Issues affecting current meter design

Underwater sensors of water flow share issues addressed independently by manufacturers. Power has become the most demanding concern since availability of cheap memory has removed data storage as the limit for self-contained current meters. Neither power nor memory is a limit with cabled observatory instruments but for autonomous installations, improvement in batteries is valuable but not sufficient. Power saving is more effective for extending deployment duration than improved batteries [1]. Fouling, by marine organisms or by corrosion, limits both cabled and autonomous instruments, degrading measurements for some modalities more than others. While there are active anti-fouling systems, most protections are passive with material selection and coatings the first line of defense. Upper ocean deployments, in the photic zone, are sometimes limited in duration by fouling with macro algae. Extending such deployment duration may require a second line of defense such as active scrapers or cutters. Traditional care for shallowly deployed current sensors involves divers to scrub transducers with abrasive pads. Below the photic zone bio fouling is less aggressive. Slippery coatings are now employed in some deployments where previously toxic coatings endeavored to prevent growth of animals and plants [2]. Plastic and titanium housings have made corrosion almost a problem of the past, although there are cost and other consequences that need to be considered [3].