西北干旱区雨量站点稀少且分布不均,为水文过程研究带来一定困难.TRMM遥感降水数据覆盖范围广、时空分辨率高,是很有潜力的降水替代品,但其在西北干旱区应用的可靠性需要评价.对TRMM网格降水量与地面实测降水量在日尺度和月尺度上进行比较,通过FBI (frequency bias index)、POD (probability of detection)、FAR (false alarm ratio)、偏差和相关系数等指标分析TRMM对降水的探测能力.结果表明:TRMM对降水的探测能力因区域、海拔和冷暖季而异,月时间尺度上TRMM对降水事件的发生频率和降水量的估计比日时间尺度更为准确,但二者探测能力都非常有限；76个格点中,日降水的FBI值都远离最优值1,POD值和FAR值则分别在0.72以下和0.37以上,离最优值较远,相关系数几乎都在0.4以下,只有14个格点的偏差在±10％之间,其余格点最大偏差高达389％.最多有9个格点的月降水FBI值达最优,14个格点的POD值达最优,24个格点的FAR值达最优,67个格点的相关系数在0.4以上,14个格点的偏差在±10％之间,只有极少数格点的全部指标都在可接受范围之内,多数站点是某些指标达最优值,而某些指标在可接受范围之外.总体来讲,TRMM遥感降水数据在西北干旱区难以直接应用,需要进一步纠正处理.
Evaluation on detective ability of TRMM remote sensing precipitation in arid region of northwest China
The arid region of northwest China is broad in area and complicated in topography.Precipitation varies significantly both temporally and spatially.However,rain gauges are very scarce and unevenly distributed.Few of rain gauges are installed at an elevation higher than 3 500 m above the sea level.Scarcity of the precipitation observation,especially,in the high mountain areas,brings great difficulties in hydrological study.TRMM remote sensing precipitation data is a potential substitute of the ground observation because of its wide coverage and high timespace resolutions.While the reliability of TRMM data is influenced by local climate,geography,topography,and some other factors,efforts have been attempted to evaluate and modify the TRMM data to improve its reliability for local application.This paper is focused on evaluating the detective ability of the TRMM precipitation data in arid region of northwest China.The evaluation was done through comparing rain gauge data with their corresponding TRMM grid data on daily and monthly scales from 1998 to 2010.Meanwhile,TRMM data was also evaluated with regard to warm and cold seasons.The daily ground observation data was from China Meteorological Data Sharing Service System.TRMM 3B42V6 data with the temporal resolution of 1 day and spatial resolution of 0.25° × 0.25° was downloaded from NASA (National Aeronautics and Space Administration).FBI (frequency bias index),POD (probability of detection)and FAR (false alarm ratio)were used to indicate the detective ability of precipitation occurrences,and the bias and correlation coefficient were used to assess the precipitation amount of TRMM data.The results indicated that performance of the TRMM data differentiated in sub-regions,warm and cold seasons,altitudes,and time scale.Regionally,TRMM overestimated the occurrence frequency of precipitation events in Hexi Corridor of Gansu Province,west of Inner Mongolia,and south of the Tianshan Mountains,and underestimated in north of the Tianshan Mountains.The False Alarm Ratio in the south Tianshan Mountains ranked the first,followed by Gansu Corridor,and the north Tianshan Mountains.TRMM performed better in warm season than in cold season due to snow covers which affected microwave signal.Performance of TRMM was affected by elevation,TRMM data tended to overestimate daily precipitation at low altitude while underestimate it at high altitude,monthly precipitation in warm season was also overestimated at low altitude while underestimated at high altitude.TRMM data gave a better estimation of precipitation monthly than daily.Among seventy-six pixels with the rain-gauges located inside,almost all of FBIs,POD s and FAR s for daily precipitation were far away from the optimal value,POD s and FAR s were smaller than 0.72 and higher than 0.37,respectively；correlation coefficients were almost smaller than 0.4； biases of fourteen pixels were within the range of ± 10％,while the largest bias for other pixels reached to 389％.As for monthly precipitation,up to nine pixels,fourteen pixels and twenty-four pixels in which FBI s,POD s and FAR s reached to optimal value,respectively； correlation coefficients of sixty-seven pixels were higher than 0.4； and there were still fourteen pixels in which biases were within the range of ± 10％.Nevertheless,pixels in which all the evaluating indices were within the acceptance range were very scarce.In summary,detective ability of TRMM precipitation products in arid area of northwest China was very limited,and modification to the data is necessary before it is properly used although it showed potential as a substitute of ground precipitation observation,and calibrating TRMM precipitation would be our next step.
arid region of northwest ChinaprecipitationTRMMhydrology
国家科技期刊平台
NSTL
万方数据
维普
