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 <EOS>