LANDSAT the granddaddy of satellite sensing systems

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LANDSAT the grand-daddy of satellite sensing
systems
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Earth Resource Technology Satellite (EARTS)

• EARTS 1 launched in 1972
• Name Changed in 1975 to Landsat 1 and Landsat 2
  launched
• Longest continuous remote sensing record for the
  globe
• Initial sensor package
• RBV (return beam vidicon) cameras projected to
  be the primary sensor (TV cameras)
• Multi-Spectral Scanner (MSS) a secondary sensor.

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1972
2000
Land Cover/Land Use change Las Vegas Nevada
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Sun-Synchronous Orbits

• The orbital angle and speed are calculated to
  bring the satellite over a given latitude at a
  specific time.
• e.g. equatorial crossing at 0945.
• Orbit advances daily repeat coverage of a given
  location every 16-18 days.

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Data transmission

• Image files are very large. A serious problem is
  onboard storage/transmission of data.
• Downlink sites receive direct transmission of
  data when the satellite is overhead.

EROS Data Center (EDC) note downlink dish.
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TDRSS (Tracking and Data Relay Satellite System)

• Geosynchronous data relay satellites.
• Acts as a relay device for other satellites.
  Constant contact with ground station, stores and
  relays data from other satellites.

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RBV (Return Beam Vidicon) Cameras

• Expected to be the primary sensor for Landsat
• green, red and NIR sensitive TV cameras.
• Never worked properly
• Abandoned as useful data collection tools early
  on
• The Multi-Spectral Scanner (MSS) became the
  primary sensor.

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MSS data collection
Rotating scan mirror focused track lines on a
detector array. Note the width of the scan
track Less than 12 degrees of angular field of
view from orbit results in 185 km of image
track. Bands were originally numbered 4-7 (RBV
sensors band designation 1,2,3)
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Russian Far East Landsat MSS Band 5 (red) 1975
Scene 185 km X 185 km Pixel resolution 80
meters
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Russian Far East Landsat MSS Band 7 (near
infra-red) 1975
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Sovetskaya-Gavan Airfields as references 1. 2. 3.
1975
Note change in forest area.
1989
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Deforestation.
1989
1975
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Changes in technology

• When Landsat 4 and 5 were launched, MSS is no
  longer the primary sensor the primary data
  collection now done by the Thematic Mapper (TM)
• TM data have higher spatial (30 meter) and
  spectral (7 band) resolution

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The TM sensor
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Politics, Economics, and Data Storage in the real
world.

• While the cost in designing, building and
  deploying a satellite is very large the most
  significant cost is transmission/correction and
  archiving the data!
• Archiving data lacks the glamour of a launch
  its the boring day to day rectification and
  storage of information.very little money gets
  spent on this task.

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Losing data

• Huge quantities of Landsat 1 and 2 data are in
  imminent danger of being lost.
• Magnetic tapes are not stable media
• The magnetic signal bleeds through the layers
  of tape
• Tapes must be fluffed on a regular basis to
  prevent contamination between tape layers
• The plastic of the tape also becomes brittle
• 3 semi-trailer loads of tapes were found
  (literally) moldering in a damp basement in
  Baltimore stored in trailers at EDC waiting for
  .

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Politics and Economics

• What is the legitimate role of Government?
• roads? bridges? defense? social security?
  welfare? topographic maps? remote sensing data?
• We hold these truths to be self-evident, that
  all men are created equal, that they are endowed
  by their Creator with certain unalienable Rights,
  that among these are Life, Liberty and the
  pursuit of Happiness. --That to secure these
  rights, Governments are instituted among Men,
  deriving their just powers from the consent of
  the governed,

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Who should make decisions? Individuals (free
enterprise) or government?

• In the 1980s major effort to reduce the size and
  scope of government (at least on paper)
• The difficult issues never get tackled its the
  easy targets.
• Satellite data made for an easy target
• EOSAT a private corp. formed to make a profit by
  selling Landsat data.
• TM scenes 4,000/each!
• By legislative fiat meteorological satellites
  kept under government control (AVHRR data became
  the sensor of choice when possible)

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The final Landsat (number 6 never made it to
orbit!)
Cost structure defined by law, as cost of
reproduction limited to 600/scene
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Oops!
Landsat 7 has a malfunction the Scan Line
Corrector (SLC), which compensates for the
forward motion of the satellite. Subsequent
efforts to recover the SLC were not successful,
and the problem appears to be permanent The
center of an SLC-off data product should be very
similar in quality to previous Landsat 7 data.
However, the scene edge will contain alternating
scan lines of missing data The proposed
solution, fill in new scenes with interpolated
data.
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Data Processing levels

• Level 0 (Raw data)
• Only useful if you're studying the RS system
  itself, or data processing systems

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Level 1 and Level 2 processing

• Processing includes
• Radiometric correction - compensating for known
  characterisitcs of the sensor.
• Atmospheric correction - compensating for the
  distortion (lens effect) of the atmosphere.
• Geometric correction - referencing the image to
  Lat/Long on the Earth's surface

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Level 3 processing

• Geocoded Projected Imagery
• The image is mapped to a projection of the Earth
• additional processing such as multiple image
  composites, indices or ratios are created etc.

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• Browse Images
• Images you can download from the net are likely
  to be browse images. These are typically GIF or
  JPEG format, although a number of others exist.
  Whilst providing a good idea of what is in an
  image, they are not useful for serious
  applications. They have the advantage of being a
  manageable size - typically of the order of
  100Kb-1Mb (compared to 100Mb for a full scene)
  and are often available free.