Summary Following the launch of the Global Precipitation Measurement (GPM) Core Observatory, two advanced high resolution multi-satellite precipitation products namely, Integrated Multi-satellitE Retrievals for GPM (IMERG) and Global Satellite Mapping of Precipitation (GSMaP) version 6 are released. A critical evaluation of these newly released precipitation data sets is very important for both the end users and data developers. This study provides a comprehensive assessment of IMERG research product and GSMaP estimates over India at a daily scale for the southwest monsoon season (June to September 2014). The GPM-based precipitation products are inter-compared with widely used TRMM Multi-satellite Precipitation Analysis (TMPA), and gauge-based observations over India. Results show that the IMERG estimates represent the mean monsoon rainfall and its variability more realistically than the gauge-adjusted TMPA and GSMaP data. However, GSMaP has relatively smaller root-mean-square error than IMERG and TMPA, especially over the low mean rainfall regimes and along the west coast of India. An entropy-based approach is employed to evaluate the distributions of the selected precipitation products. The results indicate that the distribution of precipitation in IMERG and GSMaP has been improved markedly, especially for low precipitation rates. IMERG shows a clear improvement in missed and false precipitation bias over India. However, all the three satellite-based rainfall estimates show exceptionally smaller correlation coefficient, larger RMSE, larger negative total bias and hit bias over the northeast India where precipitation is dominated by orographic effects. Similarly, the three satellite-based estimates show larger false precipitation over the southeast peninsular India which is a rain-shadow region. The categorical verification confirms that these satellite-based rainfall estimates have difficulties in detection of rain over the southeast peninsula and northeast India. These preliminary results need to be confirmed in other monsoon seasons in future studies when the fully GPM-based IMERG retrospectively processed data prior to 2014 are available.

中文翻译：

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季风主导地区基于 GPM 的多卫星降水估计的初步评估

总结 全球降水测量 (GPM) 核心观测站启动后，发布了两款先进的高分辨率多卫星降水产品，即 GPM 综合多卫星检索 (IMERG) 和全球降水卫星测绘 (GSMaP) 第 6 版。对这些新发布的降水数据集进行批判性评估对于最终用户和数据开发人员都非常重要。本研究提供了对印度西南季风季节（2014 年 6 月至 9 月）每日尺度的 IMERG 研究产品和 GSMaP 估计值的综合评估。基于 GPM 的降水产品与广泛使用的 TRMM 多卫星降水分析 (TMPA) 和基于仪表的印度观测进行了相互比较。结果表明，IMERG 估计值比调整后的 TMPA 和 GSMaP 数据更真实地代表了平均季风降雨量及其可变性。然而，与 IMERG 和 TMPA 相比，GSMaP 的均方根误差相对较小，尤其是在平均降雨量较低的地区和印度西海岸。采用基于熵的方法来评估所选降水产品的分布。结果表明，IMERG和GSMaP的降水分布得到明显改善，特别是在低降水率的情况下。IMERG 显示了印度漏失和错误降水偏差的明显改善。然而，所有三个基于卫星的降雨估计都显示出异常小的相关系数、更大的 RMSE、更大的负总偏差和印度东北部的命中偏差，那里的降水主要受地形影响。同样，三项基于卫星的估计显示，印度半岛东南部是雨影区，虚假降水量更大。分类验证证实，这些基于卫星的降雨量估计难以探测到东南半岛和印度东北部的降雨。当 2014 年之前完全基于 GPM 的 IMERG 追溯处理数据可用时，这些初步结果需要在未来研究中的其他季风季节得到证实。分类验证证实，这些基于卫星的降雨量估计难以探测到东南半岛和印度东北部的降雨。当 2014 年之前完全基于 GPM 的 IMERG 追溯处理数据可用时，这些初步结果需要在未来研究中的其他季风季节得到证实。分类验证证实，这些基于卫星的降雨量估计难以探测到东南半岛和印度东北部的降雨。当 2014 年之前完全基于 GPM 的 IMERG 追溯处理数据可用时，这些初步结果需要在未来研究中的其他季风季节得到证实。