A conical scan type spaceborne precipitation radar

The global distribution of rainfall and its variation are deeply linked to the global climate change and the abnormal weather and they have significant impacts on the human activities and social systems. In order to acquire global rainfall data, we have to rely on observations by the spaceborne rain radar or microwave radiometer. The TRMM satellite , which was launched on 28 November 1997, realized the first spaceborne rain radar called the TRMM PR. TRMM PR has been acquiring many valuable three dimensional distribution data of rainfall, which cannot be observed by other methods, for more than eleven years.

However, as the TRMM PR adopts an active phased array system composed of as many as 128 transmitting and receiving elements to scan antenna beam electrically at high speed, it becomes an extremely heavy mass, which is not always desirable for the spaceborne system. In addition, TRMM PR's single wave guide slot array antenna cannot be shared by the multi-frequency and dual polarization radar, meaning that each different frequency and polarization radar needs different slot array antenna. Therefore from a physical perspective, using multiple slot array antennas for the multi-frequency and dual polarization radar, which will be required in the future, is not preferable.

This study aims at designing of the small and light multi-parameter rain radar system which utilizes high speed mechanical scan reflector antenna, doing simulation of the rain observation from space by using cloud resolving model, and assessing of the design specification of the new spaceborne conical scanning type rain radar. We study the single frequency and polarization conical scan type rain radar which becomes the basis of the future multi-parameter rain radar system. If the small and light spaceborne rain radar that can be installed on the many satellites is proposed, opportunities of rain observations from space will increase, which will lead to more accurate observations of global rainfall distributions and its variations. That will surely bring significant contributions to studies of the global climate change and abnormal weather.

We calculated the system parameters of satelliteborne conical scan type rain radar, varying antenna diameter and apex angle of conical scan (scan angle) as two variable parameters. We run an experimental simulation on the rain observation from space, utilizing rain models and the calculated antenna pattern of the offset parabolic antenna. We propose the system parameters and block diagram for the system design of the spaceborne small and light new conical scanning type rain radar. Through the estimation of the system mass and power consumption, it was found that the estimated mass could be significantly reduced compared to TRMM PR.

From these results, it is concluded that the small and light spaceborne conical scan type precipitation radar is feasible. In addition, we also study the feasibility of the combined precipitation radar/microwave radiometer system which commonly shares the conical scan type antenna.