Roberto Formaro

The PRISMA mission

PRISMA (PRecursore IperSpettrale della Missione Applicativa) is an innovative Italian Earth Observation mission using a Hyperspectral/Panchromatic instrument based on a pushbroom scanning technique. The PRISMA mission development is completely funded by ASI (Italian Space Agency) and includes the system development program and the related applications and research activities. The system program is in the development phase (ECSS standard C/D phase) in the framework of a contract signed between ASI and an Italian Industries Consortium, including also the system on orbit commissioning. The launch is planned for the beginning of 2018. Thanks to the Low Earth, Sun Synchronous orbit placement, PRISMA will acquire up to 200.000 km2 of daily Panchromatic/hyperspectral images within an Area of interest bounded by 180°W÷180°E - 70°S÷70°N, supporting many earth observation applications with relevant data. The Italian Science Community has been involved both in supporting the system development program, mainly for Calibration and Validation activities and algorithm developments, and in promoting research and applications based on Panchromatic/Hyperspectral remote sensed data.

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.

Progress in the hyperspectral payload for PRISMA programme

The PRISMA (PRecursore IperSpettrale della Missione Applicativa) Programme is an ASI (Agenzia Spaziale Italiana) hyperspectral mission for Earth observation based on a mono-payload single satellite: an Italian Consortium is in charge to realize the mission; Selex ES has the full responsibility of the hyperspectral payload composed by a high spectral resolution spectrometer optically integrated with a medium resolution panchromatic camera. The optical design permits to cover the wavelength range from 400 to 2500 nm and it is based on high transmittance optical assemblies, including a reflective common telescope in Three-Mirror Anastigmat (TMA) configuration, a single slit aperture, a panchromatic camera (700-900 nm) and a spectrometer having two channels (VNIR and SWIR), each one using an suitable prism configuration and spectrally separated by a beam splitter, conceived to minimize the number of optical elements. High performance MCT-based detectors represent the core of the instrument. To provide the required data quality for the entire mission lifetime (5 years), an accurate and stable calibration unit (radiometric and spectral) is integrated, for the in-flight instrument calibration. The thermal design has been based on a passive cooling system: a double stage radiator, suitable oriented and protected from unwanted heat fluxes, high performance heat pipes and an operational heaters network represent the solution adopted to achieve the required thermal stability.

Multimode/multifrequency low frequency airborne radar design

This work deals with the design of multimode/multifrequency airborne radar suitable for imaging and subsurface sounding. The system operates at relatively low frequencies in the band ranging from VHF to UHF. It is able to work in two different modalities: (i) nadir-looking sounder in the VHF band (163MHz) and (ii) side-looking imager (SAR) in the UHF band with two channels at 450MHz and 860MHz. The radar has been completely designed by CO. Ri. S. T. A. for what concerns the RF and the electronic aspect, and by the University of Calabria for what concerns the design, realization, and test of SAR antennas. The radar has been installed on a civil helicopter and its operation has been validated in flight in both sounder and imager modality. Preliminary surveys have been carried out over different areas of Campania region, South Italy.

Multimode multifrequency low frequency airborne radar

In the recent years a new class of airborne radar system using low frequency have emerged. They are sounder working at VHF/UHF band and SAR (Synthetic Aperture Radar) that are able to provide high resolution images at P and L band. Behind these developments lie technological advances in antenna design, low noise amplifiers, band pass filters, digital receiver technology as well as new processing algorithms. The combination of low frequency and high bandwidth, creates a variety of military an civilian applications, ranging from the detection of targets concealed by foliage and/or camouflage or buried to forestry applications, biomass measuring, Archeological and geological exploration. Following these potentialities, the Italian Space Agency promoted the development of a new multi-mode and multi-band airborne radar system, that can be considered also a “proof-of-concept” for future dedicated spaceborne missions. The research consortium CO.RI.S.T.A. is in charge of the design, development and flight validation of such system, that is the first airborne radar entirely built in Italy.The radar is able to work either as nadir-looking sounder at VHF band (163 Mhz) and as side booking imager (SAR) at P band with two channels at 450 MHz and 900 MHz. The system uses a very flexible architecture due to the implementation of a direct digital synthesis(DDS) of transmitted signal and of stepped-frequency technology that allows the transmission of large bandwidth and facilitates multiple polarizations. Radar is controlled and timed by a powerful control unit based on FPGA technology that is also able to store all data with high data rate directly on SATA disks. Some flight campaigns have been performed on south Italy by using a helicopter of Aeronautica Militare. The present work presents a detailed system description, performance analysis, data processing algorithms and measurement campaign results description.

Airborne GPR surveys via tomographic imaging: An analysis of the reconstruction capabilities

GPR systems installed on helicopters or spotter planes represent effective monitoring tools to cover surface and underground characterization of wide areas. In this respect, the paper discusses the on field reconstruction capabilities resulting from the joint exploitation of a novel sounder system and an advanced data processing approach. The sounder system was built by CORISTA in collaboration with the Italian Space Agency, which promoted and founded the project. It is a pulsed radar working at 163 MHz and transmits a 10 MHz linearly frequency modulated signal (chirp) by using DDS (Direct Digital Synthesizer) technique. The transmitted peak power is about 200W over a 3μsec pulse length. The system exploits a log periodic antenna with four elements, GPS and an INS are used for storing position and attitude information. The data processing is faced by means of a microwave tomographic reconstruction approach, which is based on a simplified scattering model. In particular the Born approximation is adopted to formulate the imaging as a linear inverse scattering problem. The effectiveness of the system is shown by means of the tomographic images corresponding to the first trial surveys made with the sounder installed on a helicopter of the Italian Air Force.

Preliminary performance analysis and design for a distributed P-band synthetic aperture radar

This paper focuses on a new concept for spaceborne P-band radar implementation, that is distributed SAR based on formation flying. This approach can in principle allow to overcome physical constraints that limit the performance of monolithic SARs, leading in the P-band case to huge antennas and hard swath/resolution trade-offs. The proposed SAR is based on a larger transmitting satellite and a set of light-weight receiving-only platforms. This architecture also allows for multi-mission capabilities. In particular, in the P-band case forests observation and biomass estimation can be in theory combined with interferometric ice sounding. Payload concept is clarified, and a preliminary performance analysis in terms of ambiguity and coverage is proposed.

Interferometric experiments with the first Italian airborne P-band radar

This work aims to describe the characteristics and the status of development, including the results of a first preliminary testing campaign, of a low frequency airborne imaging radar developed in Italy for the Italian Space Agency.

Ring-field TMA for PRISMA: theory, optical design, and performance measurements

PRISMA (PRecursore IperSpettrale della Missione Applicativa) Hyperspectral Payload is an Electro-Optical instrument developed in Selex ES for the dedicated ASI (Italian Space Agency) mission for Earth observation. The performance requirements for this mission are stringent and have led to an instrument design that is based on a Ring-Field Three Mirror Anastigmat (Ring-Field TMA), a two channel prism dispersion based spectrometer (VNIR and SWIR), and a Panchromatic Camera. The Ring-Field TMA contains three mirrors (two conics and one conic with some higher order correction). Exceptional performance has been achieved by not only introducing 3rd order astigmatism to balance the 5th astigmatism at the ring field zone as is traditional in an Offner-type design but, additionally, 3rd order coma has been controlled to align the balance of the linear and field cubic coma terms at the same ring field zone. The predicted wavefront performance of the design over the field of view will be highlighted. An assembly and alignment procedure for the Ring-Field TMA has been developed from the results of the sensitivity and tolerances analysis. The tilt and decenter sensitivity of the design form is nearly exclusively determined by 3rd order binodal astigmatism. The nodal position is linear with perturbation, which greatly simplifies the decisions on alignment compensators. The manufactured mirrors of the Ring-Field TMA have been aligned at Selex ES and as will be reported the preliminary results in terms of optical quality are in good agreement with the predicted as-built performance, both on-axis and in the field.

The PRISMA hyperspectral imaging spectrometer: detectors and front-end electronics

Two detectors, SWIR and VNIR, and relevant front-end electronics were developed in the frame of the PRISMA(Precursore Iperspettrale della Missione Applicativa) project, an hyperspectral instrument for the earth observation. The two detectors were of the MCT type and, in particular, the VNIR was realized by Sofradir by using the CZT(Cadmium Zinc Telluride substrate of the PV diodes) substrate removal to obtain the sensitivity in the visible spectral range. The use of the same ROIC permitted to design an unique front-end electronics. Two test campaigns were carried out: by Sofradir, only on the detectors, and by Selex ES, by using the PRISMA flight electronics. This latter tests demonstrated that was possible to obtain the same detector performance, with respect of those ones obtained by a ground setup, with a flight hardware in terms of noise, linearity and thermal stability.