  In zones of loose sand, wind-blown sand dunes emerge due the linear
instability of a flat sedimentary bed. This instability has been studied in
experiments and numerical models but rarely in the field, due to the large time
and length scales involved. We examine dune formation at the upwind margin of
the White Sands Dune Field in New Mexico (USA), using 4 years of lidar
topographic data to follow the spatial and temporal development of incipient
dunes. Data quantify dune wavelength, growth rate, and propagation velocity and
also the characteristic length scale associated with the growth process. We
show that all these measurements are in quantitative agreement with predictions
from linear stability analysis. This validation makes it possible to use the
theory to reliably interpret dune-pattern characteristics and provide
quantitative constraints on associated wind regimes and sediment properties,
where direct local measurements are not available or feasible.
