Mapping the Heights of the World

11 May 2009, 10:08am

The most accurate map ever produced of the world’s land heights will help scientists make better predictions about the impact of natural disasters such as avalanches, volcanoes and floods.

Researchers at De Montfort University Leicester (DMU) created the map using data from several sources including NASA’s Shuttle Radar Topography Mission (SRTM) and several European satellites.

Global Height maps, known as Global Digital Elevation Models (GDEMs), are used in many different ways but are crucial in the study of any natural disasters which are influenced by the shape of the Earth’s terrain.

Professor Philippa Berry, who leads DMU’s Earth and Planetary Remote Sensing Laboratory (EAPRS), which created the GDEM, said: “This kind of information is critical in the study of hydrological and pyroclastic flows as it can help to predict how lava will move across the landscape after a volcanic eruption or where floodwater will run.

“It can also be applied to avalanches to see how their course might be affected by a mountain’s terrain.”

The project, entitled Altimeter Corrected Elevations 2 (ACE2), has been funded by €114,000 from the European Space Agency and the GDEM resulting from the research is now being made freely available to the public via the Internet.

NASA’s SRTM mission, carried out in 2000, was a leap forward in modelling the world’s elevations. It provided measurements on a more detailed scale than had previously been produced, however, there were areas which could not be mapped to the same level of accuracy as the rest of the model.

For example, large areas of dense vegetation were problematic as the sensors could not penetrate far into the leaf cover. This meant that in places such as the Amazon there was no way of measuring the actual height of the ground beneath the rainforest canopy.

“SRTM was a huge advance in our understanding of land surfaces and by combining it with information from a number of satellites we have been able to enhance this unique data set and produce a model that is the best yet,” Professor Berry added.

Along with the SRTM results, the ACE2 dataset uses information from five satellites; ERS1, ERS2, ENVISAT, TOPEX and JASON-1.

Professor Berry added: “Just as you can put a stone in a stream and affect the flow of the water, one bad height pixel can make a big difference to where a model predicts that water will flow over the Earth’s surface.

“The whole point of ACE2 is to give people access to elevation data and also to give them information about how accurate we believe the information is so they are able to use the model in the most effective way.”

GDEMs are used in many different applications including the design of housing developments and for engineering projects in which landscape is a factor.

They are also an integral part of Geographic Information Systems (GIS) and are therefore crucial to the work of geologists. One example is the study of vegetation growth where the information can help to analyse the reasons why plants might grow better on one side of a hill than another.

Professor Berry added: “Anybody who works with a GIS will be using this information. GDEMs are embedded in a number of applications and are fundamental to their operation.”

The model will be an important tool for satellites as it will allow the Earth’s surface to be tracked more accurately. It can also be used to interpret information about the Earth’s terrain when photographs have been taken at an angle, which is often the case with satellite images.

The model will be installed on both current and future satellite missions, including Sentinel 3 and JASON2.

Professor Berry and her team were also responsible for the first Altimeter Corrected Elevations project, known as ACE. The GDEM produced by ACE was hugely successful and gave radically improved information about elevation heights in parts of the world.

In comparison, ACE2’s GDEM features 100 times more height pixels than ACE and is a major advance in global elevation modelling.

The ACE2 model is available to download at the link below. The information is free but visitors must register before they can access the data.

ACE2 model

Geo: International