Magnetotelluric Subsurface Sounder, 15-R8043

Principal Investigators
Robert Grimm
David Stillman
Kerry Neal
Michael Vincent

Inclusive Dates:  03/01/09 – Current

Background -  Electromagnetic (EM) sounding of planetary interiors reveals key indicators of structure and geological evolution, but is not widely recognized because there has been no simple approach applicable to a variety of space missions. Magnetotellurics (MT) — used for the past half-century on Earth — can provide that broad applicability. MT determines the frequency-dependent ground impedance (and hence interior structure) from measurements of the electric and magnetic fields naturally arising from lightning, the ionosphere, the magnetosphere, and in space, from the solar wind. Modeling, sensor validation, and fielding of a prototype system will demonstrate the capability of SwRI to respond to several flight announcements of opportunity anticipated over the next few years. The initial focus is on a scale demonstration of a Venus balloon; the later stages of the project turn toward landed systems.

Approach - There are three main elements to the project. First, EM measurements from a tethered balloon will demonstrate aerial capability, specifically, the ability to perform relevant non-ground-contacting electric-field measurements and the ability to process balloon attitude information to recover the useful portion of the EM fields. Second, instrument designs suitable for modification to specific flight proposals will be produced. Third, theoretical modeling of the interiors of different satellites and terrestrial planets will determine science goals and performance requirements for future flight opportunities.

Accomplishments - Time variations in attitude and position were measured in trial tethered flights of an 8-ft.-diameter plastic balloon. A data-acquisition system (DAQ) was assembled, consisting of a laptop PC, a LABVIEW program, and two four-channel commercial ADCs. A commercial compact fluxgate magnetometer was purchased, and a high-sensitivity compact induction magnetometer was borrowed from a collaborator. These sensors were tested with the DAQ in various indoor and outdoor environments. The electrometer development fell significantly behind schedule, but is now in integration and test with the balloon. SwRI researchers anticipate several flights by the end of the year. In support of the balloon test, the first series of EM models focused on Venus. It was determined that the lightning-caused Schumann resonances are suitable for probing from tens to hundreds of kilometers into Venus, and specifically that different internal temperature configurations can be recovered. The modeling further confirmed that the measurements can be performed from tens of kilometers altitude. The second half of the project will focus on using the electrometers and magnetometers for subsurface investigations of the Moon and Mars.

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