Satellites are built to perform specific functions. Expecting a GPS1 satellite2 to collect weather3 data4 is a bit like expecting your mountain bike to pull water skiers!
Satellite missions and payloads
Satellites are grouped by the jobs they are sent into space to do, also known as their missions. Missions include communications (internet, phones and television), weather, navigation and Earth observation. All satellites will have common components like batteries and solar panels to keep them powered, but the payload components are specific to the kind of mission data they are designed to collect.
Simply explained, the satellite’s payload consists of one or more communication antennas, transmitters and receivers. Antennas and receivers collect data using instruments like radar5, GPS and cameras. These sensors receive electromagnetic radiation6 from what is being observed and convert it into signals – for example, numerical data or images. This information is transmitted (downloaded) to ground stations where it is often interpreted and analysed and made available for others to use.
The following information explores three situations in which Earth observation satellites are used to gather data.
Tracking ship movements
Aotearoa7 New Zealand’s exclusive economic zone (EEZ) is 4 million square kilometres – more than 20 times the size of our land area! New Zealand governs this area and decides who can use the resources. Our EEZ8 is far too large to monitor via marine patrol boats, so satellites are used to monitor ship movements. The Xerra Earth Observation Institute created ©Starboard Maritime Intelligence, a software platform that monitors the sea for activities like illegal fishing and dark vessels. Dark vessels either do not have automatic identification systems or they switch9 off their location-transmitting devices to avoid being detected.
Starboard uses satellites with a variety of sensors to track vessels. Sensors using synthetic10 aperture radar (SAR) send radar emissions that ping from the surface of a ship back to the satellite. Radar is more efficient than optical sensors that take images – clouds and big waves can block the satellite’s view.
The article How do we find dark vessels on the ocean? provides additional information about maritime tracking. The activity Analysing satellite data for finding dark vessels uses actual satellite data from ©Starboard Maritime Intelligence.
Monitoring endangered animals
Earth observation satellites can be very useful when monitoring animal populations11. The sensors are not in direct contact with the animals so monitoring does not disturb them or interfere with migration activities or nesting sites. Although the scientists who do the on-the-ground monitoring find the work exciting, travel to these places is often expensive, sometimes dangerous and provides only one snapshot in time. High-resolution remote sensing is able to make these sorts of measurements quickly, precisely and often.
Scientists (and citizen scientists) examine these high-resolution images to gather evidence12 about population13 numbers and learn more about the day-to-day activities of the animals. They can use this evidence to make inferences about habitat14, food webs and much more.
The article How are satellites helping albatross? provides additional information about species15 monitoring. The activity Analysing satellite data for albatross research uses actual satellite data of albatross monitoring in the Chatham Islands.
Monitoring slow slips
We usually know when an earthquake occurs – we feel the ground shaking or seismometers pick up the movements. Some of New Zealand’s land surface is gradually moving as a result of normal tectonic movement called slow slips. Sometimes the movements take days to move a few millimetres, while other slips take many months. Learning about slow slips helps scientists gain a better understanding of the relationship between slow slips and earthquakes.
One way to track these tiny movements is through the network of global navigation satellite system (commonly referred to as GPS) receivers and antennas operated by GNS Science and Land Information New Zealand. There are over 50 monitoring sites across the North Island, South Island and Chatham Islands. The receivers at these sites record very precise positions on the surface of the Earth so scientists are able to continually measure even the smallest of movements – and the bigger ones too.
The article How do we know about Earth movements? provides additional information about slow slip monitoring. The activity Analysing satellite data to track Earth movements uses actual Geonet satellite data of slow slip movements around Māhia Peninsula.
Satellites and orbits
The job a satellite is designed to do will determine the orbit16 the satellite occupies. These are three common orbits for Earth observation:
- Low Earth orbit – an orbit with an altitude17 from 200–2,000 km. This orbit is ideal for missions that require high-resolution optical or synthetic aperture radar images to provide detailed information.
- Medium Earth orbit – an orbit with an altitude that is commonly 20,000 km. This orbit is ideal for GPS satellite constellations.
- Geostationary orbit – an orbit with an altitude that is commonly 35,786 km. This orbit is ideal for tracking the weather.
Essential satellite components
These components are common in most satellites:
- Bus/frame – the frame and structure of the satellite. All other components are attached to it.
- Solar panels – to provide electrical energy for the satellite to operate.
- Batteries – to store energy from the solar panels so the satellite can operate.
- Heat control – to maintain an optimum18 working temperature19. It covers the other components to protect them.
- Computer – to control the operation of the satellite and collect, store and send data back to Earth.
- Thrusters – to move and position the satellite so the payload component and the antenna20 are pointing in the required direction.
- Transmitter/receiver – to get information from Earth to control the satellite and also to send data back to Earth.
- Antenna – the external part of the transmitter/receiver that converts information to radio waves21 (transmitter) and from radio waves (receiver).
Payload components
The satellite’s payload consists of one or more communication antennas, transmitters and receivers. These are some common components:
- Radar – this works as a transmitter and a receiver. It transmits pulses of microwave radiation towards the Earth’s surface. Each pulse bounces off objects on the Earth’s surface back to the radar detector.
- Radio GPS – this precise atomic clock22 continually transmits its time value to the Earth via radio. GPS trackers placed near tectonic plate boundaries23 communicate with at least four GPS satellites and use their time values to calculate the trackers' positions on the Earth's surface to within a few millimetres.
- Camera – a camera detects visible light coming from the Earth's surface. It is more powerful than a standard digital camera – it has a larger and more accurate optical lens24 system and a larger electronic sensor chip.
Smaller satellites usually carry one type of payload due to the cost involved in building the satellite and getting it into orbit.
Activity ideas
This resource supports the Build a satellite interactive.
Get hands-on experience with some of these components by building a 3D cardboard satellite model.
Use an app and web-based resources to spot artificial satellites as they move across the sky.
Explore different satellites and orbits in this interactive.
Something creepy is happening uses data from a slow slip near Kāpiti. Students use this information to plot and interpret data on a line graph.
The citizen science25 project Floating Forests needs the help of citizen scientists to identify kelp forests using Landsat satellite images. This could make a great classroom activity, with links to climate change26 action.
Acknowledgement
This resource has been produced with funding from the Ministry of Business, Innovation and Employment and the support of the New Zealand Space Agency.
- GPS: Global positioning system. Uses satellites, computers and receivers to determine the exact position of a receiver on Earth by calculating the time difference for signals from different satellites to reach the receiver.
- satellite: Any object that orbits around another object.
- weather: Daily or short-term conditions like temperature, cloud cover, precipitation and wind affecting a certain area.
- data: The unprocessed information we analyse to gain knowledge.
- radar: A method of detecting distant objects and determining their position, speed, or other characteristics by using very high frequency radio waves reflected from the objects’ surfaces.
- radiation: Energy that is transmitted (radiates) from a source in the form of rays or waves or particles.
- Aotearoa: The Māori name for New Zealand, meaning Land of the Long White Cloud.
- exclusive economic zone (EEZ): A seazone prescribed by the United Nations Convention on the Law of the Sea over which a country has special rights concerning the exploration and use of marine resources. It extends 200 nautical miles (370 kilometres) from the coast.
- switch: An electrical component that can make or break an electrical circuit, connecting or interrupting the current or diverting it from one conductor to another.
- synthetic: Made in a laboratory or factory by a chemical process, usually to imitate a natural process.
- population: In biology, a population is a group of organisms of a species that live in the same place at a same time and that can interbreed.
- evidence: Data, or information, used to prove or disprove something.
- population: In biology, a population is a group of organisms of a species that live in the same place at a same time and that can interbreed.
- habitat: The natural environment in which an organism lives.
- species: (Abbreviation sp. or spp.) A division used in the Linnean system of classification or taxonomy. A group of living organisms that can interbreed to produce viable offspring.
- orbit: The path of an object as it revolves around another object. For example, the path the Moon takes as it moves around the Earth is its orbit.
- altitude: 1. The height of something, usually height above sea level. 2. In astronomy, the angular distance of a natural or artificial satellite above the horizon.
- optimum: The best or maximum that can be achieved.
- temperature: A measure of the degree of hotness or coldness of an object or substance. Temperature is measured with a thermometer calibrated in one or more temperature scales. Kelvin scale temperature is a measure of the average energy of the molecules of a body.
- antenna: In physics a device used to transmit or receive electromagnetic signals such as for radio or television. Also known as an aerial. A satellite dish is a type of antenna. In biology antennae are sensory appendages that occur in pairs on the heads of insects and many other arthropods. Antenna refers to one of the jointed, movable appendages.
- radio waves: An electromagnetic wave having a wavelength between 1 millimetre and 30,000 metres. Radio waves are used for transmitting radio and television signals. Many celestial objects, such as pulsars, emit radio waves.
- atomic clock: Caesium atomic clocks operate by exposing caesium atoms to microwaves until they start to vibrate at one of their resonant frequencies. By measuring this frequency, which is an unchanging property of matter, a time measure can be established. Caesium atomic clocks are very stable, and accuracies of 1 second in 1.4 million years have been reported.
- tectonic plate boundaries: The margin formed when tectonic plates collide. For example, off the east coast of the North Island, the Pacific plate and the Australian plate are colliding, giving rise to the boundary known as the Hikurangi Margin. There are three main types of boundary: convergent, divergent and transform.
- lens: A piece of glass or other transparent material with at least one curved surface. Lenses are used to change the direction of light rays that pass through them (focusing or dispersing the rays).
- citizen science: Citizen volunteers participate in scientific projects and work in partnership with scientists to answer scientific questions.
- climate change: The large-scale, long-term increase in the Earth’s average temperatures, with associated changes in weather patterns. There is significant scientific evidence that warming is due to increased quantities of greenhouse gases in the atmosphere, with most of the rise due to human activity.
