Systems and methods for measuring depth within a borehole

A method comprising:

• receiving, from a downhole device within or associated with a drill string comprising at least one drill rod, using a computing device, a plurality of inertial measurements and a respective time value for each inertial measurement of the plurality of inertial measurements;
• detecting, by a drill rig position sensor in communication with the computing device, a change in position of a drill rig to which the drill string is secured, wherein the detected change in position of the drill rig is indicative of a length of a portion of the drill string removed from a borehole;
• determining, by the computing device, at least one depth measurement indicative of an operative length of the drill string, wherein the at least one depth measurement is determined based on the detected change in position of the drill rig;
• and
• determining, by the computing device, a depth of the downhole device within the drill string based on the plurality of inertial measurements and the at least one depth measurement, wherein determining the depth of the downhole device comprises:
• determining a potential movement of the downhole device based on the data from the at least one inertial sensor;
• and
• associating a change of depth of the downhole device corresponding to the potential movement if and only if the drill rig position sensor indicates a change in position of the drill string corresponding to the potential movement.

A system comprising:

• a downhole device comprising at least one inertial sensor;
• at least one processor;
• a memory in communication with the at least one processor, wherein the memory comprises instructions thereon that, when executed, cause the at least one processor to:
• receive data from the at least one inertial sensor;
• store the data from the at least one inertial sensor in the memory with respective correlated time values;
• and
• a drill rig having a longitudinal axis, wherein the drill rig is configured to move a drill string comprising at least one drill rod within a borehole, wherein the drill rig comprises at least one depth measurement device, wherein the at least one depth measurement device comprises:
• a drill rig position sensor that is configured to detect a change in position of the drill rig, wherein the detected change in position of the drill rig is indicative of a length of a portion of the drill string removed from a borehole, wherein the drill rig position sensor comprises a plurality of Hall Effect sensors spaced along the longitudinal axis of the drill rig.