Matched-field processing is a method for inversion of the acoustic field utilizing its spatial coherence. In this work, a matched-field processor is introduced that incorporates the spatial coherence of the acoustic field not only at a single frequency but across frequencies as well. The new processor is suitable for multitonal sources and does not require knowledge of the source spectrum which is typically unavailable in passive estimation problems. A performance evaluation on source localization under low signal-to-noise ratios shows that the new processor is significantly superior, under certain circumstances, to the conventional incoherent Bartlett processor especially in cases involving receiver arrays with a small number of phones.