Alignment and Comparison between Simultaneous GPM Dual-frequency Precipitation Radar and Ground-based Radar Observations

Precipitation observation plays a significant role in forecasting extreme weather event and advancing public understanding of Earth’s water and energy cycles. Compared with its predecessor the Tropical Rainfall Measuring Mission (TRMM), the Global Precipitation Measurement (GPM) mission extends the observation range from tropics to most of the globe and is expected to provide next generation of global precipitation product (Hou et al. 2014). The Dual-frequency Precipitation Radar (DPR) is more sensitive than its TRMM predecessor especially in the measurement of light rainfall and snowfall in high latitude regions. Though the overlapping measurements at Ku and Ka bands, the DPR is also able to discriminate between liquid and solid precipitation. As an indispensable part of the GPM validation activities, ground-based radars are commonly used to cross-validate DPR observations and verify corresponding retrievals. However, different characteristics between space and ground based remote sensors including viewing angles, frequencies, spatial resolution, and temporal mismatching make it a challenge task to directly compare the two observations. This issue becomes more complicated due to the geometrical distortion of space-based observations brought by spacecraft movements and attitude perturbations. Bolen and Chandrasekear (2003) have proposed an alignment methodology to match the resolution volumes between space and ground radars by minimizing the effects of potential geometric distortion in space radar. This method has been shown to be very effective for cross comparison between TRMM Precipitation Radar (PR) and ground radar observations.

In this paper, we implement the alignment technique in Bolen and Chandrasekar (2003) for GPM applications. The differences between DPR and PR are analyzed in order to evaluate thematching between the two observations. Precipitation observations from DPR and ground radars are then aligned onto a common gridding system for quantitative evaluation. Particularly, the coincident GPM satellite overpass events during the year of 2016 over ground based KMLB radar in Florida, KFWS radar in Texas, CSU-CHILL radar in Colorado, as well as NASA NPOL radar are investigated. The cross-comparison results are provided to illustrate the performance of GPM DPR observations in different precipitation regimes.

References:

Hou, A.Y., R.K. Kakar, S. Neeck, A.A. Azarbarzin, C.D. Kummerow, M. Kojima, R. Oki, K. Nakamura, and T. Iguchi, 2014: The Global Precipitation Measurement Mission. Bull. Amer. Meteor. Soc., 95, 701-722.

Bolen, S.M. and V. Chandrasekar, 2003: Methodology for Aligning and Comparing Spaceborne Radar and Ground-Based Radar Observations. J. Atmos. Oceanic Technol., 20, 647-659.