Pavlo Vyplavin

Implementation of Noise Radar Technology in Ground Based SAR for Short Range Applications

In this paper, results of implementation of noise radar technology in X-band narrowband ground based (GB) synthetic aperture radar (SAR) were presented. The radars under consideration use noise waveform (NW) as a probe signal and perform the range focusing by correlating the radar returns with a reference signal taken before transmission, while the way the azimuth compression is done is similar to that of the conventional SAR. Evaluation of the phase measurements precision with the help of GB NW SAR was carried out on the basis of the obtained interferograms. It has been shown that both NW SAR systems provide quite high precision of displacement measurements.It was also demonstrated that noise radar technology may provide rather high performance of radar designed for short range applications with interferometric capabilities including ground based SAR and d-InSAR systems.

Coherent imaging in the range-azimuth plane using a bistatic radiometer based on antennas with beam synthesizing

Radiometric monitoring allows us to obtain information about thermal electromagnetic radiation of objects in the chosen frequency band. Imaging of distant targets using their thermal electromagnetic radiation may be implemented with the help of bistatic radiometric systems. These systems are based upon measurement of the time difference of arrival of the radiation received by two or more antennas [1]-[3]. This approach has been developed in long wave radar astronomy to improve angular resolution of telescopes [4], [5].

Precision of target shifts detection using Ka-band ground based noise waveform SAR

There is a growing interest to using of Ground Based SAR for detection of small shifts of various objects. Such equipment can be used for detection of changes in buildings, towers, bridges and natural objects. This can help to predict and prevent possible catastrophes. We have elaborated SAR system capable of detecting such changes using noise radar technology. It uses Ka-band CW noise signals for sounding. The paper is devoted to investigation of differential SAR interferometry technique applied to surface shift detection and estimation using this system. In previous works we gave theoretical consideration of precision dependency on mechanical errors in antenna positioning system and experimentally estimated shift measurement precision for the case of stationary scene using statistical processing of data collected in multiple interferograms. Here we continue investigation of the shifts estimation precision using data collected from the sphere target being shifted. Besides, we investigate influence of the variation of the signal time-bandwidth product onto the shift measurement accuracy. The results agree very well with the previously obtained estimations.

Phase errors in noise waveform D-InSAR due to trajectory distortions in synthetic aperture sliding antenna

Influence of antenna motion distortions for the ground based D-InSAR is considered. Analysis of the relations between the phase errors and antenna positioning precision for D-InSAR antenna system is presented. The analytical relation is obtained for the phase errors of D-InSAR with linear aperture and was used in case of various antenna trajectory distortions: shifts along any direction, rotations in azimuth and elevation planes and random shifts. Theoretical results are validated via computer modeling of the noise SAR system. The results obtained via modeling and analytical relations are in a good agreement and may be used for ground based SAR antennas design and interpretations of the generated SAR interferograms.

Radar tomography using MIMO noise radar with signals time-division in transmit/receive channels

We describe MIMO approach to implementation of radar tomography and present preliminary results of its experimental validation using Ka-band noise waveform ground based SAR. The range resolution in radar tomography is determined by power spectrum width of the transmitted signal, while cross-range resolutions are defined by 2D aperture dimensions. We apply MIMO concept with time-division to emulate 2D aperture synthesis combined with range resolution due to wideband random signals which enables generation of 3D coherent radar images. Two linear synthetic apertures have been used for transmit and receive antennas oriented in vertical and horizontal directions, respectively.

Phase measurement accuracy in noise waveform synthetic aperture radar

Detection of small changes in natural formations and human-made constructions is a promising application of synthetic aperture radar (SAR). This paper deals with a specific radar, which is a ground-based SAR using noise waveform. Being fully coherent, SAR provides both phase and amplitude information for every pixel in the mapped area. This gives rise to the possibility of comparing phases between the images taken from the same position at different times in order to extract information about the changes that have occurred between subsequent radar measurements. Such a technique, called coherent change detection (CCD), allows changes of a subwavelength size to be detected. The use of a noise waveform for sounding ensures high electromagnetic compatibility and interference immunity. Moreover, it enables long integration time in the detection stage. However, the random nature of probing signals used in noise radars leads to randomness of the output signals and the preservation of residual fluctuation in the images generated. This random residual, along with external noise, influences the overall accuracy of the phase measurement in noise radar. In this paper, the theoretical and experimental investigation of this specific influence of noise on the precision of phase measurements is presented. The theoretical part of the paper is focused on the estimation of the Cramer-Rao lower bound for the phase measurements using both statistical theory and geometrical interpretation of complex signals. In the experimental part, these findings are verified with dedicated measurements of a metallic sphere displacement, carried out with the help of a ground-based noise waveform SAR.

Radar tomography via time-division MIMO noise radar

MIMO approach to implementation of radar tomography is described and preliminary results of its experimental validation using Ka-band noise waveform ground based SAR are presented. MIMO concept with time-division to of Tx/Rx channels is applied to emulate 2D aperture synthesis combined with range resolution due to wideband random signals. Two linear synthetic apertures have been used for transmit and receive antennas oriented in vertical and horizontal directions, respectively. Range resolution in radar tomography is determined by power spectrum width of the transmitted signal, while its cross-range resolution is defined by 2D aperture dimensions. This enabled generation of 3D coherent radar images in radar tomography mode.

Integrated sidelobe ratio in noise radar receiver

One of the most important characteristics of a radar signal is sidelobes level. It is known that it is possible to build a noise signal generator with power spectrum shape close to Gaussian. Such signal can provide rather low sidelobe level. On the other hand, it is well known that randomness of noise signals leads to randomness of resulting range profiles which is observed as residual fluctuations of autocorrelation also called as processing noise or noise floor. Increase of signal time-bandwidth product leads to decreasing of such residual fluctuations. Residual fluctuations can be a big drawback of noise signal for some applications and can be neglected in other ones. Mostly, this depends on possibility of using high time-bandwidth product of signal in the application. Current work is dedicated to numerical and experimental investigation of properties of noise signal. Because residual fluctuations are spread over the range profile, we have chosen such parameter as integrated sidelobe ratio of the signal (ISLR) to be used for analysis of the signal performance. We estimated ISLR for modeled noise signal with various parameters. Besides, through analysis of reference channel of existing noise radars we estimated ISLR for real systems.

Capabilities of noise radar in remote sensing applications

Nowadays noise waveform signals attract attention of radar engineers because they are inexpensive to generate both in analog and digital formats, covert, have good resistance against jamming and interference, are easily obtained using current microwave and RF circuit technology, spectrally very efficient and can share spectral bands without mutual interference, exhibit excellent waveform diversity characteristics. Coherent processing of noise signals enables to use them for phase and Doppler frequency measurements and for SAR imaging. Current work describes several radars showing current capabilities of noise radar technology such as shifts detection using Ka-band and X-band noise SAR, 3D SAR imaging and novel high dynamic range noise radars.

Ka-Band Ground-Based Noise Waveform SAR

We present main results of design and investigations of Ka-band ground based interferometric SAR which uses continuous noise waveform as a probe signal and may operate in both monostatic and bistatic regimes. Synthetic aperture antennas enable to design a portable, light weight, easy to mount device with high speed of operation suitable for SAR imaging in quasi-real time while Ka-band noise waveform signals provide all-weather high resolution, high electromagnetic compatibility and interference immunity. Experiments have shown a rather high stability and repeatability of the measurements due to both the high quality of the equipment and advanced signal processing methods. The SAR system designed is an innovative instrument for solving new tasks of precise remote monitoring of various large objects, such as sealing of big halls, dams, bridges, TV towers, hangars, etc.