Marco D'Errico

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.

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.

Attitude and antenna pointing design of bistatic radar formations

Spaceborne bistatic radar observations allow original scientific applications to be carried out. Furthermore, assuming transmitting and receiving antennas operating on separated platforms, key design issues relevant to formation flying must be solved. Mathematical models are presented for computation of attitude and pointing angles. Main design constraint is the capability of maintaining swath overlap, but selected strategy also depends on the cost of spacecraft attitude maneuvering or antenna beam electronic steering. The model has been applied considering a large transmitting/receiving primary mission and a receiving-only small satellite. In this case antenna steering was preferred. Finally, if the passive antenna is smaller than the active one, overlap maintenance is simplified, obviating the need for yaw rotations.

The BISSAT mission: A bistatic SAR operating in formation with COSMO/SkyMed X-band radar

BISSAT mission has been funded by the Italian Space Agency for a competitive Phase-A study along with five other 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. To this end, two quite different satellites must fly in formation in order to guarantee bistatic coverage within the range of latitude 65.2/spl deg/S-66.2/spl deg/N. In particular, the orbit selection for the passive satellite leads to the same orbit as for the primary radar with a difference in the ascending node right ascension and in the time of the passage on the ascending node. The main critical aim, consisting of superimposition of passive and active radar swaths, is achieved by ad-hoc steering radar antennas along the orbit. Design is critical because two existing buses, which have been developed for different purposes, are used.

A bistatic SAR mission for earth observation based on a small satellite

Abstract The authors present a new scientific space mission consisting of a satellite carrying a receiving- only SAR which receives the signal transmitted by the ENVISAT-1 SAR. The integration of ENVISAT-1 SAR and bistatic radar data offers an improved potentiality of surface classification, three-dimensional observation, and the opportunity of advanced scientific experiments in the field of bistatic scattering. The small satellite nominal orbit and the attitude manoeuvres are designed in order to maintain an adequate overlap between the two radar swaths along the whole orbit, taking into account the ENVISAT-1 attitude and pointing. A preliminary satellite design (2-year lifetime) is then performed to evaluate the orbit decay and to determine the appropriate orbit manoeuvres (every 4 days) to control the satellites relative phase. The numerical simulation shows that a spacecraft of about 584kg is able to meet the mission requirements.

From the expected scientific applications to the functional specifications, products and performance of the SABRINA missions

Orbital planning and formation flying control of SABRINA mission will allow different observation geometries characterized by inter satellites distances (baseline) variable from hundreds meters to some hundreds of kilometers. In a so vast scenario, a wide range of bistatic techniques are applicable and testable, ranging from cross and along track interferometry to multi-channel techniques and large baseline bistatic observations. This paper contains a brief description of all the bistatic techniques proposed for the SABRINA mission, most of them never experimented previously from two spaceborne platforms. Important scientific and technological applications are associated to each technique: moving target indication, topography, geology, geomorphology, oceanography, biomass evaluation, improvement of monostatic data quality, accurate pointing and attitude determination. Great effort is devoted to individuate the main functional specifications need to obtain the individuated applicative products and the expected performance of the SABRINA mission.

SAR-based sea traffic monitoring: a reliable approach for maritime surveillance

Maritime surveillance problems are drawing the attention of multiple institutional actors. National and international security agencies are interested in matters like maritime traffic security, maritime pollution control, monitoring migration flows and detection of illegal fishing activities. Satellite imaging is a good way to identify ships but, characterized by large swaths, it is likely that the imaged scenes contain a large number of ships, with the vast majority, hopefully, performing legal activities. Therefore, the imaging system needs a supporting system which identifies legal ships and limits the number of potential alarms to be further monitored by patrol boats or aircrafts. In this framework, spaceborne Synthetic Aperture Radar (SAR) sensors, terrestrial AIS and the ongoing satellite AIS systems can represent a great potential synergy for maritime security. Starting from this idea the paper develops different designs for an AIS constellation able to reduce the time lag between SAR image and AIS data acquisition. An analysis of SAR-based ship detection algorithms is also reported and candidate algorithms identified.

SPACE STATION BASED TETHERED INTERFEROMETER FOR NATURAL DISASTER MONITORING

A synthetic aperture radar interferometer based on two vertically spaced physical antennas carried along parallel paths by the Space Station and by a small tethered subsatellite is presented. This remote sensing system is aimed at producing and updating topographic maps. In particular, it offers geometric, radiometric, and temporal resolutions adequate for natural-disaster monitoring. The system performance is identified by means of a computer simulation, taking account of the tethered platform dynamics and of the Space Station orbital decay. Numerical results show the capability of observing any point of the Earth surface in the range of latitudes ±51.6 deg with a repetitivity of about 2 days, by using range steering of the antenna beams (15-45 deg). Then, the attitude pointing accuracy requirements are derived by evaluating the signal-to-noise ratio and the swath overlap decrease due to the antenna misalignment (yaw 0.15 deg, pitch 0.10 deg, roll 0.20 deg).

Wake-based ship route estimation in high-resolution SAR images

This paper presents a novel algorithm for wake detection in Synthetic Aperture Radar images of the sea. The algorithm has been conceived as part of a ship traffic monitoring system, in charge of ship detection validation and to estimate ship route features, such as heading and ground speed. In addition, it has been intended to be adequate for inclusion in an automatic procedure without human operator supervision. The algorithm exploits the Radon transform to identify the images ship wake on the basis of the well known theoretical characteristics of the wakes’ geometry and components, that are the turbulent wake, the narrow-V wakes, and the Kelvin arms, as well as the typical appearance of such components in Synthetic Aperture Radar images of the sea as bright or dark linear feature. Examples of application to high-resolution X-band Synthetic Aperture Radar products (COSMOSkymed and TerraSAR-X) are reported, both for wake detection and ship route estimation, showing the achieved quality and reliability of wake detection, adequacy to automatic procedures, as well as speed measure accuracy.

Remote sensing satellite formation for bistatic synthetic aperture radar observation

In recent years the Italian Space Agency has been proceeding to the definition and launch of small missions. In this ambit, the BISSAT mission was proposed and selected along with five other missions for a competitive Phase A study. BISSAT mission 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. Several scientific applications of bistatic measurements can be envisaged: improvement of image classification and pattern recognition, derivation of medium-resolution digital elevation models, velocity measurements, measurements of sea-wave spectra. BISSAT payload is developed on the basis of the X-band SAR of the COSMO/SkyMed mission, while BISSAT bus is based on an upgrade of MITA. Orbit design has been performed, leading to the same orbit parameters apart from the ascending node right ascension (5.24 degree(s) shift) and the time of the passage on the ascending node (1.17s shift). A minimum distance at the passage of the orbit crossing point of about 42 km (5.7s) is computed. To maintain adequate swath overlap along the orbit, attitude maneuver or antenna electronic steering must be envisaged and traded-off taking into account radar performance and cost of hardware upgrade.