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High-resolution Precipitation Observation Using Compact X-Band Weather Radar
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1. Introduction
These days there are soaring numbers of extreme weathers in the world such as torrential rain, tornadoes and so on. And needs for observation of precipitation with high spatial and temporal resolutions using dual polarimetric Doppler weather radars are growing higher and higher.
Under such circumstances Furuno has developed a dual polarimetric Doppler weather radar (See Table 1). The main features are high precision 3-D meteorological monitoring and the smallest and lightest in market[1]. It is designed to cover 30 km range and it has very high spatial and temporal resolutions, 50 m and 30 sec respectively.
Table 1: The main specifications of a dual polarimetric Doppler weather radar.
2. Evaluation of rainfall on a pin-point basis
At first, rainfall observed by the radars is evaluated on a pin-point basis. Rainfall data observed by the radars are compared with one measured by four rain gauges shown in Fig 1. Rain gauge data are acquired every 10 minutes and the radar observation of every one minute is accumulated during 10 minutes. Both data are plotted into a trend diagram and compared (See Fig 2).
Red lines indicate radar observations and blue lines indicate rain gauges. As can be seen, there are two peaks around 2:40 and 4:00 in the radar observation. The second peak is consistent with the rain measurement, but the first peak is a little bit over-estimated. But it is acceptable amount of error.
Overall radar observations have a very good correlation with rainfall measurements. High spatial and temporal resolutions of Furuno's radar, 50 m and 30 sec respectively, lead to these good results.
Fig 1 : Four rain gauges are chosen to compare rainfall observed by radars with one measured by rain gauges. The date is 03:55JST on December 10, 2013.
(a) North Syukugawa
(b) City Hall
Fig 2 : Rainfall observed by radar and one measured by rain gauges are compared for four points. Two of them are indicated above. Remarkable two peaks are shown with blue arrows.
3. Evaluation of rainfall on a basin basis
Secondly, rainfall observed by radar is evaluated on a basin basis. Discharge of a river is calculated by accumulating rainfall around the basin, using storm-water runoff simulation model, GeoHyMoS. This method is applied to the calculation of discharge of Syukugawa River which is located in Nishinomiya, Japan. It is observed during 12 hours and simulated data and observed one are compared (See Fig 3). The simulated data is 10.7 m3/s, compared to the observed one, 11.4 m3/s. The difference between both data is only 10 percents.
On the other hand, regarding a comparison on a pin-point basis, as can be seen from Fig 2, bias errors might be included in each data and it is not easy to evaluate the radar observation exactly.
This result indicates that a basin-accumulated rainfall is very effective for a rainfall evaluation and a sudden increase of discharge of a river after a heavy rain event is predicted successfully. High spatial and temporal resolutions of Furuno's radar lead to these good results.
In next step, not only rainfall observed by a radar but also predicted rainfall will be input to GeoHyMos. That's because the alert could be generated as soon as possible for customers to evacuate from a hazardous region before the severe events occur.
Fig 3 : A comparison of discharge of a river between simulation and observation at Syukugawa River. The observation period starts from 21:00JST, Dec. 9th and continues till 9:00JST, Dec. 10th, 2013.
4. Conclusions
Furuno has developed a dual polarimetric Doppler weather radar.
Rainfall data observed by the radars are compared with one measured by four rain gauges on a pin-point basis. Overall radar observations have a very good correlation with rainfall measurements.
The rainfall observed by the radar is evaluated on a basin basis. The storm-water runoff simulation model, GeoHyMoS is applied to the calculation of discharge of Syukugawa River. This result indicates that a basin-accumulated rainfall is very effective for a rainfall evaluation.
High spatial and temporal resolutions of Furuno's radar lead to these good results.
5. Acknowledgement
The research project is supervised by Professor Eiichi Nakakita of Kyoto University and Professor Satoru Oishi of Kobe University.