Antonio Moccia

Multi-Sensor-Based Fully Autonomous Non-Cooperative Collision Avoidance System for Unmanned Air Vehicles

This paper presents a fully autonomous multi-sensor anti-collision system for Unmanned Aerial Vehicles. This system is being developed by the Italian Aerospace Research Center in collaboration with the Department of Aerospace Engineering of the University of Naples “Federico II”. The research project is entitled TECVOL and is funded in the frame of the National Aerospace Research Program. The system prototype will be initially installed onboard a manned laboratory aircraft equipped for automatic control, therefore flight tests will verify the adequacy of attained performances for supporting fully autonomous flight. The obstacle detection and tracking function is performed by a multi-sensor configuration made up by a pulsed Ka-band radar, two visible (panchromatic and color) video cameras, two infrared video cameras, and two computers. One computer is dedicated to real time sensor fusion and communication with the radar and the flight control computer (by means of a deterministic data bus), the other is devoted to image processing. On the basis of the tracking estimates and of a Collision Avoidance Software, the flight control computer generates and follows in real-time a proper escape trajectory. In order to evaluate the performance of the collision avoidance system, numerical simulations have been performed taking into account the obstacle detection sensors’ accuracy, unmanned aircraft’s and intruder’s flight dynamics, navigation system accuracy and latencies, and collision avoidance logic. The relevant results helped to assess overall system performances and are discussed in depth.

Spaceborne bistatic synthetic Aperture Radar for remote sensing applications

This paper presents a performance analysis of spaceborne bistatic Synthetic Aperture Radar (SAR) for Earth observation. Since a bistatic system requires the simultaneous use of two spatially separated antennae, this paper refers to the European Space Agency ENVISAT-1 ASAR as the master mission, i.e. reflected echoes collected by ASAR are gathered also by a receiving-only slave antenna, which is on board a small satellite. Depending on orbit configuration, two mission profiles could be envisaged: two satellites flying along parallel orbits with different ascending nodes, or in one orbit plane with adequate angular separation. It is assumed that ENVISAT-1 is non-cooperative; therefore, signal synchronization and swath overlap and antenna separation control are committed to receiving-only spacecraft. To gain further insight into system geometric and radiometric characteristics and accuracy, several simulations are performed by using a computer code, which accounts for spacecraft orbit and attitude dynamics, sensor pointing geometry and Earth rotation. Numerical results and plots show the potentiality of the system for quite accurate three-dimensional measurements. In particular, thanks to system geometry, it is possible to compute target position and slant range components of velocity. Finally, further potential applications are outlined, also considering additional spin-offs for the master mission.

Spaceborne along-track SAR interferometry: performance analysis and mission scenarios

A system study of a spaceborne along-track synthetic aperture radar (SAR) interferometer is presented. This sensor has been successfully experienced for detecting moving targets by using only airborne installations. Several key issues must be addressed when spaceborne configurations are envisaged. To this end, a quantitative evaluation of system performance and measurement accuracy has been conducted. First, the identification of possible space configurations has been accomplished. In particular, the two antennas can operate on a single satellite or they can be carried along appropriate trajectories by two spacecrafts. Then, an error budget of radial velocity measurement accuracy has been performed. Finally, two possible mission scenarios are dealt in details, and numerical results are reported.

Spatial Resolution of Bistatic Synthetic Aperture Radar: Impact of Acquisition Geometry on Imaging Performance

This paper analyzes the spatial resolution of bistatic synthetic aperture radar (SAR) in general hybrid configurations, such as air- and spaceborne systems moving along independent trajectories. The gradient method is utilized to point out the effects of the acquisition geometry, namely, position and velocity of both the transmitter and the receiver, on image resolution. This general approach is applied to different realizations of bistatic SAR, such as low-Earth-orbit monostatic-bistatic SAR, spaceborne-airborne bistatic SAR, and a bistatic system consisting of a high-altitude long-endurance illuminator and lower altitude airborne receivers. The main features of the method are then put in evidence, including the derivation of analytical tools to individuate adequate relative geometries for achieving satisfactory resolutions. A comparison to the other proposed techniques for computing the spatial resolution of bistatic SAR is also reported in order to highlight some peculiarities of all presented methodologies. Finally, the good agreement between the image resolution results achieved by recently carried out bistatic SAR experiments and the ones derived by the gradient method strengthens the potentialities of the proposed approach.

A tethered interferometric synthetic aperture radar (SAR) for a topographic mission

Analyzes a spaceborne interferometric synthetic aperture radar (SAR) for high-resolution, topographic applications. Two physical antennas are vertically spaced and are carried along parallel paths by two different platforms connected by a tether. Tethered space systems have been proposed by several authors for different applications and a joint US-Italian program exists to deploy in 1992 a small satellite (Tethered Satellite System) from a Space Shuttle. A system performance analysis is carried out, considering a theoretical study and a numerical simulation. By evaluating the tethered interferometric SAR impulse response, the height of various point scatterers is computed and an error budget is obtained. Results show that this system is capable of achieving a root-mean-square (RMS) error in height measurement adequate for several applications. >

Performance of spaceborne bistatic synthetic aperture radar

This paper reports on a model developed for evaluating major system performance of a spaceborne bistatic synthetic aperture radar (SAR) for remote sensing applications. The procedure accounts for formation flying aspects. It is particularly aimed at comparison of monostatic and bistatic cases, and, as a test case, it is applied to study a novel configuration, based on a small satellite equipped with a receiving-only antenna orbiting in tandem with a large, noncooperative transmitting spacecraft, the Italian COSMO-SkyMed mission. Numerical results and plots show the effectiveness of the procedure as a mission design tool and put in evidence key issues and characteristics of the proposed spaceborne bistatic formation.

Flight Test of a Radar-Based Tracking System for UAS Sense and Avoid

Presented here is an analysis of an extensive flight campaign aimed at characterizing peculiarities, advantages, and limitations of an obstacle detection and tracking system based on a pulse radar. The hardware and software prototypical sensing system was installed onboard an optionally piloted flying laboratory from the very light aircraft (VLA) category. Test flights with a single intruder aircraft of the same class were carried out to demonstrate autonomous noncooperative unmanned aerial system (UAS) collision avoidance capability and to evaluate the level of achievable situational awareness. First, the adopted architecture and the developed tracking algorithm are presented. Subsequently, flight data gathered in various relative flight geometries, covering chasing flights and quasi-frontal encounters, are analyzed in terms of radar performance, including detection range and range and angle measurement accuracies. The analysis describes the impact of ground echoes and navigation uncertainties, system tracking reliability, and achievable accuracy in estimation of relative position and velocity. On the basis of Global Positioning System (GPS) data gathered simultaneously with obstacle detection flight experiments, a detailed error analysis is conducted. Special emphasis is given to the validation of proposed methodology to separate between intruder and ground echoes, which is a critical aspect for light aircraft due to their limited radar cross sections (RCS) and flight altitudes. In conclusion the radar demonstrates its potential to attain adequate situational awareness, however the limits of single sensor tracking are also pointed out. Above all the negative impact of poor angular accuracy on missed detection and false alarm rates is pointed out.

BISSAT: a bistatic SAR for Earth observation

This paper summarizes scientific rationale and technical approach for a bistatic synthetic aperture radar (SAR) mission (BISSAT). The study has been funded by the Italian Space Agency for a competitive Phase-A study along with other five missions. Its concept consists in flying a passive SAR on board a small satellite, which observes the area illuminated by an active SAR, operating on an already existing large platform.

Performance of Stereoradargrammetric Methods Applied to Spaceborne Monostatic–Bistatic Synthetic Aperture Radar

This paper aims to investigate the performance of stereoradargrammetric methods applied to spaceborne monostatic-bistatic synthetic aperture radar (SAR) data for digital elevation model (DEM) generation. Stereoradargrammetric techniques for robust DEM generation were successfully experienced on monostatic repeat-pass SIR-A, SIR-B, SIR-C/X-SAR, ERS1/2, JERS-1, and Radarsat data. However, novel configurations achievable by modern spacecraft flying in formation will allow for the attainment of very large baselines between the antennas in a single-pass bistatic geometry so that the height determination accuracy can benefit from both stereo effect and simultaneous acquisition. Five models for relief reconstruction by monostatic-bistatic SAR stereoradargrammetry are presented, and an error budget is assessed for each of them. Results of the sensitivity analysis exhibit metric accuracy, and therefore, the technique could be applied for height reconstruction as a methodology complementary to SAR interferometry.

Integrated VIS-NIR Hyperspectral / Thermal-IR Electro-Optical Payload System for a Mini-UAV

This paper presents the development of a modern electro-optical payload system for remote sensing from a mini-UAV. It is aimed at applications of natural disasters monitoring, in particular forest fires. Both the sensor and the mini-UAV platform are being developed at the Dept. of Space Science and Engineering (DISIS) of the University of Naples “Federico II.” The core of the system is an integrated, multi-band sensor that includes a thermal imager and a hyperspectral sensor in VNIR band. Instrument characterization, laboratory tests, and payload architecture are discussed.