  The Matter-Wave laser Interferometer Gravitation Antenna, MIGA, will be a
hybrid instrument composed of a network of atom interferometers horizontally
aligned and interrogated by the resonant field of an optical cavity. This
detector will provide measurements of sub Hertz variations of the gravitational
strain tensor. MIGA will bring new methods for geophysics for the
characterization of spatial and temporal variations of the local gravity field
and will also be a demonstrator for future low frequency Gravitational Wave
(GW) detections. MIGA will enable a better understanding of the coupling at low
frequency between these different signals. The detector will be installed
underground in Rustrel (FR), at the "Laboratoire Souterrain Bas Bruit" (LSBB),
a facility with exceptionally low environmental noise and located far away from
major sources of anthropogenic disturbances. We give in this paper an overview
of the operating mode and status of the instrument before detailing simulations
of the gravitational background noise at the MIGA installation site.
