Project B05 pursues the development of a wide range, low-noise, compact optical readout scheme for integration in novel gravitational sensors and future space-based gravity exploration missions, as set forth by project B01. The new Deep Frequenca Modulation Interferometry (DFMI)-based multi-channel inertial sensors will be deployed at the torsion balance facility in collaboration with project B06, which presents an ideal test platform for ultra-high precision force measurements, as well as a case study for future flight instrument realisations. The core metrology aspects to be investigated can be separated into two parts. First, the noise and linearity properties of DFMI itself under realistic conditions, including optical and electronic noise mitigation methods. Second, the optimal reconstruction of the test mass motion from the interferometer signals, a complex problem involving signal calibration, noise hunting, as well as real-time data processing algorithms. These investigations will make use of the extensive knowledge gained from the development of the LISA Pathfinder mission, as well as of the tools and the noise mitigation strategies being developed in collaboration with project B03, i.e., optical design methods for low-noise interferometry.