Pitch indicates the inclination of the drilling direction relative to the horizontal plane. A 3-axis accelerometer is used to calculate the pitch and roll of the drilling bit which measures the three mutually orthogonal components of the acceleration of gravity for a stationary drill bit.
The attitude information includes the pitch, roll, and azimuth of the drilling bit. Inertial guidance systems use fiber-optic gyroscopes along with highly sensitive accelerometers to locate the drill head precisely along the bore path.
Trenchlesspedia Explains Pitch
The connection of the optical gyro system from downhole to the surface is done via a transmission system that sends the pitch, roll and azimuth readings three times in a second providing the engineer with real-time measurements.
The pitch and the azimuth should be determined during the drilling process to operate the drilling machine economically hence using the term measurement while drilling (MWD).
The inertial guidance system is a type of MWD system that is used for drilling head guidance in trenchless construction methods of vertical drilling and horizontal directional drilling (HDD). It relies on knowing the initial position, velocity, and attitude, after which it measures the attitude rates and accelerations.
It does not rely on external references. To compensate for errors, two redundant accelerometers fixed at two different planes are used. The results from the two accelerometers are used to arrive at the final calculation. It can take measurements of azimuth, pitch, and roll simultaneously.