An experimental study has been made on the contribution to the effective scintillation index due to aperture averaging and interference effects when using multiple retroreflectors in free-space optical links. These studies are of relevance to asymmetric data links where modulating retroreflectors are used at the remote end of the free-space optical link. For closely spaced retroreflectors the effect of coherent interference at the receiver is seen to increase the effective variance of the received signal, whereas spatial averaging is apparent for more widely spaced retroreflectors. The scintillation index, probability density functions, and fade rates are all affected by the interference. Experiments were conducted over both a short-range (500 to ) and a long-range link. The long-range link used three retroreflectors having a spacing that was large enough that interference effects contributed minimally to the observed variance. However, the variance clearly depended on the number of retroreflectors. In addition to measuring the scintillation index, images of the returned light were recorded using a fast framing camera. These experiments were conducted over land and mixed water-land terrains in the case of the short-range links, and exclusively over water in the case of the 16-km link from Chesapeake Beach to Tilghman Island.