2015-06-18 12:14:26.0 [aaleman] revised long name per NSIDC request update AltLabel (Land, Vegetation, and Ice Sensor);
SYSTEM OVERVIEW LVIS is a pulsed laser altimeter and measures range by timing a short (<10 ns duration) pulse of laser light between the instrument and the target surface. The entire time history of the outgoing and return laser pulses is digitized using a single detector, digitizer and timing clock. This configuration unambiguously describes the range to the surface as well as the vertical distribution of surfaces within each laser footprint. The LVIS system operates at altitudes up to 10 km AGL and has a 12 degree potential field-of-view (PFOV) within which footprints can be randomly spaced across track. Scanning is performed using galvanometer-driven scan mirrors that control the pointing of both the laser and the telescope instantaneous field-of-view (FOV). Scan mirrors are positioned in a stepped pattern, stopping to fire the laser and integrate the return signal at each beam location. This raster scan pattern efficiently covers 100% of the area within the data swath. Footprint sizes from 1 to 80 m are possible, determined by the AGL altitude of the airplane and the focal length of a diverging lens in the output path. The dual axis transmit scanner allows the swath pattern to remove forward motion of the aircraft from the collection pattern. Roll compensation has also been incorporated into the software for keeping collection directly below the aircraft. OPTICAL SYSTEM The receiver system consists of a 200-mm diameter, 5-power telescope with a 25-mm exit pupil. The telescope has a 200-mm aperture, f/2 Petzval1(1 Petzval lens: a high speed, narrow FOV lens composed of two achromatic lenses positioned about an aperture stop; named after the Austrian optician Josef Petzvald) objective with a 400-mm focal length directing light through a 50-mm focal length f/1.8 eyepiece, which produces a 25-mm collimated beam. A scan mirror, located at the exit pupil of the telescope, directs the beam through a 10-nm bandpass filter and onto a 25-mm molded aspheric condenser lens which focuses onto the 0.8-mm Si:APD detector. The scan mirror is a 25x40 mm beryllium mirror that was custom designed to be lightweight for fast scanning, yet stiff enough to remain flat during and just after the intense acceleration of scanning. The receiver box can accommodate two more detectors, enabling the simultaneous collection of dual-wavelength, dual-polarization data. Table 1: System characteristics of the LVIS altimeter Telescope aperture 20 Telescope total FOV 200 mrad Detector FOV 8 mrad Detector band width 90 MHz Bandpass filter band width 10 nm Digitizer sampling rate 500 Msamp/s Digitizer effective bits 7 Laser output energy 5 mJ Laser pulse width 10 ns (FWHM*) Laser spatial energy pattern TEM00 single mode Pulse repetition rate rep-rate 100 to 500 Hz Laser output wavelength 1064 nm Data rate at 500 Hz rep-rate 300 Kbytes/s Swath width at 10 km altitude 2.0 km Footprint diameter 1 to 80 m Maximum operating altitude >10 km *Full width at half maximum. LASER The transmitter is a water-cooled, solid-state, diode-pumped, Nd:YAG oscillator-only laser, designed and manufactured by Cutting Edge Optronics (St. Louis, MO). The laser cavity is housed in a hermetically sealed aluminum enclosure that measures 45x13x13 cm. Operating at rates of up to 500 Hz, the laser emits 5 mJ, 10 ns, Gaussian-shaped (temporally and spatially) optical pulses at a wavelength of 1064 nm. Accurate ranging to a mean elevation in a wide laser footprint can be confounded by a complex spatial energy distribution across the laser spot, thus, the laser transmitter was required to have a single-spatial mode (TEM00) energy pattern. A fiber-coupling lens is placed behind the final turning mirror inside the laser enclosure to capture a small amount (<1%) of the laser output and direct it through two optical fibers (start pulse and calibration pulse with 100 m (300 ns) delay). The laser output beam is directed through the output scanner box containing filter wheels to control the output power to optimize return signal strength, a diverging lens to control the size of the footprint on the surface, a lockable pitch control for boresighting, and the galvanometer-driven output scan mirror. Group: Instrument_Details Entry_ID: LVIS Group: Instrument_Identification Instrument_Category: Earth Remote Sensing Instruments Instrument_Class: Active Remote Sensing Instrument_Type: Altimeters Instrument_Subtype: Lidar/Laser Altimeters Short_Name: LVIS Long_Name: Laser Vegetation Imaging Sensor End_Group Group: Instrument_Associated_Sensors Short_Name: INS Short_Name: LVIS Short_Name: LIDAR Short_Name: LASERS Short_Name: GPS Short_Name: ALTIMETERS End_Group Group: Associated_Platforms Short_Name: AIRCRAFT End_Group Group: Spectral_Frequency_Information Wavelength_Keyword: Near Infrared Spectral_Frequency_Coverage_Range: 1064 nm End_Group Online_Resource: https://lvis.gsfc.nasa.gov/ Sample_Image: https://lvis.gsfc.nasa.gov/index.php?option=com_content&task=blogcategory&id=96&Itemid=93 Creation_Date: 2008-05-16 Group: Instrument_Logistics Data_Rate: 500 Hz rep-rate 300 Kbytes/s Instrument_Owner: Laser Remote Sensing Laboratory, NASA Goddard Space Flight Center End_Group End_Group
LVIS
Lidar/Laser Altimeters