Systems and methods for detecting low-loss eigenmodes of a spherical waveguide bounded by the Earth's surface and its ionosphere are disclosed. One or more eigenmodes of the Earth-ionosphere waveguide may be computed based on a mathematical model incorporating electrical properties of the terrestrial surface and plasma physics of the ionospheric layer. A transmitter apparatus may be used transmit electrical power into the Earth-ionosphere waveguide in the form of an electromagnetic wave, which may, in turn, be detected by a receiver apparatus remote from the transmitter apparatus. A coupling strength between the transmitted electromagnetic wave and the one or more eigenmodes may be determined by measuring power received by the receiver apparatus in the detected electromagnetic wave. By iteratively adjusting parameters of the transmitter apparatus, determining the coupling strength, and refining a quantitative description of the eigenmodes, the eigenmodes may be harnessed for wireless power transmission throughout the Earth-ionosphere waveguide.