Topography of the Northern Hemisphere of Mars from the Mars Orbiter Laser Altimeter-Reference-Cited by-同舟云学术

Topography of the Northern Hemisphere of Mars from the Mars Orbiter Laser Altimeter

Published:1998-03-13 Issue:5357 Volume:279 Page:1686-1692
ISSN:0036-8075
Container-title:Science
language:en
Short-container-title:Science

Author:

Smith D. E.¹²³⁴⁵,Zuber M. T.¹²³⁴⁵,Frey H. V.¹²³⁴⁵,Garvin J. B.¹²³⁴⁵,Head J. W.¹²³⁴⁵,Muhleman D. O.¹²³⁴⁵,Pettengill G. H.¹²³⁴⁵,Phillips R. J.¹²³⁴⁵,Solomon S. C.¹²³⁴⁵,Zwally H. J.¹²³⁴⁵,Banerdt W. B.¹²³⁴⁵,Duxbury T. C.¹²³⁴⁵

Affiliation:

1. D. E. Smith, H. V. Frey, J. B. Garvin, H. J. Zwally, Earth Sciences Directorate, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA.

2. M. T. Zuber and G. H. Pettengill, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

3. J. W. Head, Brown University, Providence, RI 02912, USA.

4. D. O. Muhleman, California Institute of Technology, Pasadena, CA 91125, USA

5. R. J. Phillips, Washington University, St. Louis, MO 63130, USA.

Abstract

The first 18 tracks of laser altimeter data across the northern hemisphere of Mars from the Mars Global Surveyor spacecraft show that the planet at latitudes north of 50° is exceptionally flat; slopes and surface roughness increase toward the equator. The polar layered terrain appears to be a thick ice-rich formation with a non-equilibrium planform indicative of ablation near the periphery. Slope relations suggest that the northern Tharsis province was uplifted in the past. A profile across Ares Vallis channel suggests that the discharge through the channel was much greater than previously estimated. The martian atmosphere shows significant 1-micrometer atmospheric opacities, particularly in low-lying areas such as Valles Marineris.

Publisher

American Association for the Advancement of Science (AAAS)

Subject

Multidisciplinary

Reference53 articles.

1. The Mars Observer laser altimeter investigation

2. . The MOLA instrument was designed and built by the Laser Remote Sensing Branch of NASA/GSFC. The laser operated at a wavelength of 1.064 μm emitting 8-nsec-long pulses with an energy of ∼40 mJ at the diode operating temperature during operation in the MGS 35-hour elliptical orbit.

3. MOLA measures the round-trip time of flight of individual laser pulses between the MGS spacecraft and the martian surface. By interpolating the spacecraft orbital trajectory to the time of the laser measurement and correcting for the index of refraction of the martian atmosphere the one-way light time between the spacecraft and the surface is obtained. Subtraction of the range from the MGS orbit allowing for off-nadir pointing yields measurements of martian radius in a center of mass reference frame.

4. Surface reflectivity or albedo at the laser wavelength was determined from the ratio of received to transmitted laser energy. Outgoing pulse energy is sampled with an optical fiber that measures ∼95% of the outgoing pulse cross section. The received energy is derived from the area under the curve representing the best estimate of the returned pulse shape. The accuracy of the reflectivity measurement after calibration is ∼5%.

5. MOLA's return pulse width provides a measure of the footprint-scale slope or rms roughness of the terrain. The instrument detection electronics contain a bank of four parallel bandpass filters with widths of 20 60 180 and 540 nsec that correspond to footprint-scale surface slopes of 1° 3° 10° and 27°. The return pulse triggers the filter that most closely matches the width of the return. Measurement refinement is made using the difference in the times at which the leading and trailing edges of the returned pulse cross the detection threshold. The time difference is translated into an equivalent pulse spread.

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