Abstract: The technology relates to a system and method for monitoring an environment. The method comprises receiving first and second sets of data from a plurality of mobile units, wherein the first set of data is associated with a first temporal indicator, the second set of data is associated with a second temporal indicator and each mobile unit comprises: a position determining device configured to generate position data associated with a position of the mobile unit within the environment, and a laser scanning device configured to generate scan data based on a scan of at least part of the environment; determining a first parameter associated with the first set of data; determining a second parameter corresponding to the first parameter and associated with the second set of data; and determining a difference between the first and second parameters.