Imaging for Small UAV-Borne FMCW SAR

Abstract

Unmanned aerial vehicle borne frequency modulated continuous wave synthetic aperture radars are attracting more and more attention due to their low cost and flexible operation capacity, including the ability to capture images at different elevation angles for precise target identification. However, small unmanned aerial vehicles suffer from large trajectory deviation and severe range-azimuth coupling due to their simple navigational control and susceptibility to air turbulence. In this paper, we utilize the squint minimization technique to reduce this coupling while simultaneously eliminating intra-pulse motion-induced effects with an additional spectrum scaling. After which, the modified range doppler algorithm is derived for second order range compression and block-wise range cell migration correction. Raw data-based motion compensation is carried out with a doppler tracker. Squinted azimuth dependent phase gradient algorithm is employed to deal with azimuth dependent parameters and inexact deramping, with minimum entropy-based autofocusing algorithms. Finally, azimuth nonlinear chirp scaling is used for azimuth compression. Simulation and real data experiment results presented verify the effectiveness of the above signal processing approach.

Review article: Performance assessment of electromagnetic wave-based field sensors for SWE monitoring

“…Over the Arctic, snow cover that can be characterized by a two-layer snowpack structure, and assumptions can be made on its mean refractive index, thereby allowing bulk SWE to be estimated (work in progress). Hu et al (2019) also showed the usefulness of imaging FMCW synthetic aperture radar onboard the RPA. Several studies have also shown the potential of FMCW radar for different applications, such as avalanche studies (Vriend et al, 2013;Okorn et al, 2014;Laliberté et al, 2021), snow stratigraphy based on successive FMCW echo analyses (Marshall and Koh, 2005;Marshall et al, 2007), snowpack tomography (Xu et al, 2018), and ice thickness monitoring (Yankielun et al, 1993;Gunn et al, 2015).…”

A Novel Motion Compensation Approach Based on Symmetric Triangle Wave Interferometry for UAV SAR Imagery

“…The returned signal from a point target whose nearest slant range is , can be written as: (4) where is the time delay, is the instantaneous slant range (ISR), is the speed of light, is the sum of the fast time / and slow time .…”

“…Unmanned aerial vehicle synthetic aperture radar (UAV SAR) is an advanced remote sensing technique that can obtain highresolution images with high efficiency and low energy consumption for many applications, such as search and rescue operations and civil infrastructure inspection missions [1][2][3]. However, because UAVs are lightweight and due to their aerodynamic mechanisms, the paths of UAVs are disturbed easily by the atmospheric turbulence, resulting in motion errors such as trajectory deviations and variations in velocity, and attitude [4]. Generally, synchronous navigation system measurements are used to acquire geometric information for motion compensation (MoCo).…”

Low-Cost, High-Resolution, Drone-Borne SAR Imaging

“…However, spacevariant phase errors were not apparent. In [10], a method was proposed to deal with range-azimuth coupling using a squint minimization technique. Squinted Azimuth-dependent PGA and MEA were used as autofocus algorithms.…”