Appendix A: Sources of Satellite Imagery
Several data capture techniques based on satellite and aerial imagery were available at the time of publication. An overview of the main techniques is provided below. It is expected that these techniques will be revised and superseded with advances in satellite technology, and therefore that this list should not be considered exhaustive.
Optical Satellite Imagery (Thematic Mapper)
The Landsat series of satellites operates the Thematic Mapper instrument. Unfortunately, the 30m pixel size has limited its applications for individual peat slide investigations. However, Landsat-7 now offers a 15m resolution panchromatic band which enables mapping scales to 1:25,000. Furthermore the Indian, IRS-1C with 5m pixels improves mapping scales to 1:10,000. The IKONOS satellite, available since early 2000, offers data which provides 1m ground resolution imagery and enables mapping scales of 1:2,000 or greater. The French SPOT satellite provides 10m resolution panchromatic data and the ability to acquire stereo image pairs. At these scales individual flow lobes, ground fissures and subtle morphology indicative of potential peat landslides may be resolvable.
Microwave (Synthetic Aperture Radar Interferometry, InSAR)
Radar imagery, at different wavelengths and polarisation, can be obtained from both satellite and aircraft. Radar data can be acquired during the night or day and effectively 'sees' through cloud. Currently available SAR (synthetic aperture radar) data includes ERS with 25m spatial resolution, RADARSAT with 10-15m spatial resolution and stereo capability, and JERS with 18m spatial resolution. These data enable interpretation at a range of scales from regional, to local and include vegetation type, moisture content, debris sizes etc. Synthetic Aperture Radar Interferometry ( InSAR) can create digital elevation model data and detect subtle changes in elevation to the accuracy of the centimetre scale. This is particularly useful for identifying changes in topography such as subsidence and precursory ground movements on slopes.
Multi-spectral video cameras operate at the visible to near infra-red portion of the spectrum and can be mounted on low-flying aircraft. They can generate pixels of less than 1m ground resolution and are therefore suitable for large mapping scales. Field spectra obtained from in-situ measurements are used to determine different classes of iron oxide precipitates from the air and, by inference, the different pH levels of drainage systems. This may be particularly useful for the mapping of peat landslide groundwater systems.
Airborne hyperspectral scanners are much more complicated and expensive instruments than multispectral video. They can be mounted on low-flying aircraft. Remotely sensed multi-spectral data have been shown to be of considerable use for landslide investigations. Uses include the mapping of geological units in areas of poor exposure through estimation of soil moisture content, the estimation of soil thickness prone to landslides and the mapping of geomorphological features of landslides at the regional scale and the local scale.
Unmanned Aerial Vehicles ( UAVs)
UAVs (commonly referred to as drones) are increasingly being used to provide site specific high resolution photography and digital elevation data (Hackney and Clayton, 2015). Good quality data acquisition is reliant on accurate and precise ground control and careful survey planning. In the UK, the Civil Aviation Authority ( CAA) define operating regulations ( CAP393; CAP722) which constrain survey areas to within c. 500m 'line of sight' of the operator and c. 400m altitude. A license is required to use drone acquired data for commercial purposes.
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