First high-resolution tropospheric NO 2 observations from the Ultraviolet Visible Hyperspectral Imaging Spectrometer (UVHIS)

Abstract. We present a novel airborne imaging differential optical absorption\nspectroscopy (DOAS) instrument: the Ultraviolet Visible Hyperspectral Imaging\nSpectrometer (UVHIS), which is developed for trace gas monitoring and\npollution mapping. Within a broad spectral range of 200 to 500  nm and\noperating in three channels, the spectral resolution of UVHIS is better than\n0.5  nm . The optical design of each channel comprises a fore-optics\nwith a field of view (FOV) of 40 ∘ , an Offner imaging spectrometer and\na charge-coupled device (CCD) array detector of 1032×1072 pixels. A\nfirst demonstration flight using UVHIS was conducted on 23 June 2018, above an\narea of approximately 600  km2 in Feicheng, China, with a spatial\nresolution of about 25 m×22 m . Measurements of nadir\nbackscattered solar radiation of channel 3 are used to retrieve tropospheric\nvertical column densities (VCDs) of NO2 with a mean total error of\n 3.0×1015 molec cm−2 . The UVHIS instrument clearly\ndetected several emission plumes transporting from south to north, with a peak\nvalue of 3×1016 molec cm−2 in the dominant one. The\nUVHIS NO2 vertical columns are consistent with the ground-based\nmobile DOAS observations, with a correlation coefficient of 0.65 for all\nco-located measurements, a correlation coefficient of 0.86 for the co-located\nmeasurements that only circled the steel factory and a slight underestimation\nfor the polluted observations. This study demonstrates the capability of UVHIS\nfor NO2 local emission and transmission monitoring.