Radio emissions from Uranus

The Voyager Planetary Radio Astronomy Experiment detected strong 40 kHz to 850 kHz radio emissions from Uranus after closest approach and somewhat weaker emissions, but none above 100 kHz before closest approach, on the dayside of Uranus. The time variations of these emissions closely match Uranus' rotation, in a period of 17.24 h, and are evidently controlled by the strength and shape of its magnetic field. Throughout the entire encounter the polarization of the emission was approximately lefthand, corresponding to extraordinary mode. The emission associated with the nightside pole was a relatively smooth continuum (free of bursts) with a Gaussian-shaped rise and fall at low frequencies, 200 kHz for example, but a Gaussian with a central dip nearly to zero lasting a little less than two hours at frequencies above 400 kHz. Half a rotation later, when Voyager was near the magnetic equator of Uranus and farthest from the nightside dipole tip, the continuum emission was absent, but very strong, narrowband impulsive bursts appeared. Voyager successfully acquired one brief (24 seconds long) record of high time resolution radio observations in the range 500 to 700 kHz. This record, which was made near closest approach, shows a hierarchy of fast variations. Several days after closest approach, at the times of bowshock crossings outbound, the continuum emissions were modulated strongly in a manner suggestive of the presence of waves in the bowshock regions.

The instrument also recorded possible Uranian electrostatic discharges, vertex early arcs occurring in sequences of more than a dozen events with approximately ten-minute period, and, as early as several days before closest approach in the frequency range below 100 kHz, very intense isolated bursts lasting tens of minutes.     

Detectability Loss Due to "Greatest Of" Selection in a Cell-Averaging CFAR

Curves are presented showing the additional constant false-alarm rate (CFAR) loss which results when a "greatest of" logic is imple mented between the leading and lagging sets of reference cells. Thee analytical results for a square law detector and a Swerling case 1 fluctuating target are supplemented by simulation results for a nonfluctuating target, and envelope and logarithmic detector laws.     

A Sampled Data Delay-Lock Loop Implemented as a Kalman Predictor

Performance data is presented for a sampled data delay-lock-loop incorporating a Kalman predictor. The jitter response due to noise and the deterministic response to aircraft maneuvers are investigated as a function of the Kalman model parameters. The predictor's transient response to step, ramp, and parabolic inputs and the number of iterations required for convergence for typical initialization errors are determined. It is shown how values for the model parameters may be chosen to obtain satisfactory noise, maneuver, and lock-up performance.     

The Onset of Long Term Modulation in the Heliosphere in Cycle 23

The combination of Voyager 1 (77.9 AU, 34.4° N) and Voyager 2 (61.2 AU, 24.5° S) at moderate heliolatitudes in the distant heliosphere and Ulysses with its unique latitudinal surveys in the inner heliosphere along with IMP 8 and other satellites at 1 AU constitutes a network of observatories that are ideally suited to study cosmic rays over the solar minimum of cycle 22 and the onset of solar activity and the long term cosmic ray modulation of cycle 23. Through 2000.7 there have been three well-defined step decreases in the cosmic ray intensity at 1 AU with the cumulative effect being in good agreement with the net decrease in cycle 21 at a comparable time in the solar cycle. Over this period the intensity changes at Ulysses are similar to those at 1 AU. In the distant heliosphere the initial decreases appear to be smaller than those at 1 AU. However the full effects of the interplanetary disturbances producing the most recent and largest step decrease in the inner heliosphere have not yet reached V-2. This revised version was published online in August 2006 with corrections to the Cover Date.     

Optimum Windows for Image Registration

Two-dimensional cross-correlation techniques are applied to the problem of image registration under the assumption of small geometric distortion. Optimum window functions are derived for two performance measures of interest: peak-to-sidelobe ratio and mean-square registration error. The latter is examined in terms of the contribution caused by noise and the contribution caused by geometric distortion. A generalized Lagrange multiplier approach is used to derive approximate solutions assuming random images. The case of Gaussian autocorrelation functions is examined in detail. Results of applying the theoretically derived window functions to real data are presented, showing significant improvement in correlator performance.     

The telemedicine frontier: going the extra mile

Telemedicine has the potential to have a greater impact on the future of medicine than any other modality and will profoundly alter the medical landscape of the twenty-first century. In the most remote areas, it can bring high-quality health care where none is now available. In global health care, it can enhance and standardize the quality of medical care, including developing countries. In the realm of space flight, it can provide a lifeline to medical expertise and monitoring. Through its mobility, it can provide urgently needed health care in instances of natural disaster. However, a number of challenges exist in its coordination and implementation on a global scale, specifically in the international and remote disaster scenarios. In the area of spaceflight, telemedicine capability will remain a consultation/information ‘lifeline’, but additional onboard medical capability and expertise will become crucial complements as missions become more advanced and remote from Earth.     

Representations of solar EUV fluxes for aeronomical applications

The development of significantly improved representations of solar EUV inputs for computer-aided investigations of the terrestrial thermosphere and ionosphere has become attractive particularly for the present solar cycle which has been covered by reasonably complete and continuous EUV observations from the AE-E Satellite. These representations try to satisfy some rather incongruous $\text{requirements of spectral detail}$, regarding (a) the strong wavelength-dependence in the $\text{terrestrial}$ atmospheric cross sections of the various types of EUV photon interactions, (b) the great differences in the relative amplitudes of the various types of variations in the full-disk fluxes of $\text{solar}$ emissions at different wavelengths, and (c) the persisting desire to use only a $\text{small number of daily indices}$ as actual input variables for computational models supposed to cover the entire EUV wavelength range (remembering the great success of empirical thermospheric models using only two indices). These general physical and specific aeronomical demands indeed outline a very difficult task. The present study, based mainly on AE-E satellite observations during 1976–1979, represents an exploratory step, only clarifying some important developmental aspects, without recommending any specific formulations for immediately practicable adoption in aeronomical modelling at this time.