Abstract: Precipitation measurement offers fundamental information in understanding the energy flow and water cycle, which is also crucial to hydrology and water resources management. However, the precipitation measurement varies in space and time, and its accuracy becomes the toughest and vital problem. This study is carried out to estimate the precipitation accuracy of the TRMM 3B42 V6 and V7,the two versions of products in the Poyang Lake Basin, and to find out the unique advantages of V7 compared to V6, and address the prospect of application of TRMM satellite data in humid southern China. The precipitation products of V6 and V7 are picked up to evaluate accuracy with the 2003~2010 observation data andh employs statistics knowledge to quantitative analyse estimation accuracy. The results show: 1) At the year scale, both versions generally match well the actual annual precipitation in all basins. The bias of products are under 10%, especially in Raohe and Fuhe basins, where the TRMM and observed precipitation are almost identical, with the bias under 5%. However, the accuracy of V6 and V7 turns to degrade with finer temporal scale, which is more apparent in V6. The correlation coefficients of V7 is above 0.7 seasonally and monthly, which is about 0.1 higher than V6; it turns out to prove that the correlation between V7 and observed is better. What's more, the accuracy assessment is higher in the wet and warm season such as summer and autumn, but it turns to reduce with the precipitation and temperature drops, the V6 product overestimates the precipitation in summer and underestimates the precipitation in winter, which does not appear in V7 product; daily, the fitted curve of V7 matches actual precipitation curve better than V6, and V7 has better qualities in prediction of precipitation grade. 2) Both the V6 and V7 satellite data shows a precipitation pattern that is higher in the South and West and lower in the North and East in Poyang Lake Basin, which is consistent with the real situation of the precipitation for the whole eight years. The differences between TRMM and observed precipitation became large in Xiushui Basin and Poyang lake,, probably caused by terrain and the large water area; what's more, the month data can precisely reflect the changing trends of precipitation in the five major sub basins, the performance of V7 is better with fewer bias; but the bias of the V6 and V7 are both larger in Xiushui Basin than other Basins, and the correlation coefficient in the part of Gannan area is relatively low. It has been a great improvement for V7 product in total Poyang Lake Basin, especially in those two areas, but the problem still persists. The complex and high terrain of those two areas can interfere the satellite signal, which reduces the accuracy of observation. Overall, V7 product has a greater improvement than V6 product in the estimation accuracy of precipitation spatially and temporally in Poyang Lake basin, which has higher accuracy in humid southern China such as the Poyang Lake basin. V7 provides better understand in the complex hydrological process and a promising future.

Key words: Poyang Lake Basin, TRMM 3B42, V6, V7, rainfall, accuracy analysis