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This paper presents the first experimental demonstration of the virtual bandwidth synthetic aperture radar (VB-SAR) imaging scheme. VB-SAR is a newly developed subsurface imaging technique which, in stark contrast to traditional close proximity ground penetrating radar schemes, promises imaging from remote standoff platforms such as aircraft and satellites. It specifically exploits the differential interferometric SAR (DInSAR) phase history of a radar wave within a drying soil volume to generate high-resolution vertical maps of the scattering through the soil volume. For this study, a stack of C-band vertically polarized DInSAR images of a sandy soil containing a buried target was collected in the laboratory while the soil moisture was varied—first during controlled water addition, and then during subsequent drying. The wetting image set established the moisture-phase relationship for the soil, which was then applied to the drying DInSAR image set using the VB-SAR scheme. This allowed retrieval of high-resolution VB-SAR imagery with a vertical discrimination of 0.04 m from a stack of 1-m vertical resolution DInSAR images. This paper unequivocally shows that the basic principles of the VB-SAR technique are valid and opens the door to further investigation of this promising technique.

This paper introduces the concept of a fractionated MirrorSAR which is based on a set of mutually separated transmitter and receiver satellites. As opposed to previously published bi- and multistatic SAR systems, the receiver satellites are considerably simplified, as their main functionality is reduced to a kind of microwave mirror (or space transponder) which routes the radar echoes towards the transmitter. The forwarded radar signals are then coherently demodulated within the transmitter by using the same oscillator that had been used for radar pulse generation. This avoids the necessity of a bidirectional phase synchronization link as currently employed in TanDEM-X. Since the needs for fully equipped radar receivers, on-board memory and downlink are also overcome, the weight and costs of the receiver satellites can be significantly reduced. This allows for a scaling of their number without cost explosion, thereby paving the way for novel applications like multi-baseline SAR interferometry and single-pass tomography. Several additional opportunities make the MirrorSAR concept even more attractive. First, the separation of the transmitter and receiver front-ends reduces not only RF losses by avoiding switches and circulators, but it may also lower the peak power in the transmitter satellite by employing a frequency-modulated continuous wave (FMCW) illumination. This simplifies the design of the high-power amplifier and increases its efficiency. Second, the opportunity for continuous radar data collection enables new modes for the imaging of ultra-wide swaths with very high resolution, thereby overcoming an inherent limitation of conventional monostatic SAR systems. Third, the joint availability of all receiver signals in a centralized node offers new opportunities for efficient data compression, as the multistatic radar signals from close satellite formations are characterized by a high degree of mutual redundancy. Fourth, the use of a sufficiently separated transmitter satellite can avoid the risk for mutual illumination, which challenges the design and operation of fully-active multistatic SAR systems. Further advantages arise from the scalability and reconfigurability, which support new redundancy concepts and pave at the same time the way to new modes like MIMO-SAR tomography.

This paper presents monostatic radar cross section (RCS) measurements of a human hand in the frequency range from 60GHz to 90 GHz. These values are important parameters for system designs in the emerging field of radar-based gesture recognition. The measurement procedure is described in detail and results of four gestures at three different distances are depicted and analysed., acceptedVersion

Laser radar (lidar) sensors provide outstanding angular resolution along with highly accurate range measurements and thus they were proposed as a part of a high performance perception system for advanced driver assistant functions. Based on optical signal transmission and reception, laser radar systems are influenced by weather phenomena. This work provides an overview on the different physical principles responsible for laser radar signal disturbance and theoretical investigations for estimation of their influence. Finally, the transmission models are applied for signal generation in a newly developed laser radar target simulator providing – to our knowledge – worldwide first HIL test capability for automotive laser radar systems.

Polarisation diversity in radar remote sensing proved to be very successful in a variety of applications. Hydrometeors as raindrops or ice crystals are anisotropic radar targets giving rise to the use of polarisation diversity in weather radars. One advanced polarimetric weather radar is DLR's POLDIRAD in Oberpfaffenhofen. The huge data archive of this radar consists mainly of power measurements at diverse polarisation bases. This study investigates the possibility to apply the polarisation basis transformation directly on power measurements. As a result, empirical transfer functions for the change of the polarisation basis of radar reflectivities are derived. To check their validity they are applied to appropriate polarimetric radar data from the POLDIRAD.

Future spaceborne synthetic aperture radar (SAR) missions shall benefit from digital beamforming (DBF) techniques with the goal of generating high-resolution wide-swath imagery. The basic idea is to replace parts of the analog receiver hardware by digital components, increasing the flexibility of such systems. The limited transmit power rises the need of large antennas capable of electronically steering the antenna beam over a large angular domain. An innovative concept is the usage of large unfoldable mesh-reflector antennas in combination with digital feed arrays. An inherent problem of such systems is, that every feed element illuminates, after reflection from the main reflector, an essentially non-overlapping angular domain in the far field. In case of an element failure the radar system would be `blind' in the specific direction. To circumvent costly redundant receiver hardware a new approach to increase the reliability of such systems has been studied. The approach is based on a so called defocused reflector which grants visibility of the complete angular domain under failure conditions. This article presents the electromagnetic considerations leading to the defocused reflector concept. The performance of the defocused reflector system is evaluated in comparison to a conventional parabolic reflector system, utilizing digital beamforming techniques.

A Synthetic Aperture Radar (SAR) system measures among other quantities the terrain radar reflectivity. After image calibration, the pixel intensities are commonly expressed in terms of radar cross sections (for point targets) or as backscatter coefficients (for distributed targets), which are directly related. This paper argues that pixel intensities are not generally proportional to radar cross section or derived physical quantities. The paper further proposes to replace the inaccurate term radar cross section by equivalent radar cross section as the radiometric measurement quantity for SAR images. The measurement procedure as such remains unchanged. Two problems are seen with using radar cross section as the radiometric measurement quantity for point targets. First, the radar cross section is frequency and/or angular dependent for many targets, whereas a SAR system operates not at a single set but through a range of frequencies and aspect angles. This begs the question of which radar cross section within this two-dimensional range should actually be taken as the measurement result. Second, the pixel intensities seen in SAR images are the output of a filtering process, which is affected by the complex transfer function of the point target. Radar cross section, on the other hand, does not depend on phase. The equivalent radar cross section expresses the reflectivity in terms of the radar cross section of an equivalent conducting sphere which would result in the same pixel intensity as the one observed if the sphere were to replace the actual target in the scene. This distinction is crucial in defining the measurand for radiometric SAR measurements in principal, and hence it is important for radiometric SAR calibration. It is furthermore of particular practical importance for current and emerging wideband, high-resolution, and high-accuracy SAR systems.

Despite of a lot of efforts to develop a good de-speckling method for radar/SAR imagery (see e.g. [1, 2]) since 80's, this topic is still actual nowadays. Recently several path-based de-noising methods were proposed [3–6] which represent a state of the art in this field. In this paper a new de-speckling method, resulting from a signal processing viewpoint, is presented and compared to some of the methods mentioned above.

Upcoming new synthetic aperture radar (SAR) satellites such as TerraSAR-X and Radarsat-2 offer high spatial image resolution and dual receive antenna capabilities, which open new opportunities for worldwide traffic monitoring applications. If the radar cross section (RCS) of the vehicles is strong enough, they can be detected in the SAR data, and their speed can be measured. For system performance prediction and algorithm development, it is therefore indispensable to know the RCS of typical passenger cars. The geometry parameters that have to be considered are the radar look direction, incidence angle, and vehicle orientation. In this letter, the radar signatures of nonmoving or parking cars are presented. They are measured experimentally from airborne experimental SAR (E-SAR) data, which have been collected during flight campaigns in 2005 and 2006 with multiple overflights at different aircraft headings. The radar signatures could be measured for the whole range of aspect angles from 0 to 180 and with high angular resolution due to the large synthetic aperture length of the E-SAR radar sensor. The analysis for one type of passenger car and particular incidence angles showed that the largest radar cross-sectional values and, thus, the greatest chance of detection of the vehicles appear when the car is seen from the front, back, and side. Radar cross-sectional values for slanted views are much lower and are therefore less suitable for car detection. The measurements have been performed in the -band (9.6 GHz) with VV-polarization, and at incidence angles of 41.5deg and 42.5deg. The derived radar signature profile can also be used for the verification of radar cross-sectional simulation studies.