Alessandro Parizzi

Adaptive InSAR Stack Multilooking Exploiting Amplitude Statistics: A Comparison Between Different Techniques and Practical Results

Efficient estimation of the interferometric phase and complex correlation is fundamental for the full exploitation of interferometric synthetic aperture radar (InSAR) capabilities. Particularly, when combining interferometric measures arising both from distributed and concentrated targets, the interferometric phase has to be correctly extracted in order to preserve its physical meaning. Recently, an amplitude-based algorithm for the adaptive multilooking of InSAR stacks was proposed where it was shown that a comparison of the backscatter amplitude statistics is a suitable way to adaptively group and average the pixels in order to preserve the phase signatures of natural structures in the observed area. In this letter, different methods to compare amplitude statistics will be presented, compared through simulation and applied to real data. Based on these, recommendations are made concerning which method to use in practice.

Tandem-L: A Highly Innovative Bistatic SAR Mission for Global Observation of Dynamic Processes on the Earth's Surface

Tandem-L is a proposal for a highly innovative L-band SAR satellite mission for the global observation of dynamic processes on the Earths surface with hitherto unparalleled quality and resolution. It is based on the results of a pre-phase A study which started in 2013 and is currently undergoing a phase-A study. Thanks to the novel imaging techniques and the vast recording capacity with up to 8 terabytes/day, it will provide vital information for solving pressing scientific questions in the biosphere, geosphere, cryosphere, and hydrosphere. By this, the new L-band SAR mission will make an essential contribution for a better understanding of the Earth system and its dynamics. Tandem-L will, moreover, open new opportunities for risk analysis, disaster management and environmental monitoring by employing especially designed acquisition modes and techniques in combination with a reconfigurable tandem satellite configuration and an L-band SAR instrument with advanced digital beamforming techniques.

A SAR Interferometric Model for Soil Moisture

There is a need for scattering models that link quantitatively synthetic aperture radar (SAR) interferometric observables to soil moisture. In this paper, we propose a model based on plane waves and the Born approximation, deriving first the vertical complex wavenumbers in the soil as a function of geometrical and dielectric properties and successively the complex interferometric coherences. It is observed that soil moisture behaves on the phase in a similar way as tomography does, breaking the phase consistency in triplets of interferograms. The proposed model is validated with L-band airborne SAR data; preliminary inversion results based on interferogram triplets and coherence magnitudes are presented.

Wide area persistent scatterer interferometry

The persistent scatterer interferometry (PSI) is a well established radar technique to monitor the Earths displacements with millimetre accuracy. It uses men made features typically made of metal (persistent scatterers) given by chance to form interferometric phase time series spanning many years. Actually, its application is limited to urban areas only because of the high density of usable persistent scatters. In the course of ESAs Terrafirma project, a wide area product (WAP) PSI mapping is demonstrated by DLR. Subject is to map countries and continents based on the PSI technique. The WAP is foreseen to be a standard level 1 product for the future Sentinel-1 mission with its TOPS mode acquisition scenario. However, many technical problems need to be solved in order to extend the PSI mapping area from urban areas to rural and even mountainous regions. This paper reports on the wide area product, the technical challenges and their algorithmic solutions. Also, WAP example data are presented.

Toward Operational Compensation of Ionospheric Effects in SAR Interferograms: The Split-Spectrum Method

The differential ionospheric path delay is a major error source in L-band interferograms. It is superimposed to topography and ground deformation signals, hindering the measurement of geophysical processes. In this paper, we proceed toward the realization of an operational processor to compensate the ionospheric effects in interferograms. The processor should be robust and accurate to meet the scientific requirements for the measurement of geophysical processes, and it should be applicable on a global scale. An implementation of the split-spectrum method, which will be one element of the processor, is presented in detail, and its performance is analyzed. The method is based on the dispersive nature of the ionosphere and separates the ionospheric component of the interferometric phase from the nondispersive component related to topography, ground motion, and tropospheric path delay. We tested the method using various Advanced Land Observing Satellite Phased-Array type L-band synthetic aperture radar interferometric pairs with different characteristics: high to low coherence, moving and nonmoving terrains, with and without topography, and different ionosphere states. Ionospheric errors of almost 1 m have been corrected to a centimeter or a millimeter level. The results show how the method is able to systematically compensate the ionospheric phase in interferograms, with the expected accuracy, and can therefore be a valid element of the operational processor.

Wide area Persistent Scatterer Interferometry: Current developments, algorithms and examples

In recent years, Persistent Scatterer Interferometry (PSI) [1], [2] has been widely used for scientific applications and has developed into an operational and commercially rewarding remote sensing technology. Now, ESAs upcoming Sentinel-1 mission allows a continuous, repeated without gap and global mapping of the Earths surface based on Terrain Observation by Progressive Scans (TOPS). The idea at ESA is to also extend PSI processing to such large coverages, mapping countries and continents. This will support users in subsidence monitoring of volcanic and seismogenic areas, of costal lowland, of landslides in mountainous areas and of mining and ground water regulation on a small scale. For this reason, a wide area product (WAP) for PSI monitoring has been developed at DLR. The paper has three specific objectives. The first objective is to list and describe the updated algorithms. In this context, we illustrate the improvement with respective processing examples. Our second objective is to explain the characteristics of the WAP. The last objective is to provide WAP processing results for seismogenic areas. The test cases of Greece and of Turkey demonstrate WAPs potential, its applicability and use.

Ionospheric effects in SAR interferometry: An analysis and comparison of methods for their estimation

For spaceborne SAR (Synthetic Aperture Radar) systems, the dispersive effects of the ionosphere on the propagation of the SAR signal can be a significant source of phase error. While at X-band frequencies the effects are small, current and future P-, L- and C-band systems would benefit from ionospheric compensation to avoid errors in topographic retrieval. In this paper the focus is on the effects of the ionosphere on repeat-pass SAR interferometry from P- through X-bands and methods for their estimation which are demonstrated on L-band ALOS-PALSAR acquisitions1.

Measuring 3-D Surface Motion With Future SAR Systems Based on Reflector Antennae

A conventional interferometric synthetic aperture radar (SAR) system provides 1-D line-of-sight motion measurements from repeat-pass observations. Two-dimensional motions may be measured by combining two observations from ascending and descending geometries. The third motion component may be retrieved by adding a third geometry and/or by integrating along-track measurements although with much reduced precision compared to the other two components. Several options exist to improve the accuracy of retrieving the third motion component, such as combining left- and right-looking observations or exploiting recently proposed innovative SAR acquisition modes (BiDiSAR and SuperSAR). These options are, however, challenging for future SAR systems based on large reflector antennae, due to lack of capability to electronic beam steering or frequent toggle between left- and right-looking modes. Therefore, in this letter, we assess and compare the realistic acquisition scenarios for a reflector-based SAR in an attempt to optimize the achievable 3-D precision. Investigating the squinted SAR geometry as one of the feasible scenarios, we show that a squint of 13.5° will yield comparable performance to the left-looking acquisition, while further squinting outperforms this or other feasible configurations. As an optimum configuration for 3-D retrieval, the squinted acquisition is further elaborated: the different acquisition plans considering a constellation of two satellites as well as the challenges for data processing are addressed.

Absolute Height Estimation Using a Single TerraSAR-X Staring Spotlight Acquisition

The work presented in this letter exploits the long synthetic aperture radar (SAR) of a single TerraSAR-X Staring Spotlight (ST) acquisition to derive absolute heights. Here, the slight azimuth defocusing effect due to height mismatch between the true height and the height assumed in SAR focusing is analyzed. The impact is almost negligible for most of acquisition modes. In contrast, spaceborne modes with very long aperture, such as the TerraSAR-X ST acquisition mode, present sensibility that can be used to retrieve absolute heights. The accuracy depends on incidence angle, orbit type, and mainly on signal-to-clutter ratio. Two different results are presented to demonstrate that absolute heights can be retrieved with accuracy of few meters using a single TerraSAR-X ST acquisition.

High-resolution estimation of ionospheric phase screens through semi-focusing processing

Ionosphere irregularities along the synthetic aperture generate shifts and blurring that cause decorrelation. In this paper it is shown how, by partially focusing SAR images to the height of the ionosphere, it is possible to reduce the ionospheric azimuth effects and increase the coherence. This permits, even in case of turbulent ionosphere, to obtain better accuracies when separating the deformations phase from the ionospheric phase using the delta-k split-band interferometry method.