Data-dependent sampling of two-dimensional signals

Samples taken at scattered points of a finite-support two-dimensional signal can be interpolated to recover an approximation of the original signal. Given a bound on the number of samples, where should they be placed to enable the most accurate reconstruction? Or, given an error bound for the reconstruction, what is the minimum number of samples required, and where should they be placed? In this paper we introduce search schemes that provide good candidate solutions to these problems, for digital signals. Natural Neighbour Interpolation is used in iterative sample removal and movement processes to obtain sparse sample patterns. For pictures and Digital Elevation Models, fewer samples are required if the interpolant is onlyC ⁰ continuous at the data sites, than if it isC ¹. Retained samples lie on the ridges and valleys of the laplacian.     

Detection and monitoring of algal blooms using SeaWiFS imagery

Abstract

The study presented here is a part of an attempt to improve the operational algorithm used at the Centre de Météorologie Spatiale (CMS) to calculate Sea Surface Temperature (SST) from Advanced Very High Resolution Radiometer (AVHRR) data. The errors produced by SST retrieval algorithms are analysed through two experiments: an examination of the errors calculated on a validation file and an analysis of the temperatures of oceanic cloud-free areas seen under two distinct satellite zenith angles (θ) for consecutive night-time orbits. This Letter presents the part of the study dedicated to the effect of large viewing angles on the retrieval of SST. Correction terms are proposed and compared, on the same set of data, to split window algorithms using θ dependent coefficients     

The cluster scanning system

Users with severe physical impairment often use computers with one or two switches using a scanning system. Scanning is a technique of successively highlighting portions of screen. This paper presents a new scanning system that works through clustering screen objects. The system is initially calibrated through simulation and later validated through a user trial. Results show that it outperforms existing block scanning systems.     

Spectral Response Model of Backside-Illuminated HgCdTe Detectors

Backside-illuminated HgCdTe detectors fabricated on thick CdZnTe substrates have an optical path such that the incident radiation traverses the antireflection (AR) coating layers, the thick CdZnTe substrate, and finally the different layers of the detector. Modeling the spectral response first involves a coherent calculation of the transmission and reflection of a multilayer AR coating on the backside of the CdZnTe substrate. Second, a coherent calculation is made of the reflection and transmission coefficients for the stack of detector materials including wavelength-dependent complex refractive indexes for the detector materials. Third, the transmission and reflection coefficients are then used in an incoherent calculation to account for the multiple reflections in the thick CdZnTe substrate. For the coherent calculations, a stack matrix is constructed from the multiplication of matrices that track the phase and amplitude of the waves propagating across interfaces and from one side of a layer to the other side. These calculations are combined to compute the spectral response and reflectance of the detector as a function of wavelength.