Examination of InSAR tropospheric delay correction with JRA-55 reanalysis data

Abstract:

Interferometric Synthetic Aperture Radar (InSAR) phase signal contains not only surface deformations but also propagation delays due to Earth’s atmosphere, which is the principal limiting factor for InSAR application of small deformation with amplitude of a few centimeters or less. Bevis et al. (1992) showed that the tropospheric delay consists of the hydrostatic delay due to dry gases and the wet delay due to water vapor. Previous studies proposed correction methods which used GNSS delay data or numerical weather model outputs. However, it is still insignificant for detecting small surface deformation.

Jolivet et al. (2014) showed that reanalysis data like ECMWF Interim Re-Analysis (ERA-Interim) data is useful to mitigate topography-correlated tropospheric delay from InSAR data. However, previous studies used only one of the model data as a case study and didn’t apply the correction to other areas.

In this study we examined an effect of the tropospheric delay correction with Japanese 55-year reanalysis (JRA-55) data (Kobayashi et al., 2015). The horizontal resolution of JRA-55 is TL319 (approximately 60 km) and has 60 vertical layers. In addition, we estimated the tropospheric delay with ERA-Interim data for comparison. SAR data used were derived from ALOS/PALSAR around Nagoya prefecture (Path-Frame: 411-690). To avoid the spatial decorrelation, interferometric pairs with the perpendicular baseline of less 3000 m were generated. As a result, 309 interferograms were generated from 28 SAR single-look complex images.

In consequence of the tropospheric delay correction with JRA-55 and ERA-Interim data, the averaged standard deviation of all interferograms slightly reduced from 1.26716 cm to 1.25231 cm by JRA-55 and slightly increased to 1.26797 cm by ERA-Interim. We further examined the correction effect when dividing the estimated delay into the hydrostatic component and the wet component. These results showed that JRA-55 corrected these delays rather than ERA-Interim, indicating that one of the factors of correction failure by ERA-Interim would be due to the low reproducibility of the actual wet delay.

In the presentation, we will report correction effects of JRA-55 and ERA-Interim, and discuss the difference of these effects.