Mitigation of Tropospheric Delay in SAR and InSAR Using NWP Data: Its Validation and Application Examples

Abstract

The neutral atmospheric delay has a great impact on synthetic aperture radar (SAR) absolute ranging and on differential interferometry. In this paper, we demonstrate its effective mitigation by means of the direction integration method using two products from the European Centre for Medium-Range Weather Forecast: ERA-Interim and operational data. Firstly, we shortly review the modeling of the neutral atmospheric delay for the direct integration method, focusing on the different refractivity models and constant coefficients available. Secondly, a thorough validation of the method is performed using two approaches. In the first approach, numerical weather prediction (NWP) derived zenith path delay (ZPD) is validated against ZPD from permanent GNSS (global navigation satellite system) stations on a global scale, demonstrating a mean accuracy of 14.5 mm for ERA-Interim. Local analysis shows a 1 mm improvement using operational data. In the second approach, NWP derived slant path delay (SPD) is validated against SAR SPD measured on corner reflectors in more than 300 TerraSAR-X High Resolution SpotLight acquisitions, demonstrating an accuracy in the centimeter range for both ERA-Interim and operational data. Finally, the application of this accurate delay estimate for the mitigation of the impact of the neutral atmosphere on SAR absolute ranging and on differential interferometry, both for individual interferograms and multi-temporal processing, is demonstrated.

The Status of Earth Observation Techniques in Monitoring High Mountain Environments at the Example of Pasterze Glacier, Austria: Data, Methods, Accuracies, Processes, and Scales

“…This is probably mainly attributable to insufficiently modeled atmospheric turbulences. For the correction of atmospheric phase delays, the methods of Cong et al [167] are available. However, first experiments with ECMWF (European Centre for Medium-Range Weather Forecasts) ERA5 model parameters confirmed larger inaccuracies of such corrections, especially in the 'turbulent' summer season.…”

Assessment of Mitigation Strategies for Tropospheric Phase Contributions to InSAR Time-Series Datasets over Two Nicaraguan Volcanoes

“…We encourage users to exert caution when deciding to use the results from a particular correction method as the corrected data can still contain significant errors introduced by the correction (e.g., Table 3, and Figures 4b and 5b). Future work for capturing and removing the turbulent atmospheric phase delays may include approaches such as integrating the refractivity directly into the LOS direction as opposed to converting into LOS after computing the zenith total delay [36,48], or a combination of tropospheric phase delays predicted by multiple weather models and/or estimates of GPS zenith total delay or empirical phase-elevation based relations [21,29,54].…”

“…The power law method can reduce spatially varying tropospheric delays but is limited to estimating and reducing delays that fit a power law. While both the power law and linear corrections attempt to remove topography correlated phase delay, other factors such as the turbulent component delay that arises from irregular air motions in 3D space are not accounted for by these corrections [27,29].Predictive methods estimate turbulent and stratified phase delays using external datasets, such as Global Positioning System (GPS) zenith delay estimates [30], data assimilation of weather reanalysis datasets [21,[31][32][33][34][35][36], locally collected atmospheric datasets [27,37], multi-spectral estimates of water vapor [27,38,39], and mesoscale data assimilation models [40][41][42], or a combination [43,44]. Global Weather Models (GWMs) cover large regions of Earth and provide variables such as temperature, relative and specific humidity, and pressure at multiple heights within the atmosphere [33].…”

Ten Years of TerraSAR-X—Scientific Results

“…Four papers [14][15][16][17] deal with the radiometric and geometric performance validation and with the new methods which made TerraSAR-X the first SAR sensor with geodetic accuracy. Two papers about mapping urban environments [18,19] and one about the cryosphere [20] finalize the different topics covered in this special issue.…”