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Article

Comparison of Tropospheric Path Delay Estimates from GNSS and Space-Borne SAR Interferometry in Alpine Conditions

1
Institute of Geodesy and Photogrammetry, ETH Zürich, Robert-Gnehm-Weg 15, CH-8093 Zürich, Switzerland
2
Department of Electrical Engineering, National University of Computer and Emerging Sciences (FAST-NU), B Block, Faisal Town, Lahore 54770, Pakistan
3
Gamma Remote Sensing, Worbstrasse 225, CH-3073 Gümligen, Switzerland
4
Chair of Earth Observation and Remote Sensing, ETH Zürich, Stefano-Franscini-Platz 3, CH-8093 Zürich, Switzerland
*
Author to whom correspondence should be addressed.
Remote Sens. 2019, 11(15), 1789; https://doi.org/10.3390/rs11151789
Received: 29 June 2019 / Revised: 26 July 2019 / Accepted: 29 July 2019 / Published: 31 July 2019
(This article belongs to the Special Issue Feature Papers for Section Atmosphere Remote Sensing)
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 both GNSS and InSAR, and are typically removed. However, recently these delays are also recognized as a signal of interest, for example for assimilation into numerical weather models or climate studies. The GNSS and InSAR are techniques of complementary nature, as one has sparse spatial but high temporal resolution, and the other very dense spatial coverage but repeat pass of only a few days. This raises expectations for a combination of these techniques. For this purpose, a comprehensive comparison between the techniques must be first performed. Due to the relative nature of InSAR estimates, we compare the difference slant tropospheric delays ( d S T D ) retrieved from GNSS with the d S T D s estimated using Persistent Scatterer Interferometry (PSI) of 32 COSMO-SkyMed SAR images taken in a snow-free period from June to October between 2008 and 2013. The GNSS estimates calculated at permanent geodetic stations are interpolated to the locations of persistent scatterers using an in-house developed least-squares collocation software COMEDIE. The Pearson’s correlation coefficient between InSAR and GNSS estimates averaged over all acquisitions is equal to 0.64 and larger than 0.8 for approximately half of the layers. Better agreement is obtained mainly for days with high variability of the troposphere (relative to the tropospheric conditions at the time of the reference acquisition), expressed as standard deviations of the GNSS-based d S T D s. On the other hand, the most common feature for the days with poor agreement is represented by very stable, almost constant GNSS estimates. In addition, there is a weak correlation between the agreement and the water vapor values in the area, as well as with the number of stations in the closest vicinity of the study area. Adding low-cost L-1 only GPS stations located within the area of the study increases the biases for most of the dates, but the standard deviations between InSAR and GNSS decrease for the limited area with low-cost stations. View Full-Text
Keywords: tropospheric delays; InSAR; GNSS; PSI; low-cost GPS; alpine areas tropospheric delays; InSAR; GNSS; PSI; low-cost GPS; alpine areas
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MDPI and ACS Style

Wilgan, K.; Siddique, M.A.; Strozzi, T.; Geiger, A.; Frey, O. Comparison of Tropospheric Path Delay Estimates from GNSS and Space-Borne SAR Interferometry in Alpine Conditions. Remote Sens. 2019, 11, 1789. https://doi.org/10.3390/rs11151789

AMA Style

Wilgan K, Siddique MA, Strozzi T, Geiger A, Frey O. Comparison of Tropospheric Path Delay Estimates from GNSS and Space-Borne SAR Interferometry in Alpine Conditions. Remote Sensing. 2019; 11(15):1789. https://doi.org/10.3390/rs11151789

Chicago/Turabian Style

Wilgan, Karina, Muhammad A. Siddique, Tazio Strozzi, Alain Geiger, and Othmar Frey. 2019. "Comparison of Tropospheric Path Delay Estimates from GNSS and Space-Borne SAR Interferometry in Alpine Conditions" Remote Sensing 11, no. 15: 1789. https://doi.org/10.3390/rs11151789

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