PRISMA is the hyperspectral mission from the Italian Space Agency (ASI) launched in 2019. It samples the solar irradiance reflected and diffused by the earth-atmosphere system between 400 nm and 2500 nm with a spectral distance better than 11nm and a 30m Ground Sampling Distance. To answer the demanding need of hyperspectral applications, a high absolute radiometric accuracy is required and reached through the combination of on board and natural targets based calibration.
This paper describes PRISMA mission and focuses on the natural targets based calibration methods used to assess the instrument sensitivity. Two methods are used:
- PICS (Pseudo Invariant Calibration Sites) allow to cross-calibrate PRISMA with SENTINEL-2 and 3 ESA missions.
- Gobabeb and La Crau Instrumented sites known as RadCalNet sites which provide a BOA spectral BRDF through a dedicated acquisition protocol and processing as well as atmospheric parameters simultaneously to the satellite pass.
The adaptation of these methods to hyperspectral sensors calibration is presented. The calibrations results which show the very good temporal stability of PRISMA instrument are discussed as well as the methods and in situ instrumentation evolutions planned to improve the calibration of hyperspectral sensors using natural targets.
Hyperspectral space imagery is an emerging technology that supports many scientific, civil, security and defence operational applications. The main advantage of this remote sensing technique is that it allows the so-called Feature Extraction: in fact the spectral signature allows the recognition of the materials composing the scene. Hyperspectral Products and their applications have been investigated in the past years by Galileo Avionica to direct the instrument characteristics design. Sample products have been identified in the civil / environment monitoring fields (such as coastal monitoring, vegetation, hot spot and urban classification) and in defense / security applications: their performances have been verified by means of airborne flight campaigns. The Hyperspectral and High Resolution Imager is a space-borne instrument that implement a pushbroom technique to get strip spectral images over the Hyperspectral VNIR and SWIR bands, with a ground sample distance at nadir of 20m in a 20 km wide ground swath, with 200 spectral channels, realizing an average spectral resolution of 10nm. The High Resolution Panchromatic Channel insists in the same swath to allow for multiresolution data fusion of hyperspectral imagery.
Nowadays hyperspectral imaging is a well-established methodology for the non-invasive diagnostics of polychrome surfaces, and is increasingly utilized in museums and conservation laboratories for documentation purposes and in support of restoration procedures. However, so far the applications of hyperspectral imaging have been mainly limited to easel paintings or paper-based artifacts. Indeed, specifically designed hyperspectral imagers, are usually used for applications in museum context. These devices work at short-distances from the targets and cover limited size surfaces. Instead, almost still unexplored remain the applications of hyperspectral imaging to the investigations of frescoes and large size mural paintings. For this type of artworks a remote sensing approach, based on sensors capable of acquiring hyperspectral data from distances of the order of tens of meters, is needed.
This paper illustrates an application of hyperspectral remote sensing to an important wall-painting by Beato Angelico, located in the San Marco Museum in Florence. Measurements were carried out using a re-adapted version of the Galileo Avionica Multisensor Hyperspectral System (SIM-GA), an avionic hyperspectral imager originally designed for applications from mobile platforms. This system operates in the 400-2500 nm range with over 700 channels, thus guaranteeing acquisition of high resolution hyperspectral data exploitable for materials identification and mapping. In the present application, the SIM-GA device was mounted on a static scanning platform for ground-based applications. The preliminary results obtained on the Angelico’s wall-painting are discussed, with highlights on the main technical issues addressed to optimize the SIM-GA system for new applications on cultural assets.
Airborne hyperspectral imagery is valuable for military and civilian applications, such as target identification, detection
of anomalies and changes within multiple acquisitions. In target detection (TD) applications, the performance assessment
of different algorithms is an important and critical issue. In this context, the small number of public available
hyperspectral data motivated us to perform an extensive measurement campaign including various operating scenarios.
The campaign was organized by CISAM in cooperation with University of Pisa, Selex ES and CSSN-ITE, and it was
conducted in Viareggio, Italy in May, 2013. The Selex ES airborne hyperspectral sensor SIM.GA was mounted on board
of an airplane to collect images over different sites in the morning and afternoon of two subsequent days.
This paper describes the hyperspectral data collection of the trial. Four different sites were set up, representing a complex
urban scenario, two parking lots and a rural area. Targets with dimensions comparable to the sensor ground resolution
were deployed in the sites to reproduce different operating situations. An extensive ground truth documentation
completes the data collection.
Experiments to test anomalous change detection techniques were set up changing the position of the deployed targets.
Search and rescue scenarios were simulated to evaluate the performance of anomaly detection algorithms. Moreover, the
reflectance signatures of the targets were measured on the ground to perform spectral matching in varying atmospheric
and illumination conditions. The paper presents some preliminary results that show the effectiveness of hyperspectral
data exploitation for the object detection tasks of interest in this work.
A software tool for a simplified end-to-end simulation of data products from space-borne and airborne visible, nearinfrared
and short-wave infrared imaging spectrometers, starting from either synthetic or airborne hyper-spectral data,
has been developed and tested. Such a simulator is conceived as a preliminary aid tool (during phase 0⁄A) for the
specification and early development of new Earth observation optical instruments, whose compliance to user’s
requirements is achieved through a process of cost/performance trade-off. The proposed simulator is based on three
principal core modules: the reflectance scenario simulator, the atmospheric simulator and the instrument simulator. High
spatial/spectral resolution images with low intrinsic noise and the sensor/mission specifications are used as inputs.
Examples of hyper-spectral and panchromatic images for existing and future instruments are reported, showing the
capabilities for simulating target detection scenarios and image quality assessment. The Selex-ES simulator, as compared
with other existing software, implements all modules necessary for a complete image simulation, allowing excellent
flexibility and expandability for new integrated functions because of the adopted IDL-ENVI software environment. The
simulation modeling has been validated and assessed through the matching between synthetized and true spectra
acquired at ground and airborne level for clay soil mapping. A simulation of the same clay map at satellite scale has also
demonstrated a more than acceptable agreement considering the coarser spatial resolution as compared to the airborne
scale.
A software tool for end-to-end simulation of data products of spaceborne and airborne visible, near-infrared and short-wave infrared imaging spectrometers, starting from either synthetic or airborne hyperspectral data, has been developed and tested. Such a simulator is conceived as a preliminary aid tool (during phase 0/A ) for the specification and early development of new Earth observation optical instruments, whose compliance to user's requirements is achieved through a process of cost/performance trade-off. The proposed simulator is based on three different core modules: the reflectance scenario simulator, the atmospheric simulator, and the instrument simulator.The main novelty of this paper is that the modeling adopted for the simulator is validated and assessed through the matching of synthetized spectra, both radiance and reflectance, to true spectra measured on an agricultural clay bare soil by means of a hand-held point spectrometer and an airborne instrument developed and manufactured by Selex Galileo S.p.A. Both pure and mixed spectra show a high degree of matching between true and synthetic data, thereby establishing the validity of the underlying linear spectral mixing model. Furthermore, a validation of an application test has been performed for clay soil mapping at ground and airborne level. Eventually,a satellite instrument simulation of the same clay map has demonstrated a more than acceptable agreement notwithstanding the low spatial resolution.
Spectral Hemispherical Reflectance data, covering both VIS and SWIR wavebands, from 400 to 1800 nm, obtained by
the investigation of laboratory controlled polluted water samples, are presented.
In the frame of the article, the description of a dedicated equipment, consisting of a wide band illuminator based on a
super quite Xenon lamp and a colour corrected NSF6-CaF2 objective, a dedicated tank, a custom integrating sphere
coated with ZenithTM diffuser interfaced to a ASD Field Spec spectrometer, is given.
With such an equipment, spectral hemispherical reflectivity data have been achieved on water samples, "polluted", under
controlled conditions, with known quantities of oils, as examples of some typical oil pollutants of the marine
environment. The experimental data obtained by means of the proposed apparatus, collected in a controlled way, allow to
get fundamental measurement necessary to evaluate optical properties of liquids and materials to be used for optical
modelling and spectral reflectance behaviour. Such a data are difficult to be achieved in literature in such a wide spectral
range. They will serve to set up inversion algorithms for remote sensing applications.
The wide variety of possible features that can be explored through the proposed equipment, jointed to its flexibility,
constitute a reference point for future investigations on the characterisation of the reflectance properties of liquids.
This work presents a comparative experimental analysis of different Anomaly Detectors (ADs) carried out on a high
spatial resolution data set acquired by the prototype hyperspectral sensor SIM-GA. The benchmark AD for hyperspectral
anomaly detection is the Reed-Xiaoli (RX) algorithm. Its main limitation is the assumption that the local background can
be modeled by a Gaussian distribution. In the literature, several ADs have been presented, most of them trying to cope
with the problem of non-Gaussian background. Despite the variety of works carried out on such algorithms, it is difficult
to find a comparative analysis of these methodologies performed on the same data set and therefore in identical operating
conditions. In this work, the most known ADs, such as the RX, Orthogonal Subspace Projection (OSP) based algorithms,
the Cluster Based AD (CBAD), and the Signal Subspace Processing AD (SSPAD) are analyzed and compared,
highlighting their most interesting characteristics. The performance is evaluated on a new data set relative to a rural
scenario, in which several man-made targets have been embedded. The non-homogeneous nature of the background,
enhanced by the high spatial resolution of the sensor, and the presence of man-made artifacts, like buildings and
vehicles, make the anomaly detection process very challenging. Performance comparison is carried out on the basis of a
joint analysis of the Receiving Operative Characteristics and the image statistics. For this data set, the best performance
is obtained by the strong background suppression ability of the OSP-based algorithm.
The definition and preliminary design of a thermal imager for earth observation applications has been performed, justified by a thorough analysis of user requirements. A survey of international programmes and other sources have been used to derive the radiometric requirements at ground level. Then instrument requirements at top of atmosphere have been obtained by means of the usual split-window techniques for land and sea. Preliminary instrument radiometric performances have been estimated on the basis of a review of possible instrument concepts (detectors and scan modes). A trade-off analysis between instrument requirements and performances led to the identification of two classes of instruments - the first based on high performance, cooled infrared detectors, and the second relying on microbolometer technology, with lower performance but not constrained by the need for a cryocooler. The applications feasible by means of each of them have been identified. The chosen instrument baseline was that using uncooled microbolometers, for which the best spatial and radiometric resolution achievable has been assessed, in order to cover as many applications as possible in view of the analysis of requirements. The selected baseline has been further detailed, up to a complete outline of the instrument, in order to confirm the achievable performance and assure its feasibility.
The Officine Galileo (OG) Hyperspectral Camera (HYC) (currently under development in the frame of the Hypseo ASI program) consists of an high spatial resolution (20 m) imaging spectrometer working in the visible and SWIR bands, to be embarked on future low earth orbit operational satellites. The mission requirements include monitoring of vegetation, coastal/internal waters and geology/hydrology. The instrument works with a swath of 20 Km and steering capability within 500-Km across-track. It operates in about 210 spectral bands of 10 nm of resolution. The objective of the present work is the evaluation of application performances of the HYC camera compared to those of multi- spectral sensors (e.g. ETM+/Landsat 7), carried out by means of images and products simulations. For this scope some airborne campaigns have been performed with hyper- spectral sensors (VIRS, MIVIS) in a test area of Tuscany region (1), with contemporaneous collection of ground/sea truth data. HYC and ETM+ radiance images have been simulated by means of surface reflectance maps obtained from the airborne sensors, applying the MODTRAN atmospheric code and the HYC (and ETM+) instrumental models (spatial, spectral and noise degradation). The retrieval of surface reflectance has been performed by means of an atmospheric correction algorithm based on the dark pixel method. Next, two test products (forest classification and river plumes analysis) have been simulated; the first based on a maximum likelihood classification method and the second based on multivariate regression analysis. The results have been validated with ground truth data for different atmospheric conditions. Classification error decreases from 22% (ETM+) to 13% (HYC), whereas suspended sediments accuracy error decreases from 24% (ETM+) to 15% (HYC) in the tested conditions. The implemented methodology has allowed studying the better trade-off between product accuracy and instrumental requirements.
Research on the analysis of ERS1/SAR data for hydrological applications has been carried out in the Abruzzo region aiming at the integration of microwave (MW) remote sensing (RS) derived data with territorial databases for soil degradation studies. Three different field campaigns were carried out at the same time as the ERS1 overflights collecting dielectric constant, soil moisture content, and surface roughness data. Electromagnetic models (EM) were used to predict the backscattering coefficient of bare fields where ground truth data were collected. Such data were therefore compared with the ones calculated from the SAR images.
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