STANFORD UNIVERSITY
EE 350 RADIOSCIENCE SEMINAR
Professor Len Tyler

Fall 2000-2001

Date: Wednesday, October 4, 2000
Time: 4:15-5:30 PM; Refreshments at 4:00 PM
Location: 380-380Y


Radio Science with Mars Global Surveyor

Prof. Len Tyler
Electrical Engineering, Stanford University

Abstract

The MGS Radio Science Investigation is one of five experiments onboard the Mars Global Surveyor spacecraft and in a low circular orbit of Mars since March, 1999. Objectives of this investigation are observation and study of the atmosphere over a martian year, and determination of a precise model for the gravity field. MGS radio science builds on advances first achieved with the Voyager mission to the outer planets. Among these are the use of very high stability quartz oscillators as on-board frequency reference sources, attention to spacecraft and ground systems and to mission detail affecting radiometric performance, and advances in algorithms and software for data reduction and analysis.

Atmospheric occultations now number several thousand. Accuracies of retrieved surface pressure and temperature are in the range of a few pascals, and one kelvin, respectively. Atmospheric structure is obtained with a vertical resolution of about 0.8 km; recent advances in understanding of diffraction effects in occultation observations are expected to lead to an order of magnitude improvement, however. These observations reveal a number of interesting features including, a near-Chapman ionosphere controlled by solar zenith angle, strong diurnal variations in the lowest 2 km of the summer boundary layer, dynamically forced inversions in the lowest scale height in the northern winter hemisphere, and prominent atmospheric wave structures. Observations are accurately located in planetary radius, allowing study of thermal tides, the thermal wind, and the seasonal cycling of gas between the atmosphere and the polar caps.

Study of the gravity field is based on perturbations to the motion of MGS observed along the line of sight from Earth. Preliminary results provide new, very high quality observations of the northern hemisphere. Early analyses of the tracking data show that they support spherical harmonic models of degree and order 75. Direct observation of the seasonal change in mass of the polar cap is a distinct possibility.

Ancillary obserations include unusual very near forward scattering from the surface of Mars.