A method of determining a filling level of a product contained in a tank, said method comprising: generating and transmitting electromagnetic signals; propagating said transmitted electromagnetic signals towards a surface of a product contained in a tank along a probe extending towards and into said product contained in the tank; receiving echo signals resulting from reflections at impedance transitions encountered by said transmitted electromagnetic signals, including a surface echo signal resulting from reflection at said surface of said product; determining a position of a reference impedance transition using a reference echo signal resulting from reflection of said transmitted electromagnetic signals at said reference impedance transition; characterized by: determining if said reference impedance transition is located above the surface of said product based on said determined position of the reference impedance transition and a known position of the reference impedance transition; if said reference impedance transition is determined to be located above the surface of said product, determining an update level located above said surface, based on said position of the reference impedance transition; determining a measurement echo profile based on said received echo signals, the measurement echo profile including the surface echo signal; determining a disturbance echo profile using at least one of said echo signals resulting from reflection of said transmitted signals at at least one impedance transition located above said update level; combining said measurement echo profile and said disturbance echo profile to form a combined echo profile; identifying said surface echo signal using said combined echo profile; and determining said filling level based on said identified surface echo signal. generating and transmitting electromagnetic signals; propagating said transmitted electromagnetic signals towards a surface of a product contained in a tank along a probe extending towards and into said product contained in the tank; receiving echo signals resulting from reflections at impedance transitions encountered by said transmitted electromagnetic signals, including a surface echo signal resulting from reflection at said surface of said product; determining a position of a reference impedance transition using a reference echo signal resulting from reflection of said transmitted electromagnetic signals at said reference impedance transition; determining if said reference impedance transition is located above the surface of said product based on said determined position of the reference impedance transition and a known position of the reference impedance transition; if said reference impedance transition is determined to be located above the surface of said product, determining an update level located above said surface, based on said position of the reference impedance transition; determining a measurement echo profile based on said received echo signals, the measurement echo profile including the surface echo signal; determining a disturbance echo profile using at least one of said echo signals resulting from reflection of said transmitted signals at at least one impedance transition located above said update level; combining said measurement echo profile and said disturbance echo profile to form a combined echo profile; identifying said surface echo signal using said combined echo profile; and determining said filling level based on said identified surface echo signal.