Isoline Tracking Control of an Autonomous Underwater Helicopter in Unknown Marine Scalar Fields Under Noisy Measurements

For continuous boundary observation at a prescribed scalar level in unknown marine scalar fields, this paper proposes an isoline tracking method for an autonomous underwater helicopter (AUH) using only noisy local measurements. The method establishes an isoline kinematic relation based on the local scalar value and its rate of change. Without field reconstruction or compensation for unknown terms, it enables the AUH to stably approach the target isoline and maintain tangential motion, with adjustable tracking accuracy. To obtain reliable scalar-rate information from noisy measurements, a finite-time differentiator using current and historical noisy measurements was developed to suppress measurement noise while retaining the required dynamic response. A low-complexity prescribed-time velocity-matching controller was further developed in a direct algebraic form, allowing the contraction time and terminal range of the velocity errors to be specified without imposing restrictive conditions on finite initial errors. Simulation results in a suspended particulate matter scalar field and a temperature field verified the effectiveness of the proposed method.