Precision SAR processing using chirp scaling

A space-variant interpolation is required to compensate for the migration of signal energy through range resolution cells when processing synthetic aperture radar (SAR) data, using either the classical range/Doppler (R/D) algorithm or related frequency domain techniques. In general, interpolation requires significant computation time, and leads to loss of image quality, especially in the complex image. The new chirp scaling algorithm avoids interpolation, yet performs range cell migration correction accurately. The algorithm requires only complex multiplies and Fourier transforms to implement, is inherently phase preserving, and is suitable for wide-swath, large-beamwidth, and large-squint applications. This paper describes the chirp scaling algorithm, summarizes simulation results, presents imagery processed with the algorithm, and reviews quantitative measures of its performance. Based on quantitative comparison, the chirp scaling algorithm provides image quality equal to or better than the precision range/Doppler processor. Over the range of parameters tested, image quality results approach the theoretical limit, as defined by the system bandwidth     

Ocean waves and optimal SAR processing: don't adjust the focus

Concepts for the optimal processing of synthetic-aperture radar (SAR) ocean wave observations are discussed. The recommended procedure requires processing of the SAR signal data to individual looks. The Fourier transform of each look is then calculated and phase compensated, than all are combined. The method leads to an optimized wave spectral estimation for SAR data. It is emphasized that these concepts support the conclusion that the SAR processor focus setting should be equal to that for a static scene. Focus adjustment away from this value leads to results that are less than optimal     

An Agent-Based Microsimulation Model of Swiss Travel: First Results

In a multi-agent transportation simulation, each traveler is represented individually. Such a simulation consists of at least the following modules: (i) Activity generation. (ii) Modal and route choice. (iii) The traffic simulation itself. (iv) Learning and feedback. In order to find solutions which are consistent between the modules, a relaxation technique is used. This technique has similarities to day-to-day human learning.Using advanced computational methods, in particular parallel computing, it is now possible to run such a system for large metropolitan areas with 10 million inhabitants or more. This paper reports on such a simulation system for all of Switzerland. Our focus is on a computationally efficient implementation of the agent-based representation, which means that in fact each agent is represented with an individual set of plans as explained above. A database is used to store the agents' strategies, which are loaded into the simulation modules as required; the modules then feed back individual performance measures into the database. This approach allows that additional modules can be coupled easily, and without degrading computational performance.The set-up was tested for Swiss morning peak traffic. Hourly demand matrices were taken from work with the VISUM assignment package and converted to our needs. Routes were assigned via feedback learning using the agent data base. In other words, the current implementation uses a car-only versions of the modules (ii), (iii), and (iv). Resulting flow volumes are compared to the VISUM assignment results, and to field data.     

On the use of permanent symmetric scatterers for ship characterization

The symmetric scattering characterization method (SSCM) has been recently introduced for high-resolution characterization of certain targets under coherent conditions. SSCM is based on the Poincare/spl acute/ sphere representation, which supports a high-resolution decomposition of symmetric target scattering, as well as assessment and validation of the backscatter coherence. In this paper, the SSCM is investigated for ship characterization using Convair-580 polarimetric synthetic aperture radar (SAR) data. It is shown that the target Poincare/spl acute/ parameters permit identification of dominant scatterers with a significant symmetric scattering component. The polarization orientation angle of these quasi-symmetric scatterers is used to derive an estimate of the ship's pitch angle, under certain conditions. The effect of SAR system focus setting errors and Doppler centroid mistracking on the SSCM performance is investigated. It is shown that the SSCM is sensitive to the system focus setting and Doppler centroid shift. The first-order effects of these errors can be removed prior to the application of the SSCM method.     

A simple procedure for solid-phase synthesis of peptide nucleic acids with N-terminal cysteine

Problems were encountered during attempts to prepare N-terminal cysteine-substituted peptide nucleic acids (PNAs) from commercially available, Fmoc-protected monomers. These problems have been surmounted by the use of an S-t-butylmercapto protecting group on the cysteine moiety. The solid-phase syntheses are carried out via a simplified procedure which should be generally useful for manual PNA synthesis.     

Considerations for SAR image quantification unique to orbitalsystems

A discussion is presented of quantitative expressions required for the response of a synthetic aperture radar (SAR) to both point and distributed scatterers for purposes such as calibration and polarimetry. Image gains depend on the viewing geometry, which is unlike the flat Earth case, which often is assumed to apply in an orbital geometry. Image signal-to-noise ratio is dependent on footprint velocity, but the mean clutter-to-noise ratio for distributed scatterers is dependent on spacecraft velocity. When imagery of a distributed scene observed by an orbital SAR is to be calibrated by comparison to the impulse response of a reference point scatterer, for example, the velocity ratio enters the expression for peak power, but does not enter when an integral is used over the impulse response. The author also looks at the processing gain resulting from overlapping image pixels in azimuth through sampling of the pulse repetition frequency     

Spatial considerations in SAR speckle consideration

An approach to the simulation of synthetic-aperture-radar (SAR) image products is described that departs from most of the other simulation algorithms in the method of speckle generation. Speckle is prepared corresponding to the combination of the frequency weightings and look sum strategy of the radar processes desired and then multiplied by the source scene data preconditioned by the desired resolution. The method allows output pixel spacings to be specified independently of more fundamental system parameters. Typical results are presented for SIR-B images     

Acceptance of Assistive Technology by Special Education Teachers: A Structural Equation Model Approach

To investigate the acceptance of assistive technology (AT) by special education teachers, the present study developed and tested hypothesized relationships among key determinants of AT acceptance such as the facilitating condition, perceived ease of use, computer self-efficacy, result demonstrability, perceived usefulness, and behavioral intention. Results from analysis of data collected from a number of special education teachers in schools for the visually and/or auditory impaired confirmed the effects hypothesized in our conceptual model of AT acceptance. In particular, perceived usefulness was a dominant factor affecting AT usage. Facilitating condition was strongly related to perceived ease of use, whereas perceived ease of use had a significant effect on computer self-efficacy. This study also found the importance of result demonstrability factor, which had significant effects on both computer self-efficacy and perceived usefulness. This study expanded and enriched a traditional technology acceptance model by further investigating determinants associated with the acceptance of AT by special education teachers for the blind and/or the deaf. In addition, the results of the present study should provide some insights into the understanding of AT acceptance and the decisions of AT utilization, as well as its distribution and training.     

An Apparatus for Rapid Preparation of Oil and Oil-Free Meal from Brassica Seed

An apparatus for the rapid preparation of large numbers of oil and “oil-free” meal samples from Brassica seed is described. Batches of sixty 0.2 g to 2.0 g seed samples can be ground and solvent extracted simultaneously, followed by filtration, solvent washing and vacuum drying of the meal. The oil can be recovered quantitatively for gravimetric oil content determination.