Octavian Cristea

Long baseline stereovision for automatic detection and ranging of moving objects in the night sky.

As the number of objects in Earths atmosphere and in low Earth orbit is continuously increasing; accurate surveillance of these objects has become important. This paper presents a generic, low cost sky surveillance system based on stereovision. Two cameras are placed 37 km apart and synchronized by a GPS-controlled external signal. The intrinsic camera parameters are calibrated before setup in the observation position, the translation vectors are determined from the GPS coordinates and the rotation matrices are continuously estimated using an original automatic calibration methodology based on following known stars. The moving objects in the sky are recognized as line segments in the long exposure images, using an automatic detection and classification algorithm based on image processing. The stereo correspondence is based on the epipolar geometry and is performed automatically using the image detection results. The resulting experimental system is able to automatically detect moving objects such as planes, meteors and Low Earth Orbit satellites, and measure their 3D position in an Earth-bound coordinate system.

Low-cost SDR-based ground receiving station for LEO satellite operations

This paper outlines the feasibility of using Software-Defined Radio (SDR) technology for space applications by developing and setup of a low-cost VHF/UHF ground receiving station in order to support existing and future university missions. The proposed solution is based on the integration of commercial off-the-shelf components available on the market. The paper will present some of the hardware and software related issues regarding the implementation of an educational ground station for operation with Low-Earth Orbit satellites.

In-situ measurements regarding LF radio wave propagation using DCF77 time signal transmitter

This paper illustrates experimental results regarding the ionospheric LF radio wave propagation using the DCF77 time signal transmitter. The sample data collected revealed the correlation between the diurnal variations of the received signal level and the time-domain scattering of the demodulated PPS (Pulse-Per-Second) signal.

4 th of January 2011 solar eclipse induced disturbances in VLF radio waves propagation

This paper illustrates the experimental results regarding VLF radio wave propagation, obtained during the partial solar eclipse in January 4th 2011. Two VLF transmitters were monitored using a VLF receiver equipment prototype. The data collected revealed strong disturbances of the VLF radio wave propagation during the partial solar eclipse.

Characterization of LEO satellites through ground-based Doppler observations

This paper presents some practical aspects regarding the characterization of satellites orbit through ground-based Doppler observations. The monitoring focused on receiving telemetry signals from active university satellites placed on low-altitude circular orbits, which operate in the UHF amateur radio band. The experimental data was used for satellite orbital analysis with the main purpose of estimating basic orbital parameters of a LEO (Low Earth Orbit) satellite. The obtained data (Doppler curves) over multiple passes was used in order to estimate the orbital period, and from it, to derive other orbital parameters like altitude and velocity.

Aspects regarding the use of LF radio transmitters for time dissemination

This paper illustrates some aspects regarding the use of LF (low frequency) radio transmitters for precise time dissemination. The first part of the article presents some of the advantages and disadvantages of this precise time dissemination methods. The second part presents some in-situ measurements made at the limit of DCF77 transmitters coverage area where the received signal is strongly influenced by the ionospheric propagation conditions.

Surveillance of medium and high Earth orbits using large baseline stereovision

The Earth is surrounded by a swarm of satellites and associated debris known as Resident Space Objects (RSOs). All RSOs will orbit the Earth until they reentry into Earth’s atmosphere. There are three main RSO categories: Low Earth Orbit (LEO), when the satellite orbits at an altitude below 1 500 km; a Medium Earth Orbit (MEO) for Global Navigation Satellite Systems (GNSS) at an altitude of around 20 000 km, and a Geostationary Earth Orbit (GEO) (also sometimes called the Clarke orbit), for geostationary satellites, at an altitude of 36 000 km. The Geostationary Earth Orbits and the orbits of higher altitude are also known as High Earth Orbits (HEO). Crucial for keeping an eye on RSOs, the Surveillance of Space (SofS) comprises detection, tracking, propagation of orbital parameters, cataloguing and analysis of these objects. This paper presents a large baseline stereovision based approach for detection and ranging of RSO orbiting at medium to high altitudes. Two identical observation systems, consisting o...