f Enviromt. A new radio/controlled source system

Novel features of the EnviroMT system Broad band radio-signal reception For the estimation of transfer functions we only make use of the signal from distant manmade sources in the form of VLF and Radio transmitters in the LW and MW band in contrast to standard MT where the whole frequency band is considered as plane wave sources perhaps mixed with non-planar events. In Northern Europe there are generally more than two independent transmitters available in each half-octave/octave band that transfer functions can be estimated starting at 14 kHz. Controlled source with synchronous detection Whereas the standard estimation of transfer functions in the RMT mode is based upon the assumption that they are constant in each sub-band no such assumption is necessary in the controlled source mode. Here, unique transfer functions can be found right at the transmitter frequencies chosen because the transmitter consists of two independent horizontal dipole coils. Even though these transfer functions are most easily interpreted in the plane wave (or far field) case they can still be uniquely defined in the intermediate and near field range. Built in database handling In addition to showing pseudo-sections the system also provides a facility for automatic 1D inversion of selected impedance combinations (off-diagonal elements, determinant, etc.) along selected profiles. In the future even a fast 2-D inversion code will be added to the system to make it more flexible and self-contained. All the above mentioned manipulations can be done in-field. The built-in colour display unit is of excellent quality and with the fast built-in computer, in a few minutes the user can get a complete overview of the data collected along various profiles.