레이더 반사강도을 이용한 강우 감쇠특성 분석

Abstract

본 논문에서는 서로 다른 파장대를 사용하는 두개의 기상레이더를 이용하여 대기입자에 대한 감쇠 및 반사특성을 분석하고 강우량에 대한 감쇠정도를 해석하였다. 그 결과 대기중을 진행하는 전자기 에너지는 흡수와 산란에 의해 에너지를 잃게 되는데, 이 두가지 요소에 의한 손실을 조합하여 감쇠계수를 유도할 수 있었다. 현업용 측정에 이용된 레이더는 5.6cm와 10cm 사이의 파장을 사용하였고, 정량적인 관측을 하였다. 시스템에 처리기가 포함되어 있어서 보정 계수를 적용하여 데이터를 보정할 수가 있었다. 그 결과를 요약하면 다음과 같다. (1) 흡수로 인한 감쇠에 중요한 영향을 미치는 대기기체는 수증기와 산소이다. 기체 분자 때문에 생기는 산란에 의한 감쇠는 무시가 가능하며, 3cm 와 10cm 사이에서 대기중의 산소에 의한 감쇠는 극히 일정함을 알 수 있었다. (2) 서로 다른 두 파장대를 사용하는 레이더의 강우강도 반사도영상을 통해 10cm파장대와 5cm파장대의 감쇠특성을 비교분석한 결과 약 10~20dBz 의 감쇠차이가 나타남을 알 수 있었다.

The weather radar is the weather devices that observes the meteorological targets, forecasts the precipitation by detecting and tracking the precedent events before bad weather, and produces the wind field with the Doppler effects, by using the electronic waves. Currently, Korea Meteorological Administration is operating the weather radar in C-band, S-band and X-band frequency band for the research purpose. Besides Korea Meteorological Administration, Korean and U.S. Air Force, Ministry of Construction & Transportation and Korea Aerospace Research Institute are also operating the weather radar. It was possible to only detect the precipitation such as rainfall or snow with the first weather radar. But now as it enables to observe the wind with the Doppler effects to directly know the air current, it is used as the important weather data observation for mid-size weather, typhoon, cloud physical study, flood warning and safe aircraft service. The electronic waves from the weather radar computerizes the moving speed and reflectivity intensity, by using the reflective waves dispersed and returned by the meteorological targets. weather. The short electronic pulse used by weather radar detects the reflectivity intensity by detecting the weak signals returning from the meteorological target during the time between the pulses. Therefore, it is possible to measure the radial velocity by using the changes in phase difference between the pulses. The attenuation of the radar waves is mainly caused by the dispersion and absorption of the vapor, oxygen gas, rain drop or solid state of particles. The attenuation by the air gas is normally ignored because the amount is very small while the attenuation by the solid particles is much bigger than that by the gas. In other words, the attenuation is the most influenced by raindrops and the degree of attenuation is influenced by the particle diameter and its relation to the wave that is the subject of target. Likewise, the weather radar analyzes the characteristics of particle in the air with the pulse waves, and tracks on the sudden meteorological status and typhoon such as heavy rain, hail, falling of thunderbolt, for the short-time weather forecast. This paper uses the two weather radars that use different wave bands, in order to analyze the characteristics of attenuation and reflectivity for air particles and to interpret the attenuation degree for the rainfall amount. In the result, the electronic energy in the air loses its energy because of the absorption and dispersion. It was possible to derive the attenuation coefficient by combining the loss caused by these two factors. The radar for the field measurement purpose used the wavelength between 5.6cm and 10cm, with the quantitative observation. As the system contained the processor, it was possible to amend the data by applying the amending coefficient. The result is summarized as follows. (1) The air gas that makes important influence on the attenuation by absorption is vapor and oxygen. It is possible to ignore the attenuation caused by the dispersion of gas molecules, and to know the attenuation caused by the oxygen in the air was extremely constant between , 3cm and 10cm. (2) In the result of comparative analysis between the characteristics of attenuation of 10cm wavelength and 5cm wavelength through the rainfall intensity reflectivity visuals using different two wavelengths, it was noted there was differences of about 10~20dBz in attenuation.