It just became possible, thanks to a laser camera developed by physicists at Heriot Watt University in Edinburgh, UK. You can pretty much see how it works from the images above -- laser beams are bounced off the target and the duration of theirreturnjourney is measured precisely enough to detect millimeter depth changes even at extreme distances.
When they made this returnjourney, they began their characteristic nest-searching behaviour, quartering the ground in detail looking for the entrance, after travelling about ten metres.