Shigeharu Shimamura

Probabilistic Attenuation Correction in a Networked Radar Environment

A probabilistic attenuation correction technique for a single-polarization networked radar environment is proposed. The proposed technique, based on the Bayesian theory, makes a maximization of a likelihood function of Hitschfeld-Bordan (HB) reflectivity obtained by each radar node. A variance of the HB reflectivity (σHB2) is defined and regarded as instability of each HB reflectivity in the proposed technique. In the X-band simulation based on S-band real radar data, it is revealed that the corrected reflectivity obtained by the proposed technique has good accuracy, and the proposed technique works more stably than the HB technique. The proposed technique is also performed using CASA IP-1 dual-polarization radar network observations, and the corrected reflectivity by the proposed technique has a good agreement with differential phase (ΦDP)-based corrected reflectivity.

Development and observation of the phased array radar at X band

A new Phased Array Radar (PAR) system for meteorological application has been developed by Toshiba Corporation and Osaka University under a grant of NICT, and installed in Osaka University, Japan in 2012. The phased array radar system developed has the unique capability of scanning the whole sky with 100m and 10 to 30 second resolution up to 60 km. The system adopts the digital beam forming technique for elevation scanning and mechanically rotates the array antenna in azimuth direction within 10 to 30 seconds. The radar transmits a broad beam of several degrees with 24 antenna elements and receives the back scattered signal with 128 elements digitizing at each elements. Then by digitally forming the beam in the signal processor, the fast scanning is realized. After the installation of the PAR system in Osaka University, the initial observation campaign was conducted in Osaka urban area with Ku-band Broad Band Radar (BBR) network, C-band weather radar, and lightning location system. The initial comparison with C band radar system shows that the developed PAR system can observe the behavior of the thunderstorm structure in much more detail than any other radar system. The observed high temporal resolution images of the severe thunderstorm are introduced, showing the potential capabilities of the PAR system. The correlation coefficient of the reflectivity in PAR with C band radar ranges from 0.6 to 0.9 as a function of the distance from the PAR.

2-Dimensional high-quality reconstruction of compressive measurements of phased array weather radar

This paper proposes a compressive sensing method for the phased array weather radar (PAWR), which is capable of three-dimensional observation with high spatial resolution in 30 seconds. Because of the large amount of observation data, which is more than 1 gigabyte per minute, data compression is an essential technology to operate PAWR in the real world. Even though many conventional studies applied compressive sensing (CS) to weather radar measurements, their reconstruction quality should be further improved. To this end, we define a new cost function that expresses prior knowledge about weather radar measurements, i.e., local similarities. Since the cost function is convex, we can derive an efficient algorithm based on the so-called convex optimization techniques, in particular simultaneous direction method of multipliers (SDMM). Simulation results show that the proposed method outperforms the conventional methods for real observation data with improvement of 4% in the normalized error.

Osaka urban phased array radar network experiment

Osaka University, Toshiba and the Osaka Local Government started a new project to develop the Osaka Urban Demonstration Network. The main sensor of the Osaka Network is a 2-node Phased Array Radar Network and lightning location system. Data products that are created both in local high performance computer and Toshiba Computer Cloud, include single and multi-radar data, vector wind, quantitative precipitation estimation, VIL, nowcasting, lightning location and analysis. These new products are transferred to Osaka Local Government in operational mode and evaluated by several section in Osaka Prefecture.

3-dimensional compressive sensing and high-quality recovery for phased array weather radar

This paper proposes an effective three-dimensional compressive sensing method for the phased array weather radar (PAWR), which is capable of three-dimensional observation with spatially and temporally high resolution. Because of the large amount of observation data, which is approximately 1 gigabyte per minute, data compression is an essential technology to conduct a network observation by multiple PAWRs. Even though many conventional studies applied compressive sensing (CS) to weather radar measurements, their reconstruction quality should be further improved. To this end, we define a cost function for a three-dimensional recovery exploiting not only local similarity but also global redundancy of weather radar measurements. Since the cost function is convex, we can derive an efficient algorithm based on the standard convex optimization techniques. Simulation results show that the proposed method achieves normalized errors less than 10% for 25% compression ratio with outperforming conventional two-dimensional methods.

Probabilistic attenuation correction in dual-pol radar network

A probabilistic attenuation correction technique for differential reflectivity ZDR, based on the Bayesian theory, in a dual polarization networked environment is proposed. The proposed technique assumes a proportional relationship between specific differential attenuation ADP and specific differential phase KDP, and a power law relationship between backscattering differential phase δco and ZDR. The algorithm maximizes a likelihood function by minimizing a cost function, and derives coefficients in the two relationship appropriately as well as a ZDR profile. To evaluate the proposed technique, one dimensional simulation on X-band using S-band radar data is performed. In this paper, details of the algorithm of the proposed precipitation attenuation correction technique and evaluation results of the simulation are described.

Probabilistic approach for attenuation correction in multiple dual-polarimetric radar network

Conventional meteorological radar systems with high power transmitters at S-, or C-band have long coverage areas. On the other hand, dense radar network systems with low power transmitters at X-, or Ku-band has been proposed ( Junyent et al. , J. Atmos. Oceanic Technol., 27, 2010, pp. 61 – 78.) (S. Shimamura et al., 144, 36th Conference and Radar Meteorology, Breckenridge CO USA, Sep., 2013) which can fill in observation gaps in low altitudes because of earth curvature and have good accuracy and resolution. A weather radar, especially with transmitting short-wavelength pulses, is affected by precipitation attenuation. Various methods for precipitation attenuation correction have been developed in the literature. A network based attenuation correction technique in a multiple radar network has been suggested (Chandrasekar and Lim, J. Atmos. Oceanic Technol., 25, 2008, pp.1755 – 1767). In this paper, we suggest a probabilistic technique for precipitation attenuation correction based on a dual polarization radar network by using the dual-polarization attenuation correction technique ( Lim and Chandrasekar, IEEE Transactions on Geoscience and Remote Sensing, Vol.44, No.4, April 2006, pp. 1011 – 1021) (Liu, et al., Geoscience and Remote Sensing Symposium, IGARSS 2006, pp. 1910–1913).

Latest observation results of the Ku-band broadband radar (BBR) network project

Ku-band broadband radar is a short-range (15 or 20 km) high-resolution (range and temporal resolution of several meters and 1 min per volume scan with 30 elevations) weather radar to resolve fine structures of precipitation from the near surface (several tens of meters), and a networked observation with several Ku-BBRs covers the troposphere accurately and efficiently. In this paper, two latest observation results of the Ku-BBR and the Ku-BBR network are described. One is an observation of a small-scale tornado in Shonai airport by single radar, in which a fine structure of the small tornado is resolved in 4-D. The other is preliminary results of a networked observation with three Ku-BBRs in north Osaka area, in which fine structures of precipitation are resolved simultaneously and multi-directionally.

Development of the broadband radar network with high resolution

A small-baseline weather radar network consisting of the Ku-band broadband radars (BBR) for meteorological application has been developed. The BBR is a remarkably high-resolution close-range Doppler radar designed for detecting and analyzing rapidly evolving weather phenomena such as severe thunderstorms, tornadoes, and downbursts, which often cause damage to our lives seriously. A radar network with several BBRs (the BBR network) observes multi-directionally and simultaneously these severe phenomena with high resolution in space and time, and with high accuracy. In this presentation, the concept of the project and the initial observation results of the BBR network are presented.