Induced Polarization Chargeability Survey (2D)

Survey Array

Electrode spacing a 15 m

Array position (profile x) 0 m

Subsurface Target

Body depth 9.0 m

Intrinsic chargeability m₁ 55 mV/V

Body/host resistivity ratio 0.25×

Host resistivity ρ₀ 200 Ω·m

Decay time constant τ 0.35 s

Live Readout

Apparent resistivity ρₐ

— Ω·m

Apparent chargeability mₐ

— mV/V

Integral chargeability M

— mV/V

Body sensed fraction

—%

How it works

A Wenner array (four in-line electrodes C1–P1–P2–C2, each separated by spacing a) injects current I between the outer pair and measures voltage V between the inner pair. Apparent resistivity follows the standard Wenner geometric factor:

ρ_a = 2·π·a·(V / I)

Sensitivity to a buried body is not uniform — current density falls off with depth and lateral offset from the array centre. This sim approximates that with a Gaussian sensitivity kernel peaking near depth ≈ 0.5·a below the array midpoint (a simplified stand-in for the real Frechet-derivative "depth of investigation characteristic" of Edwards 1977 — shape is representative, not a precise field curve). Integrating that kernel over the buried body's cross-section gives a sensed fraction f, which sets both the apparent resistivity (mixing host ρ₀ and body ρ₀·ratio) and the apparent chargeability:

m_a = f · m₁         (host is non-chargeable, m₀ = 0)

Switching the current off, the induced voltage doesn't vanish instantly — chargeable minerals (commonly sulfides) discharge over roughly a second, following an approximately exponential decay V(t) = V₀·(m_a/1000)·e^(−t/τ). Real field instruments integrate that decay over a time window to get the standard time-domain "integral chargeability":

M = (τ/T_w)·(1 − e^(−T_w/τ))·m_a

Run profile survey — sweeps the array centre across the profile and plots apparent chargeability vs. position, the classic way an IP anomaly is actually found in the field.
Switch off current — stops injection and plots the live voltage-decay curve used to compute M.

Sensitivity kernel Chargeable body Profile / decay curve