Free space optical links get adversely affected by atmospheric turbulence besides aerosol-based scattering and attenuation, causing signal degradation at the receiving terminal. The gamma–gamma probability density function has been extensively utilized for modeling the received signal strength under all turbulence regimes. An estimator with an underlying gamma–gamma turbulence model is being proposed. For the estimation of optical signal intensity, a minimum mean square error criterion has been used to develop the proposed estimator. It is assumed that the receiver is operating under shot noise–limited conditions, and the received signal is detected using a PIN photodiode.