radar: Radar identifier.
datetime: POSIXct date of each profile in UTC.
vid: Vertically Integrated Density in individuals/km^2. vid is a
surface density, whereas dens in vp objects is a volume density.
vir: Vertically Integrated Reflectivity in cm^2/km^2.
mtr: Migration Traffic Rate in individuals/km/h.
rtr: Reflectivity Traffic Rate in cm^2/km/h.
mt: Migration Traffic in individuals/km, cumulated from the start of the
time series up to datetime.
rt: Reflectivity Traffic in cm^2/km, cumulated from the start of the
time series up to datetime.
ff: Horizontal ground speed in m/s.
dd: Horizontal ground speed direction in degrees.
u: Ground speed component west to east in m/s.
v: Ground speed component south to north in m/s.
height: Mean flight height (height weighted by eta) in m above sea level.