Haruya Minda

High Temporal Resolution Path-Average Rain Gauge with 50-GHz Band Microwave

Abstract Rain radar measures instantaneous spatial-average rainfall, while conventional rain gauges directly measure point rainfall with low temporal resolution. Thus differences in the resolution of the sensors create difficulties for rain radar validation, especially for spaceborne rain radar. Accordingly, rainfall measurement by microwave link has been proposed for several decades, as it estimates instantaneous path-average rainfall. Thus it is expected that the microwave link rain gauge will overcome, at least partly, the problems in the rain radar validation, toward which a 50-GHz band microwave link [the path-averaged rain gauge (PRG)] was developed that has been in operation since September 2000. In this paper, the authors show the potential of the PRG system by a simple model and rainfall comparison with a disdrometer and a tipping-bucket rain gauge. Differences observed by the instruments were within 15% (within 10% in half of the cases) during actual rain events in 2003. This confirmed that the ...

Radar Attenuation and Reflectivity Measurements of Snow With Dual Ka-Band Radar

There is insufficient understanding of backscattering and attenuation for the radiowave remote sensing of snow because ground measurements of snow in the Ka-band are limited. This study estimates the equivalent radar reflectivity factor (Ze) and specific attenuation (k) of snow using a dual Ka-band radar (KaR) system comprising two identical Ka-band instruments. To evaluate the estimations, estimated k-Ze plots of rain events are compared with plots estimated from the raindrop size distribution. The two k-Ze plots have similar power-law relations. In contrast, k-Ze plots of snow have complex tendencies. Among snow events, the tendencies of k-Ze relations depend on surface temperature. When surface temperature exceeds 0 °C during snow events, k-Ze data are scattered and there are k values higher than those of rain. In contrast, when surface temperature is below 0 °C during snow events, both k and Ze are low and the k-Ze plots show no relation. In the former (latter) cases, wet (dry) snow is probably dominant. The differences in k-Ze relations of snow are attributed to the differences in backscattering and attenuation characteristics between wet and dry snow. To confirm the existence of wet/dry snow, snow particle data obtained using a two-dimensional video disdrometer on the ground are analyzed. Velocity-size distributions are clearly different in wet- and dry-snow cases. For dry-snow cases, snow particles of dry snow and graupel occasionally coexisted.

Precipitation measurement using a dual Ka-band radar system for GPM/DPR algorithm development

A dual Ka-band radar system was developed by the Japan Aerospace Exploration Agency for GPM/DPR algorithm development. The system consists of two identical Ka-band radars. Both the equivalent radar reflectivity factor (Ze) and specific attenuation (k) can be estimated at each range of the path. The estimated k-Ze relations of rain, snow, and the melting layer can be used for the GPM/DPR algorithm development. Those parameters of snow at Ka band are important. Observations using the dual Ka radar system were performed in Okinawa Island, and Nagaoka, Niigata, Japan. In Okinawa Island, rain observation was conducted for confirming the performance of the measurement, and reasonable k-Ze relations of rain were obtained. In Nagaoka, snow observation was conducted. Different k-Ze relations were obtained. This was attributed to the attenuation difference between wet and dry snow.

Bird Migration Echoes Observed by Polarimetric Radar

A C-band polarimetric radar on Okinawa Island successfully observed large-scale bird migrations over the western Pacific Ocean. The birds generated interesting polarimetric signatures. This paper describes the signatures and speculates bird behavior.

Three-Dimensional Shape and Fall Velocity Measurements of Snowflakes Using a Multiangle Snowflake Imager

AbstractThis paper describes a Multiangle Snowflake Imager (MSI) designed to capture the pseudo-three-dimensional (3D) shape and the fall velocity of individual snowflakes larger than 1.5 mm in size. Four height-offset line-image scanners estimate fall velocities and the four-angle silhouettes are used to reconstruct the 3D snowflake shapes. The 3D shape reconstruction is tested using reference objects (spheres, spheroids, cubes, and plates). The four-silhouette method of the MSI improves the representation of the particle shape and volume compared to two-silhouette methods, such as the two-dimensional video disdrometer (2DVD). The volume (equivolumetric diameters) of snowflakes estimated by the four-silhouette method is approximately 44% (13%) smaller than that estimated by the two-silhouette method. The ability of the imager to measure the fall velocity and particle size distributions based on the silhouette width and the equivolumetric diameter of 3D-shaped particles is verified via a comparison with t...

Snow measurement using a dual Ka-band radar system for GPM/DPR algorithm development

Both equivalent radar reflectivity factor (Ze) and specific attenuation (k) in several snow events are measured using a dual Ka-band radar system. Different k-Ze relations are obtained depending on surface air temperature. When surface air temperature is just above 0 °C, k-Ze relations scatter and larger k values than those of rain appear. On the other hand, when surface air temperature is below 0 °C, both k and Ze are small and a slight positive trend appears in the k-Ze relations. The difference of k-Ze relations can be attributed to the difference of the backscattering and attenuation characteristics between wet and dry snow. To confirm wet/dry snow existences, 2D-video-disdrometer data are analyzed. Velocity-size distributions of wet snow events are different from those of dry snow events. Graupels also show different velocity-size distributions from wet and dry snow particles with different k-Ze relations.