Erta Ale is a remote and rarely visited volcano that is known currently to have an active lava lake in its summit crater. Erta Ale has undergone seven eruption events in the past 125 years.
Re: What are the differences between Signal ground, Chasis ground and Earth?? Signal Ground is a reference point from which that signal is measured, due to the inevitable voltage drops when current flows within a circuit, some 'ground' points will be slightly different to others. There may be several signal grounds in a circuit.
A total station is an electronic instrument used for the measurement of distances and angles from the device to the points being surveyed. By the use of trigonometry, the measured angles and distances are utilized to determine the real location of the points that are being surveyed.