The JPL and DSN convention for Doppler frequency shift is
, where
is the measured frequency
and
is the reference frequency. It is positive for a spacecraft receding from the tracking station (red shift),
and negative for a spacecraft approaching the station (blue shift), just the opposite of the usual convention,
. In consequence, the velocity shift,
, has the same sign as
but
the opposite sign to
. Unless otherwise stated, we use the DSN frequency shift convention in this
document.