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. <EOS>