A pipeline inspection system, comprising: a pipeline pig, comprising: a plurality of ultrasonic transducer elements situated in an array, wherein each of the plurality of ultrasonic transducer elements is configured to emit an ultrasonic signal into a wall of a pipeline and to receive echoes of the ultrasonic signal from the pipeline wall; characterised by: a controller configured to: select a first subset of the plurality of ultrasonic transducer elements from which to emit first ultrasonic signals into the wall of the pipeline as the pipeline pig passes through the pipeline; analyze the echoes of the first ultrasonic signals received by the first subset of the plurality of ultrasonic transducer elements to detect a feature in the pipeline wall; select a second subset of the plurality of ultrasonic transducer elements to emit second ultrasonic signals into the wall of the pipeline as the pipeline pig passes through the pipeline when the feature is detected in the pipeline wall, wherein the second subset of the plurality of ultrasonic transducer elements is selected based on a remaining wall depth of the pipeline wall and a threshold value of an amplitude; and analyze the echoes of the second ultrasonic signals received by the second subset of the plurality of ultrasonic transducer elements to determine a depth of the feature in the pipeline wall. a plurality of ultrasonic transducer elements situated in an array, wherein each of the plurality of ultrasonic transducer elements is configured to emit an ultrasonic signal into a wall of a pipeline and to receive echoes of the ultrasonic signal from the pipeline wall; characterised by: a controller configured to: select a first subset of the plurality of ultrasonic transducer elements from which to emit first ultrasonic signals into the wall of the pipeline as the pipeline pig passes through the pipeline; analyze the echoes of the first ultrasonic signals received by the first subset of the plurality of ultrasonic transducer elements to detect a feature in the pipeline wall; select a second subset of the plurality of ultrasonic transducer elements to emit second ultrasonic signals into the wall of the pipeline as the pipeline pig passes through the pipeline when the feature is detected in the pipeline wall, wherein the second subset of the plurality of ultrasonic transducer elements is selected based on a remaining wall depth of the pipeline wall and a threshold value of an amplitude; and analyze the echoes of the second ultrasonic signals received by the second subset of the plurality of ultrasonic transducer elements to determine a depth of the feature in the pipeline wall. select a first subset of the plurality of ultrasonic transducer elements from which to emit first ultrasonic signals into the wall of the pipeline as the pipeline pig passes through the pipeline; analyze the echoes of the first ultrasonic signals received by the first subset of the plurality of ultrasonic transducer elements to detect a feature in the pipeline wall; select a second subset of the plurality of ultrasonic transducer elements to emit second ultrasonic signals into the wall of the pipeline as the pipeline pig passes through the pipeline when the feature is detected in the pipeline wall, wherein the second subset of the plurality of ultrasonic transducer elements is selected based on a remaining wall depth of the pipeline wall and a threshold value of an amplitude; and analyze the echoes of the second ultrasonic signals received by the second subset of the plurality of ultrasonic transducer elements to determine a depth of the feature in the pipeline wall.