Side-looking Radar Research Articles

A New Side-Looking Scheme for Speed Estimation and Detection of Tangential Slow-Moving Targets.

A single-beam radar system cannot adopt a side-looking installation scheme, which is completely perpendicular to the moving direction of the target in an intelligent transportation system (ITS), because of its own limitations. In this paper, a side-looking radar velocity measurement system that utilizes a new signal processing method and multi-channel radar scheme is proposed. Constant false alarm rate (CFAR) and generalized likelihood ratio test (GLRT) detectors are used to detect the data processing results in different stages in order to reduce the false alarm rate of targets. At the same time, a deconvolution-based clutter map algorithm is proposed to solve the problem of clutter interference in the test environment, and its theoretical performance is verified by simulation. Finally, 77 G commercial radar is used to test the system, and the results show that this algorithm can effectively detect and accurately estimate the speed of tangential low-speed targets under clutter interference.

A Neural Network Method for Retrieving Sea Surface Wind Speed for C-Band SAR

Based on the Ocean Projection and Extension neural Network (OPEN) method, a novel approach is proposed to retrieve sea surface wind speed for C-band synthetic aperture radar (SAR). In order to prove the methodology with a robust dataset, five-year normalized radar cross section (NRCS) measurements from the advanced scatterometer (ASCAT), a well-known side-looking radar sensor, are used to train the model. In situ wind data from direct buoy observations, instead of reanalysis wind data or model results, are used as the ground truth in the OPEN model. The model is applied to retrieve sea surface winds from two independent data sets, ASCAT and Sentinel-1 SAR data, and has been well-validated using buoy measurements from the National Oceanic and Atmospheric Administration (NOAA) and China Meteorological Administration (CMA), and the ASCAT coastal wind product. The comparison between the OPEN model and four C-band model (CMOD) versions (CMOD4, CMOD-IFR2, CMOD5.N, and CMOD7) further indicates the good performance of the proposed model for C-band SAR sensors. It is anticipated that the use of high-resolution SAR data together with the new wind speed retrieval method can provide continuous and accurate ocean wind products in the future.

A C-Band Fully Polarimetric Automotive Synthetic Aperture Radar

Due to the rapid increase in 76 GHz automotive spectrum use in recent years, wireless interference is becoming a legitimate area of concern. However, the recent rise in interest of automated vehicles (AVs) has also spurred new growth and adoption of low frequency vehicle-to-everything (V2X) communications in and around the 5.8 GHz unlicensed bands, opening the possibility for communications spectrum reuse in the form of joint radar-communications (JRC). In this work, we present a low frequency 5.9 GHz side-looking polarimetric synthetic aperture radar (SAR) for automotive use, utilizing a ranging waveform in a common low frequency V2X communications band. A synthetic aperture technique is employed to address the angular resolution concerns commonly associated with radars at lower frequencies. Three side-looking fully polarimetric SAR images in various urban scenes are presented and discussed to highlight the unique opportunities for landmark inference afforded through measurement of co- and cross-polarized scattering.

Permanent Scatterers in Repeat-Pass Airborne VHF Radar Sounder for Layer-Velocity Estimation

Englacial layer velocity can provide insights on the vertical-velocity structure of the ice sheets. We present a repeat-pass interferometric approach that allows the estimation of the vertical englacial layer velocity using the radar sounder data. In contrast to the ground-based sensors, the airborne radar sounder data can potentially be used to estimate the layer velocity on a continental scale. When merged with the horizontal surface velocity and the numerical models, layer velocity can support the 3-D analysis of the ice flow and structure. Our aim is to provide the proof-of-concept demonstration that, similar to the side-looking synthetic aperture radar for imaging, the airborne radar sounder data can be used to estimate the subwavelength displacement of the englacial radio-stratigraphic layers. To achieve this, we use the phase and magnitude acquired repeatedly over the same region of interest. After the extraction of the crossing points, two acquisitions are finely registered. Then, we compute the interferometric phase for the englacial layers (which are shown to behave as PSs in the nadir sounding geometry), to estimate a vertical displacement and a velocity profile. We present the results over East Antarctica using data from the high-capability radar sounder (HiCARS) system. We show two scenarios that demonstrate the feasibility, limitations, and requirements of this approach.

Micronavigation System to Support a Radar with Synthetic Aperture aboard a Small UAV

The paper describes the experience of constructing an integrated SINS/GNSS navigation system for supporting a side-looking synthetic aperture radar, located aboard a small-sized unmanned aerial vehicle (UAV). Key features and factors that should be taken into account when developing a navigation system operated under severe conditions are studied. Flight test results are presented, including the estimates of MEMS-based micronavigation system accuracy. The analysis is based on the radio signals reflected from corner reflectors, as well as radar images obtained by constructing a matched filter based on the micronavigation system data.

Circulation Retrieval of Simulated Wake Vortices Under Rainy Condition With a Side-Looking Scanning Radar

The strength of a wake vortex can be well described by vortex circulation. In the area of aviation safety, it serves as a crucial parameter for assessing hazards caused by wake vortices, and its retrieval has attracted much attention in the past decades. Generally, radar is a very promising detection sensor for wake vortices generated under rainy condition where the scattering is mainly caused by the raindrops driven by wake vortices. This makes it possible to retrieve the circulation of wake vortices by sensing and quantifying the motion of these raindrops. This paper proposes the use of a side-looking radar, whose beam scans up and down alternatingly, for detecting wake vortices. In this method, raindrops that make major contribution to the total scattering are identified as characteristic-size raindrops, and their motion equation is established to connect their motion to the dynamics of wake vortices. When the velocity and acceleration of characteristic-size raindrops are well estimated from the Doppler spectra, the motion equation can be well solved by the nonlinear least squares method to yield the target parameter, circulation $\Gamma$ . At the same time, two other important parameters (vortex spacing $b_0$ and vortex-core height $y_0$ ) can be retrieved as well. Numerical simulation results verify good performance of the retrieval method.

Derivation of Bistatic SAR Resolution Equations Based on Backprojection

This letter introduces ground-range and cross-range resolution equations for the side-looking bistatic synthetic aperture radar (SAR). The derivation is based on the backprojection integral and the method of stationary phase. The ground-range and cross-range resolution equations are provided in closed form, making them easy for calculation. They are, therefore, helpful for bistatic SAR system development. The derived ground-range and cross-range resolution equations are validated with the bistatic data simulated mainly using the parameters of the LORA system.

Optimal Monopulse Beamforming for Side-Looking Airborne Radars

The synthesis of the optimal excitations of the sum and the difference patterns in planar active electronically scanned arrays ( $\text{AESA}$ s) for side-looking airborne monopulse radar systems is addressed. Under the assumption that each array element is equipped with a single transmit receive module ( $\text{TRM}$ ), which is shared among all patterns, the complex (amplitude and phase) $\text{TRM}$ coefficients are optimized with a customized convex programming procedure to yield a sum beam with maximum directivity and difference beams with maximum slope along the boresight direction as well as asymmetric sidelobes envelope for noise suppression from half-space. Representative results from a synthesized $\text{AESA}$ devoted to a real airborne application are illustrated and discussed to give some insights to the interested readers on the features and the potentialities of the proposed synthesis approach.

Circulation retrieval of wake vortex in fog with a side-looking scanning radar

Knowledge of aircraft wake vortex circulation is very essential for promoting aviation safety and airport capacity. In foggy conditions, cloud water droplets suspended as fog (here called fog drops) inside the wake have almost identical velocity with the wake vortex due to the weak inertia of the droplets. By taking this property into account, we propose two methods to retrieve the circulation of wake vortex in fog with a side-looking scanning radar. In the methods, while the radar beam scans alternatively up and down, the vortex cores are identified from the Doppler spectra at different incident angles, and the circulation is finally boiled down to very simple expressions related to the Doppler velocities. Numerical simulation results verify the good performance of the methods.

MIMO-SAR: Opportunities and Pitfalls

This paper reviews advanced radar architectures that employ multiple transmit and multiple receive antennas to improve the performance of future synthetic aperture radar (SAR) systems. These advanced architectures have been dubbed multiple-input multiple-output SAR (MIMO-SAR) in analogy to MIMO communication systems. Considerable confusion arose, however, with regard to the selection of suitable waveforms for the simultaneous transmission via multiple channels. It is shown that the mere use of orthogonal waveforms is insufficient for the desired performance improvement in view of most SAR applications. As a solution to this fundamental MIMO-SAR challenge, a new class of short-term shift-orthogonal waveforms is introduced. The short-term shift orthogonality avoids mutual interferences from the radar echoes of closely spaced scatterers, while interferences from more distant scatterers are suppressed by digital beamforming on receive in elevation. Further insights can be gained by considering the data acquisition of a side-looking imaging radar in a 3-D information cube. It becomes evident that the suggested waveforms fill different subspaces that can be individually accessed by a multichannel receiver. For completeness, the new class of short-term shift-orthogonal waveforms is also compared to a recently proposed pair of orthogonal frequency-division multiplexing waveforms. It is shown that both sets of waveforms require essentially the same principle of range time to elevation angle conversion via a multichannel receiver in order to be applicable for MIMO-SAR imaging without interference.

Clutter Suppression Improvement for Airborne Bistatic Sidelooking Radar with Overlapped Subarrays Alternate Transmitting

距离非平稳杂波抑制是机载双基雷达空时自适应处理面临的重要困难之一。针对此问题，该文提出一种利用重叠子阵交替发射技术来抑制距离非平稳杂波的新方法。该方法通过交替发射使机载双基正侧阵雷达的杂波脊落在发射和接收空间频率以及多普勒频率构成的3维频率空间的一个平面上，并且目标不落在该平面。由于该杂波平面具有距离平稳性，这保证了空时自适应处理可以有效地抑制该杂波平面，进而能够有效抑制距离非平稳杂波。仿真结果验证了该方法的有效性。

The space oblique conic projection

The problem of determining a suitable map projection for side-looking synthetic aperture radar (SAR) satellite imagery is examined. Using a foundation in dynamic mathematics, a new Space Oblique Conic (SOC) projection is proposed that is specifically designed for a side-looking radar imagery. The geometric model of SOC is formalized, and the projection of the central line of a side-looking field of view is established based on this model. The forward and inverse formulas for the SOC projection are derived and the projection's pattern of distortion is discussed. As an example, SEASAT-A radar imagery is considered, and a particular SOC projection model for this satellite derived.

Study on the signature of ground moving target for airborne squint SAR imaging

Compared with the side-looking Synthetic Aperture Radar (SAR), the flexible beam-pointing of squint SAR makes great application value. This paper derives the image signature of the ground moving target after the processing of Range-Doppler (RD) algorithm, the SAR signatures of ground moving targets are analyzed, including the geometry correction, the offsets and defocusing in both range and azimuth direction. Finally, computer simulation results validate its effectiveness. The research results are especially significant for moving targets detection and parameters estimation in squint mode SAR.

CONVOLUTION BACK-PROJECTION IMAGING ALGORITHM FOR DOWNWARD-LOOKING SPARSE LINEAR ARRAY THREE DIMENSIONAL SYNTHETIC APERTURE RADAR

General side-looking synthetic aperture radar (SAR) cannot obtain scattering information about the observed scenes which are constrained by lay over and shading efiects. Downward-looking sparse linear array three-dimensional SAR (DLSLA 3D SAR) can be placed on small and mobile platform, allows for the acquisition of full 3D microwave images and overcomes the restrictions of shading and lay over efiects in side-looking SAR. DLSLA 3D SAR can be developed for various applications, such as city planning, environmental monitoring, Digital Elevation Model (DEM) generation, disaster relief, surveillance and reconnaissance, etc. In this paper, we give the imaging geometry and dechirp echo signal model of DLSLA 3D SAR. The sparse linear array is composed of multiple transmitting and receiving array elements placed sparsely along cross-track dimension. The radar works on time-divided transmitting-receiving mode. Particularly, the platform motion impact on the echo signal during the time-divided transmitting-receiving procedure is considered. Then we analyse the wave propagation, along-track and cross-track dimensional echo signal bandwidth before and after dechrip processing. In the following we extend the projection-slice theorem which is widely used in computerized axial tomography (CAT) to DLSLA 3D SAR imaging. In consideration of the ∞ying platform motion compensation during time- divided transmitting-receiving procedure and parallel implementation on multi-core CPU or Graphics processing units (GPU) processor, the convolution back-projection (CBP) imaging algorithm is proposed for DLSLA 3D SAR image reconstruction. At last, the focusing capabilities

Towards an urban roughness parameterisation using interferometric SAR data taking the Metropolitan Region of Hamburg as an example

Increased surface roughness and the enhanced drag effect of the urban surface are important alterations in urban boundary layer dynamics. An enhanced roughness mapping would be beneficial for several modelling applications since state of the art roughness parameters derived from land use data do not represent the heterogeneity of urban surfaces at higher resolutions. Today most morphometric methods of urban roughness estimation are based on empirically derived functions of obstacle geometry parameters, which have conceptual and practical shortcomings. In this study we propose a new approach based on the topology, statistics and texture of overall roughness elements as represented by a Digital Height Model generated from side-looking Interferometric Synthetic Aperture Radar. These state of the art remotely sensed high resolution data are readily available for Western Europe, the US, as well as parts of Asia and the Caribbean. A set of new angular dependent urban morphology parameters is developed and tested for suitability for the mapping of roughness characteristics by way of an improved methodology. The results are very convincing and consistent over a wide range of surface characteristics.

Field Study of the Space Uniformity of Meteorological and Wave Parameters in the Coastal Zone. On the Problem of Calibration of a Side-Looking Radar on the Sich-1M Satellite as an Instrument for Measuring Wind Velocity over the Sea

We study the problem of subsatellite calibration of a side-looking radar (SLR) of the Sich-1M satellite regarded as an instrument for the evaluation of the velocity of surface wind and discuss the possibility of application of the meteorological and wave parameters measured from the stationary oceanographic platform of the Experimental Department of the Marine Hydrophysical Institute (Ukrainian Academy of Sciences) for their evaluation in the remote regions of the sea. These regions can be observed with the help of the SLR without errors introduced by the appearance of the coast in elements of space resolution. To prove the indicated possibility experimentally, we perform simultaneous measurements of the water and air temperatures, wind velocity, and the characteristics of waves both from the platform and in the water area neighboring with the platform on the side of the sea at distances of up to 4.8 km. The quantitative estimates of the degree of space uniformity of the analyzed parameters are deduced under the conditions of stable inshore wind. A conclusion is made that the platform can be used for subsatellite measurements aimed at the validation and improvement of the algorithm of reconstruction of the velocity of surface wind by using the SLR of the Sich-1M satellite.

Identification of Bed Forms Through ERS SAR Images in San Matías Gulf, Argentina

The European Space Agency (ESA) funded two projects in 1991 and 1994 concerning the observation of the Argentine coastal environment with synthetic aperture radar (SAR). Studies were carried out for the periods 1992–1994 and 1994–1997. Several ERS-1/2 satellite SAR images were acquired over the San Matías Gulf in the Patagonian coast during these two periods. SAR is a side-looking imaging radar that operates from either a satellite or an aircraft. The instrument emits a series microwave pulses toward the earth in a direction perpendicular to the flight path. Imagery is constructed from the strength and time delay of the returned signals, which depend primarily on the roughness and dielectric properties of the surface under observation and the distance from the radar. Ocean surface roughness wave-like patterns, imaged as a series of bright and dark linear features by SAR, are persistently observed over the San Matías Gulf mouth region. A total of thirty-three (33) ERS-1/2 SAR images (100 km × 100 km) from 15 different orbits from 1992 to 2000 were analyzed. This series of observations has allowed for a detailed examination of the location, persistence, and the conditions involved in the imaging of the observed wave-like patterns. Very strong tidal currents of the order of 2 m/s characterize the gulf region. The characteristics of recurrent surface patterns in the SAR images indicate that they are caused by the interaction of the tidal currents with bed forms in the bottom topography of the gulf. The location of these bed forms is poorly documented in the available bathymetric charts of the region. The SAR images show the significant potential that satellite radar observations have as a tool for detecting unmapped coastal ocean bottom features, particularly, where bathymetric mapping activities can be extremely difficult, dangerous, or costly.

Analysis of Ice Conditions in Arctic Using the Data from the Side-Looking Radar and Microwave Radiometer of the "Okean-01" Satellite Series

Analysis of Ice Conditions in Arctic Using the Data from the Side-Looking Radar and Microwave Radiometer of the "Okean-01" Satellite Series

Winter navigation in the Northern Sea Route using RADARSAT data

AbstractThe results are presented of the first winter ice navigation demonstration, using synthetic aperture radar (SAR) images from the Canadian satellite RADARSAT, onboard the nuclear icebreaker Sovetskiy Soyuz in the Kara Sea region in April–May 1998. While ERS SAR data only could cover part of the sea ice in this large area, the demonstration showed that RADARSAT ScanSAR images with 100 m pixel size could be used to map all relevant ice areas with a few 500 × 500 km scenes. SAR images transferred onboard icebreakers in near real time offer an excellent possibility to select optimal sailing routes in difficult ice conditions such as those that were encountered by this expedition. SAR images were also used for planning of operations prior to the expedition. This study compares sub-satellite sea-ice observations with RADARSAT SAR as well as Okean side-looking radar (SLR) signatures of the major ice types and features found in the Kara Sea during winter. Wide-swath SAR images will become available from several new satellites in the near future, such as Envisat, scheduled in 2001, and RADARSAT-2, in 2002. Satellite SAR images will therefore play an increasingly important role in operational ice monitoring both in the Northern Sea Route and in other ice areas.

Side-looking ADCP and Doppler radar measurements across a coastal front

Measurements are reported from two side-looking Doppler systems, which were used to study the discharge front located off the mouth of Chesapeake Bay. One system was a commercial 300-kHz narrow-band acoustic Doppler current profiler (ADCP), which was mounted at a depth of 0.6 m on the port side of a research ship. The other was a prototype X-band, vertically polarized, Doppler radar mounted at a height of about 4 m on the starboard side. Both velocity and backscatter intensity were measured along two beams to ranges of 120 m (ADCP) and 200 m (radar), so that by sailing alternately on each side of the front it was possible to make nearly simultaneous across-front measurements with both systems. Despite the differences in acoustic and radar scattering mechanisms, a combined backscatter intensity surface map could be made showing a continuous frontal signature about 10-m wide and 20 dB above background levels. Each system was also able to measure the same large-scale velocity change across the front, which was dominated by the discharging buoyant bay water flowing at about 50 cm/s relative to the ambient continental shelf water. However, within a 60-m wide zone, the radar system measured velocities up to 75 cm/s larger than the ADCP. Such large velocity differences arose from the radar's sensitivity to motions associated with waves reflecting from the region of strongest across-front current convergence. This frontal convergence was resolved only by the ADCP, which showed a horizontal current change of about 25 cm/s over 10 m and appeared to extend over the upper 2 m or so of the water column. These results show that the combined information from the acoustic and radar systems provide a more complete picture of the frontal currents and wave-current interactions than either system could provide alone.