@prefix ns0: . @prefix skos: . ns0:resource [ ] ; ns0:altLabel [ ] ; skos:definition """[Text Source: NASA GLAS Instrument Home Page, http://icesat.gsfc.nasa.gov/icesat/glas.php ] GLAS (the Geoscience Laser Altimeter System) is the first laser-ranging (lidar) instrument for continuous global observations of Earth, which will make unique atmospheric observations as an important component of the ESE climate change program. GLAS is a facility instrument designed to measure ice-sheet topography and associated temporal changes, cloud and atmospheric properties.and give us information on the height and thickness of radiatively important cloud layers which is needed for accurate short term climate and weather prediction. In addition, operation of GLAS over land and water will provide along-track topography. GLAS includes a laser system to measure distance, a Global Positioning System (GPS) receiver, and a star-tracker attitude determination system. The laser will transmit short pulses (4 nano seconds) of infrared light (1064 nanometers wavelength) and visible green light (532 nanometers). Photons reflected back to the spacecraft from the surface of the Earth and from the atmosphere, including the inside of clouds, will be collected in a 1 meter diameter telescope. Laser pulses at 40 times per second will illuminate spots (footprints) 70 meters in diameter, spaced at 170-meter intervals along Earth's surface. Heritage: MOLA Instrument Type: A three-laser system, with a single laser operating at any given time Scan Type: Nadir Viewing Dimensions: Telescope diameter is 1 m, instrument height is ~175 cm Mass: 300 kg Power: 330 W average Spatial Resolution: 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; the cross-track resolution is determined by the ground-track repeat cycle and orbit control. Duty Cycle: 100% Thermal Operating Range: 20° ± 5°C Telescope FOV: Nadir only, 375 μrad and 160 μrad (0.532 μm) Instrument IFOV: ~70 m laser footprint at nadir Group: Instrument_Details Entry_ID: GLAS Group: Instrument_Identification Instrument_Category: Earth Remote Sensing Instruments Instrument_Class: Active Remote Sensing Instrument_Type: Altimeters Instrument_Subtype: Lidar/Laser Altimeters Short_Name: GLAS Long_Name: Geoscience Laser Altimeter System End_Group Group: Associated_Platforms Short_Name: ICESAT End_Group Group: Spectral_Frequency_Information Wavelength_Keyword: VISIBLE Number_Channels: 1 Spectral_Frequency_Coverage_Range: 0.532 micrometers (atmosphere) End_Group Group: Spectral_Frequency_Information Wavelength_Keyword: NEAR INFRARED Number_Channels: 1 Spectral_Frequency_Coverage_Range: 1.064 micrometers (surface) End_Group Online_Resource: http://glas.gsfc.nasa.gov/ Online_Resource: http://icesat.gsfc.nasa.gov/ Online_Resource: http://nsidc.org/data/icesat/data.html Sample_Image: http://icesat.gsfc.nasa.gov/icesat/images/glas-inst.jpg Creation_Date: 2016-01-08 Group: Instrument_Logistics Data_Rate: ~450 kbps Instrument_Start_Date: 2003-01-12 Instrument_Owner: USA/NASA End_Group End_Group"""@en ; skos:prefLabel "GLAS"@en ; skos:inScheme ; skos:broader ; a skos:Concept . skos:prefLabel "Lidar/Laser Altimeters"@en ; a skos:Concept ; skos:narrower .