Studies of Logarithmic Radar Receiver Using Pulse-Length Discrimination

Using a logarithmic amplifier giving a detected output followed by a high-pass filter is a technique for reducing adverse effects of distributed clutter in radar receivers. A pulse-length discriminator (PLD) used as the high-pass filter is treated here. Theoretical and experimental results for the loss in detectability introduced by this receiver, as compared with a matched filter or a good approximation thereto, have been obtained. For the case of single-hit detection, losses of 4 to 8 dB are introduced by the logarithmic amplifier/pulse-length discriminator (LOG AMP/PLD) combination; for post-detection integration, the losses are reduced to 2 to 4 dB. The latter values would apply where the LOG AMP/PLD output is presented on a PPI (plan position indicator). Some experimental results of the ability of the LOG AMP/PLD receiver to reject signals of incorrect pulse length show that signals exceeding the design pulse length by more than 25 to 50 percent are effectively suppressed. No significant short-pulse discrimination is obtained from the receiver.     

The RadioAstron project: Measurements and analysis of basic parameters of space telescope in flight in 2011–2013

The results of a large number of the antenna radiometric measurements at bands of 92, 18, 6.2, 1.35, and 1.7-1.2 cm are presented by the data of the standard telemetry system of the Spektr-R spacecraft. Both special sessions of calibration object observations in the mode of a single space radio telescope (SRT) operation and numerous observations of researched sources in the mode of the ground-space interferometer were used. The obtained results agree with the first results of Kardashev et al. (2013), i.e., within 10–15% at bands of 92, 18, and 6.2 cm and 20–25% at the band of 1.35 cm. In the main, the measurements for the eight subbands at wavelengths of 1.7-1.2 cm indicate a monotonic increase in the spectral system equivalent flux density (SEFD) of noise radiation with a frequency consistent with the calculated estimates for the discussed model. The sensitivity of the ground-space interferometer for the five subbands at wavelengths from 1.35 to 1.7 cm can be higher by a factor of 1.5, and for the three subbands from 1.35 to 1.2 cm lower by a factor of 1.5 than at the band of 1.35 cm. The SRT contribution to the interferometer sensitivity proportional to the square root of SEFD is close to the design one at the bands of 92 and 18 cm and decreases the design sensitivity approximately by a factor of 1.5 and 2 at the bands of 6.2 and 1.35 cm, respectively. These differences of implemented values from the design ones were not significantly affected the scientific program implementation.     

Do we understand the inner magnetotail dynamics during substorms?

Substorm evolution of the near-Earth (|X|<15 R_E) plasma sheet has been emphasized recently because the inner tail is thought to link closely to the substorm auroral activity in the ionosphere during the early stage of substorms. In this paper, we discuss how the inner tail substorm phenomena during the late substorm growth phase and early expansion phase are accounted for by the two prevailing substorm models, namely, the near-Earth neutral line model and the current disruption model. We find that the late growth phase features are more satisfactorily accounted for by the current disruption model than by the near-Earth neutral line model. In addition, detailed observations on current disruption show evidence inconsistent with the proposed idea of dipolarization being due to plasma flow braking from reconnection in the mid-tail region, which poses a difficulty to the near-Earth neutral line model as well.     

Viscoelastic behaviour of pumpkin balloons

The lobes of the NASA ULDB pumpkin-shaped super-pressure balloons are made of a thin polymeric film that shows considerable time-dependent behaviour. A nonlinear viscoelastic model based on experimental measurements has been recently established for this film. This paper presents a simulation of the viscoelastic behaviour of ULDB balloons with the finite element software ABAQUS. First, the standard viscoelastic modelling capabilities available in ABAQUS are examined, but are found of limited accuracy even for the case of simple uniaxial creep tests on ULDB films. Then, a nonlinear viscoelastic constitutive model is implemented by means of a user-defined subroutine. This approach is verified by means of biaxial creep experiments on pressurized cylinders and is found to be accurate provided that the film anisotropy is also included in the model. A preliminary set of predictions for a single lobe of a ULDB is presented at the end of the paper. It indicates that time-dependent effects in a balloon structure can lead to significant stress redistribution and large increases in the transverse strains in the lobes.     

Simulation experiments of the cosmic ray isotope telescope on ETS VI

A computer simulation was carried out to evaluate the basic characteristics of a Δ E×E cosmic ray telescope consisting of 23 solid state detectors including 3 position sensitive detectors with large effective area. Based on the simulation, the geometric factor of the telescope is deduced to be as large as 22.5 cm²sr, almost independent of charge and energy concerned. The energy ranges to be covered by the telescope are, for example, 18–98 MeV/n for Li and 56–339 MeV/n for Fe. By analyzing simulated data, the mass resolution for iron in the overall energy range covered by the telescope is estimated as about 0.22 amu in standard deviation. The expected counting rates and mass-histograms are simulated for Galactic cosmic rays and solar energetic particles.     

Interpretation of data on laser sensing of aerosol atmosphere from space

A single-frequency lidar, using aerosol scattering as an informative component, is the simplest and reliable facility for remote sensing of the atmosphere. The information on vertical distribution of atmospheric aerosol which can be obtained using such a lidar is necessary for investigating the physics of atmospheric processes and forecast of optical state of the atmosphere. At the same time, the interpretation of data on single-frequency sounding is associated with some difficulties of fundamental character, mainly due to insufficient software of the experiment. Under such conditions the problems of optimal processing of lidar returns aiming at extracting the useful information on aerosol are of great importance, especially if one takes into account the hindering effects of atmospheric background and optical noises. This paper presents a statistical approach to this problem, and the possibilities of single-frequency sounding from space are analyzed.     

Rio de la Plata estuarine system: Relationship between river flow and frontal variability

This paper deals with the application of SeaWIFS images to characterize spatial and temporal variability of fronts in the Rio de la Plata estuarine system over the period 2000–2003. We aim to depict the relationship between river outflow and variability of fronts’ loci on monthly to ENSO-related timescales and the influence of the winds along Rio de la Plata (axial winds) on the abrupt changes in frontal dynamics over synoptic timescales. During the studied period both La Niña (July 1999–June 2000) and El Niño (April 2002–May 2003) events induced significant displacements of fronts. Three distinct fronts were analyzed between river, estuarine, coastal and marine waters of the Rio de la Plata: Main Turbidity Front, Main Marine Front, and Secondary Marine Front. Their number, location and separation seem to be mainly related to river outflow and second, to fresh (>8 m/s) axial winds. During low discharge periods (i.e. summer time and/or La Niña events) these winds induce abrupt changes in the location of fronts (100–200 km) and greater separation between them over synoptic timescale, whereas during high river discharge or ENSO years some of the variability of fronts location is explained by the river’s outflow fluctuations, especially by the high variability of the River Uruguay discharge.     

What we have not learned from the troubles with the Hubble

The Hubble space-based telescope is a great tribute to our progress in space. The ability to place an optical telescope at a significant distance from the Earth's surface, away from the interference of the planet's unsteady atmosphere, have already paid off by producing magnificent records of astronomical activities in the depths of outer space. In the past the problems with the alignment of the Hubble's optics were blamed on the manufacturers of it's optical components. The hastily set investigation concluded that the problem is a spherical aberration of the primary mirror (the primary mirror is said to be 2 microns too flat at the edges). It is suggested that the real culprit is the Parker Effect. Since the time of Galileo Galilei, all telescopes were built, aligned, and used on the Earth's surface. Hubble is the first telescope to be built and aligned on Earth for use in space. Because of this we have to consider the fundamental differences between the alignment of surface-based and space-based telescopes. For those who missed our article “The Parker Effect and Navigation in Space” published in the January issue. The Parker Effect describes the result of interaction between inertial bodies (anything that has mass) and non-inertial media (light or other E/M fields)     

Estimates of disturbances of space vehicle orbits in the upper ionosphere prior to strong earthquakes

Estimates of drag characteristics of the space vehicles with orbit heights of 450–540 and 700–900 km before and after strong (with a magnitude M ≥ 6.5) crust earthquakes of 2000–2006 are presented. The method of estimation of seismic orbital effects is presented using as an example the small Mozhaets-4 spacecraft. Two weeks prior to earthquakes, variations in the drag of low-orbital spacecraft increase. 3–6 days prior to strong crust earthquakes with epicenters on the land, the drag of low-orbit spacecraft in the upper atmosphere increases. The effect of increased viscosity of the neutral component of the atmosphere at spacecraft heights 3–6 days prior to strong crust earthquakes is consistent with the results of studies of disturbances in the ionization density variations in the ionospheric F region prior to earthquakes. No anomalies are found in the day of the earthquake. In the future, it is proposed to use elements of space debris for diagnostics of seismic orbital effects and disturbances of the upper atmosphere.