Karlus A. Camara de Macedo

The BELSAR dataset consists of high-resolution multitemporal airborne mono- and bistatic fully-polarimetric synthetic aperture radar (SAR) data in L-band, alongside concurrent measurements of vegetation and soil biogeophysical variables measured in maize and winter wheat fields during the summer of 2018 in Belgium. Its collection was funded by the European Space Agency (ESA) to address the lack of publicly-accessible experimental datasets combining multistatic SAR and in situ measurements. As such, it offers an opportunity to advance the development of SAR remote sensing science and applications for agricultural monitoring and hydrology. This paper aims to facilitate its adoption and exploration by offering comprehensive documentation and integrating its multiple data sources into a unified, analysis-ready dataset.

The TomoSense experiment comprises campaign and research activities in support of future Synthetic Aperture Radar (SAR) mission concepts at P-, L-, and C-band by the European Space Agency (ESA). The research is intended to provide a quantitative basis for the evaluation of single-pass interferometry over temperate forests at L- and C-band and investigate potential synergies between C-band convoy mission concepts and future P- and L-band missions. SAR acquisitions include P- L-, and C-band data acquired at the Eifel National Park in Germany by flying approximately 25 trajectories to provide tomographic imaging capabilities. Land C-band data were acquired by simultaneously flying two aircraft to gather bistatic data with varying interferometric baselines. Field activities include forest census (dbh, tree height and species) at 80 plots and Terrestrial Laser Scanning (TLS). The dataset is complemented by small-footprint Airborne Lidar Scanning (ALS) and derived products. Preliminary results are here shown relative to polarimetric tomography at P-band and L-band imaging.

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.

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.

The random volume over ground model has been successfully used to estimate forest parameters with the interferometric synthetic aperture radar. Besides its typical employment with polarimetric data at lower frequency bands, it has also been used with single-polarimetric X-band data to estimate forest height. Based on this approach, we propose estimating the forest interferometric height and subtract it from the X-band surface model, in order to generate a preliminary model of the terrain using X-band only. Since P-band interferometric phase center is closer to the ground, the use of the preliminary terrain model as reference reduces the interferometric phase modulation, facilitating the phase unwrapping. This is particularly important for PolInSAR terrain height estimation or long baseline interferometry, which is used in dual-band In-SAR to improve the terrain height estimation. Two datasets with three-baselines X-HH and dual-polarimetric P-HH and P-HV data, provided by Bradar, are used to demonstrate the method.

We built and analysed an airborne DInSAR time series of six P-band SAR images acquired every month over a region in the upper Amazon river basin. After proper residual motion compensation, water level changes under the foliage and terrain movements due to the river dynamics are clearly revealed. The estimations of a non-redundant and redundant network of interferograms are analysed and some consistent water variation measurements with LS residuals <; 3cm are obtained.

There are basically two methods for retrieving the ground and the canopy height from the interferometric synthetic aperture radar (InSAR) in forested areas. The first method is based on the different dual-band (DB) InSAR height estimation, typically done at X- and P-HH-bands. The second method is based on the modeling of the Polarimetric (Pol) InSAR response of the forest volumetric backscatter, typically at L- or P-band. This paper investigates the possibility of combining both methods, in the sense that the P-band derived ground height is enhanced by the use of the polarimetric data and the RVoG model. In this proposed method, only the ground phase is retrieved from the PolInSAR technique, reducing the numbers of unknowns to be inverted, while the X-band InSAR is used to estimate the canopy. Therefore, we avoid the more complex (and more failure susceptible) inversion of the PolInSAR approach. The data collected in the Amazon region with the OrbiSAR-1 sensor from Bradar (former Orbisat) is used to demonstrate the method. Better ground estimation over range is obtained with the proposed method in comparison with the single-polarization approach for different baselines.

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.

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.

Recently some experiments demonstrated that reliable DInSAR measurements can be achieved at any band and that further time-series analyses can be applied to 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 long-term airborne DInSAR survey at P- and X-band with temporal baselines of 1 year and 3 months. The survey was performed by the OrbiSAR system of OrbiSat under contract with Petrobras (PROTRAN), as part of a project to investigate the potential of DInSAR technique to identify, prior to structural damage, geohazards threats to the oil/gas pipelines in São Sebastião-SP, Brazil. After 1 year and 3 months, the P-band data have interferometric coherence equal or greater than 0.3 for approximately 80% of the imaged dense vegetated areas. At X-band, we achieved coherence equal or greater than 0.3 in the urban area. After removing all residual motion errors with proper up-to-date processing, we derived, for the P-band data, land movements with absolute accuracy in the order of centimeters. For X-band we derived land movement measurements with absolute accuracy in the order of millimeters. Through field work evidences, the paper analyses the causes of these centimeter to millimeter land movements, and how they are related to geodynamic processes and geohazard risks. 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 geohazard risk monitoring.