Device for measuring an environment, comprising: a housing , which has, on one side , a passage window made of a watertight and transparent material for the passage of a laser beam , a transmitter and a receiver for the laser beam , a deflection device arranged in the beam path of the laser beam , downstream of the transmitter and upstream of the receiver , for deflecting the laser beam , a measuring device connected to the deflection device for determining the respectively current deflection direction (α 1,i ) of the laser beam , a processor connected to the transmitter , the receiver , and the measuring device and configured to measure, by means of time-of-flight measurements of the laser beam emitted in various directions (R i ) and, thus, reflected at various scanning points (P i ) of the environment , the distances (d i ) of the scanning points in said directions (R i ) and to generate, therefrom, a scanning point cloud of the environment in a coordinate system , and a sensor for determining the refractive index (n 3 ) of a medium (M 3 ) of the environment located outside the passage window , wherein the processor is also connected to the sensor and is configured to take into account the refractive index (n 3 ) determined by the sensor when measuring the distances (d i ) and directions (R i ) of the scanning points (P i ), characterized in that the laser beam is pulsed by the transmitter with a pulse repetition rate (PRR) that can be controlled by the processor , wherein the processor is configured to decrease the pulse repetition rate (PRR) in case of a first, larger refractive index (n 3 ) determined by the sensor , and to increase it in case of a second, smaller refractive index (n 3 ) determined by the sensor . a housing , which has, on one side , a passage window made of a watertight and transparent material for the passage of a laser beam , a transmitter and a receiver for the laser beam , a deflection device arranged in the beam path of the laser beam , downstream of the transmitter and upstream of the receiver , for deflecting the laser beam , a measuring device connected to the deflection device for determining the respectively current deflection direction (α 1,i ) of the laser beam , a processor connected to the transmitter , the receiver , and the measuring device and configured to measure, by means of time-of-flight measurements of the laser beam emitted in various directions (R i ) and, thus, reflected at various scanning points (P i ) of the environment , the distances (d i ) of the scanning points in said directions (R i ) and to generate, therefrom, a scanning point cloud of the environment in a coordinate system , and a sensor for determining the refractive index (n 3 ) of a medium (M 3 ) of the environment located outside the passage window , wherein the processor is also connected to the sensor and is configured to take into account the refractive index (n 3 ) determined by the sensor when measuring the distances (d i ) and directions (R i ) of the scanning points (P i ), characterized in that the laser beam is pulsed by the transmitter with a pulse repetition rate (PRR) that can be controlled by the processor , wherein the processor is configured to decrease the pulse repetition rate (PRR) in case of a first, larger refractive index (n 3 ) determined by the sensor , and to increase it in case of a second, smaller refractive index (n 3 ) determined by the sensor . <EOS>