Received 19 October 2015; accepted 5 January 2016; published 8 January 2016
From 1997, National Hurricane Center had used jet engine to carry out sounding observation in the high troposphere and made use of GPS location system, which significantly improved the accuracy of horizontal wind field and timeliness and accuracy of typhoon forecasting  - . The United States has utilized unmanned aerial vehicle with GPS sounder to research the hurricane which maybe influenced the United States and the Caribbean, and can lower the error to 10% - 30% in the next 24 - 72 h typhoon route forecast  , and the characteristics also suggested the intensity  and moving route  . In the early of 1990s, some scientists in Australian Bureau of Meteorology had put forward aerosonde, and wished to realize the tropical cyclone reconnaissance. In Nov. 1995, MCTEX experiment had been carried out in the Northern Australia by using aerosonde and several flying tests had also been conducted in Oregon and Western Australia  . Some research had also been done in Japan. Moteki et al. (2007)  had showed some results of reconnaissance in the tropical western Pacific region including wind, temperature, relative humidity and pressure. The results suggested that because of sounding data assimilated into the model, the improved wind error is 1 - 3 m/s in the tropical Western Pacific region. A technical group called the Taiwan Aerosonde Team (TAT) has committed to research on typhoon reconnaissance  . In 2005, the TAT flew into the inner region of Typhoon Longwang and performed continuous measurements for about 10 h. This flight provides the environmental information in Longwang along a
On the basis of studying the experience on typhoon observation in the international, Meteorological Observation Centre (MOC), China Meteorological Administration had carried out the first field campaign to observe Typhoon Kalmaegi by UAV in mainland of China on Jul. 18, 2008  . This observation was successful that all data had been achieved during the observation and the UAV returned safely. Following that, MOC had adopted surrounding way to observe Typhoon Sinlaku (NO. 0813) and the essential meteorological elements had been obtained during the observation. The objective of this study is to obtain more observational data, thus to improve the accuracy of horizontal wind field and accuracy of typhoon forecasting and also do contribution to improve typhoon numerical forecasting model.
2. Observation Test
2.1. Unmanned Aerial Vehicle (UAV)
The instrument in this paper is meteorological unmanned aerial vehicle which was offered by Beijing Donghengyu Technology Development Center. The basic index of UAV is in Table 1.
2.2. Flight Track
According to the typhoon forecast from National Meteorological Center (NMC), CMA, Sinlaku maybe land at Ruian city in Zhejiang province. Therefore, Ruian city had been selected as the take-off and landing site. On the basis of the satellite image at 14:00 PM on 15 Sept. 2008 issued by National Satellite Meteorological Centre (NSMC), CMA, the flight track had been designed to surround Sinlaku. It is the first to adopt this method in mainland of China. The UAV took off at 14:33 at Ruian city (120.69˚E, 27.76˚N) and the altitude is designed as
Table 1. Main performance index.
Figure 1. UAV’s flight track to observe Typhoon Sinlaku on 15 Sept. 2008 (the blue line stands for flight track).
From Figure 1 one can see that the UAV followed the airflow and entered the typhoon internal to carry out observation. The nearest distance to the typhoon center is about
2.3. Observation Data
The UAV equipped with meteorological sensors to observe temperature, pressure, relativity humidity and wind, and the observation data transmitted to the ground receiver through Beidou navigation system. One set of data transmitted every 10 seconds. 1065 sets should be received theoretically, but 847 had been accepted in actually and the data acquisition rate was about 80%.
3. Data Analysis
3.1. Altitude and Pressure
The flight altitude was designed as
3.2. Temperature and Relative Humidity
Figure 3 shows the variability of temperature and relative humidity of Typhoon Sinlaku observed by UAV. In terms of temperature curve, during the climbing process from ground to
Figure 2. The variability of altitude and pressure of Typhoon Sinlaku observed by UAV.
Figure 3. The variability of temperature and relative humidity of Typhoon Sinlaku observed by UAV.
the maximum is 23.20˚C and the minimum is 21.50˚C. From this curve, when the flight altitude was relatively stable at
From the relatively humidity curve, one can see that during the climbing period the maximum value is 86.80%, the minimum is 80.60% and the average is 83.87%. At the beginning of climbing, there is no precipitation and the relative humidity is small. When the altitude is about
Figure 4. The variability of wind speed of Sinlaku observed by UAV.
can fly ordinarily in 3 hours, which suggests the waterproof performance of the mini-UAV is good. During the whole observation period, the maximum is 100%, the minimum is 80.60% and the average is 97.98%.
3.3. Wind Speed
During the climbing period, the maximum wind speed is 26.80 m/s and the average is 8.87 m/s. When the altitude is about
From the variability of wind speed, the standard deviation is small, furthermore, the flight state of UAV is relatively stable, which suggests it is feasible to observe typhoon by using UAV. The average value during the whole observation period is 19.68 m/s.
In this study, it was the first time to use the UAV equipped with meteorological sensors to observe temperature, pressure, relativity humidity and wind of Typhoon Sinlaku in China mainland. The following conclusions are found:
1) During this field campaign, the average meteorological elements are that temperature is 22.57˚C, relative humidity is 97.98%, wind speed is 19.68 m/s and pressure is 945.02 hPa;
2) The typhoon center has a warm structure, the closer to the centre, the higher the temperature is;
3) The UAV has the capability to observe the boundary layer of typhoon and can obtain the observation data during the flight mission.
This research work has been supported by Typhoon Special Funds of China Meteorological Administration and the Project (41475124) supported by NSFC. The authors thank the Beijing Donghengyu Technology Development Center to offer the UAV and Zhejiang Meteorological Bureau to help about the air traffic permission.