Download - Remote sensing
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Remote sensing what is it?
• Observation from a distance– Aerial photographs- very detailed– Satellite images – global view
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Oblique aerial photograph
• Viewed from an oblique angle: looking sideways
• Looks natural, easy to understand, useless for measurement purposes
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Vertical aerial photograph
• Viewed straight down giving a “map view”• Difficult to understand at first. Can be used
as a basis of mapping, after image has been rectified
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Aerial photographs: 1995 and 1972
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Map derived form aerial photographs
• Visible features are “digitised” by tracing around them on a computer screen.
• This creates the points lines and polygon symbols which build up into the map
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Stereo-photography 3-d visualisation
overlap
Photo 1 Photo 2Plane travels at constant altitude above sea level. Height above ground varies with topography
60% of image
• Overlapping aerial photographs can be used to build 3-d stereoscopic visual models. These can be used to map out contours and heights of features
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Stereoscopic reconstruction of overlapping areas
overlap
Photo 1 Photo 2
Right eye Left eye
• A stereoscope is used to view the overlapping areas simultaneously and the brain builds a 3-d model of the landscape where the images overlap.
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Digital manipulation of aerial photographs
• 3-d models can also be built by “digitally draping” photographs over a digital elevation model of the landscape.
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Satellite Remote Sensing
• Satellites give a higher viewpoint and give unrestricted coverage of the whole globe
Link to Gateway Remote sensing videohttp://gateway.rac.ac.uk/mod/resource/view.php?id=3937
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Satellite orbits
• Geostationary orbit: above the equator, 35,000 km height, orbital period 24 hours. Satellites appear fixed in sky
• Low Earth orbit, usually polar, orbital period can be less than 1 hour. Satellites seen to move across sky
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Geo-stationary meteorological satellite: Meteosat
Infra-red image from 0600March 8, 2000
“Ground” position of satellite
• Geostationary orbits, approx 33,000 km elevation over the equator. Satellite takes 24hours for one orbit, the earth rotates once in that time, so the satellite appears stationary in the sky
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Polar orbiting meteorological satellites
• Polar orbiting satellites cover the whole globe, but move, so there are long time intervals between one image and the satellites next return
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Earth observation satellites: Landsat 7 image (30m resolution)
• Earth observation satellites are designed to view the surface of the globe. Some are designed for view the oceans, others, like the Landsat series, observe the land
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2004 tsunami: Aceh province, Sumatra
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Land classification; spectral signatures: Using SPOT images
• Simultaneous Multi-spectral images can be used to classify landcover.
• The reflectance of certain landcover types are measured on each image to build up a signature of that type of cover. This is then searched for over the whole image
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Land classification; spectral signatures: Using SPOT images
• Simultaneous Multi-spectral images can be used to classify landcover.
• The reflectance of certain landcover types are measured on each image to build up a signature of that type of cover. This is then searched for over the whole image
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Land classification; spectral signatures: Using SPOT images
• Simultaneous Multi-spectral images can be used to classify landcover.
• The reflectance of certain landcover types are measured on each image to build up a signature of that type of cover. This is then searched for over the whole image
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Land classification; spectral signatures: Using SPOT images
• Simultaneous Multi-spectral images can be used to classify landcover.
• The reflectance of certain landcover types are measured on each image to build up a signature of that type of cover. This is then searched for over the whole image
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Remote sensing images:
Harnhill farm
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Aerial photograph, 2011 Spatial resolution approx. 0.2m
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GoogleMaps aerial photo, Spatial resolution approx. 1.5m
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Scanned Aerial photograph, 1995 Spatial resolution approx. 2.0m
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Landsat 5 image, circa 2001 Spatial resolution approx. 30m
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LIDAR image, 2011 Spatial resolution approx. 1.0mVertical resolution approx. 0.001m
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Landsat 5: 30m resolution
• Landsat 5 image of Gloucestershire (Landsat 6 crashed on take off. Landsat 7 is current satellite, Landsat 8 has just been launched)
Harnhill
Gloucester
Swindon
Cheltenham
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Ikonos: 1m resolution
• Commercial panchromatic image at 1m resolution. On the original image people can be seen walking in Horse Guards Parade and the spokes of the London Eye are visible
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Ikonos agricultural image 1m resolution
• Another Ikonos image showing the detail available in an agricultural image, here form Montana
• How useful is this for farmers?
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RADARSAT classified image of Flevoland, NL
• Radar, “active remote sensing”, sees through clouds and in the dark. This addresses some of the major problems with “Passive remote sensing” which measures reflected sunlight.
• The images are very difficult to interpret
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RADARSAT-Mozambique floods
• Shuttle borne radar image of the Mozambique floods• Radar is good at detecting the edge of water bodies,
which it can “see” through cloud cover
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Remote sensing summary
• Aerial photography gives us a controllable, highly detailed view of the Earth
• Satellite imagery gives global, unrestricted views which are repeated a frequent intervals
• The references to actions such as “interpretation” and “classification” lead on to things we can do with a geographic information system (GIS) using remote sensing as a source of data