A method for operating a movable compaction device during material compaction work, in which method the moisture content of the material to be compacted is monitored, said method comprising steps of - defining a compaction performance index for the material to be compacted, said compaction performance index being an electromagnetic character correlating with the volumetric moisture content of the material, - determining the compaction performance index value in number of survey points of the material to be compacted during compaction work using movable electromagnetic measurement device and - controlling the operation on the compaction device during compaction work based on determined compaction performance index values, characterized in that, the determination of the compaction performance index on each survey point includes - sending at least one wideband electromagnetic pulse to the material to be compacted with a ground penetrating radar, - receiving a reflected signal, - measuring the Power spectral density (PSDm) and Peak to Peak Amplitude (PTPm) from the reflected signal and - calculating the compaction performance index by using the measured Power spectral density (PSDm) and Peak to Peak Amplitude (PTPm), - said method further comprises steps of defining a Power spectral density reference (PSDr) and Peak to Peak amplitude reference (PTPr) by calibrating the ground penetrating radar in air or in soil and - calculating the compaction performance index by equation CPI = PSDm Direct Wave × FF + PTPm Direct Wave × AF × 100 PSDr Direct Wave × FF + PTPr Direct Wave × AF where CPI = Compaction Performance index PSDm = Power spectral Density measured PSDr = Power spectral density reference PTPm = Peak to Peak Amplitude measured PTPr = Peak to Peak amplitude reference FF = Frequency weight factor AF = Amplitude weight factor - defining a compaction performance index for the material to be compacted, said compaction performance index being an electromagnetic character correlating with the volumetric moisture content of the material, - determining the compaction performance index value in number of survey points of the material to be compacted during compaction work using movable electromagnetic measurement device and - controlling the operation on the compaction device during compaction work based on determined compaction performance index values, - sending at least one wideband electromagnetic pulse to the material to be compacted with a ground penetrating radar, - receiving a reflected signal, - measuring the Power spectral density (PSDm) and Peak to Peak Amplitude (PTPm) from the reflected signal and - calculating the compaction performance index by using the measured Power spectral density (PSDm) and Peak to Peak Amplitude (PTPm), - said method further comprises steps of defining a Power spectral density reference (PSDr) and Peak to Peak amplitude reference (PTPr) by calibrating the ground penetrating radar in air or in soil and - calculating the compaction performance index by equation CPI = PSDm Direct Wave × FF + PTPm Direct Wave × AF × 100 PSDr Direct Wave × FF + PTPr Direct Wave × AF PSDm = Power spectral Density measured PSDr = Power spectral density reference PTPm = Peak to Peak Amplitude measured PTPr = Peak to Peak amplitude reference FF = Frequency weight factor AF = Amplitude weight factor