Comparison of Tropospheric Delay Correction Methods of Insar Analysis Using A Mesoscale Meteorological Model: A Case Study From Japan

A major source of errors in interferometric synthetic aperture radar (InSAR), used for mapping ground deformation, is the delay caused by changes in the propagation velocity of radar microwaves in the troposphere. It is common to correct this tropospheric delay noise using numerical weather models because of their widespread global availability. A variety of correction methods and tools exist, and selecting the most appropriate one by considering weather models, delay models, and delay calculation algorithms is important for specific applications. We compared the performance of two tropospheric delay correction methods, RINC and GACOS, used by Japanese and international research communities, respectively. RINC software uses a method of delay integration along the slant radar line-of-sight (LOS) path, and we used the mesoscale model (MSM) provided by the Japan Meteorological Agency. GACOS for InSAR estimates delay using the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim reanalysis products along with an iterative decomposition approach.

These two methods were applied to Advanced Land Observing Satellite-2 (ALOS-2) data acquired over Tohoku and Kansai regions in Japan, where the atmospheric field is complex with significant seasonal variation. Results showed that tropospheric delay correction using the slant delay integration approach with MSM, which has a finer temporal and spatial resolution, 5x5 km and 3h, performed slightly better than GACOS that used ERA-interim product of 14x14 km and 6h resolutions (Table 1). We speculate that the difference in performance mainly originates from differences in the numerical weather models being used, although we have not tested the effect of the difference in the delay calculation algorithm. This study highlights the importance of using the best-available numerical weather model data for tropospheric delay calculations.