OCEAN SURFACE OBSERVATION BY C-BAND POLARIMETRIC WEATHER RADAR IN OKINAWA ISLAND Makoto Satake, Yukari Shusse, Katsuhiro Nakagawa, Shoichiro Kojima, and Shinsuke Sato National Institute of Information and Communications Technology, Japan email@example.com ABSTRACT We had developed a C-band multi-parameter weather radar in National Institute of Information and Communications Technology (NICT), Japan. It is a full-polarimetric radar with Doppler measurement capability. Its location is on the top of a mountain in the center of the Okinawa Island, southernmost part of Japan. Since 1992 the radar has been operated to observe precipitations in sub-tropical maritime climate region, in order to precise estimate rainfall rates and to classify precipitation particles. However, we also would like to make use of the radar for another application other than precipitation measurements. Okinawa Island is relatively small and plain, roughly 100 km in south to north, 10 km in east to west, and its highest part is about 500 m above sea level. Located at 360 m above sea level, the radar has good view to the surrounding ocean. Therefore, we would apply the weather radar to ocean surface observation. The radar has two Klystron transmitters of 250 kW, so that it can change transmitting polarization (horizontal, vertical, and so on) pulse to pulse. Its center frequency is 5.34 GHz (C-band). The backscattering echo from the targets is received in both horizontal and vertical polarizations simultaneously. The radar has typically 200 km coverage with 0.9 degree beamwidth, transmitting 2.0/1.0/0.5 sec pulses. The antenna is a parabolic one of 4.5 m diameter. The spatial resolution, therefore, is a few kilometers in azimuth and a few hundreds meters in range. Objective of our ocean surface observation are following: (1) to investigate variation of radar cross- section in HH, HV, VV polarization channels depending on wind speeds and directions, and (2) to examine polarization characteristics of backscattering from ocean surface and floating objects including ships. (HV stand for transmitting in horizontal polarization and receiving in vertical polarization.) For those objectives, we have had the radar observe ocean surfaces, in different wind conditions, since February 2007. We take a Plan Position Indicator (PPI) scan every 3 minutes with –0.5 or –1.0 degrees (downward) of antenna elevation angle, transmitting alternative H and V polarization signals. When looking downward, the coverage of radar at the sea level changes according to the elevation angles. With 0.9 degree beamwidth, –0.5 elevation looking has rather good coverage, from 20 km to 100 km at sea level. The preliminary results show that the radar cross-section is larger when the wind speed is larger. Downwind side of the island shows smaller radar cross-sections, as the island seems to block the wind. We present more detailed analysis of dependency of the radar cross-section on winds. Also we try to spot ships from the radar data, as there are several ferry boat services from the island to nearby islands. Polarimetric characteristics of backscattering signals from the ships and from the combination of the ship and the ocean surface are of our great interest.
Pages to are hidden for
"OCEAN SURFACE OBSERVATION BY C-BAND POLARIMETRIC WEATHER RADAR IN "Please download to view full document