Giovanni Alberti

The TOPSAR interferometric radar topographic mapping instrument

The authors have augmented the NASA DC-8 AIRSAR instrument with a pair of C-band antennas displaced across track to form an interferometer sensitive to topographic variations of the Earths surface. During the 1991 DC-8 flight campaign, data were acquired over several sites in the US and Europe, and topographic maps were produced from several of these flight lines. Analysis of the results indicate that statistical errors are in the 2-4-m range, while systematic effects due to aircraft motion are in the 10-20-m range. The initial results from development of a second-generation processor show that aircraft motion compensation algorithms reduce the systematic variations to 2 m, while the statistical errors are reduced to 2-3 m. >

Subsurface Radar Sounding of the Jovian Moon Ganymede

This paper provides an overview of the Europa Jupiter System Mission (EJSM) and of its scientific objectives, focusing the attention on the subsurface radar (SSR) instrument included in the model payload of the Jupiter Ganymede Orbiter (JGO). The SSR instrument is a radar sounder system at low frequency (HF/VHF band) designed to penetrate the surface of Ganymede icy moon of Jupiter for performing a subsurface analysis with a relatively high range resolution. This active instrument is aimed at acquiring information on the Ganymede (and partially on the Callisto during flybys) shallow subsurface. The paper addresses the main issues related to SSR, presenting its scientific goals, describing the concept and the design procedure of the instrument, and illustrating the signal processing techniques. Despite the fact that SSR can be defined on the basis of the heritage of the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) and SHAllow RADar (SHARAD) instruments currently operating at Mars, the EJSM mission poses additional scientific and technical challenges for its design: 1) the presence of a relevant Jupiter radio emission (which is very critical because it has a significant power spectral density in proximity of the expected SSR central frequency); 2) the properties of the subsurface targets, which are different from those of the Mars subsurface; 3) the different orbit conditions; and 4) the limited available resources (in terms of mass, power, and downlink data rate). These challenges are analyzed and discussed in relation to the design of the instrument in terms of: 1) choice of the central frequency and the bandwidth; 2) signal-to-noise ratio (SNR); 3) signal-to-clutter ratio (SCR); and 4) definition of the synthetic aperture processing. Finally, the procedure defined for SSR performance assessment is described and illustrated with some numerical examples.

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.

RIME: Radar for Icy Moon Exploration

This paper presents the Radar for Icy Moons Exploration (RIME) instrument, which has been selected as payload for the JUpiter Icy moons Explorer (JUICE) mission. JUICE is the first Large-class mission chosen as part of the ESAs Cosmic Vision 2015-2025 programme, and is aimed to study Jupiter and to investigate the potentially habitable zones in the Galilean icy satellites. RIME is a radar sounder optimized for the penetration of Ganymede, Europa and Callisto up to a depth of 9 km in order to allow the study of the subsurface geology and geophysics of the icy moons and detect possible subsurface water. In this paper we present the main science goals of RIME, the main technical challenges for its development and for its operations, as well as the expected scientific returns.

A Waveform Model for Near-Nadir Radar Altimetry Applied to the Cassini Mission to Titan

The radar altimeter of the Cassini mission to Titan operates in a transition region between pulse- and beam-limited conditions. Due to the specific observation geometry, low values of mispointing angle have been found to significantly affect altimeter impulse response (IR). This involves a nonconventional formulation of the system response which is the main goal of this paper. An analytical model of the average return power waveform, valid for near-nadir altimetry measurements, has been developed in order to cope with the particular operating conditions of Cassini mission. The model used to approximate the altimeter waveform is based on the same general assumptions of the classical Browns model (1977) but exploits a flat surface response approximation by Pronys methods. Both theoretical considerations and simulated data have been taken into account to support the accuracy of the proposed model. To infer the main geophysical parameters describing surface topography from altimetry data, a parametric estimation procedure has been used. The maximum likelihood estimator procedure has been chosen since, in principle, it can assure optimal performance as a consequence of the analytical model we used to describe the system IR. Performances of the implemented method have been numerically evaluated through simulation of data received by CASSINI in high-resolution altimeter mode.

Advanced stepped-frequency GPR development

In the framework of ARCHEO, a national research project funded by the Italian Ministry for Universities and Scientific and Technological Research, a new ground penetrating radar has been developed by the Italian Consortium for Research on Advanced Remote Sensing Systems. The system has been specially designed to meet archaeological requirements and it will be used to identify and characterize buried finds. The paper summarizes the main guidelines followed during the design phase and presents the radar architecture.

On multifrequency strategies of use of GPR systems

In the framework of ARCHEO, a national research project funded by the Italian Ministry for Universities and Scientific and Technological Research (M.U.R.S.T.), a new ground penetrating radar (GPR) has been developed by the Italian Consortium for Research on Advanced Remote Sensing Systems (CO.RI.S.T.A.). The system has been specially designed to meet archaeological requirements and it will be tested the two archaeological sites of Sinuessa and Cales, in the Southern Italy. An innovative feature of ARCHEO concerns the exploitation of that of a multiview multistatic measurement scheme (at several frequencies) rather than a more common multimonostatic (or multibistatic). In order to reconstruct buried objects starting from the measurement data collected with such an acquisition strategy, it is made use of an inverse scattering technique. With the real project ARCHEO in mind (in particular this scheme of measurement), this paper deals with a theoretical discussion on the features of the class of retrievable profiles by G.P.R. data, within the framework of a linear model for electromagnetic scattering in a two dimensional lossless half space. For a given range of frequencies exploitable, multiview multistatic measurements can be useful in G.P.R. prospecting because they can provide information on low spatial harmonic components of an unknown object not attainable from the multimonostatic scheme exploiting the same frequency range. In particular, we show that, for a given band of work frequencies, the class of the unknowns retrievable by a multiview multistatic multifrequency measurement configuration can be is not much different from that attainable within a multimonostatic configuration with the addition of multiview multistatic data taken at the lowest of the frequencies adopted.

Jupiter ICY moon explorer (JUICE): Advances in the design of the radar for Icy Moons (RIME)

This paper presents the Radar for Icy Moon Exploration (RIME) that is a fundamental payload in the Jupiter Icy Moon Explorer (JUICE) mission of the European Space Agency (ESA). RIME is a radar sounder aimed to study the subsurface of Jupiters icy moons Ganymede, Europa and Callisto. The paper illustrates the main goals of RIME, its architecture and parameters and some recent advances in its design.

Design and Validation of a Multimode Multifrequency VHF/UHF Airborne Radar

This letter deals with the design, realization, and validation of a multimode/multifrequency airborne radar designed for both surface and subsurface prospections. The system operates in the frequency band from very high frequency (VHF) to ultrahigh frequency (UHF) and works in two different modes: 1) a nadir-looking sounder in the VHF band (carrier frequency of 163 MHz); and 2) a side-looking imager (i.e., synthetic aperture radar) in the UHF band with two channels at 450 and 860 MHz, respectively. The system validation has been carried out for the “sounder” mode due to helicopter-borne surveys carried out over an area in the Campania region, Southern Italy. The surveys have provided a first proof of system capability in obtaining useful information about the surface and shallower subsurface layers over a large scale and in a relatively short time. In particular, the data collected by the sounder have been processed by means of a microwave tomographic reconstruction approach, and features consistent with tunnels buried at a depth of 15 m have been identified.

Current status of the development of an Italian airborne SAR system (MINISAR)

MINISAR is a compact airborne interferometric SAR potentially suitable for many applications but mainly finalized for the production of technical topographic maps and monitoring the evolution of landslides events and assessing their extension and risk area. The program is co-funded by the Italian Ministry for Education, Universities and Research (M.I.U.R.) The hardware consists in an airborne X-band radar, able to obtain a resolution less than a meter (because of a 280 MHz stepped chirp signal) and an altimetric accuracy less than 7 meters. Such an accuracy derives from an equivalent 1.5 meters baseline and the high gain antennas that let MINISAR to use a transmitted power of only 80 W. The system will be mounted on board of a small platform and it is thought to have future development for unmanned platform. Data will be processed using a chirp scaling algorithm in order to obtain the two Single Look Complex (SLC) images which can be then processed to obtain high accuracy Digital Elevation Model (DEM).