Identifying Wet Troposphere Delay in L-band InSAR Using Weather 2 Radar Reflectivity

Synthetic Aperture Radar (SAR) pulses undergo variable delays in the atmosphere due to pressure, temperature, and humidity changes in the troposphere, posing a major source of error in InSAR measurements. Wet troposphere delay, caused by condensed water and water vapor clouds, is particularly difficult to predict, yet can cause delays of tens of centimeters, significantly impacting surface displacement estimates. Our study employs a feature-comparison method using NOAA NEXRAD weather radar station reflectivity data to identify artifacts from wet tropospheric delays in InSAR phase change measurements derived from rapid repeat imaging data collected with the UAVSAR L-band SAR. NEXRAD's 5-minute scanning interval, compared to UAVSAR's 30-minute revisit time, enabled detection of phase artifacts caused by fast-moving and developing clouds. We identify regions in InSAR interferograms with tropospheric-induced phase artifacts by matching features common to InSAR phase outlier masks and NEXRAD high reflectivity masks. Matched results between NEXRAD reflectivity and InSAR phase noise show phase delays of up to 25 radians in L-band, corresponding to 48 cm of delay. Comparison with tropospheric delays calculated using the Generic Atmospheric Correction Online Service for InSAR (GACOS) showed that the weather model has insufficient spatial and temporal resolution to accurately estimate the observed wet troposphere delays. While our study focused on UAVSAR, the findings are applicable to other SAR missions, including the L-band NISAR mission, aiding identification and interpretation of InSAR results affected by tropospheric delays.