An apparatus collects data along water columns. A telescoping shell has an outer cylinder and an inner cylinder. An expansible chamber is defined within the outer cylinder. A fluid flow path is formed between the expansible chamber and the outer cylinder's open end. A gas source is vented to the expansible chamber. Sensors, including a pressure sensor, are coupled to the shell such that they are exposed to an ambient water environment when the apparatus is deployed therein. A vent mounted in the outer cylinder vents the expansible chamber to the ambient water environment. A controller controls the gas source and vent based on sensed pressure of the ambient water environment such that water from the ambient water environment is admitted to or expelled from the expansible chamber via the fluid flow path.