
ACTIVE EO SATELLITES
Active satellites transmit energy towards the Earth and measure the returned signal which provides information about the Earth’s surface. In general, active satellites can see through cloud.
Approximate max resolution: 25cm
HOW MUCH CAN SATELLITES SEE?
SWATH WIDTH
The width of the area viewed by the satellite is termed the swath width. Satellites with different swath widths have different temporal resolution, which is the time between observations at the same point on the Earth. Typically large swath satellites can revisit the same location more frequently.
GETTING EARTH OBSERVATION DATA
HOW DOES AN EO SATELLITE COLLECT DATA?
EO satellites travel on a range of different orbits, offering varying perspectives of the Earth. Most satellites do not continuously collect data due to limitations in power and memory. Some offer regular and reliable data acquisition while others may be more ad-hoc, collecting only 5 or 10 minutes worth of data in a 90 minute orbit. Data is stored on-board the satellite until it is in sight of a ground station to downlink the data. The time between an image being taken and being available to download can range between a month to a few minutes and is getting quicker all the time. As satellites are owned by different companies there are several data providers, each with their own pricing structure. The cost for 1km2 of land can vary between free and £190 depending on data provider though increasingly, archives of free data are being made available for processing and analysis.
HOW WELL CAN A SATELLITE SEE DETAIL?
A satellite’s ability to detect certain wavelengths of light is called its spectral resolution. Different materials such as water, soil, vegetation and buildings interact in different ways with each wavelength, making them uniquely discernible. Therefore, if you know the type of object you are trying to observe, there will be an optimum wavelength for your purpose. EO satellites’ differing spatial resolutions measure the observable detail in an image, from sub-meter to tens of kilometres.
© European Space Imaging / DigitalGlobe Image Copyright © Satellite Application Catapult Ltd 2014
1. 10m resolution 2. 10m resolution zoomed 3. 0.5m resolution of the same area
While high resolutions are used to see the world in detail, low resolutions have useful applications over large areas.
EO APPLICATION EXAMPLE
The Challenge
By 2050, the global cost of flood and storm damage is estimated to reach £600bn and will continue to grow as the climate becomes more volatile.
The Satellite Solution
Satellite data can analyse soil composition and moisture content, and measure flood water depth, and then calculate likely water flow characteristics. This information has been implemented into a 95% accurate flood model which can be used to predict the impact of flood events.