of the impinging light from the telescope is directed by the polarizing beam splitter 24 onto the focal plane array 22 thereby reducing backscatter from the atmosphere which is predominantly vertically polarized by about a factor of 25 in addition the spectral filter 42 is a dynamic spectral filter that can be tuned to pass both passive and active light from the target object which has a different wavelength i e color than the wavelength of the transmitted laser beam thereby reducing backscatter a fast spectral filter should be used for best snr one example of such a filter is the varispec u2122 liquid crystal tunable filters commercially available from channel systems inc pinawa manitoba canada the transmission of n laser beams of different wavelengths provides laser speckle diversity to improve snr by sqrt n as well as wavelength diversity if a single wavelength is used multiple frames can also provide such diversity in such cases faster speckle motion or boiling can be better as long as the speckle does not smear much within a frame other options to aid in reconstruction include a stitching of the speckle phases of the subapertures using measurements that have overlap of speckle phase between subapertures due to speckle motion and b sequential transmission or phasing of subapertures to identify each beam 39 s profile and phase on target 6 the anisoplanatic image can be reconstructed using a nonlinear optimization process 84 see fig4 a more specifically the coherent returns provide speckle images for each subaperture which when combined with the passive images or with.