Abstract
Ground-truthing is a major problem in the satellite estimation of rain rate. This problem is that the measurement taken by the satellite sensor is fundamentally different from the one it is compared with on the ground. Additionally, since the satellite has the limited capability to measure the light rain rate exactly, the comparison should also consider the threshold value of satellite rain rate. This paper proposes a ground-truth design with threshold for the satellite rain rate. This ground-truth design is the generalization of the conventional ground-truth design which considered the only (zero, nonzero) and (nonzero, nonzero) measurement pairs. The mean-square error is used as an index of accuracy in estimating the ground measurement by satellite measurement. An application to the artificial random field shows that the proposed ground-truth design with threshold is valid as the design bias is zero. The same result is also derived in the application to the COMS (Communication, Ocean, and Meteorological Satellite) rain rate data in Korea.
Highlights
It is a very difficult job to accurately observe the rain rate field in space
The error was defined as the difference between the satellite rain rate and the rain gauge rain rate
As the object of this study was to find whether the threshold applied to the satellite rain rate causes a systematic bias or not, we prepared two different rain gauge data types
Summary
It is a very difficult job to accurately observe the rain rate field in space. Rain gauge is the most traditional tool to measure the rainfall and is still assumed to be the most reliable one. The ground-truth problem is a complex procedure since the two sensors measure different quantities: (1) the rain gauge measures rain rate at a point nearly continuously in time, while (2) the satellite measures an area average of rain rate over its field of view (FOV) discretely in time While these two estimates in the long run should agree, there could be a large random difference between the two because of the different space-time sampling configurations. Since the satellite rain rate is not trusty when the rain rate is very low, the ground-truth design proposed in this study uses the data pairs only when the satellite measurement exceeds a certain threshold level.
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