Satellites can help save the environment
In 10 years, Thohoyandou in Limpopo has become unrecognisable.
Two images sit side-by-side, satellite footage of what the area in the country’s northern-most province looked like in 2004 and 2013. To the untrained eye, there is obviously less green, more brown and the grey of settlements. Satellite images often look like mosaics: a collection of small images that when seen together, create a picture and, like most art, if you inspect it more closely, you can find hidden meaning.
Humans have always changed the environment around them; building houses, cultivating crops and setting up factories have changed land use and land cover throughout history. But to manage and preserve our environment, we must incorporate and plan to protect certain biologically diverse areas and water bodies. In an article published in 2007 in journal Proceedings of the National Academy of Sciences (PNAS), Harvard University researcher Benjamin Turner wrote: “Land use and land cover, especially those caused by human activities, are the most important component of global environmental change, with impacts possibly greater than the other global changes”.
To preserve the environment and ensure that its resources — food, water and minerals, among others — are used sustainably, we need to monitor and document our land use, see how it has changed over time and use this information to predict future trends. One way we can do this is by using satellite images to piece together what is happening on the ground.
Thohoyandou is the administrative capital of the Vhembe district, surrounded by poorer villages. Once the capital of the Venda bantustan under the apartheid government, this town is now one of the fastest growing towns in the province. And we can see that by comparing satellite images, from the French SPOT-5 satellite.
In the 2013 images of Thohoyan-dou, the grey of settlements covers twice as much area as it did in 2004, showing us that substantially more people have moved from villages into the town with the land areas covered by residential and commercial buildings having almost doubled.
One of the contributing factors is the accessibility of social amenities, which are more easily available in the town than in surrounding villages. Since it is the area’s economic hub, most young graduates in the Vhembe district move to Thohoyandou after completing their education, looking for jobs and better living conditions.
In 2004, much of this area was green from space, but over the past decade the dense tree cover gradually disappeared and was replaced by clusters of roofs from both residential and commercial buildings. This can be traced to the economic growth of the town and its administrative role. The central business district land area increased and continues to expand.
Since 2004, the town’s economy has grown because of the increase in trade and commerce both in the formal and informal sectors between the town and surrounding villages. Also the town’s position as an administrative centre meant that the government built more buildings for administrative purposes, and we can see their large roofs in our satellite images.
The bare and open sections in residential areas were divided and built up, with a few cordoned off for recreational purposes: those are the sporting facilities and parks. The formerly green patches now look reddish and brown with clusters of roofs.
The information about the changes in land usage can be used by town planners, service providers, government agencies and economists, among others, to determine services, extrapolate future usage demands, and measure the development of Thohoyandou town.
Using remote sensing techniques, such as satellite imagery, rather than physical surveys, is more effective. Rather than having a person drive the area every few years to mark out land use, satellite images can provide greater detail and real-time land usage.
This information can be collected using a geographic information system (GIS), which is a computer system designed to analyse geographic data, and can assist in land use classification. These GIS techniques also allow for accuracy assessments on land classification, something which is not possible in physical surveys.
At the University of Venda, we are investigating different geographical phenomenon using GIS and remote sensing techniques. Through the South African National Space Agency, we are able to get satellite images, such as the SPOT-5 images, free or at a subsidised rate. This is important because images from private space agencies can be expensive, and beyond the reach of academic research institutions.
By doing more research into land usage and how it changes over time, we will be able to know to what extent human activities have impacted the environment. This allows us to make recommendations to government agencies on approaches and measures that can be taken to protect the environment amidst expansion and development.
Olujimi Osidele is a MSc candidate at the University of Venda.