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

Recursive and robust InSAR Phase Estimation

This paper introduces a novel scheme to recursively estimate interferometric phases from a stack of synthetic aperture radar (SAR) images. The adoption of a calibration step ensure some robustness to the buildup of phase drifts. The scheme is shown to yield comparable performance to full-covariance algorithms for a realistic decorrelation scenario. The implementation is suited for continuous processing and updating of phase products, without compromising longterm phase accuracy. It also limits the requirements in terms of data transfer between archiving and processing facility, a significant issue for processing large archives of SAR data

INTERFEROMETRIC PERFORMANCE ASPECTS FOR TANDEM-L

ABSTRACT DLR is studying a future L-band satellite mission (Tandem-L) in close cooperation with NASA/JPL (DESDynI). This mission is designed to serve a variety of applications covering Solid Earth, forests, ice, etc. through the use of several SAR techniques. We deal here with some aspects that concern Solid Earth applications and interferometry. The combination of high target coherence and the instrument large mapping capabilities calls for investigations into possible interferometric processing schemes and their associated performance. We discuss the extent of the degradations that are introduced with respect to the theoretical bounds when only multilooked interferograms between successive images are used. Improvements can be obtained by buffering a limited number of images and interferograms, depending on the decorrelation type

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

Analysis of the performance of polarimetric PSI over distributed scatterers with Sentinel-1 data

Sentinel−1 (S1) data enables effective monitoring of displacements using persistent scatterer interferometry (PSI). S1 includes VV and VH polarization channels, allowing us to apply polarimetric techniques to PSI. In short, polarimetric PSI (PolPSI) exploits the available polarization channels to enhance the identification and processing of measurement points including persistent scatterers (PS) and distributed scatterers (DS). Previous works have shown the benefits of using PolPSI for PS points with S1 data, but the corresponding analysis for DS is missing. DS points are processed by finding a neighborhood of statistically homogeneous pixels (SHP) and averaging the phase within that neighborhood. In this work we show how dual-polarimetric data are stricter on the selection of the SHP group than single-polarimetric data. Thanks to the information added by the second channel, different land covers are not mixed in the SHP group. As a result, the number of points in the SHP groups is generally smaller than with VV alone, but they are more reliable. The impact of this strategy on the resulting deformation estimates is also investigated in this work, showing that the deformation areas are fully preserved and the influence of nearby pixels associated with other scene elements is avoided.This work was supported in part by the European Funds for Regional Development and by the Spanish Ministry of Science and Innovation (Agencia Estatal de Investigación, AEI) with Project PID2020-117303GB-C22/AEI/10.13039/501100011033, and in part by the Generalitat Valenciana, Conselleria de Innovacion, Universidades, Ciencia y Sociedad Digital with Project CIAICO/2021/335. The research was also partially performed in the ESA-MOST China DRAGON-5 project ref. 59339

Monitoring the Petermann Ice Island with TanDEM-X

This paper presents the processing of TanDEM-X acquisitions for the monitoring of the topography of the Petermann ice island. In this particular case the area under study is continuously moving and the acquisition geometry is changing, so the processing of the iceberg’s DEMs is challenging and additional effects are to be considered. The SAR processing chain used is presented and the results obtained summarized, showing the effects and limitations observed during the process

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

Spatiotemporal Analysis of C-band interferometric Phase Anomalies over Sicily

Short temporal SAR interferograms present a phase which is biased with respect to the surface deformation signal. We analyse the anomalies in terms of their spatiotemporal patterns in a C-band Sentinel-1 dataset. The temporal high-pass component can be explained with moisture variations as sensed by the ASCAT scatterometer. The low-pass components need a different explanation. Considering the apparent accumulation of delay, the spatial correlation to land cover types or topographic height, and the seasonality, they are compatible with wet biomass accumulation. The strong decorrelation observed is likely related to strong vegetation extinction in C-band

InSAR Performance for Large-Scale Deformation Measurement: Impact of Tropospheric Corrections and Validations

This paper deals with the analysis of InSAR performance for large-scale deformation measurement. The study evaluatesthe use of models, especially numerical weather prediction re-analysis, to mitigate disturbances in SAR interferograms. The impact of such corrections is evaluated and, using GNSS measurements, the predicted error bars are validated on a large Sentinel-1 dataset

Fading Signal: An Overlooked Error Source for Distributed Scatterer Interferometry

We reveal the presence of a peculiar physical signal which compromises the accuracy of Earth surface deformation estimates for distributed scatterers [1]. The observed signal is short-lived and decays with the temporal baseline; however, it is distinct from the stochastic noise attributed to temporal decorrelation. To indicate its nature, this physical effect is referred to as fading signal. Designing a simple approach in the evaluation of distributed scatterers, we reveal a prominent bias in the deformation velocity maps. The bias is the result of propagation of small phase error through the time series. We further discuss the role of the phase estimation algorithms in significant reduction of the bias and put forward the idea of a unified analysis-ready InSAR product for achieving high-precision deformation monitoring