# Studies of General Precipitation Features with TRMM PR Data: An Extensive Overview
## 6 Conclusions and Prospects
### Errors and Limitations of the PR Data  
Although many qualitative conclusions were revealed, the quantitative analyses might be not very accurate due to uncertainty and errors in PR data. The quantitative calculation of rainfall rate yielded through the \(Z\)-\(R\) relationship depended on the accuracy of PR reflectivity and the estimated drop size distribution (DSD), rainfall types and drop phases. The inappropriate correction of PR reflectivity for the NUBF and the attenuation, and the discrimination error of rainfall types and drop phases would introduce errors of the rainfall rate. The estimation of the LH depended on the accuracy of rainfall rates and rainfall types of PR products. In addition, the physical processes simulated in the retrieval algorithm models might be inadequate, which could also influence the calculation accuracy of the LH. The low sensitivity of PR observation would underestimate the precipitation top, and thus gave underestimated height for lightning activity accompanied by rainfall.  
Regarding the identification of rainfall types, PR product 2A23 determines the rainfall type of stratiform and convective based on the vertical profile and the horizontal pattern of PR reflectivity. A category 'other' is given when there is no signature of either stratiform or convective rainfall. However, there could be errors of the classification results due to some limitations of PR including low sensitivity for light rain and snow, single-frequency detection at Ku-band, and the coarse horizontal resolution above the ground. This problem has already been noticed [159; 160], and could be improved by future algorithms and the next-generation space-borne precipitation radar [161; 162; 163].  
On the other hand, there are limitations of PR measurements which restrict more comprehensive and detailed studies. First of all, TRMM was a non-geostationary satellite with a narrow FOV and thus it had a low temporal resolution for flying over a certain region with few passes per day. This caused temporal sampling error of rainfall observation and QPE [165]. Secondly, the attenuation by convective rain was significant since PR worked at the Ku band and it might not be totally addressed by attenuation correction algorithms [27]. Thirdly, radar beam broadening of PR was remarkable due to a high satellite altitude and there was a coarse resolution of 5 km at the nadir. This frequently caused the partial beam filling for rainfall observation, leading to uncertainties for reflectivity and precipitation products [166]. In addition, PR worked at the Ku band and had a minimum detectable reflectivity of 18 dBZ. It could not detect light rain or snow and non-precipitating cloud, and could not observe the formation of precipitation before the rainfall occured, which was unfavorable for the analysis, monitoring, and prediction of the precipitation. Moreover, PR could not provide information of shapes and phase states of raindrops, and thus could not observe microphysics of clouds and precipitation. Additionaly, PR could not observe rainfall over extratropical regions because TRMM had a small orbit inclination.