  Waves around the lower hybrid frequency are frequently observed at Earth's
magnetopause, and readily reach very large amplitudes. Determining the
properties of lower hybrid waves is crucial because they are thought to
contribute to electron and ion heating, cross-field particle diffusion,
anomalous resistivity, and energy transfer between electrons and ions. All
these processes could play an important role in magnetic reconnection at the
magnetopause and the evolution of the boundary layer. In this paper, the
properties of lower hybrid waves at Earth's magnetopause are investigated using
the Magnetospheric Multiscale (MMS) mission. For the first time, the properties
of the waves are investigated using fields and direct particle measurements.
The highest-resolution electron moments resolve the velocity and density
fluctuations of lower hybrid waves, confirming that electrons remain
approximately frozen in at lower hybrid wave frequencies. Using fields and
particle moments the dispersion relation is constructed and the wave-normal
angle is estimated to be close to $90^{\circ}$ to the background magnetic
field. The waves are shown to have a finite parallel wave vector, suggesting
that they can interact with parallel propagating electrons. The observed wave
properties are shown to agree with theoretical predictions, the previously used
single-spacecraft method, and four-spacecraft timing analyses. These results
show that single-spacecraft methods can accurately determine lower hybrid wave
properties.
