关于莫斯科人质事件中的化学武器

对贵刊所登载之“化学武器解决了莫斯科人质事件”一文．笔者有几点不同意见提出，以下供诸乍先生指教参考。     

Pseudotransfer Function to Characterize a Hard Limiter

Results are reported on the attempt to define a pseudotransfer funtion of a circuit composed of a 2-pulse canceler and hard limiter.     

Interference Canceler Array with Reference Generating Loop

Adaptive arrays utilizing an internally generated reference signal to drive least mean square (LMS) weight determining loops have experienced difficulty arising from phase shifts induced by the reference generating circuits. The phenomenon observed is that the expected value of the weights oscillate in the steady state modulating the incoming signal. A scheme is reported which avoids this problem. It differs from earlier methods in that the reference generator has no infinite limiter so that the amplitude of the reference is not constant and in that one element is left unweighted. Alternative schemes were considered wherein the reference signal is drawn from all the array elements or from the weighted elements only. Only the latter is fully reported here, and is found superior. It is shown that in the presence of a desired signal and independent element noise, the processing scheme proposed produces weights whose expected values converge to a constant nonoscillatory state provided certain mild constraints are satisfied. In particular, if a cos ? ? 1, a being the gain and ? the phase shift of the filter in the reference generator, the weights converge. In addition, the steady state signal-to-noise power ratio (SNR) is determined. It is found that with a cos ? close to unity the SNR is that of an (N-1) element array coherently combined, where N is the number of elements. The SNR falls off with departures of a and ? from 1 and 0, respectively, but not drastically.     

Steady-State Noise Reduction Factors for the Exponential Filter

A technique is presented using state notation for deriving the steady-state noise reduction factors for an exponential filter. The technique is carried through to derive those factors for the third-order exponential filter.     

Evaluation of LANDSAT image data for land-use mapping

A computer aided extraction of land-use information from LANDSAT image data, gathered on 9 August 1975, was conducted. Specifically the study was designed to develop a method for supervised multispectral classification of LANDSAT data of a central European region and to verify the classification results on a pixel-by-pixel basis and by comparison of the land-use inventory with aerial photo interpretation in test areas. The method enables the integration and processing of additional data. For the test area Speyer in the Rhine valley with small size allotments and a variety of land-use it was found that the pixel-by-pixel comparison is rather difficult and has a high potential failure rate. Seven classes were considered. With the integration of subclasses to main classes higher classification accuracy can be reached.The highest classification accuracy could be obtained for agricultural land (97%); orchards, pasture (91%) and coniferous forest (84%) in the land-use inventory of Speyer.The study confirms that the degree of fit rises with the size of homogeneous land-use zones. The study results yield that for larger areas of homogeneous land-use in central Europe this method will reach acceptable classification accuracies for land-use inventories. The land-use information can be presented in colour coded thematic maps with the same scale and projection of existing maps.     

Regenerative hybrid arrays for interference suppression

The authors propose two regenerative hybrid adaptive arrays in which a self-generated reference signal is obtained through a detection-modulation procedure from the array output. The proposed arrays do not depend on spectrum spreading and are therefore applicable when this feature is not available. It is shown that at steady state the performance of these regenerative hybrid arrays is approximately the same as that of a hybrid array with a perfect reference signal. As to transient behavior, these arrays are shown to converge if the available imperfect steering vector can result in a few dB output signal-to-interference-plus-noise ratio with the self-generated reference disabled     

An Adaptive Interference Canceling Array Utilizing Hybrid Techniques

The steady state properties of an adaptive array utilizing prior knowledge of both approximate signal arrival direction and signal characteristics are presented. The method combines the features of a directionally constrained array and an array with a self-generated reference signal. Explicit results are obtained for output signal, interference, and noise powers assuming a single interferer is present. The inclusion of a self-generated reference circuit is shown to reduce the sensitivity to pointing error typical of arrays utilizing a zero order directional constraint, the improvement being a consequence of the reduction of the desired signal component fed back to the sidelobe canceling circuit. A relationship between the degree of sensitivity reduction and the quality of the reference signal is developed. Results of computations of signal to interference plus noise ratios for a 7-element 10-wavelength nonuniformly spaced array as a function of pointing error are presented. These results show the behavior with one interferer inside and outside the beamwidth of the quiescent array and with multiple interferers for various degrees of perfection of the reference generating circuit. In all cases the computations confirm that the otherwise severe effects of small pointing errors are substantially reduced.