In this paper, we present a reactive control law that can navigate a single, sensor-enabled vehicle to ascend or descend a scalar potential field. The design builds on our previous work on developing an online following control. The model framework enables us to establish performance bounds for the developed ascending/descending control that are related to the geometrical parameters of the field. The efficacy of our approach is demonstrated through two possible applications - source-centric mapping of a potential field and tracking of a single target, emitting a distance-related potential field.