In the Aquadopp IM6000, we have extended the Seabird Inductive Modem Module (IMM) to the 6000 m Aquadopp. As with the shallow water system (IM400), this system is designed for operation on long mooring cables with the data being transferred along the jacketed steel cable to a controlling modem that is located in a surface buoy or similar.
The purpose of the inductive modem system is to retrieve data from the instrument without the need for a sophisticated underwater cable. Instead, a low-frequency signal is generated in the jacketed steel mooring cable and seawater is used as return ground. The communication to the topside device is handled with the Seabird inductive modem whereas support for the IMM communication protocol and transfer of data from the Aquadopp to the IMM is provided by a special version of the Aquadopp firmware.
In the Aquadopp IM6000, we have modified the end bell in the system to include the inductive modem coupler. The system is composed of several parts:
As with the IM400, the Seabird IMM board is located on top of an interface board that ensures the communication between the Aquadopp electronics and between the IMM board and the inductive coil that clamps around the cable. The board is seamlessly integrated with Aquadopp electronics and can be an upgrade to any Aquadopp shipped after the summer of 2008 (firmware version 3.xx and above).
A special end-cap that includes the coil that goes around the cable (bottom yellow part in the drawing)
A clamping system that holds the Aquadopp rigidly attached to the wire (upper yellow part)
A fin (green in drawing) that is designed to ensure that the Aquadopp is stable even in the presence of significant current flow. The fin is designed to be used both with short (single-battery) and standard (double-battery) Aquadopp canisters
In contrast to the IM400, the IM6000 does not include the fishing line rejector since deep water system are unlikely to encounter any fishing activity.