Abstract. The spectra measured by the Atmospheric Carbon dioxide Grating Spectrometer (ACGS) carried by the China global carbon dioxide observation satellite (TanSat) in the band of 0.76 μm, 1.61 μm and 2.06 μm can be used for the retrieval of carbon dioxide (CO2) concentrations by fitting the observations and simulations using the optimal estimation algorithm. Accurately detecting the change of the center wavelength is highly important because of its very high spectral resolution and accuracy requirement for product retrieval. The variations of center wavelength for all three bands of ACGS have been calculated on the locations of the individual solar absorption lines by comparing the solar-viewing measurements and the high resolution solar reference spectrum. The variations with magnitudes less than 10 % of the spectral resolution for each band have been detected. The changes are probably caused by vibration and the instrument status difference between the ground and space, especially temperature variation on orbit. In addition to solar lines, the entire atmospheric spectra simulated by radiative transfer model can be used as the reference spectrum to determine the wavelength change by fitting the measured and simulated spectra. The change of wavelength determined by atmospheric spectra is closely consistent with that by solar lines. Both schemes described here can be used not only for monitoring spectral stability but also to gain spectral knowledge prior to the level-2 product processing. These minor temporal changes of wavelength on orbit should be corrected in the product retrieval.
This preprint has been withdrawn.
How to cite. Bi, Y., Wang, Q., Yang, Z., Liu, C., Lin, C., Tian, L., Zhang, N., Luo, Y., and Wang, Y.: TanSat ACGS on-orbit spectral calibration by use of individual
solar lines and entire atmospheric spectra, Atmos. Meas. Tech. Discuss. [preprint], https://doi.org/10.5194/amt-2020-20, 2020.
Received: 22 Jan 2020 – Discussion started: 20 May 2020
We have used two types of on-orbit methods to evaluate the TANSAT/ACGS wavelength calibration. The first method is to use the solar Fraunhofer absorption lines as the reference.The second method uses the entire atmospheric spectra as the reference.For TanSat ACGS, the wavelength variations derived from the two methods agree closely. The accuracy of wavelength offsets is better than 10 % of the FWHM that meet the requirements of spectral calibration of the ACGS on orbit.
We have used two types of on-orbit methods to evaluate the TANSAT/ACGS wavelength calibration....