Spatiotemporal Averaging Research Articles

Retrieving sea surface salinity with multiangular L‐band brightness temperatures: Improvement by spatiotemporal averaging

The Soil Moisture and Ocean Salinity (SMOS) mission was selected in May 1999 by the European Space Agency to provide global and frequent soil moisture and sea surface salinity maps. SMOS' single payload is Microwave Imaging Radiometer by Aperture Synthesis (MIRAS), an L band two‐dimensional aperture synthesis interferometric radiometer with multiangular observation capabilities. Most geophysical parameter retrieval errors studies have assumed the independence of measurements both in time and space so that the standard deviation of the retrieval errors decreases with the inverse of square root of the number of measurements being averaged. This assumption is especially critical in the case of sea surface salinity (SSS), where spatiotemporal averaging is required to achieve the ultimate goal of 0.1 psu error. This work presents a detailed study of the SSS error reduction by spatiotemporal averaging, using the SMOS end‐to‐end performance simulator (SEPS), including thermal noise, all instrumental error sources, current error correction and image reconstruction algorithms, and correction of atmospheric and sky noises. The most important error sources are the biases that appear in the brightness temperature images. Three different sources of biases have been identified: errors in the noise injection radiometers, Sun contributions to the antenna temperature, and imaging under aliasing conditions. A calibration technique has been devised to correct these biases prior to the SSS retrieval at each satellite overpass. Simulation results show a retrieved salinity error of 0.2 psu in warm open ocean, and up to 0.7 psu at high latitudes and near the coast, where the external calibration method presents more difficulties.

The live, the dead, and the very dead: taphonomic calibration of the recent record of paleoecological change in Lake Tanganyika, East Africa

High-resolution (annual to decadal) paleoecological records of community composition can contribute a long-term perspective to conservation biology on baseline ecological variability and the response of communities to environmental change. We present here a detailed comparison of species assemblage characteristics (species richness, abundance, composition, and occurrence frequency) in live, dead, and recent fossil ostracode samples from Lake Tanganyika, East Africa. This study calibrates the fidelity of paleoecological samples (i.e., both death and fossil assemblages) to live diversity patterns for the purpose of reconstructing community dynamics through time. Both life and death assemblages were collected from rocky sites in a mixed substrate habitat (total of ten sampling visits over 22-month period) over spatial scales of less than a meter to about 3-12 meters. Fossil assemblages were derived from sediment cores collected in sandy substrates adjacent to the rocky sites. Species richness in paleoecological assemblages is comparable to that in a year's accumulation of life assemblages sampled approximately monthly. The temporal reso- lution of the fossil samples in Lake Tanganyika could thus be as short as one year. Species abun- dance distributions were statistically indistinguishable among data sets. Rank abundance tests demonstrated that death and fossil assemblages were quite similar, although life assemblages dif- fered substantially in the composition of their dominant species. Species composition differences between life and paleoecological assemblages appear to reflect the area of spatial integration rep- resented by an assemblage—i.e., death and fossil assemblages are integrated over multiple habitat types, whereas life assemblages dominantly represent the rocky habitats where they were collected. Species occurrence frequencies in paleoecological data identified ecologically persistent species and may be useful for delimiting local species pools. Analysis of sampling efficiency indicates that approximately 28% of species in each paleoecological assemblage are ''unique''; i.e., they are not likely to be present in an additional subsample from the same sample. Ordination reveals that life assemblages of ostracodes are characterized by high spatiotemporal heterogeneity. Variability in species composition was lower in paleoecological assemblages, presumably as a result of spatial and temporal averaging. Death and fossil assemblages of Lake Tanganyika appear to preserve many characteristics of liv- ing benthic ostracode assemblages with high fidelity. Spatiotemporal averaging allows paleoeco- logical assemblages to render information about the average composition of ostracode communities over short timescales, at spatial scales of several meters, and across habitat types. Sampling shell assemblages in surficial sediments thus represents a more efficient way of assessing the average ecological conditions at a locality than repeated live sampling. Furthermore, paleoecological anal- yses can generate novel insights into long-term community variability and membership with direct relevance to conservation.

Alignment of CS2 in intense nanosecond laser fields probed by pulsed gas electron diffraction

A pulsed gas electron diffraction apparatus was developed and applied to investigate an alignment process of molecules in intense laser fields. A two-dimensional (2D) electron diffraction pattern of jet-cooled CS2 in intense nanosecond laser fields (1064 nm, ∼0.64 TW/cm2, 10 ns) was measured using short-pulsed 25 keV electron beam packets (∼7 ns) generated by irradiating a tantalum photocathode with the 4th harmonics of pulsed YAG laser light. The observed anisotropic 2D diffraction pattern was analyzed quantitatively by taking into account the spatio-temporal distributions of the laser pulses, the electron beam packets, and the molecular beam through a numerical simulation of the observed diffraction pattern. The anisotropy of the spatial distribution of molecular axes of CS2 in the laser polarization direction is accounted for by the effect of the intense laser fields. Considering the spatio-temporal averaging effect, the temporal pulse width of an electron packet required for real-time probing of the alignment process of molecules in intense nanosecond laser fields is discussed. A numerical simulation of temporal and spatial profiles of an electron packet is also performed to examine conditions for generating sub-picosecond ultrashort electron pulse for real-time probing of ultrafast molecular dynamics by the pulsed gas electron diffraction method.

Generation of scalp discharges in temporal lobe epilepsy as suggested by intraoperative electrocorticographic recordings

OBJECTIVESTo study the variability, topography, polarity, duration, and incidence of interictal epileptiform discharges (EDs) in the scalp EEG and electrocorticogram (ECoG) from 16 patients with temporal lobe epilepsy who underwent...

Hierarchical HDTV/SDTV compatible coding using Kalman statistical filtering

This paper addresses the issue of hierarchical coding of digital television. A two-layer coding scheme is presented to provide compatibility of standard-definition television (SDTV) and high-definition television (HDTV). The scheme is based on a spatio-temporal pyramid coding technique. We address the problem of interlaced-to-interlaced two-layer compatible coding where both layers are interlaced. The resolution translation is important for the visual quality of the SDTV layer and for the performance of the HDTV layer. A motion-compensated up/down deinterlacing scheme is used to improve the performance. A spatio-temporal averaging technique is used to give a better compatible prediction so that the HDTV layer has a high compression performance. To offer an improved prediction, systematic analysis of the remaining statistical redundancy of the enhancement signal is conducted. Based on an autoregressive model of the difference signal, a Kalman statistical filtering is used to exploit such a redundancy. We combine a recursive filtering and discrete cosine transform (DCT) coding using QR decomposition, where Q is an orthonormal matrix and R is an upper triangular matrix. The error accumulation is cancelled in the DCT frequency domain. The results show peak signal-to-noise-ratio improvements over simulcast as high as 1.2 dB. The new technique, which is referred to as spatial scalability using a Kalman filter (SSKF), achieves a comparable or better picture quality than that of a nonscalable approach for high-quality video coding. The near optimal performance is demonstrated by the white Gaussian noise property of the residual signal.

A model for pitch perception of short FM tones.

Over-all pitch, which is defined here as a steady pitch of frequency modulated tones other than a dynamic pitch change, may be perceived through a certain auditory spatiotemporal averaging mechanism. On this line, a model for determining over-all pitch of short FM tones was presented. The model constitutes the central feature that the frequency corresponding to over-all pitch is the one locating on a single maximum of the weighted excitation pattern at the burst end of FM tone; the weighting is larger to the portion of FM tone closer to its burst end. Applying a single tuned characteristic as the excitation pattern and an exponential decay type of weighting function to the model, some calculations were compared with the results from the pitch-matching experiments for four different types of frequency change. The agreement between the calculations and the measurements was generally good.

Spatio-temporal averaging and the dynamic visual noise stereophenomenon

When dynamic visual noise (D.V.N.) is viewed binocularly under conditions where the noise display brightness for one eye differs from that for the other, the noise appears to divide into laterally streaming planes that are separated in depth. The aim of this paper is to confirm that spatio-temporal averaging plays a role in this D.V.N. stereophenomenon. It is proposed that the duration of spatiotemporal averaging for this effect is at least 100 msec. If this is so, for a given noise density, the subjective appearance of the streaming noise planes should be independent of presentation frame rate A Raster display consists of a grid made up of a descending series of near-horizontal lines which are scanned by an electron beam. The beam scans across each line and then returns to the beginning of the line below it, which in turn is scanned. After the complete raster grid has been covered, the beam returns to the top line and repeats the sequence. In such a display “frame rate” is defined as the frequency at which the electron beam scans past any given point. (In order to avoid flicker, television receivers use “half-frames” in which half of the grid lines are scanned at the first pass and the other half are scanned at the second pass. In this paper the words “frame rate”, when applied to a television receiver, are used to describe the rate at which half-frames are scanned). The noise is created by modulating the strength of the electron beam. As soon as the beam passes a point, the brightness of that point will begin to decay; at no point is the entire screen uniformly illuminated. Thus terms such as onset and offset are not particularly meaningful in this case. In a point-to-point plot the noise is presented randomly on a two-dimensional matrix. Both the vertical and horizontal positions of the electron beam (and hence the noise dot) are changed randomly. In this case “frame rate” is a meaningless term.