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Lecture 9 Content

Lecture 9 Content. Near Polar orbiting earth resources satellites: SPOT LIDAR. SPOT LANDSAT system suffered three major drawbacks: Very high ground resolution is not possible with the mechanical MSS

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Lecture 9 Content

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  1. Lecture 9 Content • Near Polar orbiting earth resources satellites: • SPOT • LIDAR

  2. SPOT LANDSAT system suffered three major drawbacks: • Very high ground resolution is not possible with the mechanical MSS • The repetition time for any one scene is quite long, 18 or 16 days per satellite. Satellites have limited operational value especially when data is needed for monitoring purposes. • Stereoscopic viewing is only possible in narrow image overlaps, and the accuracy of height estimation is low

  3. SPOT French tackled these drawbacks as follows: • It was decided to use a pushbroom scanner. Not only can modern pushbroom scanners provide high resolution, they have a longer and more reliable life expectancy, lower power requirements, and higher geometric and radiometric accuracy • Mirrors make off-nadir viewing possible which allow any area to be viewed frequently. Oblique viewing allowed for stereoscopic viewing

  4. SPOT satellite characteristics: • SPOT in the first earth resource satellite to be launched from Europe • Other characteristics of SPOT which are similar to LANDSAT • Near-polar sun synchronous orbit • Transmission of data to ground stations with the possibility of on-board recording • SPOT sensors can sense in high resolution (10m) panchromatic mode or lower resolution (20m) multispectral mode in 3 wavelengths

  5. A single SPOT scene covers a geographical area of 60 x 60 km. • Two alternative modes of imaging are possible using SPOT: • Panchromatic: black and white, with a ground resolution of 10 m • Multispectral: colour, with 20 m ground resolution acquired simultaneously in 3 bands : green, red and near infrared.

  6. In a MSS it scans the scene from side to side and reflects radiation from the ground surface onto a detector • This process is limited by the accuracy of the rotating mirror • To overcome this problem a HRV (High Resolution Visible) scanner is used in SPOT. It does not have any moving parts, instead, it records each scan line at one go by means of a line of detectors – one detector for each area sampled on the ground • Detectors are controlled by a microchip and controls 1,728 detectors on SPOT

  7. Comparison between pushbroom scanner and MSS

  8. SPOT 1 and SPOT 2 available and launched in 1985 and 1986 respectively • SPOT 1 carry two identical pushbroom scanners which are called “High Resolution Visible” (HRV) scanners • When in panchromatic mode all of the detectors are sampled with a spatial resolution of 10m • Used for mapping scales of 1:150,000 to 1:100,000 • When in multispectral mode only half of the detectors are sampled with a spatial resolution of 20m • Used for pollution monitoring to vegetation mapping

  9. SPOT ground receiving stations

  10. SPOT Panchromatic

  11. SPOT Multispectral

  12. LIDAR • Light Detection And Ranging (LIDAR) • It is a radiometer system that uses a light beam instead of a microwave radar beam (Radar) to obtain measurements of speed, altitude, direction and range of a target • Lidar is used to precisely measure distances and properties of far-away objects • Its operation is that a powerful laser transmits a short and intense pulse of light • Very high spatial resolution, for example a DEM was created of a complete coverage of the Netherlands at a spatial resolution of 1 cm (Introduction to LIDAR, 1997).

  13. Use of LIDAR for accurate determination of terrain elevations began in the late 1970’s but its use was limited due to project cost-effectiveness • One of the most successful early applications of LIDAR was in the determination of accurate water depths • Modern LIDAR acquisition makes use of a rapidly pulsing (20,000 to 50,000 pulses/sec) laser and a highly accurate clock to measure time • The principle of LIDAR is similar to that of RADAR • Further details in lecture 10

  14. LIDAR image at ground zero NY

  15. Lidar Applications • Atmospheric science - dynamics measurements: temperatures, winds, and waves- climate measurements: clouds, aerosols, and water vapor- ozone measurements: depletions and polar stratospheric clouds- high altitude trace metal measurements: sodium and potassium- pollution monitoring • Astronomy • planetary surface relief mapping (eg lidar Mars maps by NASA) • Topographic mapping • erosion monitoring • Bathymetry (under water mapping) • harbor profiling for marine safety

  16. Forest ground and canopy measurements • used to assess forest growth and health • Building and factory construction • measurements allow for precise prefabrication, improving efficiency and reducing costs • Mine shaft mapping • allows cavern monitoring for worker safety • Aircraft docking • for safe aircraft maneuvering near airport terminals • Automobile speed monitoring • a replacement for hand-held radar guns

  17. … The End …

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