ISSN 0010-9525, Cosmic Research, 2018, Vol. 56, No. 3, pp. 190–198. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © V.D. Zakharchenko, I.G. Kovalenko, O.V. Pak, V.Yu. Ryzhkov, 2018, published in Kosmicheskie Issledovaniya, 2018, Vol. 56, No. 3, pp. 209–217.
Fundamental Constraints on the Coherence of Probing Signals
in the Problem of Maximizing the Resolution and Range
in the Stroboscopic Range of Asteroids
V. D. Zakharchenko
*, I. G. Kovalenko
, O. V. Pak
, and V. Yu. Ryzhkov
Volgograd State University, Volgograd, 400062 Russia
LLC First Service, Volgograd, Russia
Received July 19, 2016
Abstract—The problem of coherence violation in stroboscopic ranging with a high resolution in the range
due to mutual phase instability of probing and reference radio signals has been considered. It has been
shown that the violation of coherence in stroboscopic ranging systems is equivalent to the action of mod-
ulating interface and leads to a decrease in the system sensitivity. Requirements have been formulated for
the coherence of reference generators in the stroboscopic processing system. The results of statistical mod-
eling have been presented. It was shown that, in the current state of technology with stability of the fre-
quencies of the reference generators, the achieved coherence is sufficient to probe asteroids with super-
resolving signals in the range of up to 70 million kilometers. In this case, the dispersion of the signal in cosmic
plasma limits the value of the linear resolution of the asteroid details at this range by the value of ~2.7 m.
Comparison with the current radar resolution of asteroids has been considered, which, at the end of 2015,
were ~7.5 m in the range of ~7 million kilometers.
Radar astronomy has a number of specific features,
which makes its application in the problems of studying
small bodies of the solar system (asteroids, comet
nuclei, and in the distant future of dwarf planets closest
to the Earth), which are often preferable compared with
the use of traditional astronomy (we will conditionally
call it astronomy using passive methods of measurement).
The disadvantage of passive ways of determining
the linear dimensions of celestial bodies and their sur-
face details is that the measurement error increases
proportionally to the range to the measured object.
The matter is that passive measuring systems created
based on telescopes are goniometric such that the
error in determining the angle leads to error in estimat-
ing the transverse linear dimensions proportionally to
the range to the object under study. Moreover, passive
methods for the ground-based optical telescopes are
subject to dependence on the state of optical transpar-
ency and turbulence in the atmosphere. These defi-
ciencies are deprived of active measurement methods,
including the methods of the radar sounding of space,
the resolution of which along the line of sight is deter-
mined by the properties of the used signals and does
not depend on the range to the object.
In addition, the use of radar methods when studying
celestial bodies by probing them with broadband signals
in the super-resolution mode allows one to obtain addi-
tional information on the reflecting properties of
objects in the third dimension (along the line of sight in
depth) in the form of a radar portrait, while traditional
astronomy allows one to construct only two-dimen-
sional portraits of bodies in the picture plane.
Increasing the spatial resolution of three-dimen-
sional images of remote space objects during radar
sounding from Earth is an important problem of
astronomy. At present (late 2015–early 2016), the
record values of the radar resolution of asteroids were
~7.5 m in the range of ~7 million kilometers [1, 5].
The factors that prevent the achievement of maxi-
mum resolution are the fundamental constraints dic-
tated by both the physics of the processes of radiation
and propagation of radio signals and by the current level
of technology development, including (1) the limita-
tions on the power of the radio signal, (2) the loss of sig-
nal coherence due to the nonideality of the equipment
(instability of reference frequency generators), and
(3) the dephasing of the signal, as it propagates in cos-
mic plasma due to dispersion. In this paper, we confine
ourselves to the discussion of the second and third
items, the question on the requirements for the power of