Table B2.4.

Key benefits and limitations of using satellite imagery for low-cost road projects

Key benefitsKey limitations
• Depending on which satellite data is used, a single image can cover a relatively large area. For example, a Landsat image covers an area of 185×185 km.
• Can provide a perspective or view of the landscape that cannot normally be achieved by other means. This could help to provide information about an area that may not be obvious from ground level, such as how a particular feature within the landscape relates to other parts of that landscape.
• The availability of information that is beyond the visible part of the electromagnetic spectrum, such as infrared imagery. Such data can be used to enhance image interpretation.
• The increasing availability of products derived from the satellite data, such as Digital Elevation Models (DEMs).
• Frequent repeat collection of images: many satellites have the capability to collect an image for any given area at least once a month.
• Low levels of distortion away from the centre of the image, particularly when compared with aerial photographs.
• The potential for digital image analysis, such as automatic classification.
• The increasing availability of high-resolution imagery and stereo capability using DEM or stereo images.
• Although there is almost complete global coverage of archived satellite imagery, there are gaps in some areas (particularly the tropics and high latitudes) where there is either limited data coverage or the data in the archive are not to the highest environmental quality standards (cloud cover, atmospheric haze, poor solar illumination, etc).
• In some areas there is only low spatial resolution available, meaning that only large objects can be seen and identified.
• The relatively high costs of high-resolution, large-scale imagery though these costs are becoming reduced significantly.
• In most cases there is no ability to view the images in stereo (without also obtaining a DEM and draping the imagery over this).
• The images can be difficult to interpret and sometimes require high levels of technology for processing.
• Seasonal variations in lighting conditions or vegetation cover can influence image interpretation.
• The interpretation of satellite imagery for landslide mapping (as with aerial photographs) does require a reasonably high level of skill, experience and familiarity of the area (or environmental conditions) being studied.