Satellite sensing
Satellites are equipped with a wide range of super sense technology. Sensors have been developed that can detect radiation returns for many parts of the electromagnetic spectrum. At the shorter wavelength end, they can detect visible light much as a conventional camera, which is very useful for many mapping and monitoring applications. Near-infrared radiation is particularly useful for detecting living plant material, while thermal infrared detects temperature and has applications in weather forecasting and climate analysis. The microwave end of the spectrum supports a variety of applications including detecting the size and bulk of forests, mapping geological features, detecting rainfall, and detecting the size and direction of ocean waves.
The advantage of using sensors attached to satellites is that they can gather data very quickly over a large area.
Sensing storm damage
In 2004, a huge storm caused widespread landslides in the North Island of New Zealand. Scientists from Landcare Research used the French SPOT-5 satellite to map more than 64,000 landslides. The biggest problem was that this French satellite could not see through the clouds, so data could only be collected after the storm had passed. Stephen McNeill from the Informatics team at Landcare Research wanted to use another type of radar satellite that could operate 24 hours per day in any weather conditions.
Mapping landslides using radar satellite
A series of images comparing satellite images of landslips in the Whanganui hill country in 1998 and 2004. Landslips show up as brighter areas.
Acknowledgement: Radarsat R-Data © Canadian Space Agency 1998, 2004. All rights reserved
The accuracy of the SPOT-5 satellite was tested by comparing those images with the Canadian Space Agency’s Radarsat-1 satellite. Storm damaged areas show up as brighter areas on the satellite images.
Sensing changes in wetlands
Satellites have also been used to detect changes to plant communities in wetland environments. Landcare Research has been working with the Department of Conservation at the vast (17,000 ha) Awarua Wetlands site in Southland.
Satellite images of the Awarua Wetlands site
Sensors from optical or radar satellites can provide scientists with information about the 2005 fire damage, regeneration of wetlands vegetation and also the effects of climate change.
Satellite images are taken of Awarua Wetlands using the European Space Agency’s Envisat satellite. Data can be gathered at 1-year intervals to show changes in plant distribution that might have been caused by birds, storms, fire and humans.
The Awarua Wetlands have been burnt at various times in the past. Stephen McNeill at Landcare Research uses SPOT satellite images to determine fire damage and to study the recovery of the various wetland plants after the fire. This information helps organisations such as the Department of Conservation determine the best types of management for these vulnerable habitats.
Applying sensing data to dairy farming
Another exciting area of research using optical sensors is in the dairy, beef and sheep farming industries. At Landcare Research, David Pairman’s latest project uses radar imagery collected from the TerraSAR-X satellite to identify pasture biomass using specialised computer programs and colour-coding.
Radar images of dairy pasture on two different days
Remote sensing scientists use the TerraSAR-X radar satellite and computer-adapted colour-coded images to determine pasture biomass levels. The left-hand image is annotated with paddock names, while the numbers on the right-hand image represent grass height (cm). The darker shades represent longer grass. A dark strip in paddock N-2 in the right-hand image would have been caused by an electric fence preventing the cows from eating it.
Acknowledgement: Images originated from the German TerraSAR-X satellite.
David Pairman believes this satellite data could provide farmers with crucial information to assist in the optimal management of their pastures for efficient milk production.
Problems using satellite sensing
There can be problems using satellite sensing. As satellites orbit the Earth many kilometres up in space, it might take several days or weeks before some satellite are stationed over a specific site, and this time delay may affect the accuracy of the information received.
The data received by the satellite is compared with the data gathered by scientists working at ground level. For example, to test for biomass accuracy, the height of the grass is measured and the data is compared to the data provided by the TerraSAR-X satellite.
Nature of science
Scientists use specialised computer programmes alongside satellite data for weather analysis, mapping plant cover of farms and other areas such as wetlands. Scientists often compare the information from satellite sensors with samples from the field and adjust the results accordingly.
Activity idea
Learn a few strategies to interpret observations from satellite images.
