First retrieval of tropospheric nitrogen dioxide columns from the Environmental Monitoring Instrument (EMI) onboard the Chinese GaoFen-5 satellite
Abstract
The EMI instrument onboard the Chinese GaoFen-5 satellite was has been successfully launched on May 9, 2018. The EMI instrument is a nadir-viewing push broom spectrometer, measuring earthshine radiances and solar irradiances in the wavelength range of 240 to 710 nm at a moderate spectral resolution (FWHM) of 0.3 to 0.5 nm (depending on wavelength). EMI consists of an Offner imaging spectrometer with four spectral channels, and each channel is equipped with a two-dimensional (spectral and spatial) CCD detector which enables a field of view (FOV) of 114° and 0.5° in the swath and flight direction, respectively. The four spectral channels cover the following wavelength ranges: 240-315 nm, 311-403 nm, 401-550 nm, and 545-710 nm for the UV1, UV2, VIS1, and VIS2 channels, respectively. The spatial resolution of the instrument is 24*13 km. An EMI NO2 retrieval algorithm has been developed. The EMI NO2 slant column densities were retrieved by analyzing the earthshine spectra at the wavelength range of 410-470nm using the DOAS technique. Cross section of other trace gas absorption such as liquid and vapour water, O3, O4, and Ring effect are included in the DOAS analysis. The EMI NO2 SCDs were then converted to vertical column densities (VCDs) by using the concept of air mass factor (AMF). The AMFs were calculated based on the NO2 profiles derived from the GEOS-Chem chemistry transport model simulations with a horizontal resolution of 2°×2.5° using the radiative transfer model VLIDORT. Vertical columns over China were calculated with a regional chemistry transport model WRF-Chem at a resolution of 10km. The tropospheric-stratospheric separation of the total NO2 column was realized by a novel reference sector method. The first retrieval results of EMI NO2 VCDs are presented. The result shows the EMI instrument is able to capture the spatial and temporal variability of NO2 pollution levels and show good agreement with other satellite observations.
- Publication:
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EGU General Assembly Conference Abstracts
- Pub Date:
- April 2019
- Bibcode:
- 2019EGUGA..2119012Z