SANSA | FAQs
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FAQs

All your space questions answered.

Earth Observation

How do I obtain Earth observation satellite images from SANSA?

You will have to register on our online catalogue and select the images you require using the link: http://catalogue.sansa.org.za/.

Do I have to pay for Earth observation satellite images?

All our online images are free to students and government departments. Private entities can access LANDSAT, CBERS, SAC-C, and SumbandilaSat at no cost and SPOT data at discounted rate.

What is Earth observation?

Earth observation refers to the gathering of information about Earth’s chemical and biological systems using remote sensing technology and other field techniques.

What is remote sensing?

Remote sensing is the science of acquiring information about an object without being in physical contact with it.

Which satellite data does SANSA EO provide?

Online satellite images: SPOT 1- 6, LANDSAT 5 and 7, CBERS 2, SAC-C, and SumbandilaSat. We are resellers of Digital Globe products (World View 1-3, Geo Eye1, Quick Bird 2, and IKONOS), AIRBUS Products (Pleiades and TerraSAR-X) and MDA Products (RadarSAT).

Can I get earth observation sample data and information?

Yes, you can get SPOT and PLEIADES images using this link: http://www.geo-airbusds.com/en/23-sample-imagery

What are Value Added Products (VAPs)?

Value Added Products (VAPs) are the products derived from satellite images by physically changing those images in a way which enhances their value. For example, Human Settlement, Flood Potential and NDVI (normalised difference vegetation index) layers are all VAPs extracted from satellite images.

Where can I access training materials and tutorials?

Students, government officials and any person interested in learning some basic to advanced skills in remote sensing can visit our Fundisa Portal Page http://fundisa.sansa.org.za/ to access a range of tutorials, links to open source software, and training data.

What are possible applications that I can use earth observation data for?

Earth Observation data can be applied in a wide range of fields, including but not limited to disaster management (floods, fire, drought mapping), settlement mapping, land cover/use mapping, water resource management, and vegetation management.

Do I need approval from a supervisor before ordering the data?

Yes. If you are a student, your supervisor has to acknowledge the project in writing to eocustomers@sansa.org.za.

Are there any science outreach programmes to learners and communities at large?

Science advancement is one of the priority programmes at SANSA, aiming to reach learners and community members across South Africa, to educate them about a range of opportunities that exist in the space sector.

Do I need to register on the catalogue to search for data?

Yes. You first need to register before you can view, order and download data from the SANSA catalogue.

What are the processing levels that I can obtain from SANSA EO?

Multiple levels are available. This can depend on the sensor and processing system.

Does SANSA provide any bursaries, internships, and studentships? How do I apply?

SANSA EO annually advertises bursaries for post graduate students, and internships and studentships are offered from time to time. Be on the look out for these opportunities and apply.

What kind of VAP(s) can I obtain from SANSA EO and how?

There is a range of Value Added Products (VAPs) developed by SANSA EO scientists. Contact customer services at eocustomers@sansa.org.za to find out more about these.

Are there any training courses to stakeholders offered by SANSA? How can I apply?

SANSA EO is committed to capacity building within South Africa and its neighbours. From time to time, training courses are offered on various topics. Be sure to frequently check our website for advertised courses.

How can I access Fundisa Resources in my university?

Each year, SANSA EO distributes Fundisa disks to all South African Universities. These contain open software, tutorials, and remote sensing data. Visit your Geography/GIS department to ask about the Fundisa Disk or contact customer services eocustomers@sansa.org.za to locate the data champion at your university.

Different applications have different data needs. Who can I contact for advice?

You can contact our Data, Products and Customer Services unit (DPS) for good advice on which data you need depending on the application of interest.

For additional questions and assistance, please contact customer services at eocustomers@sansa.org.za.

Space Engineering

What is a satellite?

A satellite is an object that revolves around a planet in a circular or elliptical path. Earth and the moon are ‘natural’ satellites. Man-made satellites are machines, made by people, that are launched into space and orbit Earth or another body in space. There are thousands of man-made satellites that may be used to take pictures of our planet, the sun or other objects. These pictures help scientists learn about Earth, the solar system and the universe. Other satellites send TV signals, GPS locations or phone calls around the world.

 

What is an orbit?

This is a path that satellites follow. In orbit, the farthest point from Earth is the apogee; the nearest is called the perigee.

 

What are the components of a satellite?

Satellites come in many shapes and sizes, but most have at least two things in common – an antenna and a power source. The antenna is used to send and receive information. The power source can be a solar panel or battery. Many satellites carry cameras and scientific sensors. They may gather information about Earth’s land, air and water or they may collect data from the solar system and universe. All satellites have a metal or composite frame and body known as a bus. The bus holds everything together in space and provides enough strength to survive the launch. All satellites also contain an on-board computer to control and monitor different systems, as well as an altitude control system which keeps the satellite pointed in the right direction.

 

What comprises a system?

A system is an integrated set of elements that accomplish a defined objective. These elements include products (hardware, software and firmware), processes, people, information, techniques, facilities, services, and other support elements.

 

What comprises a sub-system?

A sub-system is a coherent and somewhat independent component of a larger system. Each component is a sub-system of the original system and carries out a part of the system task.

Space Operations

What does SANSA Space Operations do?

The tracking, telemetry and command (TT&C) group provides companies globally with space operations and applications, as well as applied research and development (R&D) and innovation in these areas. The group builds, maintains and hosts antennas and ground stations, and supports satellite launches, as well as what happens to the satellites during their lifecycles and in emergencies. The station at Hartebeesthoek also undertakes orbit transfers and testing, carrier monitoring and remote sensing reception, and provides international clients with mission control services and the hosting of ground infrastructure. Clients throughout southern Africa benefit from a host of satellite technology services such as project management; systems and radio frequency engineering; soil testing; civil and electrical, high-voltage alternating current works; procurement, import and logistics; installation and integration of antenna systems; acceptance testing and commissioning; and developing procedures for operations and maintenance.

 

What is a geostationary orbit?

A geostationary orbit is one in which a satellite orbits the Earth at exactly the same speed as the Earth turns, which positions it in the same spot directly above the Equator to provide uninterrupted coverage of a specific area on Earth. Satellites move along three types of orbits: Low Earth Orbits (LEO, earth observation data satellites); Medium Earth Orbits (MEO, navigation satellites); and Geostationary Earth Orbits (GEO, communication satellites).

 

What is space junk?

Space junk is a term for human-made objects that orbit around Earth without any useful purpose, because of equipment failure, damage, or because they are obsolete. The objects range from spent rocket stages and defunct satellites, to explosion and collision fragments. The orbits of these objects often overlap the trajectories of spacecraft and can therefore pose a potential collision risk. Space junk occasionally falls to Earth: a piece of debris from outer space was found on a farm in South Africa. The piece eventually arrived at Hartebeesthoek where its probable origins were investigated by members of the TT&C team. It can still be seen there today.

 

What is an apogee?

The apogee is the remotest point of a satellite’s elliptical (non-circular) orbit around the Earth. Such a satellite has variable altitude and orbital speed, and the point of highest altitude is called apogee. The term also applies to the maximum distance between the satellite and the centre of the Earth, approximately 6,400 km. At apogee, a satellite travels more slowly than at any other point. It is the best time to access a satellite because it is accessible for a comparatively long time. If a directional antenna is used at a ground-based station, it is relatively easy to track the satellite because the position of the antenna does not have to be adjusted quickly or often.

 

What is an antenna?

A satellite antenna is a dish-shaped, parabolic device designed to receive microwaves from communications satellites that transmit data or broadcasts, such as satellite television. The parabolic shape reflects the signal to the focal point of the dish. A feed horn, mounted on a mast from the center of the dish or on tripod legs attached to the edge of the dish, conveys radio waves between the transmitter and/or receiver (transceiver) and the reflector. Antennas serve as interfaces between uplinks (signals transmitted from Earth) and downlinks (signals transmitted to Earth) and the electronics inside the satellite. The antennas at Hartebeesthoek have different dish sizes and slew rates and accommodate a number of frequency bands and tracking modes.

 

What is slew rate?

The slew rate of an antenna is its ability to respond to change. An amplifier with low slew rate will ‘lag’ in its response to instantaneous power requests, as the power curve cannot be met and the amplifier will not mimic the input curve correctly. If the slew rate is matched to the input it will provide an accurate response and therefore a realistic output.

 

What is telemetry?

Telemetry is the transmission of radio signals and data, automatically and at a distance, such as between a ground station and an satellite to record information or operate guidance apparatus.

Space Science

What is space weather?

Space weather is the effect that gases coming from the Sun have on the Earth’s magnetic field, which can result in damage to technological systems like satellites, navigation and communication technology. These gases are called solar wind, and can reach speeds of more than 500 kilometres per second depending on solar activity like flares and sunspots. Disturbances in the solar wind shake Earth’s magnetic field and pump energy into the radiation belts. Space weather is growing in importance as mankind becomes increasingly dependent on technological systems.

 

Does the Sun itself spin? If so, how fast?

The rotation period of the Sun varies from about 25 days at the equator to over 30 days at the poles, so it takes roughly two weeks for a feature to cross the solar disc when looking at it from Earth.

 

What is the role of a Space Weather Centre?

A Space Weather Centre delivers space weather products and services that meet the evolving needs of the nation. It gathers data about the state of the Sun, Heliosphere, Magnetosphere, and Ionosphere in real time, to form a picture of the environment between the Sun and the Earth. With this information, forecasts, watches, warnings and alerts are prepared by the Space Weather Centre and issued to anyone affected by space weather.

 

How do you monitor events on the sun?

The SANSA Space Weather Centre uses ground- and space-based sensors and imaging systems to view activity at various depths in the solar atmosphere.

 

What is a solar flare?

A solar flare is an intense burst of radiation from the sun, caused by the release of magnetic energy associated with sunspots. Solar flares are seen by the photons (or light) released across the spectrum. X-rays are the primary wavelength monitored in the classification of solar flares. Flares also contribute to the acceleration of protons and other charged particles that may accompany a significant event.

 

Does all solar activity impact Earth?

We can divide solar activity into four main components: solar flares, coronal mass ejections, high speed solar wind, and solar energetic particles.

Solar flares impact Earth only when they occur on the side of the Sun facing Earth. Because flares are made of photons, these travel out directly from the flare site, so if we can see the flare, we can be impacted by it.

Coronal mass ejections (CMEs) are large clouds of plasma within a magnetic field that erupt from the Sun. These clouds can erupt in any direction, and then continue on in that direction, plowing right through the solar wind. Only when the cloud is aimed at Earth will the CME hit Earth and cause impacts.

High speed streams of solar wind coming from the Sun come from special areas on the Sun known as coronal holes. These holes can form anywhere on the Sun and usually the winds they produce impact Earth only when they are closer to the equator than to the solar poles.

Solar energetic particles are high-energy charged particles, mostly released by coronal mass ejections. Where the cloud of a CME plows through the solar wind, the solar energetic particles are travelling much faster and because they follow the magnetic field lines in the space between the Sun and the Earth. Therefore, only the charged particles that follow magnetic field lines that intersect the Earth will have an impact on Earth.

 

Have scientists seen changes in the intensity of space weather?

On a short time scale, the intensity of space weather is always changing.  Conditions can be mild one minute and stormy the next. On longer time scales, space weather varies with the solar cycle.  The solar cycle is an average 11 year cycle where the number of sunspots goes from very few per month, to many, and back to very few.  At solar minimum, we might see no sunspots, whereas at solar maximum, we can have 200 sunspots in a month. Solar flares, coronal mass ejections and solar energetic particles all increase in frequency as we get closer to solar maximum.  High-speed wind streams are more frequent at solar minimum, which means we have to watch space weather carefully no matter where we are in the solar cycle.

 

What are sunspots and how do they relate to space weather?

The magnetic field in sunspots stores energy that is released in solar flares. As a result, flares usually occur in a cycle that mimics the 11-year sunspot cycle. Other forms of space weather such as geomagnetic storms and proton radiation showers follow a similar cycle. Sunspots usually occur in groups; usually as pairs, but sometimes in complicated arrangements with many spots and complex shapes. These unusual regions most often produce solar flares. Space weather forecasters use the complexity and shapes of sunspots to make flare forecasts: the more complex the groups of spots, the more likely that a flare will occur.

 

What is the solar maximum and solar minimum?

At solar minimum, the sun may go many days with no spots visible. At maximum, there may be several hundred spots on any day.

 

What are the Northern Lights and are they related to space weather?

When the sun is active, it often produces mass ejections that interact with Earth’s magnetic field. Electric currents begin to flow in the upper atmosphere, and these currents produce the aurora borealis (Northern Lights) and the aurora australis (Southern Lights), which occur almost simultaneously around both the north and south poles, respectively.

 

How do you forecast space weather?

Space Weather Centre forecasters analyse near-real-time ground- and space-based observations to assess the state of the solar-geophysical environment (from the Sun to the Earth, and points in between). They also analyse the 27-day recurrent pattern of solar activity. Comparing this analysis to past situations, and using numerical models similar to weather models, forecasters are able to predict space weather on timescales of hours to weeks.

 

Why is forecasting space weather important?

Some of the specific effects of space weather on Earth systems include interference with short wave radio, problems with electric power grids, the decay of satellite orbits, and radiation hazards for satellites and for astronauts during some phases of space missions.

 

How does the “South Atlantic Anomaly” affect satellites?

The South Atlantic Anomaly is a dip in the Earth’s magnetic field which allows cosmic rays and charged particles to reach lower into the atmosphere. The anomaly is always there, but it does change in intensity. The SAA is populated with high energy particles that can penetrate the skin of the spacecraft and cause upsets in spacecraft electronics.