Microphysics of Cosmic Plasmas: Hierarchies of Plasma Instabilities from MHD to Kinetic

In this article, we discuss the idea of a hierarchy of instabilities that can rapidly couple the disparate scales of a turbulent plasma system. First, at the largest scale of the system, L, current carrying flux ropes can undergo a kink instability. Second, a kink instability in adjacent flux ropes can rapidly bring together bundles of magnetic flux and drive reconnection, introducing a new scale of the current sheet width, ?, perhaps several ion inertial lengths (δ _i ) across. Finally, intense current sheets driven by reconnection electric fields can destabilize kinetic waves such as ion cyclotron waves as long as the drift speed of the electrons is large compared to the ion thermal speed, v _D ?v _i . Instabilities such as these can couple MHD scales to kinetic scales, as small as the proton Larmor radius, ρ _i .     

Estimation Using Stochastic Feedback with Applications to Integrated Navigation Systems

This paper discusses an approach to linear estimation through use of a "control" fed back into the system to cancel out the effect of disturbances or error signals. Although this approach has very restricted application, it has found important usage in integrated navigation systems where one subsystem is an inertial measurement system. This approach is shown to be suboptimal and is compared with the optimal with respect to estimation accuracy and sensitivity to modeling errors. The feedback approach to estimation is shown to be similar to error estimation and correction in which the error states of the system are estimated and external correction applied. For discrete estimation using the feedback approach it is shown that error variance and Kalman gains for one-stage prediction should be used. Two examples are considered which compare the feedback approach to the optimum estimation approach. The system of the first example is quite simple, but provides simple analytical comparisons of the two estimation approaches. The second example system consists of a single-axis inertial guidance system and an independent position measuring system. Accuracy and sensitivity to modeling errors are compared. Other advantages and disadvantages of the two estimation approaches are discussed.     

Synthetic Aperture Processing with Limited Storage and Presumming

The number of transmitted pulses associated with the Doppler histories of a side-looking radar may greatly exceed the desired azimuth compression ratio of the system. This discrepancy is taxing if the storage required for the azimuth processing is provided by cores, magnetic drums, and the like. Thus, as a practical matter, one considers presumming of the data prior to correlation in an attempt to achieve the desired performance with a minimum amount of digital storage. In this paper, the optimum (in terms of resolution) presummer is derived, along with the optimum apportionment of the available storage capacity between the presumming and correlation operations. Under the condition (or generally pessimistic approximation) that the illumination pattern of the antenna uniformly illuminates a Doppler bandwidth equal to the PRF of the radar, the optimum presumming coefficients are the first Np Fourier coefficients of a function which is one of the Doppler bandwidth to be correlated and zero on the remainder of the PRF bandwidth, where Np is the number of transmitted radar pulses over which presumming is provided. Increasing Np reduces the degradation due to presumming, but may leave inadequate storage for correlation. Hence, we optimize the apportionment between the two operations and present the obtainable resolution as a function of total storage and the number of transmitted pulses in the received Doppler history.     

Multiple sensor geocoded data

The problem of integrating remotely sensed images acquired from different sensor systems is primarily associated with their registration into a common reference projection. This registration problem has to be considered not only between the image data themselves but also with other data already existing in various geographical data bases.The advent of the second generation of earth observation satellites is emphasizing this situation by providing imagery in different geometric configurations. Images will be acquired from many sensors at different spatial resolutions (LANDSAT MSS and TM, SPOT HRV MLA and PLA) on different dates and modes (panchromatic, multispectral, nadir and off-nadir).In order to provide image data in a geometric format compatible with the Canadian National Topographic System, Canada is developing a Multi-Observational Satellite Image Correction System (MOSAICS) that will provide geocoded data resampled into a common reference projection. This paper presents the characteristics of the geocoded products with examples from multiple sensors and different dates, and addresses the processing requirements of the satellite ground station. It also illustrates the use of digital processing techniques to derive digital elevation information from geocoded stereo imagery.     

Civilizations and Sea Level Change

Climate and sea level changes have been relatively stable for the last few centuries. The delicate balance between global and oceanic systems, however, may be altered due to the increased warming of the earth's average surface temperature. A few degrees increase could cause a 15-17 cm sea level rise by the year 2000, resulting in wide spread flooding of low lying areas. Recent studies indicate the global sea level is rising and extensive coastal flooding is anticipated. If these changes continue through the next century, we may be faced with a loss of our present culture. Oscillating sea levels since the late Pleistocene at times have left the floors of the continental margins and inland seas exposed, increasing the total earth's land surface by 8%. It was during these events that North America and island refugia including England, Indonesia, Japan and Australia were invaded and colonized by man. However, the swinging sea levels and shoreline displacements of as much as 120 m per year must have been very disruptive to the inhabitants of the coastal region and evidence of their cultures must have eroded away due to the relentless cycle of the coastal processes.     

Space and ESDP—a growing partnership?

The ‘European satellites for security’ conference was held in Brussels, 18–19 June 2002, at a time when interest in the military use of outer space was clearly growing. But doubts remain as how to far such interest will be translated into action. This article reports on some of the impressions gained at the conference.     

Active polar gullies on Mars and the role of carbon dioxide

The detection of geologically recent channels and gullies on Mars has been interpreted as evidence for recent water activity on this arid and cold planet. The presence of active water would have considerable implications for the history of Mars and for the potential for an active near-surface biota; however, water is not the only substance that can flow and may actually be one of the least likely candidates when the modern permafrost environment is considered. Here, a key site of recent gully and channel development on Mars is reported at 71 degrees S in Sisyphi Cavi, within the annual zone of polar CO2 ice and snow accumulation. Superposition of channel features over and/or through the defrosting CO2 snowpack shows that the channels are active at the present day and probably have fluid flows every spring during the annual defrosting. In itself, this is a significant observation as active fluid flows of any nature have not yet been proven on Mars. However, the ambient temperature at the time of gully activity appears to require a role for CO2 in the formation of the channels, rather than water. A model is proposed for gas-lubricated flow in the channels based on avalanching of CO2 snowpack and clastic debris. If similar mechanisms are responsible for all the recent gullies on Mars, then perhaps no near-surface astrobiological targets are available.