HR: 0800h
AN: G21C-1288    [Abstracts]
TI: Space-based Swath Imaging Laser Altimeter for Cryospheric and Topographic Mapping
AU: * Abshire, J B
EM: James.Abshire@gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Science and Exploration Directorate, Greenbelt, MD 20771 United States
AU: Harding, D J
EM: David.J.Harding@nasa.gov
AF: NASA Goddard Space Flight Center, Science and Exploration Directorate, Greenbelt, MD 20771 United States
AU: Sun, X
EM: Xiaoli.Sun@gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Science and Exploration Directorate, Greenbelt, MD 20771 United States
AU: Krainak, M A
EM: Michael.Krainak@gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Applied Engineering and Technology Directorate, Greenbelt, MD 20771 United States
AU: Shuman, C A
EM: Christopher.Shuman@gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Science and Exploration Directorate, Greenbelt, MD 20771 United States
AU: Dabney, P W
EM: Phil.Dabney@gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Science and Exploration Directorate, Greenbelt, MD 20771 United States
AB: Over the past decade numerous investigations using airborne laser altimeters have shown that a wealth of information can be contained in wide swath imaging altimetry of the Earth's surface. However there are substantial challenges to achieve similar quality measurements at the considerably longer ranges and faster velocities of a space mission. During this time the ICESat mission and the GLAS laser altimeter were developed to help determine the elevation response of the Greenland and Antarctic polar ice sheets to global climatic change. ICESat's primary purpose is the precise measurement of ice sheet surface elevation. This is so that elevation changes can be determined with an accuracy of <1.5 cm/year for averages of measurements made within areas of ~100 x 100 km. The ICESat mission was launched in January 2003, and to date GLAS has made over 900 million measurements of the Earth surface and atmosphere. The GLAS altimeter samples the surface elevation along a single nadir-pointed profile line from a 94 degree 600 km orbit. It measures the echo pulse waveform (ie range distribution) within 65 m laser footprints which are spaced ~170 m along-track. The GLAS instrument uses a 6 nsec wide laser pulse, 1 nsec digitizer, and a stable single channel receiver with an analog detector. All these enable stable measurements with a high SNR in the echo pulse, and a measurement precision of <2.5 cm per measurement over flat areas. The ICESat investigation uses spatial averaging of the measured elevation differences at cross-over points between the ascending and descending profiles as its primary means to determine elevation change. We are developing a new approach for a next-generation space-based laser altimeter based on our experience in developing GLAS and in calibrating the ICESat measurements. This is a swath imaging laser altimeter mission concept being developed to allow topographic mapping from space to provide precise elevation images for global measurements of land topography, glaciers, ice sheets, and sea ice. Our objective is to measure surface heights to <10 cm in 5-10 m spots, which are contiguous along and cross track. The swath width is scalable between 100m and 1 km, and the mission lifetime goal is 5-10 years. Our approach measures an echo pulse for each spot, via sub-nsec pulse width laser transmitters and photon-counting detectors, in a robust push-broom configuration. The swath width, in combination with precise spacecraft pointing, allows overlapped repeat coverage of temporally variable surface elevation features, a key to determining trends in elevation changes. We are considering several candidate measurement wavelengths and laser measurement approaches. These include short pulse micro-pulse altimetry techniques, along with higher duty cycle digital modulation approaches, such as pseudo-noise (PN) code ranging. We will discuss a comparison of these measurement approaches for space, and show some recent measurement demonstrations we have made in the lab and across a horizontal path using PN-code modulated fiber lasers at 1570 nm.
DE: 0794 Instruments and techniques
DE: 1640 Remote sensing (1855)
DE: 1855 Remote sensing (1640)
DE: 5464 Remote sensing
DE: 5494 Instruments and techniques
SC: Geodesy [G]
MN: Fall Meeting 2005