SORAS (Stratospheric Ozone RAdiometer in Seoul), a ground-based 110 GHz microwave radiometer for measuring the stratospheric ozone vertical profile

A ground-based 110 GHz radiometer was designed to measure the stratospheric ozone vertical profile by observing the 110.836 GHz ozone emission spectrum, and the instrument is operational at Sookmyung Women's University (37.54 degrees N, 126.97 degrees E) in Seoul, South Korea. In this paper, we detail the instrumental design, calibration procedures, correction methods, and the retrieved ozone vertical profile. The instrument is a heterodyne total power radiometer. It down-converts the observed 110.836 GHz ozone frequency to 0.609 GHz, with a frequency resolution of 61 kHz and a bandwidth of 830 MHz. The spectral intensity is digitized using a fast-Fourier-transform spectrometer. For hot-cold calibration, we use microwave absorbers at room temperature and liquid nitrogen as calibration targets. Tropospheric opacity is corrected using the continuous tipping curve calibration. The measured opacities were compared with simulated values from the Korea Local Analysis and Prediction System (KLAPS) data. Additionally, since 2016, the stratospheric ozone profiles over Seoul have been demonstrated for the vertical range of 100-0.3 hPa (16-70 km), with validation performed by comparing them to the ozone profiles from the Microwave Limb Sounder (MLS) on the AURA satellite.