Vertical RFID Antenna Arrays: A System for Full Water Column Detection

Detection of PIT tagged out-migrating juvenile salmonids in large natural rivers is problematic because the antenna systems currently available are typically incapable of interrogating the upper portions of the water column where fish may travel. Low juvenile detection rates hamper studies of many kinds including those designed to understand population-level effects of flow management and habitat restoration. We have developed an antenna system dubbed the FIN (Fish Interrogation Nodes) capable of detecting fish through the whole water column at variable river flows and stages. These arrays are composed of individual vertical antenna housings anchored to either the channel bed or an above-water support system through an articulated shackle that allows for deflection and passage of debris and ice. We power one to many FIN antenna coils through individual transceivers and can link up to 6 FIN antennas together with a novel cabling approach and alternation of coil winding direction for each adjacent FIN. This system produces detection fields that are strongly coupled between individual FINs that then function as a single antenna for purposes of multiplexing and synchronization.