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A forward-looking 36 GHz radar for aircrafts and helicopters is presented. It uses the rotating synthetic aperture for obtaining the azimuth resolution and independent radars with different antenna elevation angles for obtaining the elevation resolution. Main radar functionalities are the guidance for landing phase including the three-dimensional view, strike avoidance, moving target indication and detection of stationary air and ground obstacles. This article describes the radar principle, its modeling and an implementation example for a given operational requirement.

A real-time monitoring system based on ground-based synthetic aperture radar interferometry (GB-InSAR) were developed and deployed with the objective to gain understanding of landslide dynamics in an area in Xerem (district of Duque de Caxias - RJ, Brazil). The area is subjected to landslide risk and the deployed system aims to provide subsidies to the authorities to prepare actions related to prevention and evacuation, and serve as the basis for a future early-warning system in the framework of the Civil Defense of Duque de Caxias. The system consists of a compact and rugged X-band GB-InSAR newly developed by Bradar, Brazil. The processing and monitoring methodology are proposed. Two campaigns, totaling six days, were carried out. The acquisitions of the first campaign occurred without rain. In the second campaign, rain events, varying from light to torrential rainfall, occurred for a period of time, in subsequent days, during the radar acquisitions. New insights on landslide dynamics are revealed. The monitoring data show that, approximately 10 h after heavy rainfall, the terrain movement on a slope reached 4 mm/h during ca. 5 to 8 h, resulting in velocities of 20 to 32 mm/day.

Remote sensing has been widely employed for monitoring land cover and usage by change detection techniques. In this paper, we cope with the early detection of the first signs of deforestation, which is the gateway for illegal activities, such as unauthorized urban sprawl and grazing use. In recent years, object-based approaches have emerged as a more suitable alternative than pixel-based methods for change detection in remote sensing images. Even though several classifiers have been tested, there was little effort in selecting appropriated features for the classification of detected changes. After a deep analysis of the existing segmentation, feature extraction, and classification approaches, we propose an object-based methodology that consists of: 1) segmenting multitemporal Xband high-resolution synthetic aperture radar (SAR) images into superpixels employing the simple linear iterative clustering algorithm; 2) extracting features using the object correlation images framework and with the gray-level cooccurrence matrix; and 3) classifying areas into unchanged, deforestation, and other changes by means of a multilayer perceptron supervised learning technique. Experiments were performed using high-resolution SAR images obtained by the airborne sensor OrbiSAR-2 from BRADAR in challenging scenarios of the Brazilian Atlantic Forest, including a wide variety of vegetation, rivers, sea coasts, urban, harvest and open areas, and humidity changes. We perform an extensive experimental analysis of the results, comparing the proposed method with a state-of-the-art approach. The results demonstrate that our method yields an improvement of over 10% in the accuracy while detecting changes and classifying deforested areas.

There are basically two methods for retrieving the ground and the canopy height from interferometric synthetic aperture radar (InSAR) in forested areas. The first method is based on the difference between InSAR height estimations from dual-band (DB) systems, typically operating at X- and P-bands HH. The second method is based on the modeling of the polarimetric (Pol) InSAR response along the forest vertical structure, typically at L- or P-band. This paper proposes the combination of both methods, so that the ground and total tree height estimations are improved and become available alongside the interferometric forest height with the usage of polarimetric data and the RVoG model adoption in both bands. In the proposed method (DB-PolInSAR), first, the ground phase is retrieved from the RVoG inversion through a straightforward line fit of the P-Band polarimetric data in the complex plane. Fixing the ground height coming from the previous P-band inversion and applying the RVoG model to the X-band interferometric data, we estimate the total tree height. Repeat-pass dual-polarimetric (HH and HV) P-band data and single-pass three-baseline HH X-band data acquired with the airborne OrbiSAR sensor of Bradar over the Amazon region of Urucu are used to demonstrate the proposed method. Comparisons between the dual-band PolInSAR and the dual-band single-polarization cases are performed for five different P-band single-baseline configurations. Better ground estimation over range is obtained with the proposed method. Furthermore, the three-antenna single-pass X-band data enabled a robust RVoG total tree height inversion.

Recently, structural monitoring by radar remote sensing has become more necessary for both economic and security reasons. Infrastructure monitoring with no incorporated deformation sensors (e.g., old generation water dams for which regulations did not impose monitoring capabilities) is usually performed by regular in situ topographic surveys. However, these surveys cannot be performed very often, and alternative methods are desirable. A feasible nonintrusive way to monitor such a structure is with interferometric synthetic aperture radar (SAR) data that can be acquired with monostatic/bistatic sensors.

In a large number of scenarios and missions, the technical, operational and economical advantages of UAS-based photogrammetry and remote sensing over traditional airborne and satellite platforms are apparent. Airborne Synthetic Aperture Radar (SAR) or combined optical/SAR operation in remote areas might be a case of a typical "dull, dirty, dangerous" mission suitable for unmanned operation – in harsh environments such as for example rain forest areas in Brazil, topographic mapping of small to medium sparsely inhabited remote areas with UAS-based photogrammetry and remote sensing seems to be a reasonable paradigm. An example of such a system is the SARVANT platform, a fixed-wing aerial vehicle with a six-meter wingspan and a maximumtake- of-weight of 140 kilograms, able to carry a fifty-kilogram payload. SARVANT includes a multi-band (X and P) interferometric SAR payload, as the P-band enables the topographic mapping of densely tree-covered areas, providing terrain profile information. Moreover, the combination of X- and P-band measurements can be used to extract biomass estimations. Finally, long-term plan entails to incorporate surveying capabilities also at optical bands and deliver real-time imagery to a control station. This paper focuses on the remote-sensing concept in SARVANT, composed by the aforementioned SAR sensor and envisioning a double optical camera configuration to cover the visible and the near-infrared spectrum. The flexibility on the optical payload election, ranging from professional, medium-format cameras to mass-market, small-format cameras, is discussed as a driver in the SARVANT development. The paper also focuses on the navigation and orientation payloads, including the sensors (IMU and GNSS), the measurement acquisition system and the proposed navigation and orientation methods. The latter includes the Fast AT procedure, which performs close to traditional Integrated Sensor Orientation (ISO) and better than Direct Sensor Orientation (DiSO), and features the advantage of not requiring the massive image processing load for the generation of tie points, although it does require some Ground Control Points (GCPs). This technique is further supported by the availability of a high quality INS/GNSS trajectory, motivated by single-pass and repeat-pass SAR interferometry requirements.

Three different features of FOPEN (foliage penetration) SAR are presented, namely, forest ground modeling, slow movement measurements under the foliage and concealed target detection. The paper discusses, through latest results and ongoing work examples, how these features can be put together in order to derive new and valuable monitoring information under the vegetation cover such as risk assessment, illegal activities detection and early warning.

Airborne single-pass SAR interferometry (InSAR) is a standard and operational technique for generating accurate and precise digital elevation models (DEM). But as DEM demand on fidelity and fast delivery grow over the years, the InSAR technology is challenged by the need of offering the same high-quality DEM over large areas on practically any type of surface and topography. The intent of this paper is to demonstrate the importance of the adoption of the topography- and aperture-dependent motion compensation (TAD-MoCo) for airborne single-pass InSAR in mountain areas. Furthermore, we present the DEM obtained using a TAD-MoCo and a multi-baseline (MB) interferometry framework for airborne single-pass InSAR. DEM over forested terrain in mountains with very strong height variations are generated free of residual motion errors and without need of phase unwrapping with the OrbiSAR system of Bradar.

This paper reports an accurate numerical analysis of some technological solutions for embedded airborne radars in the P- and X-bands applied to remote sensing. The propagation analyzes are based on Floquet and transient simulations by taken into account the influence of an entire fuselage from a commercial plane and the vegetation electromagnetic characteristics, similar to Amazon rainforest, in order to reproduce a realistic situation.

This paper describes how high-precision digital elevation models (DEMs) are obtained over the Wadden Sea using the AeS-1 airborne interferometric radar. The Wadden Sea is an intertidal zone along the coast having height variations less than 5 m over 30 km and is free of vegetation. The resulting DEM has a grid spacing of 2.5 m and an absolute height accuracy of 5 cm root mean square (rms), as verified by theodolite measurements. This paper describes the radar system, the processing techniques, the test area, the results, and the verification procedure.

The paper addresses the analysis of high resolution interferograms relevant to urban areas and achieved by means of the X-band OrbiSAR system. The OrbiSAR system is an airborne SAR sensor capable of acquiring single pass and repeat pass interferometric SAR data at very high resolution. Such a system is thus capable of providing very appealing single-pass and repeat-pass interferometric data-sets characterized by high resolution. In this work, two data-sets, acquired over the urbanized cities of São José dos Campos and São Sebastião--SP, Brazil, will be analyzed with a twofold aim: first, to provide insight for the retrieval of high accuracy DEM on urbanized areas, second to show some results obtainable with the airborne Differential SAR Interferometry technique over urban areas

In this paper we present the design overview of the UAV-based P- (repeat-pass) and X-band (single-pass) interferometric SAR system of OrbiSat, Brazil. The main objective is to built a compact and flexible InSAR system capable of performing accurate topographic survey and differential interferometry. To our knowledge, this is the first UAV-based In-SAR system with such characteristics, multi-band and fixed-baseline (X-band), to be projected. The status, and some main project results and solution are described and depicted.

This paper describes the capabilities of the TELAER X-Band airborne SAR system, which has been upgrading according to a Italian National Research Council (CNR) funding. Such a system upgrading consists first of all in the realization of a multi-antenna system able to carry out, simultaneously, Across-Track (XT) and Along-Track (AT) SAR Interferometry (InSAR). Moreover, the system upgrading is also aimed at improving the performances achievable in repeat-pass applications, such as Differential SAR Interferometry, (DInSAR), which require very precise measurement of the tracks described during the flight by the SAR antennas.

Recently, some experiments demonstrated that reliable DIn-SAR measurements can be achieved at any band and that further time-series analyses can be applied for airborne data. However, most of the airborne DInSAR results, including the time-series, published so far have focused on short-term analyses (baselines within hours or few days). This paper presents the first worldwide airborne DInSAR survey at P- and X-band for measuring the land movements occurred within 1 year and 3 months. The survey was performed by the OrbiSAR system of OrbiSat under contract with Petrobras (CENPES), as part of a experiment with the objective to identify possible threats to the pipeline due to land movements in Sao Sebastiao-SP, Brazil. The measurements at P-band show reliable and coherent movements in 80% of the imaged vegetated areas with accuracy in the order of centimeters. At X-band we were able to reliably measure coherent movements in urban areas with accuracy in the order of millimeters. Through field work evidences, the paper analyses the causes of these small scale land movements, and howthey are related to geodynamic processes. A comparison between the DInSAR and in-loco inclinometer measurements is presented. The paper suggests some possible operational scenarios and discusses on the potential of the airborne DInSAR for land movement monitoring.

We present in this work a first assessment of the imaging and topographic mapping capabilities of the InSAeS4 system, which is a single-pass interferometric airborne X-Band Synthetic Aperture Radar (SAR). In particular, we first provide a brief description of the InSAeS4 sensor. Then, we discuss the results of our analysis on the SAR and interferometric SAR products relevant to the first flight-test campaign. More specifically, we have exploited as reference the GPS measurements relevant to nine Corner Reflectors (CRs) deployed over the illuminated area during the campaign and a laser scanner Digital Elevation Model (DEM). From the analysis carried out on the CRs we achieved a mean geometric resolution, for the SAR products, of about 0.14 m in azimuth and 0.49 m in range, a positioning misalignment with standard deviation of 0.07 m in range and 0.08 m in azimuth, and a height error with standard deviation of 0.51 m. From the comparison with the laser scanner DEM we estimated a height error with standard deviation of 1.57 m.

Various remote sensing technologies are presently used to derive land surface and sub surface information. Each individual system (sensor) has its own advantages and disadvantages. The new airborne interferometric RADAR system OrbiSAR-1, developed, manufactured and operated by Orbisat da Amazonia's Remote Sensing Division, created a new way of automated mapping. Due to the use of microwaves as sending and receiving impulses of the sensor, the system is independent of day light and can therefore even map at night. As the microwaves are not influenced by the presence of clouds, the system can even map in bad weather situations, like rain or closed cloud coverage.

In the last decade, interferometric SAR (InSAR) has reached a wide acceptance as being a suitable tool to generate high-precision digital elevation models. Especially in tropical areas, with nearly permanent cloud coverage, InSAR provides a cost-efficient means for mapping large areas in short time periods. However, the interaction of microwaves with vegetation is strongly dependant on their frequency, demanding a careful interpretation of the extracted information. Short waves like X-band are mainly scattered back from the top of the canopy, whereas P-band penetrates the foliage and gets reflected from trunk and soil, thus carrying the phase information (and therefore the height information as well) from bald earth. For the generation of topographic maps, generally the ground elevation rather than the surface elevation is required, whereas the surface and ground elevation together enable the estimation of additional physical parameters like vegetation height, density, or biomass.

P-band interferometric SAR sensors are currently gaining a wider recognition due to their capability to penetrate vegetation coverage, thus offering the possibility to derive the ground topography of vegetated regions such as forests or agricultural areas. Aerosensing's AeS-1 airborne SAR system operates in its P-band mode at 415 MHz with a bandwidth of 70 MHz, providing data with a ground resolution of approximately 3 m. Processing of these data needs particular operations in order to face several effects inherent in the airborne repeat-pass characteristic of the sensor. Subject of this paper is the end-to-end processing chain of AeS-1 data with respect to operational ground topography estimation. Elevation measurements are validated against a high-resolution digital surface model.

The goal of this paper is to present the generation of high resolution digital surface models using airborne AeS-1 interferometric SAR data, their automatic geocoding and mosaicing. In order to be able to carry out these steps, high precision differential Global Positioning System data, high frequency attitude data of the platform, exact time synchronization and range delay of the system must be known. Since in the airborne case motion instabilities are large, due to dynamic properties of the aircraft and atmospheric turbulences, precise motion measurements of the platform are extracted and considered during the SAR processing. Once that all these basic requirements are fulfilled, one is able, using the processing reference tracks, and exploiting a forward-backward geocoding, to convert the phase differences to elevation data and to geolocate them by taking into account all geodetic and cartographic transforms. Results based on 400 MHz X-band InSAR data show that the derived surface model has a positioning accuracy in the order of 0.5 m and a height accuracy better than 0.3 m.

This paper addresses a new PU algorithm based on the fusion of a region growing and an iteratively working 2D least-square PU. By the mutual support of the two algorithms it is possible to combine the advantages of both and to eliminate the errors occurring if each one is working independently. The resulting unwrapped phase is characterised by a local stability gained from the contribution of the global method as well as the global stability given by the local method. The performance of the presented PU fusion is significantly better in comparison to the performance of the conventional methods.

In this paper we investigate a least square algorithm to retrieve forest parameters from interferometric, fully polarimetric radar remote sensing P-band data, based on an interferometric optimization scheme which is applied to maximize the separation of scattering phase centers related to the pertinent interferometric coherences in order to obtain most accurate parameter inversion results. A recently developed approach is especially adopted to airborne P-band data, introducing a least square minimization scheme in which synthetic interferometric coherences computed from a scattering model, which is based on a randomly oriented volume over a non-penetrable ground, are compared with three interferometric coherences measured by the P-band sensor. Through fitting of the synthetic and the measured interferometric coherences, the pertinent candidate parameters of the optimization problem can be retrieved. These parameters are the forest volume thickness, the volume extinction coefficient, the interferometric phase related to the underlying topography, and the effective ground-to-volume amplitude ratios related to the interferometric coherences. Through a weighted superposition of all the interferometric coherences provided by the fully polarimetric radar sensor these coherences can be maximized and introduced as the right-hand side of the parameter optimization problem. Experimental results obtained from P-band fully polarimetric single baseline interferometric data acquired over the amazon rain forest are shown in order to demonstrate the potential of the proposed approach. Furthermore, a (chi) 2-test is performed on the data to prove the validity of the introduced scattering model for rain forest vegetation.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The processing of synthetic aperture radar images usually does not include topographic information, and therefore significant radiometric uncertainties remain, making the processed data not directly suitable for signature analysis, for classification purposes or to relate SAR data to geophysical parameters. An accurate SAR data calibration in areas with terrain variations can only be accomplished considering high resolution elevation data, precise position and attitude data of the antenna, and the appropriate SAR geometry. Using these information one is able to correct each pixel in terms of radiometry. The AeS-1 interferometric SAR system allows the generation of high resolution surface height information at X-band. A rigorous approach to radiometrically calibrate the amplitude data is presented in this paper. Surface heights and slope variations derived from the interferometric phase are exploited for this purpose, considering also precise antenna pointing variations and topography for the antenna gain correction. The presented method is demonstrated for a test site having different terrain morphologies.

Presents an international cooperative study in the field of volcano monitoring by means of SAR interferometry. The case study of the SIR-C/X-SAR mission over Mt. Etna, Sicily, Italy is detailed.

The authors exploit the interferometric multifrequency potentiality of the SIR-C/X-SAR system which is equipped with an L-, C-, and X-band sensor. They present a solution to improve the unwrapping performance of the C- and X-band data by considering the L-band unwrapped pattern. A new algorithm for the generation of a single digital elevation model (DEM) combining L-, C-, and X-band information is presented. This solution is based on the fusion of the unwrapped phase patterns by using a Kalman filter. The proposed fusion operation also accounts for the coherence characteristics of the three data sets. The selected test site is the Mt. Etna region in Italy which is very interesting from the volcanological and geological point of view. Numerical assessments of the achieved results are provided by evaluating the height accuracy with respect to a reference DEM.

Repeat-pass interferometry data have been acquired during the first and second SIR-C/X-SAR missions in April and October 1994. This paper presents the first results from X-SAR interferometry on four different sites. The temporal separations were one day and six months. At two sites the coherence requirements were met, resulting in high quality interferograms. A digital elevation model has been derived. The limitations of the X-SAR interferometry are discussed.

Repeat-pass interferometry data were acquired during the first and second SIR-C/X-SAR missions in April and October 1994. This paper presents the first results from X-SAR interferometry at four different sites. The temporal separations were one day and six months. At two sites the coherence requirements were met, resulting in high quality interferograms. A digital elevation model in ground range geometry has been derived. The limitations of the X-SAR interferometry are discussed. >

The performance of the reflectivity displacement method is reported. The reflectivity displacement method extracts all the necessary motions of the aircraft from the radar backscatter signal using a new radar configuration and new methods for evaluating the azimuth spectra of the radar signal. Hence, an inertial navigation system is unnecessary for many applications. An error analysis of this method is carried out, and a comparison of two processed images with and without motion compensation is shown, proving the estimated performance. >

Radar remote sensing is a tool of increasing importance in the study of volcanic sites. Synthetic aperture radar (SAR) is a high-resolution imaging tool used to survey areas which are not practical or safe to be directly inspected. With the introduction of the across-track SAR interferometry (IFSAR) technique, digital elevation models (DEM) can be produced. The usefulness of such interferometric products depends on the ability to extract information that can be used for geological interpretation. We analyzed the shuttle imaging radar C (SIR-C)/X-SAR multifrequency multipass interferometry mission over Mount Etna, Sicily, and we performed a supervised geological interpretation of the coherence maps and a fractal-based analysis of the IFSAR DEMs. The first permits us to recognize different volcanic terrain and to distinguish between vegetated and unvegetated areas, while the second allows us to validate the IFSAR DEMs and to detect large-scale geological features. This latter analysis, performed over the photogrammetric DEM, enabled us to recognize artifacts caused by digitizing and resampling. Obviously, IFSAR DEMs are not affected by these problems. As a consequence, IFSAR products are a valuable aid in geological interpretation.