Tropospheric Atmospheric Heterogeneities of ALOS-2 Interferograms in the Greater Bay Area

L-band advanced land observing satellite-2 (ALOS-2) images are a good source of radar data with better coherence than C-band images. However, significant ionospheric effects are often associated with L-band interferograms. In addition, the tropospheric delay can also be severe in subtropical coastal environments. In this work, different methods are adopted, adapted, or proposed to evaluate the tropospheric signals in ALOS-2 interferograms in the Shenzhen region. Ionospheric effects are estimated by the split spectrum method. Tropospheric delays are estimated through their height dependence or numerical weather prediction models. In addition to the conventional weighting methods that consider distance, variation, and Gaussian models, a stepwise approach to estimate tropospheric signals from height or to scale numerical weather models is proposed in this study. A combination of spectrometer observation and air mass trajectories is also proposed to assess topography-independent tropospheric signals, specifically the moderate resolution imaging spectroradiometer (MODIS) water vapor fields and the Hybrid Single-Particle Lagrangian Integrated Trajectory model. Meanwhile, possible cloud and wind patterns are observed from interferogram. This work demonstrates the feasibility of stepwise estimation of stratified signals using height information or numerical weather models. It also shows the potential for air mass trajectories to move water vapor fields to mitigate the influence of time difference between SAR and spectrometer acquisition times.