Addressing the challenge of point ahead angle (PAA) in satellite-based free-space optical communication systems, this paper introduces a novel wavefront sensing method, the Projected Pupil Plane Pattern (PPPP), utilizing the transport-of-intensity equation (TIE). Laboratory experiments confirm its viability. The PPPP method, rooted in TIE, can deduce wavefront distortions due to atmospheric turbulence by analyzing variations in light intensity distribution over different transmission distances. Utilizing the back Rayleigh scattering from the communication laser, PPPP's atmospheric turbulence measurements align with the satellite's direction, offering an effective solution to PAA-related issues in satellite-ground laser communications. In our experiments, a 1-m ground telescope simulates an upward laser transmitter and captures the backscattered light for imaging. We measure wavefront distortions caused by atmospheric turbulence up to 10 km using backscattered light from altitudes of 10 km and 17 km. These distortions are simulated using a spatial light modulator or a transparent plastic sheet. The results demonstrate that PPPP and the commonly used Shack-Hartman wavefront sensor provide comparable wavefront reconstructions for various distortions, with the reconstructed phase's residual difference around 30% of the initial phase.