Modulated HF heating of the auroral electrojet is used to inject ELF signals into the magnetosphere that are observed on the low altitude DEMETER spacecraft. The HF heater is a component of the High-Frequency Active Auroral Research Program (HAARP) facility in Gakona, Alaska, (located at L ~ 4.9). Simultaneous observations of all six components of the ELF electromagnetic fields on the DEMETER spacecraft are used to estimate the total ELF power radiated downward into the Earth-ionosphere waveguide. ELF signals generated by the HAARP heater are also simultaneously observed at a nearby ground-based site, allowing a comparison of the ELF power in the Earth-ionosphere waveguide versus that detected on DEMETER. The estimated values of power onboard DEMETER at different frequencies range from 0.32W to 4W, while the values of power estimated from a ground receiver at a distance of 36 km from HAARP range from 2.71W to 4.22W.