  Precision timing is the key ingredient of ongoing pulsar-based gravitational
wave searches and tests of general relativity using binary pulsars. The
conventional approach to timing explicitly assumes that the radio emitting
region is located at the center of the pulsar, while polarimetric observations
suggest that radio emission is in fact produced at altitudes ranging from tens
to thousands of kilometers above the neutron star surface. Here we present a
calculation of the effects of finite emission height on the timing of binary
pulsars using a simple model for the emitting region geometry. Finite height of
emission changes the propagation path of radio photons through the binary and
gives rise to a large spin velocity of the emission region co-rotating with the
neutron star. Under favorable conditions these two effects introduce
corrections to the conventional time delays at the microsecond level (for a
millisecond pulsar in a double neutron star binary with a period of several
hours and assuming the emission height of 100 km). Exploiting the dependence of
the emission height on frequency (radius-to-frequency mapping) and using
multi-frequency observations one should be able to detect these timing
corrections even though they are formally degenerate with conventional time
delays. Although even in the most accurately timed systems the magnitude of the
finite emission height effects is currently somewhat below timing precision,
longer-term observations and future facilities like SKA will make measurement
of these effects possible, providing an independent check of existing emission
height estimates.
