International audienceAround fifty LORAN (LOng RAnge Navigation) transmitters in the northern hemisphere currently launch continuously pulsed 100 kHz radio waves into the Earth's atmosphere for marine navigation. It is discovered that the 100 kHz radio waves from the LORAN transmissions can be detected by the DEMETER satellite at an altitude of 660kmabovethetransmitters.Thesenovelelectricfieldmeasurementsinspaceenablethedeterminationofthenocturnaltransionosphericattenuationbycomparisonwithgroundbasedelectricfieldmeasurements.Theelectricfieldmeasurementsonthesatelliteindicatethatthenocturnaltransionosphericattenuationof100kHzradiowavesfromLORANtransmissionsisequivalenttoanocturnalsubionosphericattenuationofthe100kHzradiowavesatadistanceof7-9 Mm. The radio waves exhibit an average subionospheric attenuation of 5dB/Mmanditisconcludedthatthenocturnaltransionosphericattenuationof100kHzradiowavesis35-45 dB. This result enables future space missions to quantify the intensity of lightning discharges associated with transient luminous events and terrestrial gray flashes