Motion Compensation in ISAR Imaging Using Time-Frequency Techniques - Time-Frequency Transforms for Radar Imaging and Signal Analysis - page 124

In this chapter, we examine the use of time-frequency analysis for
achieving ISAR motion compensation. In Section 6.1, we review some of
the existing motion compensation algorithms for translation motion and
rotational motion removal. In Section 6.2, we introduce an adaptive joint
time-frequency (AJTF) procedure for extracting the phase of a prominent
point-scatterer on the target from the radar data. We show how the extracted
phase information can be used in conjunction with the prominent point
processing (PPP) model to achieve motion compensation. In Section 6.3,
we illustrate this algorithm using both simulation and measurement data.
In Section 6.4, we discuss the case when the rotational motion of the target
is not confined to a 2D plane.

6.1 Motion Compensation Algorithms

In real-world ISAR data collection, the target being imaged is usually engaged
in complex maneuvers that combine translation and rotational motions (see
Figure 6.1). Unless a good motion compensation algorithm is implemented,
serious blurring can result in the ISAR image formed by the Fourier transform,
which assumes that all the point-scatterers in a range cell behave with linear
phase across different pulses. A motion compensation algorithm typically
consists of two parts, range alignment and Doppler tracking. Among all

Figure 6.1 Complex target motion during ISAR image collection can be considered a

combination of translation and rotational motions with respect to the radar.