Normalized histograms for different wave parameters as a function of heliocentric distance. The wave parameters are as follows: Panel a: Wave amplitude. Panel b: Wave amplitude normalized by the background magnetic field. Panel c: Duration of the wave packets. Panel d: Frequency width. Panel e: Frequency in the plasma frame normalized by the local electron cyclotron frequency. Panel f: Histogram of the frequency in the spacecraft frame normalized by the electron cyclotron frequency for sunward (in purple) and anti-sunward whistler waves (in pink).