The ability to rapidly determine mixed layer depths (MLDs) over large regions would significantly advance efforts to understand and model the dynamics of the upper ocean. Remote sensing technologies are an ideal choice for achieving this goal. This study is an investigation into the applicability of LiDAR systems for measuring MLDs. Beam attenuation at 660 nm (c660) was used as a proxy for particle concentration and hence backscattering. Using a global data set collected during WOCE cruises from 1988-1997, five published algorithms were employed to compute MLDs from either density or temperature profiles. Given the absence of published optically-based MLD algorithms, two new methods were developed for use with c660 profiles. Comparison of the algorithms revealed reasonable correlation between hydrographically derived MLD and optically derived MLD values, when the data was sorted by ocean and season. Accepting a 20 m disparity, a 60 percent agreement was found between a hydrographical-optical algorithm pairing with an r2 of 0.94. Higher correlation between the hydrological and optical techniques may be possible by accounting for the time of year, location, diel MLD cycle and by operating during early morning hours when the upper water column is well mixed and photosynthetic activity is minimal.Zawada, D.G., J.V. Zaneveld, E. Boss, and W.D. Gardner, 2004. A Comparison of Hydrographically- and Optically-Derived Mixed Layer Depths. AGU Ocean Sciences Meeting, Portland, OR, Jan.