A model is presented for the specular reflectivity from a surface containing mounds and craters. These features are described using a pyramidal geometry that leads to a non-Gaussian distribution of terrace heights. The model is used to interpret and compare in situ synchrotron X-ray reflectivity measurements from homoepitaxially grown Cu(0 0 1), Ag(0 0 1) and Ag(1 1 1). Temperature-dependent vacancy trapping at low temperature is observed in each of these systems and it is found that the effects of surface mounds are manifested in the X-ray reflectivity for Ag(1 1 1) and Cu(0 0 1) but not for Ag(0 0 1).