We report the development of the software-based polarization spectrometer‘ PolariS ’and early results from commissioning on the Nobeyama 45-m radio telescope. PolariS aims to detect the Zeeman effect of CCS line to measure ~ 100 μG magnetic fields in star-forming molecular cores. The PolariS consists of the K5/VSSP32 digitizer and a Linux-based PC with a GPU to process full-Stokes spectroscopy of 2 x 131072 ch for bandwidth of 4 or 8 MHz. We have verified performance of PolariS and succeeded to take full-stokes spectra of SiO masers. Since the code is open at GitHub everybody can utilize it.
We propose the Allan Variance method to identify spurious signals with sensitive detectability. With this method, detection level of -56 dB with respect to the system noise can be achieved within the integration time less than 10 min. Detected spurious signals can be mitigated by masking these channels before spectral bunching to required spectral resolution. We will present the principle of the method and the performance taken through the ALMA system verification activity. This method can be applied for universal single-dish spectroscopy.