Othmar Frey

ETH Zurich / GAMMA Remote Sensing AG · n/a

Riverbank erosion occurs along many of the Earth's river systems, affecting riverine populations by destroying agricultural land and housing. In this study, we detected past events of riverbank erosion along the Jamuna River in Bangladesh using time series of Sentinel-1 satellite radar imagery, ground-range-detected (GRD) data with a 12 d revisit c...

Agile synthetic aperture radar (SAR) platforms such as car-borne and UAV-borne SAR systems require combined inertial navigation systems (INS) and global navigation satellite systems (GNSS) to measure the radar sensor trajectories used for focusing and interferometric processing. Measurement inaccuracies from INS/GNSS systems lead to residual phase...

The coherent backscatter opposition effect (CBOE) enhances the backscatter intensity of electromagnetic waves by up to a factor of 2 in a very narrow cone around the direct return direction when multiple scattering occurs in a weakly absorbing, disordered medium. So far, this effect has not been investigated in terrestrial snow in the microwave spe...

The Ku-band provides opportunities for investigations of snow morphology through radar observations, since it exhibits a relatively high amount of scattering even from snow layers of limited depth, while maintaining low absorption. Due to technological and practical challenges, the bistatic parameter space of Ku-band radar observations of natural m...

Riverbank erosion occurs along many of the Earth’s river systems, affecting riverine populations by destroying agricultural land and housing. In this study, we detected past events of riverbank erosion along the Jamuna River in Bangladesh using time series of Sentinel-1 satellite radar imagery, ground range detected (GRD) data with a 12-day revisit...

The coherent backscatter opposition effect (CBOE) enhances the backscatter intensity of electromagnetic waves by up to a factor of two in a very narrow cone around the direct return direction when multiple scattering occurs in a weakly absorbing, disordered medium. So far, this effect has not been investigated in terrestrial snow in the microwave s...

This article presents the bistatic operation mode and the performance analysis of KAPRI, a terrestrial frequency-modulated continuous wave (FMCW) Ku-band polarimetric radar interferometer capable of acquiring bistatic full-polarimetric datasets with high spatial and temporal resolution. In the bistatic configuration, the system is composed of two i...

The accuracy of surface displacements measured by differential radar interferometry is significantly degraded by the atmospheric phase screen (APS). This paper presents a practical and efficient approach for APS mitigation based on the coherent pixels technique (CPT) displacement velocity estimation algorithm. In the proposed approach, all motionle...

In this paper, we present examples of DInSAR-based measurement of surface displacements using a novel compact L-band SAR system that can be mounted on mobile mapping platforms such as a UAV or a car. The good DInSAR system performance is demonstrated and, particularly, we also show a use case in which a car-borne system setup is employed to map sur...

The WBSCAT microwave scatterometer operates between 1 and 40 GHz, is fully coherent and polarimeteric for ground-based measurements of radar backscatter.

High spatio‐temporal variability of atmospheric water vapor affects microwave signals of Global Navigation Satellite Systems (GNSS) and Interferometric Synthetic Aperture Radar (InSAR). A better knowledge of the distribution of water vapor improves both GNSS‐ and InSAR‐derived data products. In this work, we present a collocation framework to combi...

Terrestrial radar interferometry (TRI) can measure displacements at high temporal resolution, potentially with high accuracy. An application of this method is the observation of the surface flow velocity of steep, fast-flowing aglaciers. For these observations, the main factor limiting the accuracy of TRI observations is the spatial and temporal va...

Terrestrial radar interferometers (TRI) are complimentary to spaceborne synthetic aperture radar systems for deformation monitoring in natural terrain: they permit shorter revisit times and greater flexibility in acquisition mode and timing. The additional diversity offered by polarimetric data can also be beneficial for TRI observations because po...

In this paper, we present first results of carborne and UAV-borne mobile mapping of potential surface displacements with a compact repeat-pass interferometric FMCW SAR system at L-band: (1) glacier-flow-induced displacements were measured at Stein glacier in the Swiss alps in car-borne mode along a slightly curved road section; (2) a valley slope w...

We compare tropospheric delays from Global Navigation Satellite Systems (GNSS) and Synthetic Aperture Radar (SAR) Interferometry (InSAR) in a challenging mountainous environment in the Swiss Alps, where strong spatial variations of the local tropospheric conditions are often observed. Tropospheric delays are usually considered to be an error for bo...

In the context of differential synthetic aperture radar in-terferometry (DInSAR), precise trajectory estimation of the SAR platform is necessary to minimize residual phase errors induced by inaccurate knowledge of the 3D acquisition geometry. Inertial navigation systems (INS) and global navigation satellite system (GNSS) are usually employed to tra...

Space-borne microwave techniques, such as the Global Navigation Satellite Systems (GNSS) or Synthetic Aperture Radar Interferometry (InSAR), are subjected to the atmospheric delay. The delays estimated by one technique can be useful for mutual corrections. The GNSS technique is characterized by very high temporal but sparse spatial resolution. In c...

In this study we evaluate the feasibility of using the tropospheric delays retrieved from Global Navigation Satellite Systems (GNSS) for the space-borne Synthetic Aperture Radar Interferometry (InSAR). The GNSS-based tropospheric models are interpolated for the points of 37 InSAR COSMO-SkyMed satellite acquisitions in a period that spans from 2008...

Synthetic aperture radar (SAR) tomography with repeat-pass acquisitions generally requires a priori phase calibration of the interferometric data stack by compensating for the atmosphere-induced phase delay variations. These variations act as a disturbance in tomographic focusing. In mountainous regions, the mitigation of these disturbances is part...

Repeat-pass differential SAR interferometry (DInSAR) using spaceborne SAR data or stationary terrestrial radar data is an established technique to measure surface displacements. However, repeat-pass DInSAR from agile platforms (airborne/car-borne) is challenging due to residual motion errors. This is particularly true for high-frequency radar where...

Differential synthetic aperture radar (SAR) tomography allows separation of multiple coherent scatterers interfering in the same range-azimuth resolution cell as well as the estimation of the deformation parameters of each scatterer. In this way, the spatio-temporal tomographic inversion serves as a means to resolve the layover and simultaneously i...

Terrestrial radar systems are used operationally for area-wide measurement and monitoring of surface displacements on steep slopes, as prevalent in mountainous areas or also in open pit mines. One limitation of these terrestrial systems is the decreasing cross-range resolution with increasing distance of observation due to the limited antenna size...

The estimation of deformation parameters using persistent scatterer interferometry (PSI) is limited to single dominant coherent scatterers. As such, it rejects layovers wherein multiple scatterers are interfering in the same range-azimuth resolution cell. Differential synthetic aperture radar (SAR) tomography can improve deformation sampling as it...

Presentation slides for "Geostatistical Analysis and Mitigation Of Atmosphere Induced Phase In Terrestrial Radar Interferometric Observations Of An Alpine Glacier"

Terrestrial Radar Interferometry is used to map surface displacement velocites with high temporal resolution, irrespective of sunlight and cloud cover. The main factor limiting estimation accuracy are variations in the atmospheric refractive index, observed as atmospheric phase screens (APS). A statistical model for APS assuming a separable spatio-...

Spatial and temporal variation of the free electron concentration in the ionosphere affects SAR interferograms, in particular at low radar frequencies. The split-spectrum method permits separating the ionospheric and the non-dispersive phase terms using spectral sub-band images. In this work a reformulation of the split-spectrum method facilitates...

A geostatistical analysis of the atmospheric phase screen (APS) affecting Ku-Band terrestrial radar interferometric (TRI) observations of a fast-flowing alpine glacier is made assuming a separable spatio-temporal covariance structure. Such a structure facilitates the mitigation of APS: the atmospheric phase affecting individual interferograms can b...

Differential interferometry using ground-based radar systems permits to monitor displacements in natural terrain with high flexibility in location, time of acquisition, and revisit time. In combination with polarimetric imaging, discrimination of different scattering mechanisms present in a resolution cell can be obtained simultaneously with the es...

In alpine regions, drastic height variations result in frequent layovers which are rejected during typical persistent scatterer interferometric (PSI) analyses. We investigate the use of differential SAR tomography as an add-on to PSI to resolve layovers of temporally coherent scatterers and simultaneously measure their average deformation. Due to...

In this entry, the basic principles of synthetic aperture radar imaging are introduced from a general physics perspective instead of tackling the topic from the more widespread signal processing point of view. Thus, the material is thought to be accessible to any scientist or the general reader with some basic knowledge of physics and calculus. The...

An acknowledgement provided by the authors was lost during production for the above paper [1] . It is provided here as follows:

First results using the new Sentinel-1 SAR look very promising but the special interferometric wide-swath data acquired in the TOPS mode makes InSAR processing more challenging than for normal stripmap mode data. The steep azimuth spectra ramp in each burst results in very stringent co-registration requirements. Combining the data of the individual...

Persistent scatterer interferometry (PSI) is in operational use for spaceborne synthetic aperture radar (SAR)-based deformation analysis. A limitation inherently associated with PSI is that, by definition, a persistent scatterer (PS) is a single dominant scatterer. Therefore, pixels containing signal contributions from multiple scatterers, as in th...

Persistent scatterer interferometry (PSI) typically rejects layovers. Therefore, layover-affected urban areas may suffer from inadequate deformation sampling. SAR tomography, when used as an add-on to PSI, reveals additional deformation samples by resolving layovers. In this paper we quantify the relative gain in deformation sampling, while taking...

This paper addresses the system characterization and the polarimetric calibration of the Ku-Band Advanced Polarimetric Interferometer (KAPRI). KAPRI is an FMCW ground-based real aperture radar system that uses slotted waveguide antennas. The rotation of the antennas introduces undesired phase ramps in azimuth. We present a geometrical model to acco...

The SnowScat device, a fully-polarimetric scatterometer originally designed to measure the radar cross-section of snow at a frequency range from 9.2 to 17.8 GHz (X-band to Ku-band), has recently been extended towards a high-resolution tomographic measurement mode. Such tomographic profiling observations provide further insights into the complex ele...

First results using the new Sentinel-1 SAR look very promising, but the special interferometrie wide-swath (IWS) data acquired in the FOPS mode makes InSAR processing challenging. Fhe steep azimuth spectra ramp in each burst results in very stringent co-registration requirements. Combining the data of the individual bursts and sub-swaths into consi...

Persistent scatterer interferometry (PSI) assumes the presence of a single temporally coherent scatterer in a range-azimuth pixel. Multiple scatterers interfering in the same pixel, as for the case of a layover, are typically rejected. Conventional SAR tomography (3D SAR) is a means to separate the individual scatterers in layover. Advanced tomogra...

Persistent Scatterer Interferometry (PSI) inherently assumes a single temporally coherent scatterer inside a range-azimuth resolution cell. This restriction leads to the rejection of numerous persistent scatterer (PS) candidates, particularly in urban areas where layovers occur frequently. Moreover, in case of high-rise buildings, it is necessary t...

SAR tomography as an extension to persistent scatterer interferometry (PSI) approaches has the potential to improve the level of detail of retrievable information, in particular, in the case of layover scenarios in urban areas. In this paper, a processing approach is sketched that eventually allows for retrieving a 3-D point cloud of point-like sca...

Agile SAR platforms such as an automobile require a flexible SAR processing scheme to account for nonlinear sensor trajectories during the synthetic aperture. In this contribution, a parallelized implementation of a time-domain back-projection SAR focusing algorithm based on NVIDIA's CUDA GPU computing framework is presented and discussed using a c...

In this contribution, a car-borne SAR and InSAR experiment is described. The slope of a valley was imaged by means of a single-pass InSAR system mounted on a car driving on roads along the bottom of the valley. The GAMMA portable radar interferometer GPRIII hardware with a modified antenna configuration was used for data acquisition. The experiment...

Persistent scatterer interferometry relies on the assumption that only one dominant scatterer is present per range-azimuth resolution cell. If this criterion is not met the point target candidate is discarded during the iterative processing sequence. This one-scatterer assumption contrasts with the fact that in urban scenarios layover is an ubiquit...

Precise terrain-corrected georeferencing of synthetic aperture radar (SAR) images and derived products in range–Doppler coordinates is important with respect to several aspects, such as data interpretation, combination with other geodata products, and transformation of, e.g., terrain heights into SAR geometry as used in differential interferometric...

In this contribution Persistent Scatterer Interferometry (PSI) processings done in the framework of the FP7 Project PanGEO over a number of European sites are presented. After a short introduction of the PanGEO project, we present the data used, the processing done and the results of the PSI analysis. The influence of specifics as the presence of l...

n this contribution, tomographic imagery obtained from estimating the 3-D localization and the polarimetric signature of backscattering sources within a forest environment from fully-polarimetric multibaseline SAR data at L- and P-bands are presented. Both, polarization diversity and spatial diversity were exploited jointly within the tomographic f...

Persistent Scatterer Interferometry (PSI) is widely used to determine ground deformation rates and histories. The data sets processed are increasing in size due to larger areas considered, higher resolution, and higher point den- sities. Working with lists of several million points and related networks reduces the computational efficiency. In this...

A notable obstacle hindering widespread application of SAR tomography for 3D mapping of vegetation is the relatively large number of acquisitions that are needed to obtain a high resolution and a good rejection of spurious responses in the direction perpendicular to the line of sight. In this paper, we discuss the impact of different baseline const...

In this paper, a time-domain back-projection based tomographic processing approach to a 3-D reconstruction grid is detailed, with the focusing in the third dimension being either modified versions of multilook standard beamforming, robust Capon beamforming, or multiple signal classification. The novel feature of the proposed approach compared to pr...

Forest canopies are semitransparent to microwaves at both L- and P-bands. Thus, a number of scattering sources and different types of scattering mechanisms may contribute to a single range cell of a synthetic aperture radar (SAR) image. By appropriately combining the SAR data of multiple parallel flight paths, a large 2-D aperture is synthesized, w...

SAR tomography at L- and P-bands reveals 3-D structural information of forested areas. A drawback, however, are the large number of samples, i.e. overflights, typically used for such configurations. Based on two fully-polarimetric tomographic SAR data sets, at L- and P-bands, we analyze the sensitivity of backscattering from a forest volume as meas...

ERS-ENVISAT Tandem (EET) cross-interferometry (CInSAR) pairs are characterized by long 2km baselines and short 28 minute time intervals. Over some sites multiple pairs are available. In our work we discuss multi-pass interferometric techniques and investigate for several applications, including DEM generation, mapping of fast motions and grounding...

Processing of ScanSAR data for interferometric applications requires careful attention to the phase and position accuracy to obtain interferometric products with high correlation and continuous phase across the bursts. We describe an interferometric processing system developed for ScanSAR data acquired by the ALOS PALSAR instrument able to produce...

In this paper, two fully-polarimetric tomographic SAR data sets of a forested area, at L-band and P-band, are analyzed with respect to the localization of scattering sources and scattering mechanisms. In particular, the 3D SAR data is examined regarding the performance of three different tomographic focusing techniques multilook standard beamformin...