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Satellite and aerial surveys

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  • 1. Data capture from above:GPS and remote sensing Global positioning systems Aerial photography Satellite imagery
  • 2. Global positioning system (GPS)• Current system run by USA military• Gives normal accuracy of ~5m• European alternative called Galileo under construction• Systems use satellites to allow users to calculate their position in the Earth
  • 3. Global Positioning Systems (GPS) satellite based navigation • 24 satellites in orbit, 21 functioning at any time • Each broadcasts its ID, the time and its orbital position • The user receives this data and calculates the receiver’s position in relation to the satellite • If the receiver can pick up signals from at least 4 satellites, it can calculate its position on the Earth’s surface
  • 4. Important points to note about GPS• The satellites transmit data which is picked up by the user’s receiver on the ground• Nothing is transmitted from the user to the satellite• GPS only gives your geographical position in real time, it does not create images or maps
  • 5. Satnav• GPS tells you where you are now• Satnav unit has built in digital maps• GPS position is displayed on the map• Satnav unit then calculates the route from current position to destination
  • 6. GPS based yield mapping at the RAC GPS satellitesGPS data:location of yield samples Yield Map smart card Yield data: t/ha at each sample point
  • 7. Mapping yield levelsYield class maps for sixadjoining plots. The yielddata, shown in colour, comesfrom the yield meter, all theGPS tells you is the locationof the yield samples lowest yield highest yield 1993
  • 8. Examples of data collection: GPS data collection Mobile GPS and data recorder Weed patch centroids, extent and species
  • 9. Examples of GPS use by US Geological survey
  • 10. Remote sensing what is it?• Observation from a distance – Aerial photographs- very detailed – Satellite images – global view
  • 11. Oblique aerial photograph• Viewed from an oblique angle: looking sideways• Looks natural, easy to understand, useless for measurement purposes
  • 12. 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
  • 13. Aerial photographs: 1995 and 1972
  • 14. 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
  • 15. Stereo-photography 3-d visualisation• 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 Photo 1 Photo 2 Plane travels at constant altitude above sea level. Height above ground varies with topography overlap 60% of image
  • 16. Stereoscopic reconstruction of overlapping areas• 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. Right eye Left eye Photo 1 Photo 2 overlap
  • 17. Digital manipulation of aerial photographs• 3-d models can also be built by “digitally draping” photographs over a digital elevation model of the landscape.
  • 18. Sources of aerial photographs• UK aerial photography is available on-line, or can be commissioned• www.getmapping.com is one source
  • 19. Satellite Remote Sensing• Satellites give a higher viewpoint and give unrestricted coverage of the whole globe Link to Gateway Remote sensing video http://gateway.rac.ac.uk/mod/resource/view.php?id=3937
  • 20. 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
  • 21. Geo-stationary meteorological satellite: Meteosat• 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 Infra-red image from 0600 March 8, 2000 “Ground” position of satellite
  • 22. 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
  • 23. 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
  • 24. 2004 tsunami: Aceh province, Sumatra
  • 25. 2004 tsunami: Aceh province, Sumatra
  • 26. 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
  • 27. 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
  • 28. 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
  • 29. 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
  • 30. Remote sensing images:Harnhill farm
  • 31. Aerial photograph, 2011Spatial resolution approx. 0.2m
  • 32. GoogleMaps aerial photo,Spatial resolution approx. 1.5m
  • 33. Scanned Aerial photograph, 1995Spatial resolution approx. 2.0m
  • 34. Landsat 5 image, circa 2001Spatial resolution approx. 30m
  • 35. LIDAR image, 2011Spatial resolution approx. 1.0mVertical resolution approx. 0.001m
  • 36. Landsat 5: 30m resolution• Landsat 5 image of Gloucestershire (Landsat 6 crashed on take off. Landsat 7 is current satellite) Cheltenham Gloucester Harnhill Swindon
  • 37. 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
  • 38. 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?
  • 39. 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
  • 40. 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
  • 41. 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

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