Signal-to-Noise ratio of CSEM data in shallow water

Conventional controlled source electromagnetic CSEM surveying was designed for deep water. In shallow water <300 m the magnetotelluric noise and the air wave present problems for the method. The source signal is continuous with energy concentrated in a few discrete frequencies. A transient broad-bandwidth source signal, with the same energy spread out over the bandwidth, allows significant gains in signal to noise ratio. Deconvolution gives more than an order of magnitude increase in signal- to-noise ratio; correlated noise, including magnetotelluric noise, can be reduced by a further order of magnitude; and the air wave becomes separable from the earth response - a further gain of about 15 dB. For the same source energy the transient source signal is superior by about 40 dB a factor of 100.