Space-based GMTI radar

There are currently three synthetic aperture radar ground moving target indication (SAR-GMTI) radars on orbit that can measure the motion of cultural and some natural targets on the earth’s surface. Although these radars are... [ view full abstract ]

There are currently three synthetic aperture radar ground moving target indication (SAR-GMTI) radars on orbit that can measure the motion of cultural and some natural targets on the earth’s surface. Although these radars are synthetic aperture radar imaging systems, they can be configured to detect and measure the velocity of moving objects using what are traditionally called GMTI signal processing algorithms. GMTI is fundamentally a measurement process whose outputs are information vectors which can be inserted into image planes as image points during the processing. This tutorial is intended for an audience that is familiar with SAR imagery and has some familiarity with SAR processing and the complex plane representation of signal information.

This tutorial will introduce the principles of GMTI radar configurations and signal properties, will introduce the signal property basis of SAR image formation, and will look at the impact of the radar signal sampling on the measurement of moving target properties using multiple radar apertures. The Radarsat-2 instrument design will be used to define example GMTI configuration cases. GMTI analysis will be introduced using combined displaced phase center aperture (DPCA) signal subtraction for target detection and along-track interferometry (ATI) concepts for moving target detection and speed measurements. Key points will be illustrated using outcomes from DRDC SAR-GMTI development research. Sampling ambiguity impacts on GMTI processing outcome dependence on signal -channel time registration (interpolation) will be discussed. When data planes from separate channels are correlated in signal processing, the mathematical product operation introduces a quadrature modulation effect that cross modulates moving target and stationary signals. The impact of target-background intermodulation on GMTI analysis is introduced and discussed in terms of measurement outcome variability.

The covariance matrix approach to stationary clutter suppression and moving target detection is introduced. Physically large moving targets appear in SAR-GMTI data as ensembles of moving target samples. Some uses of the ensemble properties are introduced and discussed. When the number of GMTI radar apertures is greater than two, the increased number of mathematical degrees of freedom and be exploited in various ways. Applications to target speed measurement accuracy and sampling ambiguity suppression are discussed.