Othmar Frey


Last Name

Frey

First Name

Othmar

ORCID

0000-0003-1795-6087

Organisational unit

03849 - Hajnsek, Irena / Hajnsek, Irena

Search Results

Publications 1 - 10 of 131
  • A Study on Integrated SAR Processing and Geocoding by Means of Time-Domain Backprojection
    Item type: Conference Paper
    Frey, Othmar; Meier, Erich; Nüesch, Daniel (2005)
    Proceedings of International Radar Symposium 2005
  • Polarimetric Calibration of the Ku-Band Advanced Polarimetric Radar Interferometer
    Item type: Journal Article
    Baffelli, Simone; Frey, Othmar; Werner, Charles; et al. (2018)
    IEEE Transactions on Geoscience and Remote Sensing
  • Tomographic Profiling with Snowscat Within the ESA Snowlab Campaign: Time Series of Snow Profiles Over three Snow Seasons
    Item type: Conference Paper
    Frey, Othmar; Werner, Charles L.; Caduff, Rafael; et al. (2018)
    IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium
  • Focusing SAR Data Acquired From Non-Linear Sensor Trajectories
    Item type: Conference Paper
    Frey, Othmar; Magnard, Christophe; Rüegg, Maurice; et al. (2008)
    Proceedings of IEEE International Geoscience and Remote Sensing Symposium, 2008. IGARSS 2008
  • SAR tomography for spatio-temporal inversion of point-like scatterers in urban areas
    Item type: Conference Paper
    Siddique, Muhammad A.; Wegmüller, Urs; Hajnsek, Irena; et al. (2015)
    2015 IEEE International Geoscience and Remote Sensing Symposium (IGARSS)
  • Analyzing Tomographic SAR Data of a Forest With Respect to Frequency, Polarization, and Focusing Technique
    Item type: Conference Paper
    Frey, Othmar; Meier, Erich (2010)
    2010 IEEE International Geoscience and Remote Sensing Symposium
    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 beamforming, robust Capon beamforming, and MUSIC, as well as for both, the two frequency bands and the different polarimetric channels.
  • Detection of Railway Track Anomalies Using Interferometric Time Series of TerraSAR-X Satellite Radar Data
    Item type: Journal Article
    Bernhard, Philipp; Haener, David; Frey, Othmar (2024)
    IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing
    In this study, we investigate a new approach to detect railway track anomalies based on surface displacements retrieved from interferometric time series of satellite radar data. The condition of the ballast substructure is critical for the longevity of railway tracks. Early detection of problematic track sections allows for interventions to extend service life. In chordbased measurements, as routinely performed with survey trains, undulations in relative height along the track are used as a proxy for detecting track anomalies. These train-based methods for track condition assessment are costly and are limited by the availability of track recording vehicles. We developed and assessed a similar approach using spaceborne SAR data to derive variations of surface deformations as a proxy for track anomalies. Utilizing time series of TerraSAR-X observations, we conducted a persistent scatterer interferometry (PSI) analysis to estimate surface deformations along railway tracks. We developed a new methodology for analysing the obtained deformation rates and their longitudinal variability over approximately 50 km of railway tracks of the Swiss Federal Railways network. We analysed various features and assessed their potential to identify track anomalies. Comparing our results to the track classification based on the chord-based measurements we found a correlation of our derived PSI-based features to problematic track sections using the chord-based classifications as a reference. Our proposed approach of a satellite-based track anomaly detection system provides a useful and potentially cost-effective additional source of information to monitor railway tracks.
  • Car-borne and UAV-borne mobile mapping of surface displacements with acompact repeat-pass interferometric SAR system at L-band
    Item type: Conference Paper
    Frey, Othmar; Werner, Charles L.; Coscione, Roberto (2019)
    Proceedings of 2019 IEEE International Geoscience and Remote Sensing Symposium (IGARSS 2019)
  • On the Consistency of Tropospheric Delays Over Mountainous Terrain Retrieved From Persistent Scatterer Interferometry, GNSS, and Numerical Weather Prediction Models
    Item type: Journal Article
    Shehaj, Endrit; Frey, Othmar; Moeller, Gregor; et al. (2024)
    IEEE Transactions on Geoscience and Remote Sensing
    The tropospheric refraction along the signal path is the same for global navigation satellite systems (GNSS) and radar interferometry. However, different observation geometries, spatiotemporal sampling, signal processing methods, as well as signal wavelengths yield rather complementary measurements. The origin of this research is the question whether tropospheric delays retrieved at GNSS permanent stations can support persistent scatterer interferometry (PSI) processing for the retrieval of surface displacement in mountainous terrain, which is challenging because of spatial gaps due to radar layovers, shadowing, and temporal decorrelation in combination with strong variations of water vapor. We analyze maps of tropospheric path delays obtained by collocation of GNSS-estimated delays and PSI processing of an interferometric stack of Cosmo SkyMed X-band synthetic aperture radar (SAR) data in a mountainous region in Valais, Switzerland. We aim to assess the consistency and differences among the datasets to better understand their ability to sense small-scale structures in the lower atmosphere. In addition, we compare them with maps of tropospheric path delays derived from Consortium for Small-Scale Modelling (COSMO-2) numerical weather model (NWM) data. We investigate several factors affecting the interpolation of the GNSS zenith delays to the locations of the persistent scatterers, such as assumptions in the collocation, network size, and resolution. We assessed the meteorological parameters of the NWM to find potential correlations between specific meteorological conditions and different levels of (dis)agreement of delay maps; a clear correlation was not found. We found that the delays estimated from collocated GNSS measurements and PSI tend to have a different dependency on the terrain altitude. The PSI-derived path delays obtained from the X-band SAR data stack capture small-scale spatial variations also visible in NWM delay maps; whereas, at a larger scale, mismatches are found. It appears that the current GNSS network in the mountainous area of the Valais is not dense enough to capture strongly varying tropospheric refraction. We can conclude that denser networks (with a resolution of 5-10 km) in the interferometric SAR (InSAR) footprint region and a careful choice of the assumptions in our interpolation method would make GNSS more suitable for helping PSI processing.
  • Geostatistical Analysis and Mitigation of Atmosphere Induced Phase in Terrestrial Radar Interferometric Observations of an Alpine Glacier
    Item type: Conference Paper
    Baffelli, Simone; Frey, Othmar; Hajnsek, Irena (2018)
    EUSAR 2018 12th European Conference on Synthetic Aperture Radar Electronic Proceedings, 04 - 07 June, 2018, Aachen, Germany
Publications 1 - 10 of 131