Controlled Source Electromagnetic Method
The Controlled Source Electromagnetic Method (CSEM) measures sub-surface resistivity structure through the measurement of the electromegnetic fields resulting from stimulation by a towed source.
CSEM equipment consists of a transmitter, affixed to a small instrument platform, and a string of 5 receivers, spaced 200 metres apart along a 1 kilometre cable. The CSEM sends a precise electromagnetic signal from a transmitter (TX) dipole which is recorded at several seafloor receiver (RX) dipoles located at a range of distances from the transmitter. The subtle changes in resistivity of the sediment between the TX and RXs are due to the displacement of conductive pore water by electrically-insulating gas hydrate. Through repeated soundings, the CSEM will track changes in resistivity and reveal the evolution of the gas hydrate deposit.
The CSEM method used is described theoretically by Edwards (1997) and experimentally by Schwalenberg et al (2005).
Individual instruments of the above category, which are (or have been) connected to our observatories. Click an instrument for detailed information.
|CSEM Receiver||Marine Technology Centre|
Click the instrument categories below for descriptions and lists of instruments belonging to that category.