Unequal switching delays in binary cross-correlation experiment:†

The use of pseudo-random binary sequences (p.r.b.s.) as system input perturbations has become standard practice in the field of identification. Normally, cross-correlation between input and output yields the system impulse response. This is not so if the actual input is a distorted p.r.b.s., the distortion taking tho form of unequal switching delays. This paper describes a theoretical approach which allows calculation of the effects of such distortion on the impulse response estimates. Using these results, a method is devised to remove the effects of a second typo,of distortion, i.e. that which results from unequal input transdvicer time constants. The proposed method allows the removal of secondary peaks but results in increased distortion of parent peaks. A second method, using inverse-repeat sequences, is also investigated. Simulation results are included.     

Peat resource mapping in Lewis using remote sensing techniques and automated cartography†

Abstract

The application of methodology developed for peat resource survey has illustrated the usefulness of multi-level and multi-band aerial photography in classifying Landsat multispectral imagery. Ground truthing to characterize the thematic maps plotted from the aerial photography and Landsat imagery was based primarily on vegetation surveys. The results of this work are illustrated with a series of maps and photographs and the usefulness of the approach is assessed.     

Unity and non-unity feedback: a comparison†

The paper compares the unity feedback with the non-unity feedback servo problem from the point of view of sensitivity and the minimum order of the realization. It is proved that the non-unity feedback solution has smaller sensitivity ‘on the band of interest’ and that the ‘dimension’ (defined in a precise sense) of the non-unity feedback solution is never smaller than that of the unity feedback solution.     

The relation between reflected radiation and yield on the Broadbalk winter wheat experiment†

Abstract

In the classical experiment on Broadbalk field, Rothamsted, winter wheat has been grown continuously under various treatments since 1843. Reflected radiation in red (R) and near-infrared (NIR) wavebands was measured over the field in 1987, twice with an airborne multispectral scanner (MSS) from an altitude of 600m and five times with a muhiband radiometer from 2 m above the crop surface. The normalized difference vegetation index, NDVI= ( NIR?R)/ (NIR + R), was calculated for each date and its relation with harvest yield investigated.

The NDVI determined from the airborne MSS data was correlated with yield, and the correlation was found to increase if the variable effect of productivity was introduced into the relationship. The NDVI values calculated from the ground radiometry were more strongly correlated with yield, however. The differences in yield on Broadbalk are caused mainly by the amounts of nitrogen-containing fertilizer applied. The results suggest that the radiation measured by airborne MSS can give a rough guide to yield and nitrogen nutrition, whereas ground radiometry could be used to predict yield and potential deficiencies of nitrogen.     

Feedback information rate and entropy in a discrete system†

A multi-state deterministic system controlled via a noisy Binary Symmetric Channel (BSC) is modelled by an equivalent Markov chain. The system performs a random walk whose mean deviation from zero is numerically equal to the expected number of steps between zero crossings, and whose entropy is equal to the average amount of transmitted control information between zero crossings. Simple expressions are found for the received control information and for the mutual information via the BSC.     

Expanded subalphabets in the theories of languages and semigroups†

A new type of code, called an expanded subalphabet, is introduced. It is shown that the following four conditions on a subset L of the free monoid A ^? over a finite or infinite alphabet A are equivalent: (1) L is the submonoid generated by an expanded subalphabet; (2) L is a retract; (3) L is the fixed language of an endomorphism; (4) L is the stationary language of an endomorphism. Expanded subalphabets are used as a tool for the investigation of fixed languages (=retracts). Special results for the case of a finite alphabet are given and the relationship with the theory of L-systems is indicated.     

Continuous localization and mapping of a pan–tilt–zoom camera for wide area tracking

Pan–tilt–zoom (PTZ) cameras are well suited for object identification and recognition in far-field scenes. However, the effective use of PTZ cameras is complicated by the fact that a continuous online camera calibration is needed and the absolute pan, tilt and zoom values provided by the camera actuators cannot be used because they are not synchronized with the video stream. So, accurate calibration must be directly extracted from the visual content of the frames. Moreover, the large and abrupt scale changes, the scene background changes due to the camera operation and the need of camera motion compensation make target tracking with these cameras extremely challenging. In this paper, we present a solution that provides continuous online calibration of PTZ cameras which is robust to rapid camera motion, changes of the environment due to varying illumination or moving objects. The approach also scales beyond thousands of scene landmarks extracted with the SURF keypoint detector. The method directly derives the relationship between the position of a target in the ground plane and the corresponding scale and position in the image and allows real-time tracking of multiple targets with high and stable degree of accuracy even at far distances and any zoom level.     

On a method of Porter in the eigenvalue assignment problem†

In a recent article in this Journal, Porter (1969 a) described a simple and attractive alternative procedure for synthesizing a linear feedback control law which will realize a certain pre-selected closed-loop eigenvalue pattern for a linear dynamical system. The purpose of the present note is to investigate the conditions for applicability of Porter's method. In addition, another method is proposed.     

Improving geological mapping in the Arabian Shield using Landsat Thematic Mapper imagery—Jabal Duhayyah area

Abstract

The Jabal Duhayyah area spans the contact between two tectonic zones of the southern Arabian Shield. By utilising principal components analysis of the Landsat-TM data, it was easy to locate this contact precisely as well as to improve and update available geological maps. Previously unmapped lithologics were distinguished and mapped during the processing of the images. Field-checking confirmed these findings and a new geological map was constructed.

Satellite imagery (e.g. Landsat) could be a valuable mapping tool in the well-exposed Arabian Shield, even where it is already mapped at the 1:100000 scale.     

Gap-singular systems: definition and consequences in trajectory planning†

This article introduces the concept of gap-singularities to underline particular phenomena related to the choice of the outputs in some non-linear systems. It is shown that, when bounds on the variables are considered, this property induces a topological isolation of the gap-singular trajectories in the outputs domain. In the context of differentially flat systems, a procedure to detect gap-singularities is provided because it is related to the existence of a singularity of flatness. The examples that are presented in this article show that taking gap-singularities into account can improve some trajectory planning algorithms based on an optimal control approach like in the Nonlinear Trajectory Generation software.     

Optimization of system reliability: a survey of problems and techniques†

The paper provides a survey of the work performed over the last two decades on the system reliability optimization. The relevant system models are first given and a set of problems, covering most cases, are formulated. Then, the optimization techniques, used for solving these problems, are briefly described, and a number of representative illustrative examples are collected. It is hoped that the paper helps in obtaining a global view of the state of art of the field of optimal reliability design.     

Mean and variance of the arc length of a Gaussian process on a finite interval†

The first and second moments of the distribution function of the arc length of a Gaussian process on a finite interval are obtained in terms of the covariance function of the derivative process. A closed expression (in terms of a modified Bessel function) was obtained for the first moment; however, the second moment had to be evaluated numerically. Numerical calculations were carried out for three typical covariance functions.     

Depth resolved detection of oceanographic variables in the St. Lawrence estuary using a laser fluorosensor: instrument characteristics and first results†

A 64-channel Laser Environmental Airborne Fluorosensor (LEAF) system for sea surface oil detection was modified for continuous depth-resolved detection of gelbstolT and chlorophyll a spectral fluorescence, and water Raman scattering. The system was successfully tested during shipborne and airborne experiments in the St. Lawrence Estuary. System performance was studied, and the best integration time to optimize the signal to noise ratio (S/N) was determined using dilTerent statistical procedures such as the geophysical and robust statistical methods. In general, raw data indicated S/N of about 150, 10, and 4 for Raman. gelbstolT and chlorophyll a signals, respectively. Results with calibrated LEAF spectra clearly indicated that, with this system, water Raman scattering, geibstolT and chlorophyll a signals could be detected down to a maximum depth of 4·8 m. Spatial distribution of these quantities compared well with simultaneously observed ill Silll structure of oceanographic variables, such as, underwater light attenuation, salinity and chlorophyll a fluorescence. In the perspective of modelling primary production in coastal and estuarine waters in the St. Lawrence system (Case II waters), the utilization of LEAF should provide an adequate representation of the spatial and temporal variation pattern of oceanographic variables, at scales between those from ships and satellites.     

The effect of parameter variation on the periodic oscillations in a non-linear system†

The effect of parameter variation on the periodic oscillations in a non-linear control system is discussed analytically and the concept of root-locus has been introduced to analyse the different dominating modes of oscillation. The theoretical formulation is based on the fact that the transient behaviour of a non-linear system, in the vicinity of the steady-state oscillation, is described by a linear differential equation with periodic coefficients.     

Centres for space science and technology education: a United Nations initiative†

The availability of environmental and Earth resources data acquired by satellites can assist all countries to gain a better understanding of how to safeguard their environment as well as ensure a more efficient management and productive harnessing of their natural resources, However, in order for the developing countries to share in the benefits inherent in remote sensing technology and in programmes related to environmental information systems, particularly through their participation in international, regional and national programmes and projects, there must be an adequate and long-term commitment to and an investment in the development of skills and knowledge in the discipline at the local level. This article focuses on the United Nations initiative to establish regional Centres for Space Science and Technology Education which should provide a unique opportunity for the development of such an indigenous capability. These Centres have the potential to contribute significantly to the implementation of the recommendations of the Rio Conference, otherwise known as Agenda 21 and to the successful execution of the programme of activities of the user communities in the developing countries.     

Applicability of the Mix–Unmix Classifier in percentage tree and soil cover mapping

The Mix–Unmix Classifier is a simple novel method developed to address the problem of under‐determination in linear spectral unmixing. This paper tests the applicability of the Mix–Unmix Classifier in percentage mapping of tree cover and different soil types from single bands of satellite imagery. Various transformations were executed on African Moderate Resolution Imaging Spectroradiometer (MODIS) data bands 1, 2, 3, 4, 6 and 7. The equatorial rainforest is most distinguishable under skewness. The skewness transformation band is unmixed into two endmembers: tree (endmember of interest) and non‐tree (background). The resulting percentage tree cover map was compared with a University of Maryland percentage tree cover map of the continent, giving a correlation coefficient of 0.87. Fraction images of three soil types were generated from Japanese Earth Resources Satellite (JERS) synthetic aperture radar (SAR) L‐band data covering a section of Jordan. The soil types considered were hardpan topsoil, Qaa topsoil, and topsoil of herbaceous layer. The correlation coefficients of the Mix–Unmix Classifier‐derived fraction images versus reference fraction images for the three soil types were 0.89, 0.87 and 0.89, respectively.     

Functional relationships between the conventional steady-state error characteristics and the weighting matrices in the quadratic performance index†

The requirements for achieving a desired value of steady-state error for an optimal control system utilizing the quadratic performance index with a linear plant arc derived for step, ramp and parabolic inputs. These requirements result in a number of the elements of the Riccati matrix being specified in terms of known parameters. It is shown that for an all-pole plant the control system cannot follow a parabolic input. For the stop input the q ₁₁ element of the Q matrix is specified as one for an all-pole plant or in terms of the fixed plant parameters for a pole-zero plant. Depending on the number of requirements and the order of the system it may be necessary to assume values for the remaining elements of the Q matrix in order to solve the reduced Riccati equation.     

Simultaneous determination of the optimal production–inventory and product inspection policies for a deteriorating production system

In this paper, we attempt to find a method for the optimization of production–inventory and product inspection policies for deteriorating production systems. Taking advantage of the nature of a deteriorating production system, a strategy would be not to inspect the first s items of the batch. Therefore, an inspection policy which disregards the first s (DTF-s) items of the batch is proposed. Under the DTF-s policy, we do not inspect the first s produced items but inspect only those items from the (s+1)th till the end of the production run. The objective of this study was the joint determination of the production lot size and the inspection policy s, resulting in a minimization of the expected average cost per unit time. Based on this model, the underlying conditions necessary for the existence of an optimal policy are given. Two commonly used inspection strategies, no inspection and full inspection are discussed. Under both inspection strategies, an optimal production–inventory lot is bounded by the traditional economic quantity. The case of full inspection is shown to be an extension of previously reported results. The option of investing in the process of quality improvement is also discussed. Finally, numerical examples are given to illustrate the method and its advantages in the conclusion.Scope and purposeThis paper considers the relationship between production, inventory and inspection in a deteriorating production system which may transit from the “in-control” state to the “out-of-control” state after a period of operation. Once the transition to the “out-of-control” state has occurred, it is assumed that some percentage of the items produced are defective or of substandard quality. However, in many cases, defects in a defective item can only be identified by an inspection process which carries an inspection cost. Those inspected items which are found to be defective are reworked at some cost before being shipped. On the other hand, defective items which are not inspected will be passed to the customer, incurring a much larger warranty cost. In order to operate such a system economically, tradeoffs among production setup, inventory, inspection and defective cost must be analyzed. Deterioration of the production system is an inherent process in all manufacturing industries. An understanding of the relationship among production, inventory and inspection for such systems will help managers to maintain efficient and economic control of operations.