InSAR bias and uncertainty due to the systematic and stochastic tropospheric delay

Abstract:

We present an approach to quantify the InSAR bias and uncertainty due to the tropospheric delay by evaluating the systematic and stochastic components of the temporal variation of the delay. We show that the systematic component is dominated by the seasonal variations with annual and semi-annual periodicities. Our results demonstrate that the systematic component biases the displacement time-series and velocity depending on the SAR acquisition times. We investigate the uncertainty due to the stochastic component of the delay before and after the stratified tropospheric delay correction using the atmospheric models.

We apply the approach to evaluate the systematic and stochastic components of the tropospheric wet delay using a 2002-2011 time-series of daily MODIS precipitable water vapor products across the western India plate boundary and stratified delay estimated based on the ERA-I global atmospheric model. Our results show a maximum displacement bias of ~23 cm due to the annual variation of the wet delay and a maximum relative velocity uncertainty of ~8 mm/yr due to the stochastic delay. The uncertainties for seven Envisat tracks obtained from the MODIS and ERA-I correlate with the uncertainties obtained from the scatter of the InSAR range-change time-series, indicating that the scatter of InSAR displacement time-series can be predicted with independent delay time-series from MODIS and ERA-I. Our results show that the stratified tropospheric delay correction using ERA-I, mitigates the systematic component of the delay and reduces the scatter due to the stochastic delay. Non-stratified wet delay and residuals of the stratified wet delay correction due to the inaccurate atmospheric model and low spatial and temporal resolution of the model dominate the uncertainty of the InSAR displacement time-series and velocity.