A synthetic aperture microwave near-field system is used to image biophysical objects in order to investigate the nature of radar-target interaction. Two different imaging algorithms for focusing data collected over a two-dimensional planar aperture are investigated. The first of these is the single frequency backward propagation technique which is mathematically simple to implement and provides a high degree of resolution. Secondly, a multifrequency development of the backward propagation algorithm is presented and derived from two separate perspectives. This latter algorithm, known as the auto-focusing algorithm, requires no information about the range of the target from the aperture. Full characterisation by simulation of both algorithms is carried out and different filtering techniques are investigated. The backward propagation algorithm is applied to the polarimetric imaging of three different leafless trees and a sugar beet plant at the X-band frequency of 10GHz. The images so produced demonstrate that the backscattered signal is dependent on the orientation of individual tree elements with respect to the polarisation. Furthermore, multiple scattering terms can be identified within the structure of the tree. The auto-focusing algorithm is applied to the polarimetric imaging of two trees at 10GHz and repeat measurements are made over several months. As with the single frequency measurements, the backscattered signal is dependent on the orientation of individual tree elements relative to the polarisation. The relative contributions from the leaves and branches of the trees to the backscattered signal are assessed and found to be seasonally dependent. Measurements are also carried out to investigate the variation of backscatter from a beech tree with varying incidence angle. It is demonstrated that at small angles of incidence, the leaves are the dominant source of backscatter but at large incidence angles, the branches and trunk of the tree have the greatest contrbution.

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

As the communications industry continues to expand, two current trends are becoming apparent: the desire to support an increasing diversity of communications services, (voice, video, image, text, etc.), and the consequent requirement for increased network capacity to handle the expected growth in such multi-service traffic. This dissertation describes the design, performance and implementation of a high capacity switch which uses fast packet switching to offer the integrated support of mulit-service traffic. Applications for this switch are considered within the public network, in the emerging metropolitan area network and within local area networks. The Cambridge Fast Packet Switch is based upon a non-buffered, multi-path switch fabric with packet buffers situated at the input ports of the switch. This results in a very simple implementation suitable for construction in current gate array technology. A simulation study of the throughput at saturation of the switch is first presented to select the most appropriate switch parameters. Then follows an investigation of the switch performance for multi-service traffic. It is shown, for example, that for an implementation in current CMOS technology, operating at 50 MHz, switches with a total traffic capacity of up to 150 Gbit/sec may be constructed. Furthermore, if the high priority traffic load is limited on each input port to a maximum of 80% of switch port saturation, then a maximum delay across the switch of the order of 100 μsecs may be guaranteed, for 90% of the high priority traffic, regardless of the lower priority traffic load. An investigation of the implementation of the switch by the construction of the two fundamental components of the design in 3 μm HCMOS gate arrays is presented and close agreement is demonstrated between the performance of the hardware implementation and the simulation model. It is concluded that the most likely area of application of this design is as a high capacity multi-service local area network or in the interconnection of such networks.

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Three computer programs that are basic to the processing and development of tree -ring chronologies are now available. They were designed to refine and replace older programs that were previously furnished by the laboratory. Program RWLIST replaces program RWLST and is used for data inspection. Programs INDEX and SUMAC replace INDXA. INDEX is used for curve fitting procedures while SUMAC does summaries of series of indices, analysis of variance and cross-correlation. The new programs represent an increase in efficiency and flexibility in use. They are written in current ANSI Fortran IV and will be readily adaptable to most computing environments.

Skeleton plotting is an established manual technique for representing the relative narrowness of tree rings in a single radius. These plots can be used as a visual aid to crossdating. This paper describes a method for deriving these plots by computer. The method uses a low-pass digital filter, running means, and standard deviations of ring-width measurements. When the manual and computer plots are compared for the same series, approximately 85% agreement is found. Examples of results are presented for specimens from sensitive, moderate, and complacent sites. FORTRAN program listings are included for two subroutines for (a) identifying small rings and (b) producing the plot.

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No description available.