On some spectral properties of TanDEM-X interferograms over forested areas

This letter reports about some obervations over rainforest (in Brazil and Indonesia), where the spectra of TanDEM-X interferograms show distinct features, almost a signature, which is explained and modelled in terms of the scattering properties. Supported by comparisons with simulations, the observations exclude any homogeneous, horizontally-layered forest; instead, they are compatible with a model with point scatterers clustered in clouds. Such a model, with high extinction and large gaps that allow significant penetration, is able to explain to a good degree the observations

SIGNAL: A Ka-band Digital Beam-Forming SAR System Concept to Monitor Topography Variations of Ice Caps and Glaciers

This paper discusses the implementation of an endto- end simulator for the BIOMASS mission. An overview of the system architecture is provided along with a functional description of the modules that comprise the simulator

Observations and discussions of TanDEM-X interferogram spectra over rain forest

This paper reports about some obervations over rainforest (in Brazil and Indonesia), where the spectra of TanDEM-X interferograms show distinct features, almost a signature, which is explained and modelled in terms of the scattering properties. Thanks to the comparison with simulations, the observations exclude a homogeneous, horizontally-layered forest; instead, they are compatible with a model with point scatterers clustered in clouds. Such a model, with high extinction and large gaps that allow significant penetration, is able to explain to a good degree the observations

Digital Beamforming Architecture and Techniques for a Spaceborne Interferometric Ka-Band Mission

The paper presents the instrument concept and performance of a Ka-band single-pass interferemetric mission proposed for measuring topography and topographic changes. A formation flying constellation of two compact synthetic aperture radars (SAR) satellites equipped with innovative digital beamforming hardware and advanced operation modes is described

Vegetation characterization through the use of precipitation-affected SAR signals

Current space-based SAR offers unique opportunities to classify vegetation types and to monitor vegetation growth due to its frequent acquisitions and its sensitivity to vegetation geometry. However, SAR signals also experience frequent temporal fluctuations caused by precipitation events, complicating the mapping and monitoring of vegetation. In this paper, we show that the influence of a priori known precipitation events on the signals can be used advantageously for the classification of vegetation conditions. For this, we exploit the change in Sentinel-1 backscatter response between consecutive acquisitions under varying wetness conditions, which we show is dependent on the state of vegetation. The performance further improves when a priori information on the soil type is taken into account.1010FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP2013/50943-

Coherent stacking of SAR images for efficient interferometric processing

Large datasets of satellite SAR missions dedicated to deformation monitoring will require intensive and dedicated interferometric processing techniques. Decorrelation effects will prevent simple processing approaches, but optimal algorithms are computationally intensive. This paper shows results of a novel efficient algorithm that aims at exploiting scatter component that are stable over time, without being isolated point targets. The concept is proved valid for simulated data and limited examples in X-band, more interesting results are hoped for the L-band case

Capon- and APES-Based SAR Processing: Performance and Practical Considerations

This paper discusses the use of Capon's minimum-variance method (MVM) and Amplitude and Phase EStimation (APES) spectral-estimation algorithms to synthetic aperture radar range�azimuth focusing. The rationale of the algorithms is discussed. An implementation of a Capon or APES processing chain is explained, and processing parameters such as chip-image size, resampling factor, and diagonal loading are discussed. For multichannel cases, a joint-processing approach is presented. A set of Monte Carlo simulations are described and used to benchmark Capon- and APES-based processing against conventional matched-filter-based approaches. Both methods improve the resolution and reduce sidelobes. APES yields generally better estimates of amplitude and phase than Capon but with worse resolution. Results with RADARSAT-2 quad-polarization data over Barcelona are used to qualitatively study the real-life performance of these algorithms

A Novel Strategy for Radar Imaging Based on Compressive Sensing

Radar data have already proven to be compressible with no significant losses for most of the applications in which it is used. In the framework of information theory, the compressibility of a signal implies that it can be decomposed onto a reduced set of basic elements. Since the same quantity of information is carried by the original signal and its decomposition, it can be deduced that a certain degree of redundancy exists in the explicit representation. According to the theory of compressive sensing (CS), due to this redundancy, it is possible to infer an accurate representation of an unknown compressible signal through a highly incomplete set of measurements. Based on this assumption, this paper proposes a novel method for the focusing of raw data in the framework of radar imaging. The technique presented is introduced as an alternative option to the traditional matched filtering, and it suggests that the new modes of acquisition of data are more efficient in orbital configurations. In this paper, this method is first tested on 1-D simulated signals, and results are discussed. An experiment with synthetic aperture radar (SAR) raw data is also described. Its purpose is to show the potential of CS applied to SAR systems. In particular, we show that an image can be reconstructed, without the loss of resolution, after dropping a large percentage of the received pulses, which would allow the implementation of wide-swath modes without reducing the azimuth resolution

SAR Image Stacking for the Exploitation of long-term coherent Targets

This paper shows that in a repeat-pass dataset of SAR images a long-term coherent component, when present, can be recovered by coherent temporal filtering of the SAR images and can successively form interferograms with higher SNR. The validity of the idea is confirmed through simulations and one example with real TerraSAR-X data. The theoretical necessity of using long-term interferograms is also discussed and linked to autoregressive processes, starting from the observation that the optimal weighting is given by the inverse of the covariance matrix

Advanced Digital Beamforming Architectures and Operation Modes for and Enhanced SIGNAL Mission Concept

Recently, a team of scientist lead by the German Aerospace Center (DLR) have proposed a Ka-band single-pass interferometric mission concept named SIGNAL (SAR for Ice, Glacier aNd globAL Dynamics). SIGNAL main goal is to estimate accurately and repeatedly topography and topographic changes variations associated with mass change or other dynamic effects on glaciers, ice caps and polar ice sheets. To achieve the required elevation accuracy, in the order of a few decimeter, a formation flying constellation of two compact satellites was proposed as the only way to obtain the desired cross-track baseline. One of the attractive features of Ka-band is the possibility to design relatively compact systems. However, traditional fixed beam designs Ka-band immediately fail to provide either or both the desired sensitivity (due to the small receive antenna) or the required swath. Thus, some form of digital beamforming is a must. In addition, short antennas lead to high azimuth resolution, but also to a narrow unambiguous swath. In previous work this swath limitation was partially solved by proposing a dual-swath solution using beamforming in elevation only, with a relatively large gap between swathes. This approach improves the global mission coverage, but also adds complexity to the processing and geophysical interpretation. An alternative to achieve wider continuous swathes is to use multiple azimuth phase centers. By introducing multiple antennas spaced in the along-track direction, the system immediately gains the capability to acquire along-track interferometric data. Thus, if properly designed, the resulting SAR can be operated in a wide-swath mode, and in a narrower swath ATI mode. In the particular case of SIGNAL, this means that the two-satellite system could be switched between a wide-swath cross-track interferometric mode, and an also wide swath ATI mode, where in this second case the wide swath would be achieved by combining the narrower ATI mode swathed of each of the two satellites. With this, the SIGNAL would gain the capability to accurately measure ocean currents, which would clearly extend the potential scientific user base. The paper will present the proposed enhanced SIGNAL architecture, and describe possible operating modes. Besides the aforementioned wide-swath and ATI-modes, the paper will also discuss ping-pong multi-baseline acquisitions modes exploiting a novel sub-pulses technique in order to keep a low PRF. For all these modes, the SAR performance will be described. Also the final interferometric performance, in terms of relative height errors or of ocean surface velocity errors will be discussed