The molecular orientation at surfaces plays a key role in many of the interesting optical properties of organic thin films. Accurate determination of molecular "tilt" angles and the distribution in tilt angles is essential for an improved understanding, of performance characteristics, i.e., the structure-function relationship. While there are several spectroscopic techniques available for measurement of molecular orientation at solid surfaces, little effort has been dedicated to understanding the contributions of surface roughness on measured orientation values. In this paper, following an overview of spectroscopic techniques and previous approximations of surface roughness effects, a quantitative theory for treating surface roughness contributions to molecular orientation measurements made by linear dichroism is presented. The theory is sufficiently general that it may be extended to other spectroscopic techniques, such as second-harmonic generation. It is anticipated that knowledge of the molecular orientation with respect to the local surface (i.e., accounting for surface roughness) will provide a better understanding of the orientation in organic thin films.