[[file:applying-magnetotellurics_fig16-3.png|300px|thumb|{{figure number|1}}Typical MT setup for a natural-source survey.]]
[[file:applying-magnetotellurics_fig16-3.png|300px|thumb|{{figure number|1}}Typical MT setup for a natural-source survey.]]
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The natural-source data-acquisition system typically measures four components: E<sub>x</sub>, E<sub>y</sub>, H<sub>x</sub>, and H<sub>y</sub>. The E<sub>x</sub> component is oriented perpendicular to the E<sub>y</sub> component. This is also true for the H-field components.
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The natural-source data-acquisition system typically measures four components: E<sub>x</sub>, E<sub>y</sub>, H<sub>x</sub>, and H<sub>y</sub>. (See [[Magnetotellurics survey measurements]].) The E<sub>x</sub> component is oriented perpendicular to the E<sub>y</sub> component. This is also true for the H-field components.
The predominant low-frequency ( 1.0 Hz) source is equatorial thunderstorm activity.
The predominant low-frequency ( 1.0 Hz) source is equatorial thunderstorm activity.