3:00 PM - 3:15 PM
[MTT37-06] Utilizing Dense Tropospheric Delay Products from GNSS in InSAR Noise Correction
Keywords:InSAR, GNSS, Tropospheric delay
Interferometric Synthetic Aperture Radar (InSAR) has been widely used to measure surface displacements using the phase differences between two acquisition dates. Many Earth phenomena have been studied using InSAR, such as ground deformation caused by volcanic activity, earthquakes, and other geophysical processes. A major challenge in achieving millimeter-level accuracy is the inability to correct for the changes in the propagation velocity of radar microwaves in the troposphere. Specifically, the different states of the troposphere for the two acquisition dates result in artifacts of typically a few cm and often exceeding 10 cm, and they frequently exhibit spatial characteristics similar to the deformation signals, which further complicates the target signal extraction.
Global Navigation Satellite System (GNSS) measurements of zenith tropospheric delay (ZTD) can be used for correcting the tropospheric delay noise that appear in InSAR to enhance the accuracy to centimeter/millimeter level. We plan to develop a method to use the ZTD products obtained from the SoftBank GNSS network and the GNSS Earth Observation Network System (GEONET) operated by the Geospatial Information Authority of Japan (GSI) for InSAR corrections in Japan. Since using the GEONET data only has been shown to be superior to other existing methods, The method to be developed would attain an unprecedented level of performance of tropospheric noise reduction in InSAR.
In this study, we compared the values of our ZTD calculation using GNSS data from GEONET and SoftBank networks based on calculation methods (GipsyX and RTKLIB), its data sources, mapping functions (VMF1 and GMF) and cut-off angles. We basically use InSAR data to assess the effectiveness of the correction. Specifically, under the assumption that the majority of InSAR noise is due to tropospheric delay, we measure the effectiveness of the correction by the consistency between the differential tropospheric delay calculated by the GNSS at the SAR acquisition timings and the InSAR values.
The results obtained by PPP processing with GipsyX2-0 showed better consistency with the ZTD products of the F5 solution of GSI. The differences between GipsyX and RTKLIB were within a few centimeters, which significantly impacts tropospheric delay correction. We concluded that GipsyX is more suitable for InSAR correction, and GipsyX was used for the subsequent analyses. The ZTD values obtained from the GEONET network aligned better with the InSAR data than those from the SoftBank Corp. network, with differences at a centimeter level. The GMF mapping function performed slightly better than the VMF1, although the differences were less than a centimeter. The values estimated with a cut-off angle of 15° minimized the InSAR noise compared with the cases of cut-off angles of 20°, 30°, 40°, and 50°.
We further tested the Iterative Tropospheric Decomposition (ITD) model that interpolates the point-wise delay values onto InSAR pixels, and evaluate its effectiveness in correcting tropospheric delay noise in InSAR.
Acknowledgements: The SoftBank's GNSS observation data used in this study was provided by SoftBank Corp. and ALES Corp. through the framework of the "Consortium to utilize the SoftBank original reference sites for Earth and Space Science". The GEONET F5 tropospheric delay product was provided by Geospatial Spatial Authority of Japan. InSAR processing was conducted using the RINC software (Ozawa et al., 2016).
Global Navigation Satellite System (GNSS) measurements of zenith tropospheric delay (ZTD) can be used for correcting the tropospheric delay noise that appear in InSAR to enhance the accuracy to centimeter/millimeter level. We plan to develop a method to use the ZTD products obtained from the SoftBank GNSS network and the GNSS Earth Observation Network System (GEONET) operated by the Geospatial Information Authority of Japan (GSI) for InSAR corrections in Japan. Since using the GEONET data only has been shown to be superior to other existing methods, The method to be developed would attain an unprecedented level of performance of tropospheric noise reduction in InSAR.
In this study, we compared the values of our ZTD calculation using GNSS data from GEONET and SoftBank networks based on calculation methods (GipsyX and RTKLIB), its data sources, mapping functions (VMF1 and GMF) and cut-off angles. We basically use InSAR data to assess the effectiveness of the correction. Specifically, under the assumption that the majority of InSAR noise is due to tropospheric delay, we measure the effectiveness of the correction by the consistency between the differential tropospheric delay calculated by the GNSS at the SAR acquisition timings and the InSAR values.
The results obtained by PPP processing with GipsyX2-0 showed better consistency with the ZTD products of the F5 solution of GSI. The differences between GipsyX and RTKLIB were within a few centimeters, which significantly impacts tropospheric delay correction. We concluded that GipsyX is more suitable for InSAR correction, and GipsyX was used for the subsequent analyses. The ZTD values obtained from the GEONET network aligned better with the InSAR data than those from the SoftBank Corp. network, with differences at a centimeter level. The GMF mapping function performed slightly better than the VMF1, although the differences were less than a centimeter. The values estimated with a cut-off angle of 15° minimized the InSAR noise compared with the cases of cut-off angles of 20°, 30°, 40°, and 50°.
We further tested the Iterative Tropospheric Decomposition (ITD) model that interpolates the point-wise delay values onto InSAR pixels, and evaluate its effectiveness in correcting tropospheric delay noise in InSAR.
Acknowledgements: The SoftBank's GNSS observation data used in this study was provided by SoftBank Corp. and ALES Corp. through the framework of the "Consortium to utilize the SoftBank original reference sites for Earth and Space Science". The GEONET F5 tropospheric delay product was provided by Geospatial Spatial Authority of Japan. InSAR processing was conducted using the RINC software (Ozawa et al., 2016).