A typical Earth observation satellite is made up of the following:Observation instrumentThe observation instrument acts as a camera andis one of the most important parts of the satellite. Ittakes ‘pictures’ (observation data) and sends theseback to a data-recording and telemetry unit.Telemetry allows you to measure the Earth from faraway (remotely) and report the information.Telemetry subsystemThis subsystem sends the data it observes as wellas information about units onboard the satellite tothe ground station.Command subsystemA command subsystem almost works like yourbrain! It sends commands to the rest of the unitson the satellite.Data storage subsystemThe data storage subsystem stores the image andhousekeeping data of onboard subsystems for acertain amount of time.Navigation subsystemThis system produces the information about the satellite’sposition in space. Attitude control subsystemThis tells the ground station that monitors the satellite what thesatellite’s direction is compared to that of Earth. The satellite’scameras and imager normally point towards specific targets(e.g. the sea or land) with its solar panels facing the Sun.

Through satellite technology, we can get important data abouthuman activities. We can also analyse the Earth as a global systemof natural processes that are all connected. The information fromanalysing the satellite data increases our Earth science knowledgeand helps decision-makers to address challenges.

A great advantage of space-based observation isthat it can cover a large geographical area.

Typical uses for satellite data include agriculturalmonitoring, predicting where possible humanhealth problems may arise (for example, changesin rainfall has an effect on the spreading of ticks and mosquitoes)and security (disaster management), land-use change (e.g. if the soilis being eroded by human activities), solid-earthhazards (e.g. earthquakes, tsunamis), climate andweather changes, and water resources.

These things may affect and influence the way we live, work and even survive on Earth!

Some challenges are:◆ Changing ice sheets and sea level

Will the major ice sheets, such as those of Greenland or the WestAntarctic, collapse? If they do – how quickly will it happen andhow fast will the sea level rise?

◆ Large-scale and persistent shifts in rainfall and water availabilityWill we have more droughts in specific places? How will thisaffect wildfires and will a decrease in snowfalls change the waywe store water?

◆ Air pollution across continentsHow will continuing economic development affect the productionof air pollutants, and how will these pollutants move acrossoceans and continents?

◆ Shifts in ecosystem structure and function inresponse to climate changeHow will coastal and ocean ecosystems respond to changes inthe climate, particularly those systems with a lot of human activity,such as fishing? If temperature and rainfall changes, what will theimpacts be on animal migration patterns?◆ Human health and climate change

Will previously rare diseases become common? How willmosquito-borne viruses spread with changes in rainfall

and drought? Will we be able to predict the outbreakof certain diseases, such as bird flu?◆ Extreme events, including severe storms, heat

waves, earthquakes, and volcanic eruptionsWill tropical cyclones and heat waves become

more frequent and more intense?

What are the limitations ofEarth observation?Satellite orbits are mostly higher than 500 km, which leadto lower resolution (i.e. detail that is not as fine as what itwould be in an aircraft taking a photo at 10 km abovethe ground – in the same way you will see much moredetail on the leaf of a plant by standing next to it, thanthe person sitting in an aircraft or the satellite that isoutside of Earth’s atmosphere).

Other drawbacksinclude high cost ofsatellite observation,and limitations ininstrument sensitivityand the number ofspecies that can bemeasured.

This is why scientistsoften combine spaceand ground-basedmeasurements whentrying to understandearth systems.

What isspace science?

A broad definition of space science is anyscientific field that studies events in space or

space flight. This normally includes anythingfrom about 80 km and higher – outside of

Earth’s atmosphere.

How do we observeEarth from space?Earth observation satellites can study theatmosphere (meteorological observation), orthe sea, land, and even oceanic winds.

What about ‘spy’ satellites?To a certain extent, the technology used inEarth observation satellites can monitor theactivities of humans, for example buildingroads. Communication satellites could beused to monitor radio and microwave-based telecommunications.

However, some 'spy’ satellites gather datathat could be used to monitor cloud coveror the rate of desertification and landdegradation. In fact, in the USA the spaceagency NASA works with a number ofpartners, including their Department ofHomeland Security.

Research, satellites and computer modelscan give data that can respond to any threat tothe USA’s infrastructure. Although satellites aretraditionally used for mapping and disaster relief,they can also be used for law enforcement orborder security. Some people see this as an intrusionof their privacy.

Different satellites used by NASA

Satellite dishes at the CSIR-run space ground station. atHartebeesthoek.

EasyScienceis produced by the South

African Agency for Science andTechnology Advancement (SAASTA), an

operational unit of the National ResearchFoundation. SAASTA’s mission is to

promote the public under-standing, appreciationand engagementwith science andtechnology amongall South Africans.

Visit the website:www.saasta.ac.za

for moreinformation.

How does space technology benefit us?

BLUE PLANETTaking a Look at the

Space science is a rapidly emerging field in South Africa.The government is establishing the South African Space Agency

and our own unique micro satellite, SumbandilaSAT will belaunched soon. This satellite will take pictures of Southern Africa to

help with research, planning and management in areas such asagriculture, the fishing industry, water resources, urban planning,

and losses caused by disasters such as fires and oil spills.

Earth Observation from Space

Propulsion subsystemA propulsion subsystem gives

the necessary power tochange the flight path (orbit)and attitude of the satellite.Power subsystem

A power subsystem workslike the heart of the

satellite in that itsupplies the electric power

necessary for operation.Thermal control subsystemThis subsystem keeps the temperaturesof onboard units within set ranges sothat the satellite works properly. Processing subsystemThis controls the entire satellite operations.

Left: TerraSAR X stripmap,multidate intensity compositeover the Swartland.

Right: TerraSAR X stripmap,multidate coherence compositeillustrating structuraldifferences between newlyplanted wheat (left) andrecently germinated rye (right).

At a glittering awards function in Pretoria, threelearners from the Eastern Cape beat stiff competitionto win the finals of a national debates tournament.

Over the last weekend in September, the top debating teamsfrom North West Province, the Eastern Cape, Gauteng, Free

State, Mpumalanga, Limpopo and KwaZulu-Natal faced eachother in an eloquent battle of wits. In the final round themembers of the Eastern Cape team, Andrew de Blocq,Anade Situma, and Ndzwayiba Makabongwe trumped worthyopponents Rebone Matabane, Sizwe Moagi, and KgweranoMpamonyane of the Limpopo team.

Earth observation from spaceis closely linked to militaryapplications. For example,the global positioning system(GPS) started out as a military

navigation system but quicklyfound its way into non-military

applications – from ocean andland navigation to personal

navigation by civilians (look aroundyou to see how many cars on the road

have a GPS on the dashboard!).Remote sensing uses instruments that often rely on

very high quality optics (the behaviour of electromagneticlight). The optics is used with a sensor that can detect

radiation at some specified frequencysuch as infrared, visible or ultraviolet.

For example, the advanced visible and near-infrared radiometer (AVNIR) is an optical sensor

used for observing land and coastal zones invisible and near-infrared regions. The datafrom AVNIR tell us more about desertification,the destruction rate of tropical forests andpollution of coastal zones.

Space science careersSpace science is very broad and includes a number of fieldsthat seem unrelated. Careers include space geodesy (deter-mining the position of geographical points, the shape and sizeof Earth), aeronautics, orbital dynamics, satellite technology,oceanography, land management, mapping,forestry, agriculture and GIS. All of thesecan be split into fields of specialisation.Anybody with post-school training inmathematics, physics, electronics,engineering, geology, geophysics,geography, computer science, statisticsor nearly any subject, will be able topursue a career in space science.

Research and development inspace science and its applicationsBillions of dollars have been invested in the development of spacescience projects. Apart from the USA, many countries are involved inspace research, including Russia, China, Japan, India, Pakistan,Australia, South Africa, Nigeria and Brazil.

New developments in space research will lead to satellites that areable to measure:

◆ solar and Earth radiation

◆ soil moisture and freeze-thaw for weather and water cycle processes

◆ ice sheet height changes for climate change

◆ make-up of land surface for agricultural and mineral classification

◆ atmospheric gas columns for air quality forecasts.

Right: The same area on3 April 2000 with heavyinundations (rising watersoverflowing normally dryland) due to cyclone Elinethat hit the coast inFebruary 2000.

Data from AVNIR and other sensors on Earthobserving satellites are often included in ageographical information system (GIS). Satellitedata are collected at different spatial (happeningin space), spectral (a range of electromagneticradiation in certain wavelengths) and temporal(relating to time) resolutions for agriculturalapplications and crop measurement. Data fromthis can give information about irrigated landscapemapping or soil conditions. This data can be usedin a GIS where different layers of information canbe stored. A researcher can then access theselayers of information to find out if a certain soil type– given a certain amount of water at a certain timeof the year – produces more or less crops thananother area that received water at a differenttime of the year.

Most satellites have some form of communicationslink to transfer the data to a control or groundstation on Earth. Earth observation satellites usea radio link to transfer data. Future satellites mayuse laser links, resulting in more data that willenable higher data rates, i.e. more data passedon in a shorter time.

Links to military, optics, GIS, communication

Lerato Senoko is a remotesensing/geographic informationsystems analyst at the Institutefor Satellite and SoftwareApplications.

Tammie Lotz is a remote sensing researcherat the CSIR’s Satellite Applications Centre

Jessie Ndaba is an engineerat Sun Space andInformation Systems Ltd.

Andrew de Blocq of St Andrews College inGrahamstown also received the prize for thebest overall speaker.

The national debates tournament, an initiativeof the SAASTA in partnership with the South African SchoolsDebating Board gives learners an opportunity to develop andfine-tune their skills in scientific research, critical thinking andinformation literacy, as well as their ability to work as a teamto present logical, clear arguments.

The Deputy Minister of Science and Technology, DerekHanekom, in his keynote address highlighted the insightand understanding the young learners displayed regardingissues of environmental concern and the fact that povertymarches along with problems such as pollution of naturalresources like water.“It is up to us and future generations to find smart waysand smart actions to solve these problems,” he told theaudience. “Our challenge is to find the right formula to offerall the people of the world a decent, sustainable lifestyle. Itis therefore imperative that we understand life systems sothat we know how to protect our natural resources.”

Deputy Minister of Science and Technology, DerekHanekom, with the winning team of the SAASTAnational school debates competition. The EasternCape learners are Ndzwayiba Makabongwe,Anade Situma and Andrew de Blocq.

Eastern Cape learners take top honoursin national debates tournament

Left: Landsat 7 imagefrom 5 July 1999.

Globalsecurity

Country legislations around occupying space

Several countries, notably Australia, USA, Sweden,Russia, Canada, UK and Israel, have space legislationto guide and regulate their space activities. SouthAfrica is developing a Space Agency, and hasrecently drafted a SpaceAgency Bill, whichcommits to

research anddevelopment in

space science.

Eastern Cape learners take top honoursin national debates tournament

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Maputo Bay(Mozambique) with theLimpopo River estuary.