Broadband reflectometry is used to obtain density profiles in fusion plasmas using waves reflected at different plasma layers. The reflected signal can be severely affected by plasma fluctuations and/or fast density changes. In order to understand the plasma response, a finite difference time domain two-dimensional full wave code was developed. The code was used to study typical situations of fusion plasmas where important profile movements occur: when a rotating magnetic island is present and during an ELM. The numerical results are in good agreement with experimental results obtained in ASDEX and ASDEX Upgrade in the situations above. Our study demonstrates that contributions from the plasma movements are important and should be taken into account to obtain accurate profile measurements