Time-Domain Electromagnetics

Time-domain electromagnetic (TDEM) systems measure the subsurface electrical conductivity by injecting a stepped current waveform into a transmitter loop and recording the decaying secondary magnetic field generated by induced eddy currents in conductive geological formations after the primary current switches off. The decay rate and amplitude of this transient response characterize the electrical properties of subsurface materials — identifying conductive targets including mineralized zones, groundwater aquifers, saline intrusions, and unexploded ordnance from surface measurements.

The transmitter loop — typically a square or rectangular wire frame from 10 to 200 meters per side — carries a steady DC current. The current switches off rapidly in microseconds. This switching induces eddy currents in conductive subsurface materials. These currents decay at rates determined by the conductivity and geometry of the host material. Furthermore, receiver coils inside or near the transmitter loop record the decaying magnetic field as a voltage time series across multiple time gates from microseconds to milliseconds after switch-off. Early time gates sample shallow conductive targets. Late time gates reach deeper formations — investigation depths of 50 to 500 meters depending on transmitter moment and ground conductivity.

The Geonics PROTEM and EMIT SmartTEM represent professional portable TDEM systems. These use multi-turn receiver coils and high-moment transmitter loops. They cover investigation depths from 5 meters on small-loop configurations to over 400 meters on large fixed-loop setups. Additionally, airborne TDEM systems mount transmitter loops on fixed-wing or helicopter platforms — surveying hundreds of kilometers per day at line spacings of 50 to 200 meters for regional groundwater and mineral exploration programs. Data inversion software converts time-gate voltage decay curves into layered resistivity models — identifying aquifer depths, conductive ore bodies, and stratigraphic boundaries in three-dimensional subsurface space.

These systems serve Pakistan’s groundwater development programs for agricultural irrigation in Punjab and Sindh, mineral exploration contractors targeting copper and gold deposits in Balochistan and KPK, Pakistan Army EOD UXO clearance survey programs in former conflict zones, environmental site investigation contractors, and university geophysics research departments in Lahore and Karachi.

Tactical Supply Pakistan supplies time-domain electromagnetic systems for groundwater survey, mineral exploration, UXO clearance, and environmental geophysics procurement across Pakistan.