D. L. Kirchner

Radar Soundings of the Subsurface of Mars

The martian subsurface has been probed to kilometer depths by the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument aboard the Mars Express orbiter. Signals penetrate the polar layered deposits, probably imaging the base of the deposits. Data from the northern lowlands of Chryse Planitia have revealed a shallowly buried quasi-circular structure about 250 kilometers in diameter that is interpreted to be an impact basin. In addition, a planar reflector associated with the basin structure may indicate the presence of a low-loss deposit that is more than 1 kilometer thick.

Radar Soundings of the Ionosphere of Mars

We report the first radar soundings of the ionosphere of Mars with the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument on board the orbiting Mars Express spacecraft. Several types of ionospheric echoes are observed, ranging from vertical echoes caused by specular reflection from the horizontally stratified ionosphere to a wide variety of oblique and diffuse echoes. The oblique echoes are believed to arise mainly from ionospheric structures associated with the complex crustal magnetic fields of Mars. Echoes at the electron plasma frequency and the cyclotron period also provide measurements of the local electron density and magnetic field strength.

THE WIDE-BAND PLASMA WAVE INVESTIGATION

As part of the Cluster Wave Experiment Consortium (WEC), the Wide-Band (WBD) Plasma Wave investigation is designed to provide high-resolution measurements of both electric and magnetic fields in selected frequency bands from 25 Hz to 577 kHz. Continuous waveforms are digitised and transmitted in either a 220 kbit s-1 real-time mode or a 73 kbit s-1 recorded mode. The real-time data are received directly by a NASA Deep-Space Network (DSN) receiving station, and the recorded data are stored in the spacecraft solid-state recorder for later playback. In both cases the waveforms are Fourier transformed on the ground to provide high-resolution frequency-time spectrograms. The WBD measurements complement those of the other WEC instruments and also provide a unique new capability for performing very-long-baseline interferometry (VLBI) measurements.

Low‐frequency radar sounding of temperate ice masses in Southern Alaska

We present the Warm Ice Sounding Explorer (WISE), a low-frequency (2.5 MHz) radar for the sounding of temperate ice. WISE deployment in southern Alaska in 2008 and 2012 provides comprehensive measurements of glacier thickness, reveals deep valleys beneath glaciers and the full extent of zones grounded below sea level. The east branch of Columbia Glacier is deeper that its main branch and remains below sea level 20 km farther inland. Ice is 1000 m deep on Tazlina Glacier. On Bering glacier, two sills separate three deep bed depressions (>1200 m) that coincide with the dynamic balance lines during surges. The piedmont lobe of Malaspina Glacier and the lower reaches of Hubbard Glacier are entirely grounded below sea level 40 and 10 km, respectively, from their termini. Knowledge of ice thickness in these regions helps better understand their glacier dynamics, mass balance, and impact on sea level. Key Points Low frequency radar sounding works extremely well in Alaska Ice is much thicker than suggested by limited surveys Data reveals full extent of areas grounded below sea level ©2013. American Geophysical Union. All Rights Reserved.

MARSIS data inversion approach: Preliminary results

An approach to the inversion of the data available from the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument on Mars Express is described. The data inversion gives an estimation of the materials composing the different detected interfaces, including the impurity (inclusion) of the first layer, if any, and its percentage, by the evaluation of the values of the permittivity that would generate the observed radio echoes. The data inversion method is based on the analysis of the surface to subsurface power ratio and the relative time delay as measured by MARSIS. The constraints, due to the known geological history of the surface, the local temperature and the thermal condition of the observed zones and the results of other instruments on Mars Express and other missions to Mars, have to be considered to improve the validity of the utilized models and the obtained results that are given in parametric way.

Low-frequency radar sounding of ice in East Antarctica and southern Greenland

Abstract We discuss a decameter-wavelength airborne radar sounder, the Warm Ice Sounding Explorer (WISE), that provides ice thickness in areas where radar signal penetration at higher frequencies is expected to be limited. Here we report results for three campaigns conducted in Greenland (2008, 2009, 2010) and two in Antarctica (2009, 2010). Comparisons with higher-frequency radar data indicate an accuracy of ±55 m for ice-thickness measurements in Greenland and ±25 m in Antarctica. We also estimate ice thickness of the Qassimiut lobe in southwest Greenland, where few ice-thickness measurements have been made, demonstrating that WISE penetrates in strongly scattering environments.