Basically, we envision to have two vertical poles (masts) suspending a vertical array of movement sensors (similar to flowmeters) on a thin stainless steel wire grid. The grid could be a 8x8 array, 1 meter apart, 7 meters x 7 meters (see image). We can design and make optimized impellers with magnets and encapsulated hall effect sensors to get nice digital inputs for arduinos using the PULSE function, no problem.
The hall effect sensors output a digital signal, but if I understand correctly Tony, drivers may be needed to get that signal up to the surface.
Ideally, we need impellers (pitch, profiles, inertia,...) that turn fast, with many poles to have the highest pulse rate possible. Ideally, we need to read velocities below 0.1m/sec. The hall effect sensors and drivers (and arduinos for that matter) could be dipped, placed housings and encapsulated in epoxy or silicon gel. Careful care must be taken to avoid water creeping in from wires (lost a nice enclosed webcam that way once..;-)
If we have microcontrollers on each sensor, they can count pulses, average results, send back formatted and table calibrated serial data when prompted with an interrupt. I have no problem encapsulating 64 little arduinos for this. What would be a good choice for this?
Humm. Do you think that 3144 Hall effect sensors could drive a 5V pulse signal up 20 meters of shielded wire to the arduinos?