The OLYMPEX field campaign took place over the Olympic Peninsula of Washington during winter 2015-2016. During the intensive observing period, several aircraft flights obtained multi-frequency airborne radar measurements at X-, Ku-, Ka, and W-band from radars aboard the ER-2 and DC-8 aircraft. In addition, ground radars at S- and X-band performed RHI scans under the aircraft ground tracks. These coincident datasets provide a wealth of complementary information about the hydrometeor particle sizes, shapes, and orientations.In order to synthesize these measurements and test the robustness of scattering models, an optimal estimation retrieval based upon a Hitschfeld-Bordan profiling algorithm has been developed. This algorithm retrieves profiles of the particle size distribution parameters Nw and Dm, and, in the ice phase, relative proportions of aggregate, pristine, and rimed particles, using scattering models with different size-density and size-aspect ratio relationships. Under this formulation, only the pristine particles are horizontally aligned and capable of producing non-zero ZDR and KDP.From the nadir-looking airborne multifrequency radars, we find that aggregates may be readily distinguished from rimed and pristine particles owing to their uniqueness in triple-frequency space. However, rimed and pristine particles occupy a similar region in this space and thus polarimetric measurements greatly enhance their identification in our retrieval framework. With these capabilities we will present analyses of three-dimensional hydrometeor mapping obtained during various OLYMPEX cases. Some features retrieved in these cases include a layer of enhanced aggregation about 2km above the melting layer, hypothesized to be maintained by orographic uplift. This layer is often situated above a layer of denser, aligned particles. Regions of riming and supercooled liquid water beneath generating cells are also identified by our retrieval algorithm. Comparisons to in-situ observations and evaluation of scattering models will be presented.
A critical component of the Global Precipitation Measurement (GPM) Mission validation strategy involves use of dual-polarimetric (DP) ground-based radar (GR) products. Both operational and research DP radars across the U.S. and several international locations are used with coincident GPM dual-frequency precipitation radar (DPR) data in a significant expansion of the original TRMM-based “validation network architecture” (VN; Schwaller and Morris, 2011, J.Tech.). The VN radar databases consist of millions of geometrically matched DPR and GR precipitation volumes. Not only does it serve as a tool for validation of satellite-based precipitation retrieval algorithms and GR calibration but also a valuable resource for precipitation science and for complimenting future convective precipitation-related satellite missions.
We have designed and tested a digital receiver suitable for the reception of 6 GHz instantaneous baseband signals. It is based on a Tektronix TADC-1000 12.5-GS/s 8-bit digitiser module, a Tektronix TIPA-3100 HAPS Interposer board and a Synopsys HAPS62-Virtex6 Prototyping Motherboard. This motherboard is also employed for filtering and signal processing. The ADC module uses an external clock from the interposer board and can accept a range of input clock frequencies between 1.6 and 3.125 GHz, resulting in sample rates of between 8 and 12.5 GS/s in single-channel mode. The external clock and digital data are supplied to and processed via the HAPS62 board. A 2048-channel weighted overlap-add (WOLA) and FFT structure separate the input signal into approximately 5-MHz sub-bands to allow subsequent high-resolution processing to obtain continuous spectral information over the input bandwidth. This system meets present-day demands on high-resolution wideband digital back-ends for RF spectrum monitoring. This technology could be part of the next generation wideband signal intercept systems for the future detection, classification and location of modern complex RF signals.
One of the major issues in testing Automatic Target Recognition (ATR) systems lies in having a sufficient amount of trusted data to be able to estimate efficiency and reliability of the developed algorithms. Generally synthetic data is used because real world data is not easy to obtain or too expensive for academic research. This paper describes an original low-cost automatic acquisition system designed to build a database of RCS acquired with real planes (airliners), in bistatic configuration, at low frequency (VHF). The described system uses ADS-B for target position and a network connected set of Software Defined Radio (SDR) receivers for RF processing. This setup was used to build a RCS database of 1300 commercial airliners in less than two weeks close to Paris-Orly international airport. The webbased graphical user interface was used over this time to remotely monitor the system and make demonstrations.
Radar and electronic warfare (EW) systems operate in an increasingly cluttered electro-magnetic (EM) environment. Evaluating system hardware with a variety of spectral and emitter scenarios helps characterize system performance in the presence of multiple emitters of interest and potential interferers that can be either non-intentional or intentional. DAC technology has evolved to the point where wide instantaneous bandwidths and high resolution is available with the current generation of arbitrary waveform generators (AWG). The true power of an AWG is in its ability to generate virtually any waveform downloaded into its memory making it easy to create radar and communications emitters scattered across a synthetic test range that simulates thousands of cubic miles of airspace. This paper will propose new approaches to spectrum and emitter simulation using high precision AWGs and investigate their use in applications which in the past have required a much more complicated, costly and multi-instrument solution. It will explore unique methods for baseband waveform creation, extending scenario length through the efficient use of memory, and upconversion of wideband composite signals to RF and microwave frequencies.
Space debris are man made objects distributed at different altitudes around Earth. The space debris environment represents a serious hazard for both past and future space activities and a collision avoidance system is desirable to protect operative spacecraft and human activities. In this paper we investigate on the performance of an Italian bistatic C band radar system configuration for surveillance of space debris at the orbital altitude range of the COSMO-SkyMed radar satellites, approximately 620 km. In the nearly future this system should be realized and constituted by the Medicina (Emilia-Romagna) radiotelescope receiver and a continuous wave (CW) transmitter located in Noto (Sicily). The bistatic radar sensitivity, as a function of object size and altitude, is evaluated for both catalogued and uncatalogued objects near COSMO-SkyMed orbit. Finally some simulation results will be presented to show the expected performances of the system.
The purpose of the paper is to show how the Universal Software Radio Peripheral (USRP) technology, typically used for implementing telecommunication systems, can be used for realizing passive radars. Specifically in this paper a multiband passive radar is considered. A preliminary study on the signals of opportunity is presented where real and simulated radar ambiguity functions have been evaluated. An experimental system has been set up and live data acquired both for UMTS and DVB-T signals in order to verify the capability of the proposed passive radar demonstrator.
A ionospheric channel model based on raytracing theory is here proposed. Several HF ionospheric channel models based on statistical approach have been presented [1]–[3]. The here proposed model combines the statistical method with the deterministic method, using a raytracing approach. By means of raytracing we are able to simulate any ionospheric channel condition by varying the transmission frequency in the HF band, the elevation angle, the transmitter geographical coordinates, the season, the time of day and the solar activity. The here proposed model is a useful tool to simulate a signal received by an OTH (Over-The-Horizon) radar, that uses the ionosphere as transmission channel.
In ISAR imaging, it's well known that rotating parts of a target such as wheels or rotors induce additional features in the Doppler frequency spectrum. These features are called micro-Doppler effect and appear as sidebands around the central Doppler frequency. They can provide valuable information about the structure and motion of the rotating parts and may be used for target identification. In this paper, we propose a fine analysis of the Doppler returned by reflectors of a rotating wheel. Thanks to the to micro-Doppler signature we are able to extract information on its geometrical features (position, orientation). The method has been performed on simulated and experimental data and provides satisfactory results.
As TerraSAR-X, due for launch in June 2007, will be an operational scientific mission with commercial potential, product quality is of crucial importance. The success or failure of the mission essentially depends on the calibration of the TerraSAR-X system ensuring the product quality and the correct in-orbit operation of the entire SAR system. This paper describes the calibration procedures for TerraSAR-X and the dedicated activities to be performed during the five months commissioning phase. Results from on-ground tests are discussed with respect to geometric and radiometric calibration of the TerraSAR-X system.
In this paper the structure of maximum likelihood (ML) CFAR for lognormal clutter is derived assuming that some reference samples are censored to avoid destructive effect of interfering targets. It is shown that under some acceptable approximations we will achieve in a simple structure for this detector which is suitable for real time processing. The proposed detector is compared with non censored ML CFAR (i.e. logt CFAR) via simulation. It is shown that while the proposed detector is a little weaker than logt CFAR in homogeneous clutter, in non homogeneous clutter it outperforms the logt CFAR. (4 pages)
Assessment of the frequencies and polarizations behaviour of the radar cross section (RCS) of moveable targets with an unpredictable trajectory and/or targets with unrepeatable behaviour is difficult using single frequency/polarisation measurements. The variations of the RCS require a large number of measurements in order to acquire a representative RCS of the target over the spectrum of frequencies and different polarisations. The paper presents a RCS measurement radar system developed to measure RCS at different frequencies and polarizations, the relevant meteorological and oceanographic data and target movement simultaneously thus making it easy to assess RCS results and measurement quality. The system was developed for the Royal Norwegian Navy. (4 pages)
An optimal radar transmitter and receiver architecture is proposed for increasing the available degrees of freedom for beamforming optimization by exploiting the capability to transmit linearly independent waveforms from each element of a phased array radar. This effectively encodes clutter returns with a spatial signature which enhances clutter-rejection performance in a combined space/fast-time processor.The theory which enables the exploitation of the additional degrees of freedom is developed for a general set of linearly independent waveforms and demonstrates that the overall transmit-receive performance in a clutter-limited scenario is independent of the transmit waveforms and, moreover, that the optimality achieved is better than that which would be achieved by adaptive transmit and receive weights in a conventional adaptive beamformer. Furthermore, it is proposed that transmit waveforms can be conveniently synthesized as linear superpositions of orthogonal functions with appropriate range ambiguity and spatial cross-correlation properties, and transmit and receive architectures are devised for both transmit beampattern/waveform synthesis and optimal space/fast-time processing. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.
This paper considers the problem of detecting and classifying a radar target signal and a jamming signal produced by a deception electronic counter measure (ECM) system based on a digital radio frequency memory (DRFM) device. The disturbance is modeled as a complex correlated Gaussian process. The jamming is modeled as a signal belonging to a cone whose axis is the true target signal. Two different approaches are analyzed, based on the adaptive coherent estimator (ACE) and on the generalized likelihood ratio test (GLRT), yielding both to a two-block device. The performance of the two detection/classification algorithms are evaluated, analytically, when possible, and by Monte Carlo simulation.
This paper experimentally evaluates the dynamic range of a digital radar at L-band employing both direct digital synthesis and direct RF sampling, thus minimizing analogue components. Noise-like radar waveforms and pulse to pulse waveform agility are utilized to improve the signal to noise ratio and reduce the sidelobe levels to improve the dynamic range of the radar system. (5 pages)
In modern radar systems, using stepped-frequency pulse train is an effective approach to achieve high-range resolution (HRR) with narrow instantaneous bandwidth and low system complexity. However, if the parameters of stepped-frequency (SF) radar (such as single pulse bandwidth, frequency step size and sampling instant) are not prudently designed, ‘ghost image’ phenomenon (also called range ambiguity in some literature) will corrupt the synthetic HRR profiles. The relationship between parameters of the SF radar and the ghost images is provided analytically. A new synthetic range profiling algorithm is developed to generate HRR profiles without ghost images by using the least-squares (LS) estimation. For targets with negligible radial velocities, the new LS profiling algorithm can eliminate the ghost images successfully, and introduces less signal-to-noise ratio loss. With this algorithm, the restriction on the frequency step size is less rigid than the traditional unambiguous criterion. Consequently, a higher range resolution could be obtained. Simulations and field experimental results are also presented.
This paper presents an optimum steady-state filter as an explicit solution to the periodic nonuniform sampling (PNS) tracking system. Closed-form, generalized filter gains and relationships for PNS tracking are obtained through solving coupled Riccati equations. A time proportion parameter is introduced. Together with the Tracking Index, it plays a fundamental role in steady-state analysis of time-variant Kalman Filter. Analytic solution is obtained for the first-order model while numerical solution for the second-order case. Using steady-state PNS filter gains, a constant-gain filter (CGF) is constructed to avoid overburden of computation without much performance loss.
Vehicle classification is of great importance to the development of Intelligent Transportation Systems. In this paper, a novel ground vehicle classification approach using unmodulated CW radar is proposed. The radar is set up to look forward down to the road; vehicles are modelled as body targets composed of multiple scattering centers. Analysis shows that the spatial distribution of scattering centers can be derived from the Doppler signature of radar echo. Hough Transform is performed to estimate the distribution which is then used for classification. In experiments, vehicles are classified into three types at an average accuracy of 94.8%.
