Two-dimensional spatial heterodyne spectrometer for atmospheric nitrogen dioxide observations.

A broadband monolithic spatial heterodyne spectrometer (SHS) system is built for measuring nitrogen dioxide in the atmosphere based on our newly developed fabrication technique. This system is calibrated and tested with Hg, Kr and Xe lamps, as well as monochromator output illuminated by a high-voltage Xe lamp (as a white light source). The obtained overall efficiency profile presents an effective spectral range of 425-495 nm (when the efficiency values are greater than 40%). The maximum fringe visibility is ~0.85. The measured instrumental line shape function gives an actual spectral resolution of ~0.073 nm. The effect of phase distortion of this 2-D SHS system can be neglected. Direct solar-irradiance spectra in the NO absorption band were measured with the SHS system. The measured spectra are consistent with the results simulated by Modtran6 within the SHS spectral range. The vertical column contents of NO, VC(NO), derived from the SHS data by the direct sun - differential optical absorption spectroscopy (DS-DOAS) method coincide closely with the simultaneously acquired (OMI) satellite data.