Ground validation of satellite-based precipitation products is necessary to evaluate the performance of satellite observation at local, regional, and global scales. The evaluation of the rainfall data accuracy will reveal both its strengths and weaknesses, thereby determining its suitability for hydrometeorological applications. To reach this goal, this study comprehensively evaluated and characterized the systematic bias in the Global Precipitation Measurement (GPM) Integrated Multi-SatellitE Retrievals for GPM (IMERG) precipitation product, to be compared with its predecessor Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA), based on the wide-spread ground-based observation data, PRISM (Parameter-Elevation Regression on Independent Slopes Model) over the Conterminous United States. The evaluation was conducted for daily datasets from June 2000 to the end of December 2019, in which IMERG and TMPA overlap using statistical error metrics both in space and time. While some statistical measures do not show significant improvement in daily IMERG compared to TMPA, systematic bias is substantially diminished. We detected systematic bias related to the vertical relief for both IMERG and TMPA but with a substantial decrease in the IMERG. The systematic bias in both satellite products distinctively differs in the summer and winter seasons, but, both products showed high performance in summer. According to our findings, the spatiotemporal performance of the IMERG precipitation product varies in different seasons, regions, time scales, and topographic conditions but with superiority over the TMPA daily product.

卫星降水产品的地面验证对于评估卫星观测在地方、区域和全球范围内的性能是必要的。降雨数据准确性的评估将揭示其优势和劣势，从而确定其对水文气象应用的适用性。为实现这一目标，本研究全面评估和描述了全球降水测量 (GPM) 综合多卫星反演 GPM (IMERG) 降水产品的系统偏差，并将其与其前身热带降雨测量任务 (TRMM) 多卫星反演进行比较。卫星降水分析 (TMPA)，基于广泛的地面观测数据，PRISM（独立坡度模型的参数高程回归）在美国本土上空。评估是针对 2000 年 6 月至 2019 年 12 月底的每日数据集进行的，其中 IMERG 和 TMPA 在空间和时间上使用统计误差指标重叠。虽然与 TMPA 相比，一些统计指标未显示每日 IMERG 的显着改善，但系统偏差已大大减少。我们检测到与 IMERG 和 TMPA 的垂直起伏相关的系统偏差，但 IMERG 大幅下降。两种卫星产品的系统偏差在夏季和冬季都有显着差异，但两种产品在夏季都表现出较高的性能。根据我们的研究结果，IMERG降水产品的时空表现在不同的季节、地区、时间尺度和地形条件下有所不同，但优于TMPA日产品。