Accuracy of using point targets for SAR calibration

The peak and integral methods for radiometric calibration of a synthetic aperture radar (SAR) using reference point targets are analyzed. Both calibration methods are shown to be unbiased, but the peak method requires knowledge of the equivalent rectangle system resolution which is sensitive to system focus. Exact expressions for the RMS errors of both methods are derived. It is shown that the RMS error resulting from the peak method is always smaller than or equal to that from the integral method for a well-focused system. However, for robust radiometric calibration of SAR, or when nonlinear phase errors are present, the integral method is recommended, because it does not require detailed knowledge of the impulse response and the resulting RMS error is not dependent on system focus     

The cataclysmic variable SS Cygni

In this work we will try to give the most general panorama, comparatively with the conciseness, on SS Cygni which is the brightest dwarf nova.The dwarf novae form a sub-class of the more vaste panorama of the Cataclysmic Variables (CVs). For this reason firstly we will describe in general the CVs and the current theories which attempt to describe their physical behaviour (Sections 2 and 3). The up-to-date observational properties of SS Cygni (Section 4) and a discussion on their explanation within the framework of theories (Section 5) will allow us to draw the conclusions (Section 6) and to argue the most convenient line of investigation (Section 7) both experimental and theoretical for a better understanding of the underlying physics of these systems.     

Mathematical modeling of response of ecosystems with different structure to external impact.

A mathematical model was used to study the response of ecosystems of different structures to external impact. The response was measured as a sensitivity coefficient: the magnitude of the system's response vs. the change of the factor in the inflow. The formula has been obtained to calculate the sensitivity coefficient for ecosystems containing different numbers of trophic links. The derived sensitivity coefficients demonstrate that the degree of compensation for the external impact can differ depending on the type of system regulation and the length of the trophic chain. E. g. the sensitivity coefficient decreases with complexity of trophic links in an ecosystem for top-down controlled systems and impact of degree of openness on sensitivity e.g. closed ecosystems show higher sensitivity then fully open ecosystem to impacts also bottom-up control system show less sensitivity then top-down. Grant numbers: N99-04-96017, N25.     

On the relative abundance of helium ions in the topside ionosphere

Based on data from satellite INTERCOSMOS-BULGARIA-1300, the latitudinal distribution of oxygen and helium ions in the topside ionosphere is discussed for night-time equinox at high solar activity. A comparison with the corresponding IRI-79 distribution is made. The vertical IRI ion composition profile is checked with measurements made with VERTICAL-10 rocket. Some recommendations are made in order to improve the IRI-modelling of the ion composition in the topside ionosphere.     

Vegetation health: Nature's climate monitor

Observational data to effectively evaluate weather effects, which accumulate into current climate status, are available for affluent nations but often are inadequate elsewhere. Data acquired by satellite sensors in the visible-near infrared portion of the reflected solar energy spectrum have been accumulated daily since 1965 and for the earth's emitted radiance in the 11000 nm window since 1972. With the advent of the TIROS-N satellite in 1978, the solar reflected energy has been sensed in two separate channels and beginning with NOAA-6, the second vehicle of the TIROS-N family, these two channels became complementary rather than overlapping. This feature makes vegetative monitoring possible and now is being exploited to provide daily experimental products. These global vegetative index (GVI) arrays have been used to observe and map the effects of droughts, floods, adverse winds and thermal stresses on the global arable lands. These data and the related sea surface temperatures, both derived from satellite data, provide realistic measures of the global climate and can assist climatic forecasting.     

Relative abundance of H and He in outer ionosphere

A mathematical model is used to study the relative abundance of H⁺ and He⁺ ions in the topside ionosphere. It is found that the daytime light-ion densities are strongly coupled with the neutral densities. This fact arises difficulties in modelling the ion composition for IRI without taking into account any particular reference atmosphere. As an example, the transition heights between O⁺---H⁺ and O⁺---He⁺ are shown, plotted against the neutral densities. The supposed linear dependance gives a clear evidence that all light-ion ionization below these heights will experience stronger influence by the neutral atmosphere.     

10. The surface and interior of venus

Present ideas about the surface and interior of Venus are based on data obtained from (1) Earth-based radio and radar: temperature, rotation, shape, and topography; (2) fly-by and orbiting spacecraft: gravity and magnetic fields; and (3) landers: winds, local structure, gamma radiation. Surface features, including large basins, crater-like depressions, and a linear valley, have been recognized from recent ground-based radar images. Pictures of the surface acquired by the USSR's Venera 9 and 10 show abundant boulders and apparent wind erosion.On the Pioneer Venus 1978 Orbiter mission, the radar mapper experiment will determine surface heights, dielectric constant values and small-scale slope values along the sub-orbital track between 50°S and 75°N. This experiment will also estimate the global shape and provide coarse radar images (40–80 km identification resolution) of part of the surface. Gravity data will be obtained by radio tracking. Maps combining radar altimetry with spacecraft and ground-based images will be made. A fluxgate magnetometer will measure the magnetic fields around Venus.The radar and gravity data will provide clues to the level of crustal differentiation and tectonic activity. The magnetometer will determine the field variations accurately. Data from the combined experiments may constrain the dynamo mechanism; if so, a deeper understanding of both Venus and Earth will be gained.     

The influence of space flight factors on viability and mutability of plants.

The experiments with air-dried Crepis capillaris seeds aboard the Soyuz 16 spaceship and the orbital stations Salyut 5, 6, 7 have revealed an increase in the frequency of aberrant cells in seedlings grown from flight-exposed seeds during the flight (experiment) and after the flight on Earth (flight control) as compared to the ground-based control. The increase in seedlings grown during the flight is more significant than in the flight control. During the flight Arabidopsis thaliana developed from cotyledons to the flowering stage. Analysis of seeds setting on these plants after the flight has shown a reduction in the fertility of these plants and an increase in the frequency of recessive mutants ("Light block-1"). An increased frequency of mutants was also retained in the progeny of plants which had passed through a complete cycle of development during the flight ("Fiton-3"). Suppression of embryo viability was observed in all experiments and expressed itself in reduced germinating ability of seeds from the exposed plants and in the early death of seedlings. Damages resulting from chromosome aberrations are eliminated in the first postflight generation and damages resulting from gene mutations and micro-aberrations are preserved for a longer time.     

Current sheets in the solar atmosphere

The 2D and 3D numerical simulation is used for the investigation of current sheet (CS) creation above the active region. The current sheet in the solar corona can be created either in vicinity of a magnetic field singular line by focusing disturbances or at the interaction of the super-Alfvenic plasma flow with the perpendicular magnetic field.