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Free keywords:
General Relativity and Quantum Cosmology, gr-qc, Astrophysics, Instrumentation and Methods for Astrophysics, astro-ph.IM
Abstract:
Interspacecraft ranging is crucial for the suppression of laser frequency
noise via time-delay interferometry (TDI). So far, the effect of on-board
delays and ambiguities in the LISA ranging observables was neglected in LISA
modelling and data processing investigations. In reality, on-board delays cause
offsets and timestamping delays in the LISA measurements, and PRN ranging is
ambiguous, as it only determines the range up to an integer multiple of the
pseudo-random noise (PRN) code length. In this article, we identify the four
LISA ranging observables: PRN ranging, the sideband beatnotes at the
interspacecraft interferometer, TDI ranging, and ground-based observations. We
derive their observation equations in the presence of on-board delays, noise,
and ambiguities. We then propose a three-stage ranging sensor fusion to combine
these observables in order to gain optimal ranging estimates. We propose to
calibrate the on-board delays on ground and to compensate the associated
offsets and timestamping delays in an initial data treatment (stage 1). We
identify the ranging-related routines, which need to run continuously during
operation (stage 2), and implement them numerically. Essentially, this involves
the reduction of ranging noise, for which we develop a Kalman filter combining
the PRN ranging and the sideband beatnotes. We further implement crosschecks
for the PRN ranging ambiguities and offsets (stage 3). We show that both
ground-based observations and TDI ranging can be used to resolve the PRN
ranging ambiguities. Moreover, we apply TDI ranging to estimate the PRN ranging
offsets.
