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 satellites
GPS data:
location of yield samples
Yield Map
smart card
Yield data:
t/ha at each
sample point
7. Mapping yield levels
Yield class maps for six
adjoining plots. The yield
data, shown in colour, comes
from the yield meter, all the
GPS tells you is the location
of 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
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
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
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
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
