Multipath, wherein a signal arrives at the receiving antenna by more than one path, is a significant and largely unmodeled source of GPS positioning error. We present a technique for mitigating specular multipath in GPS carrier phase measurements using the signal‐to‐noise ratio (SNR), in which the frequency and amplitude content of non‐stationary oscillations in SNR are modeled to extract multipath parameters (direct and reflected signal amplitudes, and the phase difference between direct and indirect signals). The frequency content of SNR data is estimated using wavelet analysis, then used to initialize an adaptive least squares process to solve for time‐varying multipath parameters. Multipath corrections derived from these parameters are applied to the phase observables. We demonstrate this technique using campaign GPS data collected over a large salt flat (Salar de Uyuni), specifically a tripod‐mounted station which experienced long‐period (300–2000 s) multipath oscillations in SNR from ground reflections. By contrasting position solutions before and after applying multipath corrections, we demonstrate a reduction in carrier phase postfit residual RMS of up to 20% for static positioning, and 1–7 dB reduction in spectral power at multipath periods for kinematic positions.