Abstract
Use of Frequency Modulated Continuous Wave (FMCW) Synthetic Aperture Radar (SAR) systems requires to accurately know the electronic parameters of the system. In particular, the use of an incorrect value of the Frequency Sweep Rate (FSR) introduces geometric distortions in the focused images. Recently, a method, that we name FSR Estimate Through Corner reflectors (FSRETC), has been proposed to estimate the FSR value actually employed by the radar. The method is based on the use of the SAR image focused with the available erroneous FSR. Moreover, it exploits a number of Corner Reflectors (CRs) deployed over the illuminated area. In this work, we provide an assessment of the capabilities of the FSRETC algorithm. The overall analysis is performed through the use of a real dataset consisting of 10 acquisitions carried out in 2018 (5 acquisitions) and 2019 (5 acquisitions) with an airborne FMCW SAR system. The presented experimental analysis shows that even with a single acquisition, use of two CRs sufficiently far from each other in the range direction, allows achieving an accurate estimate of the searched FSR. Moreover, it is shown that the obtained estimate is very stable over the time. Therefore, the overall procedure can be applied only once, since the estimated values can be safely used for the subsequent missions, at least for the time interval considered in the work, that is, 14 months. In addition, the presented results pose the basis for an enhanced measurement strategy that allows effective application of the FSRETC algorithm through the use of only one CR.
Highlights
In the last years, an increasing interest toward Synthetic Aperture Radar (SAR) systems [1] mounted onboard aerial platforms, such as airplanes [2,3,4,5,6], helicopters [7], unmanned aerial vehicles (UAVs) [8,9] and drones [10,11], is registered [12]
In order to assess the capabilities of the FSR Estimate Through Corner reflectors (FSRETC) algorithm, we have carried out a number of experiments by exploiting the data acquired during two flight campaigns carried out in 2018 and 2019, respectively, with an airborne Frequency Modulated Continuous Wave (FMCW) SAR system named AXIS [16]
We have assessed the robustness of the FSRETC algorithm proposed in [15] to estimate the Frequency Sweep Rate (FSR) value employed by a FMCW SAR
Summary
An increasing interest toward Synthetic Aperture Radar (SAR) systems [1] mounted onboard aerial platforms, such as airplanes [2,3,4,5,6], helicopters [7], unmanned aerial vehicles (UAVs) [8,9] and drones [10,11], is registered [12]. Use of an incorrect FSR value during the focusing procedure leads to an undesired stretching along the range direction of the final SAR image [15] To overcome this problem, a method to estimate the FSR value used by the radar has been presented in [15]. An experimental analysis on the robustness of the FSRETC algorithm with respect to variations of the number and positions of the used CRs misses. This strategy is based on the use of a variety of radar acquisitions, spatially and temporally separated each-other, in substitution of the variety of CRs deployed over the illuminated area.
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