This paper presents the results of experiments carried out with rocket-triggered lightning and the related theoretical analysis. It describes the test setup and presents the electric field waveform recorded at the earth surface alongside with the simultaneous measurement of the lightning return stroke current at the channel base. The relevant parameters that allow the validation of a model to correlate the two waveforms are presented, i.e., the return stroke velocity, the distance from the lightning channel base, and the earth parameters (resistivity and permittivity). A theoretical analysis is also presented, which models the phenomenon by the superposition of an induced and a conducted component, providing results that are in good agreement with the measurements. Finally, the paper presents a discussion about the range of validity of the theoretical model and analyzes the behavior of the two components of the electric field.