Earth observation data archiving in the USA and Europe

The growing number of Earth observation satellites are producing exponential increases in the amount of data produced. These data sets contain valuable information on the state of the environment to accurately monitor and predict the impact of global change. Global change investigations require access to long-term data. This paper is a review of the current archiving practices of NOAA, NASA, SPOT, ESA and the DLR. It is demonstrated that despite recognition at a regional and organisational level of the importance of data archiving much work remains to be done. Funding responsibility is identified as a particularly problematic area of data archiving: it is an issue along with the need for easy accessibility and adequate metadata that will need to be resolved to ensure that future generations have access to adequate Earth observation data archives.     

Intermediate-term periodicities in relativistic solar electron fluences during solar cycles 22 and 23

In this paper, we have investigated the intermediate-term periodicities of the relativistic (E > 10 MeV) solar electron flares measured by IMP-8 satellite of NASA for the time period of 1986–2001. This period of investigation includes the entire solar cycle 22; ascending, maximum and a part of descending phase of the current solar cycle 23. To determine accurately the occurrence rate of electron flux, we have employed three different spectral decomposition techniques, viz. fast Fourier transformation (FFT); maximum entropy method (MEM) and Lomb–Scargle periodogram analysis method. For solar cycle 22, in the low frequency range, power spectrum analysis exhibits statistically significant periodicities at ∼706, ∼504 and ∼392 days. In the intermediate frequency range, we have found a series of significant periodicities ∼294, ∼221, ∼153, ∼86, ∼73 and ∼66 days. For short term, periodicities of ∼21–23, ∼31 and ∼37 days were found in power spectrum. When solar cycle 23 is considered the significant periodicities are ∼20, ∼23, ∼29, ∼39, ∼54, ∼63, ∼118, ∼133 and ∼154 days. These results provide evidence that the best known Rieger period (∼153 days), appeared in the high energetic electron flux data for cycle 22 and also likely during maxima of cycle 23. The existence of these periodicities has been discussed in the light of earlier results.     

GPS code and carrier multipath mitigation using a multiantennasystem

Multipath is a major source of error in high precision Global Positioning System (GPS) static and kinematic differential positioning. Multipath accounts for most of the total error budget in carrier phase measurements in a spacecraft attitude determination system. It is a major concern in reference stations, such as in Local Area Augmentation Systems (LAAS), whereby corrections generated by a reference station, which are based on multipath corrupted measurements, can significantly influence the position accuracy of differential users. Code range, carrier phase, and signal-to-noise (SNR) measurements are all affected by multipath, and the effect is spatially correlated within a small area. In order to estimate and remove code and carrier phase multipath, a system comprising a cluster of five GPS receivers and antennas is used at a reference station location. The spatial correlation of the receiver data, and the known geometry among the antennas, are exploited to estimate multipath for each satellite in each antenna in the system. Generic receiver code and carrier tracking loop discriminator functions are analyzed, and relationships between receiver data, such as code range, carrier phase, and SNR measurements, are formulated and related to various multipath parameters. A Kalman filter is described which uses a combination of the available information from the antennas (receivers) in the multiantenna cluster to estimate various multipath parameters. From the multipath parameters, the code range and carrier phase multipath is estimated and compensated. The technique is first tested on simulated data in a controlled multipath environment. Results are then presented using field data and show a significant reduction in multipath error     

Earth observation and UK science policy

This paper examines the way in which Earth observation is linked to UK science policy through the 1993 UK science White Paper and subsequent policy statements, and how the central theme of partnership has been developed in practice. An example of crop yield prediction is given to illustrate the strengths and the weaknesses of the approach. The UK science and space strategies are set in the context of the European Strategy for Space and links are made to the US global change research strategy.     

Modelling the neutral gas environment of comets with special application to P/Halley

A technique has been developed which allows relatively accurate modelling of cometary gas production from nothing more than a visible light curve. Application to P/Halley suggests the production rate of parent molecules will be about 2.6 × 10²⁹ per second on March 10, 1986, for example. The uncertainties and intrinsic limitations in this approach are outlined. The theory is then extended to predictions of abundance of other gaseous species, and a photometric model of these gases provided. Combined with the dust model of N. Divine, preliminary predictions of the luminance of P/Halley as seen in any direction from inside the coma or outside can be provided for λλ3000–7000.     

Phase Detector Response to Noisy and Noisy Fading Signals

Transfer characteristics of sinusoidal, triangular, and sawtooth-type phase detectors in response to noisy and noisy fading signals have been studied in detail. A new analytical model of the swatooth-type phase detector has been suggested. Detailed experimental results have been supplemented in support of the theoretical findings. Both the theoretical findings and the experimental results clearly indicate that the superiority of a sawtooth-type phase detector over the other two varieties is completely lost in noisy and noisy fading environments.     

Microelectronics effects as seen on CRRES.

A MicroElectronics Test Package (MEP) measured total dose degradation and single event upsets (SEUs) on 60 device types on the Combined Release and Radiation Effects Satellite (CRRES) in an 18 degrees inclination orbit between 350 km and 36000 km from July 1990 to October 1991. Simultaneous measurements of the high energy particle environment were used to make a direct cause and effect comparison of the energetic particle backgrounds and microelectronic performance characteristics. The galactic cosmic ray background for the period of the CRRES mission was at a minimum. The SEUs experienced from the cosmic ray background were correspondingly few in number, but surprisingly produced an equal probability of upset over an L-shell range of 8.5 Earth radii (RE) down to less than 3.0 RE. Cosmic ray induced upset frequencies in proton sensitive chips were over 2 orders of magnitude lower than those produced by protons in the heart of the inner proton radiation belts. Multiple upsets, those produced when a single particle upsets more than one memory location, were just as common from protons as from cosmic rays.     

Analog Computer Needed!

Science and technology advance neither steadily nor continuously. Concepts deemed obsolete and confined to oblivion find their niche in new developments. Discarded old methods revive as the key ingredients to new designs. Analog computing was the birthplace of two important technologies: Computer simulation, as applied to system design, was founded. The operational amplifier, to become the basis for modern linear circuitry, was perfected. Valuable as it was, analog simulation's quasi-hardware approach to analysis aggravated users as much as it aided them. When digital simulation languages arrived, simulation engineers readily adopted them. When the microprocessor transformed digital computers into inexpensive circuit components (more like gates, flip-flops, amplifiers, etc. than computers,) there arose unlimited prospects for digital control. But, the discrete digital and continuous analog worlds are not compatible. Timing discontinuities and variable resolution limitations create problems. Control system designs, especially microprocessor based ones, need laboratory development. For hands-on testing, the analog computer is as handy an instrument as a controls engineer could have. Its two unique and valuable functions are: Simulator of Systems to be Controlled... The electrical analogs or physical models, analog computer simulations offer predictable yet realistic representations of mechanisms and processes to be controlled. Programmable Linear Circuits Manifold... The terminal points for high quality, linear circuit devices, analog computer patch panels offer the only formal means of programing linear signal processing, interface and control circuits. This paper offers a discussion of these two analog computing uses.     

New technologies and data integration

The fourth workshop of the Earth Observation Data Policy and Europe (EOPOLE) project was held in Brussels, Belgium, 18–20 October 1999 at the offices of the European Commission DG Research, with Yves Reginster of Gere SA, Luxembourg, as guest speaker. The purpose of the workshop was to discuss the data policy issues raised by new technologies and by integrating Earth observation (EO) data with non-EO data. They included risks and reliability of output products, transfer of experience with new projects and intellectual property rights.     

Commercialization of space — the investment opportunities

This report by Ray Williamson of the US Office of Technology Assessment, looks at the prospects for commercialization of space into the 21st century and discusses the relative benefits of private v government investment. The report is taken from a revised version of an article originally appearing in the October 1982 issue of Futures. A fully updated paper will appear in Michiel Schwarz and Paul Stares (eds), ‘The Exploitation of Space: Policy Trends in the Military and Commercial Uses of Space’ (Butterworths, Guildford, UK, 1985).