Each year commercial, private and military aircraft jet engines are damaged by the ingestion of foreign objects. Annual engine repair costs for ingestion damage is in the tens of millions of dollars. Bird strikes represent the major foreign object threat to aircraft engines, although large hail and objects found on the ramp can also damage an engine. A radar based foreign object ingestion detection system concept, the subject of this paper, is capable of determining when an object as small as 4 millimeters has entered a fan jet engine. Additionally, such a system is capable of determining the relative size of the object and the approximate point within the engine where the object impacts the engine. These data can be displayed in real time to the pilot. In addition, the information recorded in the data base can be used by the mechanics between major engine inspections to determine if a detailed inspection of the turbine blade roots or other hard to access engine parts is required. Long term statistical data developed by the system can also be used as a measure of the foreign object and bird ingestion problem at various airports and improve the reporting of ingestion and bird strike events above the currently estimated 20 percent reporting rate.

High-quality automatic target recognition algorithms implemented with a real-beam radar require imagery with resolved target characteristics. This paper presents an iterative autofocus estimation algorithm that improves the quality of high-resolution 2D inverse synthetic aperture radar images. The algorithm uses the derivative of the phase history of isolated point scatterers to estimate the initial conditions for the target motion parameters of a maneuvering vehicle. The algorithm was tested using simulated data. We report on the agreement between the actual and estimated values of range and entropy.

Lynx is a high resolution, synthetic aperture radar that has been designed and built by Sandia National Laboratories in collaboration with General Atomics (GA). Although Lynx may be operated on a wide variety of manned and unmanned platforms, it is primarily intended to be fielded on unmanned aerial vehicles. In particular, it may be operated on the Predator, I-GNAT, or Prowler II platforms manufactured by GA Aeronautical Systems, Inc.

Frequency-modulated continuous wave radar systems have been used for many years to determine range and velocity in a wide variety of military and commercial applications. The modulation waveform can be sinusoidal, triangular or sawtooth. Each form has its advantages, but, since the triangular and sawtooth modulation can be approximated with a sinusoidal modulation, the analysis in this paper will concentrate on sinusoidal modulation. For moving targets, the envelope of the signal used for determining the Doppler frequency is a function that varies according to the range. If the mixing is performed with a sine wave that is the n^th multiple of the modulation frequency, then the envelope is an n^th-order Bessel function that varies according to the range. These envelopes can be used on their own to determine range based on tabulated values of the Bessel function. A second approach is to use the difference between two Bessel functions of different orders to identify a certain range. The choice of Bessel functions depends on the carrier frequency and the target range. Amplifiers can be used to modify the identification range.

The practical application of adaptive digital beamforming (ADBF) to phased array radar systems has been demonstrated by several systems, most notably MESAR. However, MESAR and the other fielded radar systems employing ADBF are limited to narrow bandwidth operation. The next generation of defense radar systems currently under development are considering ADBF architecture, but with wideband waveforms. New radar system architectures are mandated by the requirement for simultaneously accomplishing wide bandwidth and ADBF, particularly for the precision measurement and tracking environment of ballistic missile defense. This paper describes approaches to developing wideband architectures suitable for this and similar applications.

The Army Research Laboratory synthetic aperture radar system is placed atop a boom lift, and therefore the system is termed a `BoomSAR'. The UWB character of this system, covering a frequency spectrum from 40 - 1200 MHz, makes accurate polarimetric calibration a nontrivial matter. The response of the standard trihedral fiducial target is poorly understood at VHF and UHF frequencies, for which the wave interaction with the soil can be an important issue. Here we employ a rigorous method-of-moments analysis of UWB scattering from a trihedral reflector over ground. The soil is modeled as a lossy, dispersive half space, accounted for rigorously via the half-space Green's function. The numerical algorithm is used to evaluate the angle-dependent, polarimetric frequency dependence of scattering from a trihedral target, at VHF and UHF frequencies. This comprehensive study of UWB scattering from a trihedral over soil is critical for system calibration.

The Army Research Laboratory has been investigating the potential of low-frequency, ultra-wideband radar to provide part of the solution to the very difficult mine detection problem One of the issues associated with using this type of radar is that it spans a very wide frequency range and angular space, making it difficult to use `normal' calibration techniques. Thus, ARL has been investigating techniques to calibrate the ARL ultra-wideband BoomSAR data to gain a better understanding of the signal response from clutter, mines, and other targets of interest. In this paper, we present results from data collected in Yuma Proving Ground on various types of mines. In particular, we compare the radar cross-section of the mines, predicted using method of moments models versus the measured response from the mines, as indicated by the calibrated ultra- wideband radar imagery.

Ultra wideband (UWB) radar is an emerging technology with potential for all-weather, remote sensing of objects obscured by foliage or buried underground. Multiple octaves of frequency coverage and 90 degrees or more of viewing angles across a synthesized aperture are used to obtain high spatial resolution mapping of scattering behavior. Additionally, fully polarimetric responses can be measured, providing a multichannel characterization of objects in a scene. However, the diversity in wavelength and viewing angle presents significant challenges for system engineering and data interpretation. In particular, the multichannel UWB system poses unique imaging challenges arising from the variation of the UWB antenna response. We present an overview of calibration techniques for polarimetric wideband imagery, and introduce an image domain calibration technique using calibration targets.

We report here on the use of rigorous scattering models for SAR-based detection of buried UXO. In this paper we concentrate on the algorithm used for the scattering computations, the fast multiple method (FMM), and in the talk we will demonstrate how this is applied to subsurface- target detection, using data from the Army Research Laboratory BoomSAR. The FMM is applied to scattering from an arbitrary, 3D perfect conductor situated above or below a lossy, dielectric half space. Example results are presented for an electrically large target buried in a lossy, dispersive half space, with comparisons presented between the FMM and a rigorous method of moments solution.

This paper will describe novel techniques and results of the current project to employ advanced signal processing techniques to detect and classify subsurface layers. In particular, a computational fast layer tracking processing technique will be described along with results of the algorithm. It is expected that the ground penetrating radar and the results of current research will assist the Florida Department of Transportation in determining more accurate road layer thickness profiles, assessing road subsurface conditions with less coring, and rehabilitating roads with less manpower than is now required. Such capabilities will allow potentially serious problems to be corrected before they become costly and will also provide a useful tool for future road design and improvement.

This paper will describe the results attained from advanced signal processing techniques used to improve analysis and interpretation of ground penetrating radar (GPR) profile data. It is anticipated that the GPR processing software and its algorithms will aid the Florida Department of Transportation in recognition and localization of geophysical anomalies through more informative subsurface images, while maintaining the desired non-invasive nature of GPR analysis methods.

Ultra-wideband (UWB) synthetic aperture radar (SAR) is a promising new technology that has the potential for detecting and recognizing targets obscured by foliage or buried beneath the ground. The Army Research Laboratory (ARL) is conducting a significant research effort in Automatic Target Detection/Recognition (ATD/R) algorithms for UWB SAR. The goal of the current ATD/R algorithm research effort is to develop a baseline algorithm approach to accompany newly developed UWB SAR hardware into near-term technology demonstration programs. To accomplish this goal, ARL has assembled a team of researchers from within ARL and from several universities, having expertise in radar, electromagnetics, signal processing and target recognition. Many new and promising ideas currently are being exploited. An evaluation environment was needed to support the integration of those ideas into a coherent algorithm approach. The University of Florida, as part of this project with ARL, has developed a software environment for the development, integration and evaluation of UWB SAR ATD/R algorithms. This paper describes the software environment that serves as the vehicle for integrating the efforts of the various algorithm researchers by providing a set of standards and tools that will enable the various algorithms to be hosted on the same computer system, access a common database, and be evaluated in various combinations against a statistically significant quantity of field-collected data.

We present an automatic target detection (ATD) algorithm for foliage penetrating (FOPEN) ultra-wideband (UWB) synthetic aperture radar (SAR) data using split spectral analysis. Split spectral analysis is commonly used in the ultrasonic, non-destructive evaluation of materials using wide band pulses for flaw detection. In this paper, we show the application of split spectral analysis for detecting obscured targets in foliage using UWB pulse returns to discriminate targets from foliage, the data spectrum is split into several bands, namely, 20 to 75, 75 to 150, ..., 825 to 900 MHz. An ATD algorithm is developed based on the relative energy levels in various bands, the number of bands containing significant energy (spread of energy), and chip size (number of crossrange and range bins). The algorithm is tested on the (FOPEN UWB SAR) data of foliage and vehicles obscured by foliage collected at Aberdeen Proving Ground, MD. The paper presents various split spectral parameters used in the algorithm and discusses the rationale for their use.

We have applied the Optimal Brain Surgeon (OBS) pruning strategy to a polynomial discriminator in order to reduce the number of coefficients it employs. The polynomial discriminator multiplies various combinations of test features by the respective coefficients and then sums the products to obtain a discriminant that is compared to a threshold. The test features are derived from the radar data associated with the cell under test, while the coefficients are determined a priori by minimizing the mean-squared error (MSE) between the actual and the desired value of the discriminant over the training set. The OBS pruning strategy examines the Hessian matrix of a network's error surface-- derived from the training data--to determine which coefficients can be eliminated without adversely affecting the MSE. Besides simplifying the network, such a reduction may also allow for improved network performance when an unseen test data is input. We present the application of the OBS pruning strategy to reduce the dimensionality of a polynomial discriminator and show that the reduction in dimensionality does not adversely affect performance.

The paper discusses the necessity and feasibility of designing a SAR system for detection of low-signature stationary and moving targets, e.g. concealed by foliage. In particular, we investigate the basic requirements, measurement principles and signal processing algorithms. We show that the problem can be formulated using the same principles as ultra-wideband SAR by adding multiple antenna elements. Time-domain signal processing is emphasized, and we formulate such SAR algorithms to simultaneously focus both stationary and moving targets. The computational effort to the basic algorithm is dramatically reduced by factorization into a number of recursive stages. In this manner, the time-domain algorithm has essentially the same numerical efficiency as FFT-based methods. We also include a brief description of the present development of an airborne SAR system with an antenna array and operating in the 200 - 800 MHz band called LORA.

This paper describes some new results on a signal processing approach for airborne surveillance radars. This is a space- time adaptive processing technique that simultaneously processes temporal data from sum and difference ((Sigma) (Delta) ) beams to suppress clutter returns. The approach also includes employing spatial adaptive pre- suppression to suppress wideband noise jammers in a two- stage processor.

The joint influence of multipath propagation and rain attenuation effects and also the land and rain clutter on the millimeter wave radar operation, in particular, on the maximum detection range and target detectability is considered. The parameters of millimeter wave radar are compared with parameters of analogous radar of X-band and the comparison is carried out for two cases: with frequency change an antenna aperture is constant (1) and with frequency change an antenna gain is constant, i.e. the proportional change of antenna aperture takes the place (2). The results of this analysis are presented for different types of terrain (quasi-smooth, rough, rough with vegetation, etc.) and rains with intensity from 2 to 10 mm/h. It is shown that for constant antenna aperture and joint effects of multipath propagation and rain attenuation the all-weather millimeter wave radar is more effective than analogous X-band radar at ranges less than 2 - 4 km.

The paper deals with the problem of measuring electrical and geometrical parameters of the layer medium. The measurements are based on the control of radio wave reflection coefficient as a function of frequency. Based on solution of the system of transcendental equations for reflection coefficient such parameters of the homogeneous layer medium as complex dielectric permeability, depth of the layer and complex dielectric permeability of the lower homogeneous hemispace.

This paper describes the development of a radar sensor system used for automotive collision avoidance. Because the heavy truck may have great larger radar cross section than a motorcyclist has, the radar receiver may have a large dynamic range. And multi-targets at different speed may confuse the echo spectrum causing the ambiguity between range and speed of target. To get more information about target and background and to adapt to the large dynamic range and multi-targets, a frequency modulated and pseudo- random binary sequences phase modulated continuous wave radar system is described. The analysis of this double- modulation system is given. A high-speed signal processing and data processing component are used to process and combine the data and information from echo at different direction and at every moment.

A novel universal demodulator for remote sensing satellites is proposed and implemented in this paper. Compared with traditional multiple-function demodulator, this novel demodulator is much simpler mainly due to using a kind of new Intermediate Frequency (IF) filter and a programmable bit synchronizer. The new IF filter can accomplish the function which will be done by the IF filter and the base band filter in the traditional multiple-function demodulator, while the programmable bit synchronizer can synchronize different bit streams with different transmission rates. The demodulator has already been field tested with satisfactory result.

In this paper we discuss the problem of subsurface target imaging in lossy, inhomogeneous medium with the presence of the air-ground interface. A subsurface imaging radar system using optimal processing procedures and multifrequency holographic approach and characterizing with controlling parameters has been analyzed. It was found the values of contrast coefficient for subsurface object reconstruction on the background signal scattered by upper surface layer that demonstrate high resolution of the image estimated. The resolution of reconstructed images depends on the synthetic aperture length, soil type (electric conductivity and dielectric permittivity), geometrical parameters, central frequency, frequency band and antenna directivity. The novel filtering techniques was proposed in this paper. By mean of use new filters it is possible to increase the quality of the subsurface imaging. Different results of the numerical calculation and simulation of the filtering algorithms are presented. These results show the effectiveness of new algorithms of reconstruction and filtration in the problem of subsurface radar imaging.

This paper presents a 3D interferometric inverse-synthetic- aperture-radar (In-ISAR) imaging technique for high- frequency electromagnetic scattering diagnosis of complex radar targets. The high-frequency electromagnetic scattering data are obtained from both anechoic chamber measurements and theoretical predictions. The 2D ISAR images are obtained from the frequency-azimuth space data, and the 3D In-ISAR images are derived from two ISAR images at different incidental altitudes by interferometrical processing. Computational and experimental imaging results are shown for both simple point-like targets and complex aircraft models.

The reader will find this paper is organized into three complementary sections. First, we define the research objectives U.S. Army Research Laboratory and other defense organizations share. We then report in detail on the signal processing/image formation techniques developed as part of our mission program. We conclude with a discussion on the use of these algorithms and tools with the emerging data from major defense-wide collections. Imaging concepts are discussed and various quality metrics are provided.