A novel spectrally tunable calibration source based on a digital micromirror device (DMD) and Ebert-Fastie optical configuration with two working modes (narrow-band mode and broad-band mode) was designed. The DMD is set on the image plane of the first spectral tuner, and controls the wavelength and intensity of the light reflected into the second spectral tuner by switching the micromirror array’s condition, which in turn controls the working mode of the spectrally tunable source. When working in narrow-band mode, the spectrally tunable source can be calibrated by a Gershun tube radiant power radiometer and a spectroradiometer. In broad-band mode, it can be used to calibrate optical instruments as a standard spectral radiance source. When using a xenon lamp as a light source, the stability of the spectrally tunable source is better than 0.5%, the minimum spectral bandwidth is 7 nm, and the uncertainty of the spectral radiance of the spectrally tunable source is estimated as 14.68% at 450 nm, 1.54% at 550 nm, and 1.48% at 654.6 nm. The uncertainty of the spectral radiance of the spectrally tunable source calibrated by the Gershun tube radiometer and spectroradiometer can be kept low during the radiometric calibration procedure so that it can meet the application requirement of optical quantitative remote sensing calibration.

The carbon dioxide spectrometer (CDS) on board the Chinese Carbon Dioxide Observation Satellite (TanSat) is a high spectral and spatial resolution grating spectrometer with three specific spectral bands dedicated to atmospheric CO ₂ detection. The CDS’s design and on-ground spectral calibration are presented in this paper. The instrument line shape functions and spectral dispersion were characterized using a tunable diode laser-based testing system for all spectral pixels of the CDS placed in a thermal vacuum chamber.

A transfer radiometer (TR) applied to an on-orbit radiometric benchmark transfer chain has been developed, which can achieve the high-precision transformation of power and radiance responsivity and transmit the radiance responsivity traced to the cryogenic radiometer to remote sensors, such as an imaging spectrometer, so that the on-orbit remote sensors can achieve the high accuracy calibration of 10⁻³ magnitude. Radiance comparison experiments between the TR and the radiance standard of the National Institute of Metrology (NIM) were carried out to demonstrate the absolute accuracy of the TR radiance measurement. At 780.0 nm and 851.9 nm, the relative measurement uncertainties of the TR filter-free channel were 0.24% (k = 1). Additionally, the radiance measurement results of the TR were consistent with those of the NIM radiance meter, and the radiance measurement results’ relative differences between the TR and the NIM radiance meter were approximately 0.04% at 780.0 nm and 851.9 nm. The relative measurement uncertainties of TR 780.4 nm and 851.8 nm filter channels were 0.89% (k = 1) and 0.84% (k = 1), respectively. Additionally, the radiance measurement results of the TR 780.4 nm and 851.8 nm filter channels were consistent with the radiances of the integrating sphere source calibrated by the NIM at 780.4 nm and 851.8 nm; the relative differences between the radiances measured by the two TR filter channels and the radiances of the integrating sphere source itself were better than 0.56%. This proved that the TR could measure the monochromatic source radiance with a measurement uncertainty of 0.24% and measure the broadband source radiance with a measurement uncertainty better than 0.89%. The TR can be applied to the radiometric benchmark transfer chain to improve the measurement precision of on-orbit remote-sensing instruments.

In order to meet the high-accuracy calibration requirements of satellite remote sensing instruments, a transfer radiometer for an on-orbit radiometric benchmark transfer chain has been developed, which provides vital technical support for realizing the radiometric calibration uncertainty of the order of 10⁻³ for remote sensing instruments. The primary role of the transfer radiometer is to convert from the spectral power responsivity traceable to a cryogenic radiometer to the spectral radiance responsivity and transfer it to the imaging spectrometer. At a wavelength of 852.1 nm, the combined uncertainty of the radiance measurement comparison experiment between the transfer radiometer and a radiance meter is 0.43% (k = 1), and the relative deviation of the measurements between the transfer radiometer and the radiance meter is better than 0.36%, which is better than the combined uncertainty of the radiance measurement comparison experiment. This demonstrates that the transfer radiometer can achieve radiance measurements with a measurement uncertainty better than 0.3% (k = 1).