Mitigation of anthropogenic impacts on North Atlantic right whales and other at-risk species is critical, but challenging given the cryptic nature of whale behaviour and the limitations of conventional visual surveys. Using passive acoustic monitoring (PAM) to alert ocean users to whale presence in near real-time can provide an effective mitigation option. The Woods Hole Oceanographic Institution (WHOI) has developed the digital acoustic monitoring (DMON) instrument and low-frequency detection and classification system (LFDCS) to detect and classify baleen whales in near real-time from autonomous platforms (e.g., buoys and gliders). A limitation of many PAM systems, including the DMON/LFDCS, is the uncertainty in acoustic detection range from the monitoring platform. The main goal of this study was to determine the range-dependent accuracy of the DMON/LFDCS on mobile and fixed platforms. Over a 4 week period (28 Feb to 30 Mar) in the spring of 2017, we deployed a DMON/LFDCS-equipped Slocum glider and a hydrophone array alongside an extant DMON/LFDCS buoy at a shallow (30m) site approximately 15 km Southwest of Martha’s Vineyard, USA. We applied a normal mode back-propagation technique to the array data to localize right whale upcalls, then conducted a call-by-call comparison between calls detected on the array and those detected by the glider or buoy to determine the probability of detection for each platform. The results help us to better understand and improve the performance of our monitoring system, which in turn allows us to disseminate more accurate information about whale distribution to research, government, and industry stakeholders. [Note: this has been updated from the abstract that appeared in the OSM 2018 program]