The frequency dependence of attenuation in marine sediments is investigated using in situ measurements from a wide-band acoustic probe system during the Shallow Water 2006 (SW06) experiment. Direct-path pulse propagation measurements within the 10–80 kHz frequency band show linear frequency dependency of attenuation in dB/m at two silty-sand sites on the New Jersey Shelf. The measurements also show evidence of mild velocity dispersion within the 10–80 kHz frequency band. The measured attenuation and velocity dispersion curves are in good agreement with those predicted by an extended Biot theory for sediments with a distribution of pore sizes [Yamamoto and Turgut, J. Acoust. Soc. Am. 83, 1744–1751 (1988)]. Attenuation roll-off measurements (dB/m kHz) were also conducted within a 3–8 kHz frequency band using a chirp-sonar subbottom profiler. The comparable levels of attenuation roll-off are observed from the chirp sonar and acoustic probe measurements. [Work supported by ONR.]