Orthogonal Channel Coding For Simultaneous Co-And-Cross Polarization Measurements

 

Polarimetric variables are an essential part of algorithms for improved rainfall rate estimation, attenuation correction and hydrometeor identification. In such systems the transmit polarization state is changed according to some fixed pattern that is repeated. The simultaneous mode and alternating mode waveforms are commonly used in weather radars. In the simultaneous mode of operation , the horizontal and vertical polarization states are transmitted simultaneously and samples of both horizontal and vertical co-polar return are obtained A drawback of the simultaneous mode is its inability to measure cross-polar parameters such as linear depolarization ratio. In this paper a methodology to estimate cross-polar signals with simultaneous mode waveform is presented. In this method the horizontally and vertically polarized transmit waveforms are coded with orthogonal phase sequences. The performance of the phase coded waveform is determined by the properties of the phase codes. This paper presents the performance of the cross-polar and co-polar parameter estimation based on the simulation as well as data collected from CSU-CHILL radar. The CSU-CHILL radar system is capable of transmitting horizontal and vertical polarization states simultaneously. Two orthogonally polarized waves are transmitted using two separate (but identical) transmitters with dual channel reception of orthogonally polarized waves. The CSU-CHILL radar's klystron transmitters and the digital waveform synthesizer enable the use of orthogonal phase coding on the horizontal and vertical polarization channels respectively.