Eulerian Measurement

A Eulerian measurement observes a fluid property at a fixed point in space as the water flows past, the opposite of the Lagrangian approach that follows a moving parcel. Moored current meters, bottom-mounted ADCPs, tide gauges, and instrumented moorings all return Eulerian time series: velocity, temperature, or salinity recorded at set coordinates and depths over weeks to years. The frame underlies the field-based form of the Navier-Stokes equations and the flux divergences used to compute transport across a section. Eulerian arrays resolve the time variability at a place, which complements the spatial coverage that drifters and floats provide in the Lagrangian frame.