Drilling system that measures the fluid level in a wellbore during drilling of the wellbore

A method of measuring a fluid level in a wellbore during drilling of the wellbore using a drilling system comprising a drill pipe, the method comprising:

• attaching a plurality of sensor sleeves along the drill pipe,
• drilling the wellbore with the drill pipe, while filling the wellbore with drilling fluid,
• measuring the fluid level in the wellbore in time intervals by:
• transmitting a sensing signal from each sensor sleeve in a direction of the fluid level,
• receiving, by the plurality of sensor sleeves, each sensing signal reflected on the surface of the drilling fluid,
• determining a distance between each sensor sleeve and the fluid level from the transmitted and received sensing signals,
• determining the sensor sleeve that is closest to and above the fluid level, called the offset sensor sleeve,
• determining a fluid level offset, wherein the fluid level offset is a length of the drill pipe from the offset sensor sleeve to a surface of the wellbore, and
• determining the fluid level by adding the fluid level offset and the distance between the offset sensor sleeve and the fluid level.