Kidd Chris, Becker Andreas, Huffman George J, Muller Catherine L, Joe Paul, Skofronick-Jackson Gail, Kirschbaum Dalia B
University of Maryland, College Park, Maryland, 20740 and NASA/Goddard Space Flight Center, Greenbelt, Maryland, 20771.
Deutscher Wetterdienst, Offenbach am Main, Germany.
Bull Am Meteorol Soc. 2017 Jan;98(1):69-78. doi: 10.1175/BAMS-D-14-00283.1. Epub 2017 Jan 23.
The measurement of global precipitation, both rainfall and snowfall, is critical to a wide range of users and applications. Rain gauges are indispensable in the measurement of precipitation, remaining the standard for precipitation information across the Earth's surface for hydro-meteorological purposes. However, their distribution across the globe is limited: over land their distribution and density is variable, while over oceans very few gauges exist and where measurements are made, they may not adequately reflect the rainfall amounts of the broader area. Critically, the number of gauges available, or appropriate for a particular study, varies greatly across the Earth due to temporal sampling resolutions, periods of operation, data latency and data access. Numbers of gauges range from a few thousand available in near real time, to about a hundred thousand for all 'official' gauges, and to possibly hundreds of thousands if all possible gauges are included. Gauges routinely used in the generation of global precipitation products cover an equivalent area of between about 250 m and 3,000 m. For comparison, the center circle of a soccer pitch or tennis court is about 260 m. Although each gauge should represent more than just the gauge orifice, auto-correlation distances of precipitation vary greatly with regime and the integration period. Assuming each Global Precipitation Climatology Centre (GPCC) -available gauge is independent and represents a surrounding area of 5 km radius, this represents only about 1% of the Earth's surface. The situation is further confounded for snowfall which has a greater measurement uncertainty.
全球降水量（包括降雨和降雪）的测量对于广泛的用户和应用而言至关重要。雨量计在降水量测量中不可或缺，仍然是用于水文气象目的的地球表面降水信息的标准测量工具。然而，它们在全球的分布有限：在陆地上，其分布和密度各不相同，而在海洋上，雨量计极少，并且即便进行了测量，这些测量可能也无法充分反映更广阔区域的降雨量。至关重要的是，由于时间采样分辨率、运行周期、数据延迟和数据访问等因素，全球范围内可用的或适用于特定研究的雨量计数量差异极大。雨量计的数量从近实时可用的几千个，到所有“官方”雨量计约十万个，若将所有可能的雨量计都包括在内则可能达到数十万。用于生成全球降水产品的常规雨量计覆盖的等效面积在约250米至3000米之间。相比之下，足球场或网球场的中心圆约为260米。尽管每个雨量计应代表的不仅仅是雨量计的孔口，但降水的自相关距离会因气候条件和积分周期而有很大差异。假设每个可从全球降水气候学中心（GPCC）获取的雨量计都是独立的，且代表半径为5千米的周边区域，这仅占地球表面的约1%。对于降雪而言，情况更为复杂，因为降雪的测量不确定性更大。
