The requirement to conduct measurements across the big water areas and in the ocean depths arises a problem of creating devices to measure an electric field, being either set on the high-speed mobile carriers, or implemented as the sounders, which investigate a vertical or horizontal structure of the electric field of ocean. Manufactured, designed, and hypothetical devices for measuring poor electric fields of the ocean were analyzed. The analysis allowed us to prove that there is a need in creation of modulation sensors (with modulation of a non-electric origin) either with periodically changing capabilities of measuring bases, or with space-changing (and therefore, time-changing) position of measuring base of primary converters, as the most effective in terms of allocation and measurement of the modulated signal from unmodulated noise.

The paper considers the mathematical models of modulation sensors of electric field intensity in the ultralow-frequency range, which are set on the mobile carriers. It justifies a choice of two basic models of primary converters with a change of the measuring base in space, i.e. with the "changing" base and with the "rotating" base. A feature of the offered models with vertical sounding is the minimum value of noise because of rotation of measuring electrodes in a magnetic field of Earth, and hydrodynamic noise. The paper shows that noise caused by the relative movement of sensor and water completely disappears in two cases:

1. for a vertical sounder in the autonomous mode or a horizontal sounder with zero buoyancy in the specified shape of water;

2. in a case when the sensor has no component of measuring base in the considered area, for example, for the sensor with in-line array of electrodes located in the horizontal plane.

The paper proves advantage of the model with "rotating" measuring base, which provides the maximum power transfer from the primary converter to loading for all relative positions of an external electrode and contact orifice. For the sensor with "rotating" measuring base, it defines optimum, in terms of a maximum, power transferred to the matched loading, and ratios of its constructive sizes.