Satellite imagery based adaptive background models and shadow suppression

Accurate segmentation of foreground objects in video scenes is critical for assuring reliable performance of vision systems for object tracking and situational awareness in outdoor scenes. Most existing techniques for background modeling and shadow suppression require that a number of parameters be “hand-tuned” based on environmental conditions. This paper presents two contributions to overcome such limitations. First, we develop and demonstrate a satellite imagery based approach for selecting appropriate background and shadow models. It is shown that the illumination conditions (i.e. cloud cover) of a scene can be reliably inferred from visible satellite images in the local region of the camera. The second contribution presented in the paper is introduction and evaluation of a Hybrid Cone-Cylinder Codebook (HC3) model which combines an adaptive efficient background model with HSV-color space shadow suppression into a single coherent framework. The structure of the HC3 model allows for seamless fusion of the satellite data. We are thereby able to exploit the fact that, for example, shadows are more pronounced on sunny days than cloudy days, allowing for more sensitive detection. The paper presents a set of experiments using day long sequences of videos from an operational surveillance system testbed. Results of these experimental analyses quantitatively illustrate the benefits of using satellite imagery to inform and adaptively adjust background and shadow modeling.     

A statistical model of FM-TV spectra for satellite interference and distortion prediction

The requirement for a model of FM-TV spectra in the planning procedure of satellite communication systems is introduced. Based on long-term measurements of live TV channels, statistical properties of video spectra are examined and probability distributions for the luminance and chrominance components are proposed. The spectrum of the frequency-modulated signal is then derived, and signal distortion due to bandlimiting is calculated. Adjacent and cochannel interference effects are also investigated, with example cases illustrating influences of subcarrier loading and energy dispersion. The proposed model, which describes FM-TV spectra in terms of random variables, makes it possible to examine relative effects of system parameters, and will, therefore, be of benefit in the planning of new satellite services.     

Radiation analysis and errors associated with the monopulse operation of a satellite direction finder

This work describes the radiation performance of a novel concept for direction and location finding, using stationary satellite beacons. The received signals are processed with a monopulse four-element array. The monopulse mode is generated using the phase excitation of the radiating elements. For accurate processing the radiation phase should correspond with the bearing angle around the boresight direction. Phase deviations, however, occur in this phase pattern owing to the discrete excitation of the elements. Therefore, detailed analyses are presented for this phase pattern, its attainable gain and the depolarization effects, in order to select the kind of array elements, and their spacings, which minimize the phase pattern deviations. The dipoles and the slots, as array elements, yield better phase performance, smaller size and simpler structures than horn radiators, at the expense of worse depolarization.     

Multifunctional Optical Terminals for Microsatellite Clusters – Design Tradeoffs

We study optical terminals with both communication and ranging capabilities for their potential use in short range free-space applications, typically encountered within a cluster of microsatellites. For our considerations we assume satellites with a unit mass between 10 kg and 100 kg, with mutual distances on the order of a few km, and per link data rates range from a few kbits/s to some 100 Mbit/s. We discuss possible network topologies and multiple access methods, andcompare the performance characteristics of different intensity modulation formats, taking into account not only the task of communication but also that of accurate intra-cluster distance measurement. Our considerations revealbasic tradeoffs to be observed when designing such multifunctional optical terminals.     

Development of a prototype,experimental single-channel sequencing navstar gps receiver: Part I—Hardware implementation

Late in 1988 the Navstar GPS satellite navigation operational phase is planned to commence, offering world-wide, continuous and precise position-fixing and timing information to observers on land, sea, air and in space. This paper describes the development of a particular type of Navstar receiver—a single-channel, single-frequency, sequencing C/A code unit—and results of various tests carried out on the present phase-II satellite constellation. Part I of the paper deals essentially with the NAVSTAR satellite system and receiver hardware implementation, whereas Part II concentrates on receiver software and system performance.     

Field test results of multi-channel digital tv transmission at 15 and 30 Mb/s through an intelsat satellite using a PSK/FDMA system

This paper describes field test results of multi-channel digital TV transmission using a PSK/FDMA system and the related subjective test results of received TV pictures. The picture quality of the multi-channel 15 or 30 Mb/s transmission for both NTSC and PAL systems through the INTELSAT POR satellite are subjectively evaluated for various bit-error rates. In addition, subjective evaluations were made at various values of earth-station e.i.r.p. to compare the picture quality of digital transmissions with that of current half-transponder FM transmission.     

Satellite networks in the isdn era

The concept of an integrated service digital network (ISDN) is becoming topical for the evolution of world-wide telecommunications. In fact the consultative committees (CCITT and CCIR) have worked actively on the definition of the ISDN and its functions, and many PTTs and other operating companies are engaged in programmes aimed at introducing digital transmission and switching in the public switched telephone network (PSTN) with a view to establishing the first versions of an ISDN. Satellites are well prepared to operate in an ISDN environment. The present competition with fibre optics and other terrestrial carriers may perhaps limit the initial contribution of satellites to the establishment of trunk routes in the first ISDNs, but in the medium term the particular characteristics of flexible distribution of information over very large areas may become of fundamental importance, and many satellite-based networks developed independently may give concrete support to the ISDN. In the long term satellites may experience an even deeper degree of integration, by providing part of the switching facilities of the ISDN on board.     

The effects of coil–stretch transition behavior of polyfluorene inks on single droplet formation during inkjet printing

For drop-on-demand (DOD) inkjet printing, stable and single ink droplet formation without satellite dots is the key to improve the print quality. The formation of stable and single droplet is influenced by filament break up and the polymer chain’s coil–stretch transition behavior. In this paper, the droplet formation behaviors of polyfluorene (PFO) ink at various driving voltages (V), polymer chain’s coil–stretch transition mechanism and its effects on single ink droplet formation are investigated. It indicates that when 58 < V ≤ 63 V, a single and stable droplet is formed with a pulse time of 38.5 μs. At this stage, the Weissenberg number (Wi) < 0.5, the PFO molecular chain is coiled to guarantee stable and single droplets. When V > 63 V, Wi > 0.5, the PFO molecular chain is stretched because of the high hydrodynamic forces, resulting unwanted satellite droplets. When 55 < V ≤ 58 V, the droplet shrinks into the nozzle, which indicates that the kinetic energy supplied by the deformation of the piezoelectric transducer isn't enough to force the droplet to be jetted from the nozzle.     

The influence of space irradiated PIN photodetector on BER in satellite laser communication system

By analyzing the radiation dose on PIN photodetectors in space radiation environment, the variation of photocurrent and dark current after radiation is obtained. On the basis, the bit error rate of satellite laser communication based on space radiation dose of PIN photodetectors is established. According to simulation, when radiation dose is about 1.6 × 10³ Gy and 7 × 10⁴ Gy, bit error rate reaches 10⁻⁶ induced by 50 MeV and 10 MeV protons separately; and when radiation dose is within the range of 5 × 10 Gy–6 × 10⁵ Gy, electrons and gamma-ray irradiation also cause increase in bit error rate to 10⁻⁶. The principle of damage dose on bit error rate is investigated, and the influence of decision threshold on bit error rate is further discussed. The result shows that when radiation dose is 1 MGy, if decision threshold is increased from 4.3 × 10⁻⁷ A to 5.5 × 10⁻⁷ A, bit error rate will decrease about 4 orders of magnitude. Hence, a proper decision threshold can improve system bit error rate efficiently.     

An analytical theory for avoidance collision between space debris and operating satellites in LEO

This paper provides a Hamiltonian formulation of equations of motion of an artificial satellite or space debris moving in Low Earth orbit (LEO). This Hamiltonian is the base to develop an analytical theory of order three, which the theory has been formulated using canonical transformations using Hori-Lie method. The theory accounts for the influence of the Earth gravity field up to degree and order of geopotential harmonics (50 × 50), luni-solar perturbations, solar radiation pressure, atmospheric drag, albedo forces, and the post Newtonian effects arising from Schwarzschild solutions. In this theory, we pay particular attention to the resonance and very long period perturbations, which are modeled with the use of semi-secular terms. The fourth order Runge–Kutta numerical integrator is used to integrate the equations of motion in order to compare with the analytical theory. Including all possible perturbations, in particularly Aledo force and post Newtonian effect in addition to the adequate section of the integrator found to have an importance on the improving the accuracy of the current theory compared with the previous solution. The orbital theory is precise and enables the short term predictions on a few centimeters level. Finally, we show some results concerning the short term dynamics of a different satellite and space debris in LEO under the influence of the considered perturbations.