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We analyze the common surface reflection and full‐wave inversion methods to retrieve the soil surface dielectric permittivity and correlated water content from air‐launched ground‐penetrating radar (GPR) measurements. In the full‐wave approach, antenna effects are filtered out from the raw radar data in the frequency domain, and full‐wave inversion is performed in the time domain, on a time window focused on the surface reflection. Synthetic experiments are performed to investigate the most critical hypotheses on which both techniques rely, namely, the negligible effects of the soil electric conductivity (σ) and layering. In the frequency range 1–2 GHz we show that for σ > 0.1 Sm⁻¹, significant errors are made on the estimated parameters, e.g., an absolute error of 0.10 in water content may be observed for σ = 1 Sm⁻¹. This threshold is more stringent with decreasing frequency. Contrasting surface layering may …