The accurate detection of near-space (20?100 km) atmospheric density profiles plays a pivotal role in spacecraft orbit optimization, aircraft thermodynamic performance evaluation, and space environment monitoring. Nevertheless, conventional optical remote sensing techniques are limited by constraints such as low light flux, inadequate spectral resolution, and coarse vertical sampling intervals, which pose significant challenges to the detection of fine-scale structures associated with key dynamic processes. Aiming at the demand for space-borne high-precision detection of near-space atmospheric density profiles, optical design and performance verification of hyperspectral atmospheric density profile imager (HDI) are conducted. Using single frame limb observation image by HDI, high-spatial-resolution hyperspectral information of oxygen A-band absorption spectrum and airglow radiation spectrum can be acquired over an atmospheric vertical height range of approximately 100 km, while simultaneously inverting atmospheric density profiles and temperature profiles.

Based on the principle of spatial heterodyne interferometric imaging spectroscopy (SHIS), the HDI optical system is designed. It can meet the high-precision detection requirements for near-space atmospheric density profiles, which include high signal-to-noise ratio (greater than 100 under typical spectral radiance), hyperspectral resolution (better than 0.04 nm), and fine vertical sampling interval (better than 0.1 km).

To meet the technical index requirements of HDI, relationships between basic parameters of each functional component and residual polarization sensitivity characteristics of HDI are analyzed, and the optimized design of the optical system is completed. The optical system includes a front component with orthogonal heterogeneous optical field modulation, a spatial heterodyne interferometer, and a re-imaging component. The front component consists of a front cylindrical lens and a collimator lens. The front cylindrical lens group has a focal length of 534.5 mm, a spectral field of view of ±1.85°, and corresponds to a horizontal atmospheric width of 160 km. The front collimator lens group has a focal length of 461.6 mm, a spatial field of view of ±1.185°, and corresponds to a vertical atmospheric height range of 102 km. Consequently, the sampling resolution interval of HDI in the spatial dimension is approximately 0.1 km.

In spatial heterodyne interferometric spectrometers, there are various polarization-sensitive components such as diffraction gratings, mirrors, and beam-splitting prisms. When the optical system itself exhibits residual polarization sensitivity, it not only impairs the radiometric measurement accuracy of the spectrometer but also leads to image separation in imaging spectrometers. The HDI polarization response model and measurement platform are established. Test results indicate that by incorporating a quartz wedge-type depolarizer between the field diaphragm of the front cylindrical lens group and the mirror in the HDI optical system, and adjusting the depolarizer to ensure the maximum image separation occurs in the spectral dimension, the influence of the depolarizer on the spatial dimension imaging quality and reconstructed spectral accuracy of HDI can be minimized.

Ground tests and calibration results confirm that HDI meets all design specifications. Spectral characterization shows an operational range of 756.8?771.4 nm, which fully covers the primary absorption region of the oxygen A-band (759?769 nm). Calibration with tunable laser and wave-meter yields a measured spectral resolution of 0.0394 nm, which is in close agreement with theoretical predictions. Under typical entrance pupil radiance, during limb observation at an orbital altitude of 520 km, with spatial binning of 20 pixel in the atmospheric vertical direction (corresponding to a vertical profile spatial resolution of 2 km), the average spectral signal-to-noise ratio (SNR) is 149. However, due to the detector heat sink cooling temperature of -16.2 ℃, which is slightly higher than the designed value of -20 ℃, the dark current noise of HDI in orbit has increased marginally. Consequently, the average spectral SNR of HDI is slightly lower than 149, but it still satisfies the requirement (≥100).

The development of HDI makes a significant advancement in space-borne hyperspectral detection of near-space atmospheric parameters. These technical achievements not only provide critical data support for current aerospace atmospheric monitoring missions but also lay a foundation for long-term global atmospheric density profile remote sensing.

To meet the requirements of data applications, a variable-scale data binning processing method will be adopted in the future to retrieve high-precision atmospheric density profile data products. Additionally, to accurately assess the on-orbit spectral resolution of HDI and its capability for airglow spectrum in the middle and upper atmospheres, it is planned to reconfigure the on-orbit operating parameters of HDI. This reconfiguration aims to detect and analyze the hyperspectral characteristics of atmospheric tracers at altitudes above 80 km, while also conducting research on the retrieval of atmospheric temperature profiles in the near-space region (80?110 km).