Based on the extended Huygens-Fresnel principle and ITU-R atmospheric turbulence model (the altitude-dependent model proposed by International Telecommunication Union-Recommendation in 2001), the treatment includes the effect of the atmospheric turbulence both on the laser beam as it propagates to the target and on the scattered field as it propagates back to the receiver. The covariance function and variance of the scattering intensity are derived considering the fluctuations of the log-amplitude and phase, and the numerical results are presented. The influences of wavelength, receiver altitude and propagation distance on the covariance function and normalized variance of the scattering are discussed.