Author:
Zhao Min Jie,Si Fu Qi,Zhou Hai Jin,Wang Shi Mei,Jiang Yu,Liu Wen Qing
Abstract
Abstract. An environmental trace gases monitoring instrument (EMI) is a nadir-viewing
wide-field imaging spectrometer, which aims to quantify the global
distribution of tropospheric and stratospheric trace gases, and is planned to
be launched on 9 May 2018. The selected wavelength bands for EMI are
ultraviolet channels: UV1 (240–315 nm), UV2 (311–403 nm) and visible
channels: VIS1 (401–550 nm), and VIS2 (545–710 nm). The spectral resolution
is 0.3–0.5 nm, and the swath is approximately 114∘ wide to achieve
a one-day global coverage. The preflight calibration of the EMI is discussed
in this paper. A tunable laser and rotating platform are adopted for an EMI
wavelength calibration of the entire field of view. The accuracy of the
wavelength calibration is less than 0.05 nm. In addition, the solar
calibration mode shows the same results compared with Earth observation mode.
A thermal vacuum test is performed to investigate the influence of in-orbit
thermal vacuum conditions on the EMI, and EMI spectral response changes with
pressure, optical bench temperature, and charge-coupled device (CCD) detector
temperature are obtained. For a radiometric calibration of UV1, a diffuser
plate with a 1000 W xenon lamp, which produces sufficient UV output, is
selected. An integrating sphere system with tungsten halogen lamp is selected
for the UV2, VIS1, and VIS2. The accuracies of radiance calibration are
4.53 % (UV1), 4.52 % (UV2), 4.31 % (VIS1), and 4.30 % (VIS2). The
goniometry correction factor and irradiance response coefficient of the EMI
are also calibrated on the ground for an in-orbit calibration of the solar. A
signal-to-noise ratio (SNR) model of the EMI is introduced, and the EMI
in-orbit SNR is estimated using the SNR and MODTRAN radiance
models.
Funder
National Natural Science Foundation of China
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