Data Retrieval and Power Replenishment

A project log for BoatDetect

detect, log, and analyze boat traffic

John OpsahlJohn Opsahl 07/25/2020 at 20:330 Comments

Two of the most challenging features of any in situ environmental measurement data logger, like the BoatDetect device, is how to retrieve data from the device and how to replenish it's power source. The technologies to achieve these tasks can become particularly complex and expensive when deploying the device underwater. 

To meet the current cost target for the BoatDetect device, the strategy is to have the user locate the device by GPS coordinates (initially recorded by the user at deployment), physically retrieve the device, download the data from a memory card, and replace or charge the batteries at every battery recharge interval. While I generally understand this to be the correct strategy for the BoatDetect device, I believe a significant change to the device is needed to make this process more convenient for the user. 

Up until now, I have been proposing that the BoatDetect device be tethered to the bottom and float underwater at a distance from the surface. The main inconvenience of this approach is that the user has to visibly locate the underwater device and "fish" the it out of the water to retrieve it. If for whatever reason the device came untethered from the bottom or shifted location from initial deployment, the user might waste a significant amount of time looking for a BoatDetect device that simply is not at that location anymore. And if the water is too murky, the user has no chance of retrieving the device once deployed.

The operational inconveniences of the current approach have convinced me that a surface level indicator of the device's location is required. Even more so, placing all components at the water surface in a "buoy" would make the batteries and memory card immediately accessible and open up many opportunities for future developments such as visible and audible warnings to boaters, solar panels, transmitted GPS location, and wireless data transfer. The main challenges that I anticipate with a buoy solution is that the device now needs to be visible to boaters at night and is more likely to be tampered with. This change in approach will increase the material cost of the device beyond the initial $40 USD target, but the reduction in operational costs is likely to offset the material cost increase.