Improved ambiguity estimation using a modified fractional Radon transform

Abstract

Ambiguity estimation is critical for the positioning of a moving target truly. Traditional real-value Radon transform (RRT) has been used to estimate the slope of target's trajectory such that the ambiguity number can be derived. However, the unknown azimuth velocity of the target makes it difficult to determine the ambiguity number because the quadratic range cell migration (QRCM) caused by the platform velocity reduces the sensitivity of the RRT in the estimation. Also, the RRT does not work well when the signal-to-noise ratio (SNR) is low. Here, a method that uses the second-order Keystone transform (SOKT) to eliminate the QRCM and the modified fractional Radon transform (MFrRT) to estimate the ambiguity number was proposed. The method was simple and applicable in the low-SNR situation. Implementation considerations were presented. Finally, the effectiveness of the method has been shown using simulated and acquired synthetic aperture radar datasets.

High Speed Dim Air Target Detection Using Airborne Radar under Clutter and Jamming Effects

“…The simulation results validate the proposed method by comparing the probability of detection of (OSTAP /SOKT/IFrRT) with the recently references, (SOKT /MFrRT) [20], (SOKT/FrFT/RFT) [19], (RFT) [10], (STAP) [21], and without applying any method.…”

“…The RFT is an effective way to measure, which adopted a small and discrete number of slopes exists in the (r,τ) do-main, the slope of a straight-line [20]. Since the RFT only uses the amplitude information, its result can be impacted by the low SNR.…”

“…Comparing to the RFT, the FrRFT can be greatly extended to the range curvature and the Doppler frequency migration effect in the integration time, and restricted by minimizing coherent integration gain and dwell of an antenna beam. From (30), there is a second-order phase term of the slow time that can adversely influence the coherent accumulation of the signal, so the dechirping operation [20] is used to remove the influence and express as ( )…”

“…Tian et al [19] proposed a combination of the second-order Keystone transform (SOKT) and the fractional Fourier transform (FrFT), and (RFT) for range migration and Doppler ambiguity compensation but they ignored the jamming and clutter effects. Recently G. Sun et al [20] proposed a method that uses SOKT to eliminate the quadratic range cell migration (QRCM) and the modified fractional Radon transform (MFrRT) to estimate the ambiguity number. They used the MFrRT to improve the ambiguity estimation, but this method is limited for only low signal to noise ratio (SNR) and ground moving targets in synthetic aperture radar (SAR) applications, with limited speed to 150 m/s.…”

“…The new contributions from this work are, first, applying OSTAP to increase the SNR, to overcome the limitation of [20] that is only applicable in lower SNR levels, second, taking into consideration all the interference effects (jamming, clutter, noise) not only clutter in [20], third, using the combination of SOKT/IFrRT for range migration, and Doppler ambiguity estimation compensation with lower complexity than using SOKT/FrFT/RFT in [19], fourth, the first time to apply these methods in signal processing (monostatic radar) not only in image processing (SAR) [19], [20]. The simulation results validate the proposed method by comparing the probability of detection of (OSTAP /SOKT/IFrRT) with the recently references, (SOKT /MFrRT) [20], (SOKT/FrFT/RFT) [19], (RFT) [10], (STAP) [21], and without applying any method.…”