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Image GLAS Instrument Description

Measurement Approach

  • Uses Nd:YAG laser with 1064 and 532 nm output
  • Height measurements are determined from the round-trip pulse time of the infrared pulse flight
  • Cloud and aerosol data are extracted from the green pulse
  • Swath: Nadir viewing
  • At 40 pulses per second, the centers of 70 m spots are separated in the along track direction by 170 m for a 600 km altitude orbit; cross track resolution is determined by the 183 day ground track repeat cycle which yields 15 km track spacing at the equator and 2.5 km at 80 degrees latitude

Accommodation Issues

  • Mass: 300 kg
  • Duty cycle: 100%
  • Power: 330 W average
  • Data rate: ~450bps
  • Thermal control by: radiators supplemented by heaters, heat pipes
  • Thermal operating range: 20 deg +/- 5 deg C
  • Telescope field of view: nadir only, 375 microradians
  • Instrument field of view: ~70 m laser footprint at nadir at 1064 nm
  • Pointing requirements (platform+instrument):
    • Control (3 sigma): 30 arcsec roll, 60 arcsec pitch, 1 degr yaw
    • Post-processed pointing knowledge (1-sigma): 1.5 arcsec (roll and pitch axes, to be provided by instrument-mounted star trackers laser reference sensor gyroscope)
  • Post-processed position requirements: radial orbit for ice sheet to < 5 cm and along-track/cross-track position to < 20 cm (to be provided by spacecraft-mounted GPS receiver and SLR array)
  • Physical size: telescope is 100 cm in diameter, height is ~175 cm

Content Last Update: January 1999

Last Modified: Mon Jan 06, 2003