Theory Inject electric current into water column with a dipole and measure electric field at a distance dipole receiver A solution to these problems is to measure the electrical conductivity profile using an active EM source and receiver on the bottom of the estuary. The salinity in the water acts as conductivity to complete the circuit of the sediment and water column. The correlation between salinity and conductivity is very tight over the period of a year. The electric currents hug the bottom in relation to the delta, the “skin depth”: with higher

Theory Electric Field Skin Depth for AC signals: Permeability AC angular frequency Conductivity

Instrumentation 2nd Version- Longitudinal Arrangement Transmitter Receivers - + 20 m 6 m **Not to scale**

Correlation between conductivity and salinity from Saturn01 Inversion Methods Times of signal change is related to thicknesses that are roughly high: Correlation between conductivity and salinity from Saturn01 Sigma Profiler dipole strength divided by the received electric field for all 6 frequencies: 270 Hz – 27.7 kHz (black-green)

Inversion 2 Fill Method Using a dipole model of electric field: P- dipole strength, E- received electric field r- distance from transmitter to receiver - skin depth, - conductivity of water within that layer Rearranging to solve for conductivity:

Results Inversion from Sigma Profiler data to salinity profiles for second deployment Inversion 1- Cut-off Method Conductivity time series determined from calculating threshold from low to high conductivity values and interpolating to zero. Inversion 2- Fill Method Conductivity time series determined by calculating conductivity values for each time step and frequency and applying them below the corresponding The first model does not determine regions of medium conductivity very well. The second model does not give an exact shape of conductivity over time and has some trouble at low conductivities. Salinity measured from Saturn01 CTD mooring