  We report on the first ground-based measurement of the relativistic beaming
effect (aka Doppler boosting). We observed the beaming effect in the detached,
non-interacting eclipsing double white dwarf (WD) binary NLTT 11748. Our
observations were motivated by the system's high mass ratio and low luminosity
ratio, leading to a large beaming-induced variability amplitude at the orbital
period of 5.6 hr. We observed the system during 3 nights at the 2.0m Faulkes
Telescope North with the SDSS-g' filter, and fitted the data simultaneously for
the beaming, ellipsoidal and reflection effects. Our fitted relative beaming
amplitude is (3.0 +/- 0.4) x 10^(-3), consistent with the expected amplitude
from a blackbody spectrum given the photometric primary radial velocity
amplitude and effective temperature. This result is a first step in testing the
relation between the photometric beaming amplitude and the spectroscopic radial
velocity amplitude in NLTT 11748 and similar systems. We did not identify any
variability due to the ellipsoidal or reflection effects, consistent with their
expected undetectable amplitude for this system. Low-mass, helium-core WDs are
expected to reside in binary systems where in some of those systems the binary
companion is a faint C/O WD and the two stars are detached and non-interacting,
as in the case of NLTT 11748. The beaming effect can be used to search for the
faint binary companion in those systems using wide-band photometry.
