Bob Grimm - MTDEM

Mars Time Domain Electromagnetic Sounder

Time-domain electromagnetic (TEM or TDEM) sounding is widely used to measure ground conductivity as a function of depth. The most common implementation uses a large transmitter loop (~100 m in diameter) and a compact, multiturn receiver loop. When electrical current is abruptly extinguished in the transmitter loop, eddy currents flow in the ground, depending on conductivity, and their magnetic fields are detected at the receiver. TDEM does not depend on geometrical detail (like a radar antenna) of the coils yet is very sensitive to subsurface conductors (the method was invented for ore exploration). Our Mars Time Domain Electromagnetic Sounder (MTDEM) prototype was built by Ball Aerospace (Barry Berdanier) with funding from NASA ASTID and PIDDP (R. Grimm, PI). The system was tested in the lab and in the field in Colorado and Hawaii (TRL 5-6). Our current work focuses on development of a ballistic deployment system for the transmitter loop (TRL 3, to achieve 5-6), as well as integration and miniaturization of the electronics.

MATLAB graphical user interface time-domain EM design tool, used both for prototype specification and to assess likely instrument performance on Mars. Displayed parameters are for prototype in Hawaii.

Maui, HI, test site is in the middle distance, near the coast. Basal seawater in coastal regions of Hawaiian islands is a good analog to martian aquifer.

MTDEM electronics, powered by car battery for field test.Where's Barry? At least the loop reel is orange.

Final results for MTDEM field test, compared to commercial system (the orange box!). Seawater - which is depressed below sea level by a freshwater lens - was detected at depths up to 250 m. Thickness of freshwater lens is well fit by a model of uniform recharge and seaward groundwater flow. Under Mars conditions, saline water could be detected at depths of several kilometers with this system.