An automatic audio-magnetotelluric equipment,controlled by microprocessor,for the telesurvellance of the volcano Momotombo (Nicaragua)

A campaign of audio-magnetotelluric soundings in the crater of Momotombo has shown that the structure of this volcano is suitable to a surveillance by this method; it has an only central activity, and the resistivity versus the depth decreases suddenly at least 100 times at about 270 m. So, this technical paper describes the equipment designed and built in order to measure every 2 hr the apparent resistivity in a given direction, at seven frequencies regularly spaced from 5 to 312 Hz. The data are preprocessed to fill only 32 bytes: they are

- on the one hand, printed locally for the close surveillance;

- on the other hand, transmitted by an ARGOS platform and received in Garchy via satellite for searching studies