Rainfall Observation of the Ku-band Broadband Radar Network in Osaka, Japan

A small-baseline weather radar network is a novel strategy to detect small-scale weather phenomena such as thunderstorms, tornadoes, and downbursts which often cause damage to our lives seriously. Collaborative Adaptive Sensing of the Atmosphere (CASA) [1] and X-band radar network (X-net) [2] have proposed a new radar network system using short-range X-band radars to observe the lower troposphere. Conventional S-, C- and X-band weather radars cover a wide area (100 through 450 km in radius) with range resolution of more than 100 m and temporal resolution of 5 min roughly, which are appropriate for precipitation systems of macro- or mesoscale. And, conventional weather radars constantly observe in altitudes above 1 or 2 km in the most covered planer area since earth's curvature more affects in the longer ranges. However, small-scale phenomena as mentioned above have a duration of 10-20 min mostly and a spatial scale of 100 m roughly, and occur in altitudes below a few kilometers. Therefore, it is significantly difficult for conventional weather radars to detect these small-scale phenomena [3, 4, 5]. A weather radar network consisting of the Ku-band broadband radars (BBR) [6, 7], which we have been proposing and developing, can observe these small-scale phenomena with high accuracy and detection efficiency. The BBR is a short-range (15 km) pulse-Doppler radar with remarkably high resolution (range and temporal resolution of several meters and 1 min per volume scan, respectively) to detect and analyze them. The small coverage is almost never affected by earth's curvature, and the distributed radars cover a wide area. Additionally in the radar network installation, a weather phenomenon in the overlapped areas is multi-directionally and simultaneously observed by several BBRs. Data integration of reflectivities obtained by several BBRs with a use of weighting function is equivalent to an average of composite average functions [3] of the BBRs. In the most parts of the overlapped observational area, crossed pattern of several composite average functions accomplishes high spatial resolution of several meters two- or three-dimensionally due to the range resolution in spite of its poor beam width of 3 deg. This presentation shows configuration and signal processing of the BBR, and the initial observation results of the BBR network operated in Osaka, Japan. Spatial resolution of multi-directional and simultaneous observation in the BBR network is presented in details in another presentation in this conference. Two BBRs (called Toyonaka and SEI radar) have already been deployed in Osaka, Japan, and one more BBR will be installed. The former two BBRs are deployed 14.32 km apart and covering 294.18 km2 redundantly. In Figure 1, the initial results of simultaneous observations in the two-BBR network are shown. The observation results of both BBRs are integrated with a simple weighting function depending on distance from each BBR, and high-quality images of precipitation are accomplished by complimenting each other. Fig. 1. Initial Observation results at 13:54, 55, 56, 57, and 58 on Sep. 14, 2010. Left (Panels (a-1) through (a-5)) and center (Panels (b-1) through (b-5)) panels are results of the Toyonaka and SEI radar, respectively. Right panels (Panels (c-1) through (c-5)) are integrated results from both radars. In each panel, upper and lower triangles indicate the Toyonaka and SEI radar, respectively. The two dash circles and a solid circle are on ranges of 5, 10, and 15 km from each BBR, respectively. In Panels (a-1) through (a-5) and Panels (b-1) through (b-5), circles indicate ranges from Toyonaka and SEI radar, respectively. In Panels (c-1) through (c-5), circles from both BBRs are described. [1] F. Junyent, and V. Chandrasekar, “Theory and characterization of weather radar networks,” J. Atmos. Ocean. Technol., vol. 26, pp. 474-491, 2009. [2] M. Maki et al., “X-band polarimetric radar network in the Tokyo metropolitan area - X-NET -,” paper presented at ERAD 2008, Finnish Meteorol. Inst., Helsinki. [3] R. J. Doviak and D. S. Zrnic, Doppler Radar and Weather Observations, San Diego, CA: Academic, 1993. [4] V. N. Bringi and V. Chandrasekar, Polarimetric Doppler Weather Radar: Principles and Applications, Cambridge, U.K.: Cambridge Univ. Press, 2001. [5] R. A. Houze, Jr., Cloud Dynamics, San Diego, CA: Academic, 1993. [6] Mega, T., K. Monden, T. Ushio, K. Okamoto, Z. Kawasaki, and T. Morimoto, “A low-power high-resolution broad-band radar using a pulse compression technique for meteorological application,” IEEE Geosci. Remote Sens. Lett., 4(3), 392–396, 2007. [7] Yoshikawa, E., T. Ushio, Z. Kawasaki, T. Mega, S. Yoshida, T. Morimoto, K. Imai, and S. Nagayama, “Development and initial observation of high-resolution volume-scanning radar for meteorological application,” IEEE Trans. Geosci. Remote Sens., 48, 3225–3235, 2010.