Elastic thickness estimates for Venus from line of sight
accelerations
D. McKenzie and F. Nimmo, Icarus 130,198-216, 1997
(PDF file
(3239K) available)
A new method of obtaining the transfer function, or admittance, Z,
between the Fourier transforms of
topography and gravity of a planet is proposed that uses the line of sight
(LOS) Doppler velocities directly. The expected LOS accelerations are first
calculated from the spherical harmonic coefficients of the topography, the
latitude, longitude and height of the spacecraft, and the direction of Earth
viewed from the planet. The admittance can then be obtained using standard
signal processing methods, by comparing the LOS acceleration calculated from the
topography with the time derivative of the observed LOS Doppler velocities. This
method is applied to the Magellan data from cycle 4 for Atla, and shows that the
short wavelength behaviour of the admittance is that expected from an elastic
layer whose thickness T_e is 30 +/-5 km. The main contribution to
the short wavelength gravity field comes from the large volcanoes Ozza, Maat
and Sapas Montes. Comparison with admittance estimates from spherical
harmonic gravity fields and from local inversions shows that these methods
produce estimates of Z(k) that do not fit those expected from a simple
flexural model. The T_e values from Beta and Ulfrun of 27.5 and 33 km are similar
to that of Atla, whereas Eistla (20.5 km) and Dali (12 km) give smaller
values. No reliable value can yet be estimated from Aphrodite, probably
because the topography is poorly determined. These estimates of T_e cover the same
range as those from flexural modelling of topography.
Francis' Page
Department of Earth Sciences
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nimmo@esc.cam.ac.uk
This page was last modified on 27 Oct 1997.