To improve the swath width and quantitative accuracy of hyperspectral payloads on a geostationary orbit, a long-slit polarization-insensitive imaging spectrometer is designed and demonstrated in this paper. For the wide swath, several long-slit spectrometers with the same specification have been designed and compared. The result shows that the Wynne-Offner spectrometer has advantages in increasing slit length and reducing volume, and it is suitable for being spliced for ultra-wide swath. To solve the problem of inaccurate radiation measuring caused by the polarization of imaging spectrometers, the requirement for linear polarization sensitivity (LPS) is theoretically analyzed and assessed. As diffraction grating is the main polarization-sensitive element in an imaging spectrometer, we propose to increase the apical angle of the grating groove to reduce its LPS and compensate its residual polarization by specially polarized optical films coated on lens surfaces, thus the polarization-insensitive system is achieved. At last, a VNIR spectrometer with superior spatial and spectral performance is developed, and its slit is 61.44 mm long. The maximum LPS of this system is reduced from 10.0% to 2.3% (test 2.5%) after the depolarization design, which greatly reduces the uncertainty of the measuring radiation caused by polarization. The developed imaging spectrometer can play a role in quantitative hyperspectral remote sensing, especially in wide-swath applications on geostationary orbit.

The optical system of an imaging spectrometer working on a geostationary earth orbit (GEO) covering a full optical spectrum of 0.3–12.5 μm is analyzed and designed. It enables a ground coverage of 400 × 400 km by internal scanning and achieves a high spatial resolution of 25 m. The full spectrum is divided into five sub-bands, and each band adopts four spectrometers to splice in the field of view to achieve the ultra-long slit required by the wide swath. The total length of the slit is up to 241.3 mm. This paper focuses on compact spectrometers with long slits that can meet the splicing requirements and points out that low spectral distortions, low stray light, high signal-to-noise ratio, and uniform spectral response are necessary for high-fidelity performance. The Offner and Wynne–Offner high-fidelity spectrometers based on convex blazed gratings are designed, and prototypes of each band are developed as well. The properties of long slits and convex blazed gratings are presented. The maximum length of a single slit is 61.44 mm. The groove density of gratings for five bands ranges from 8.8 lp/mm to 312.1 lp/mm, and the peak efficiency is up to 86.4%. The alignment and test of the spectrometers are introduced. Results show that the developed spectrometers have high fidelity and fulfill all requirements.

As space technology develops the optical systems with aperture more than 10 meters are needed. Constrained by the system mass and transport ability of launch vehicle, it's impossible to manufacture these optical systems by conventional technology. It is one of the most novel technologies to manufacture large aperture, ultra-lightweight space optical systems by using membrane mirror as the primary mirror. The membrane mirror is made of thin polymer membrane instead of glass, so it is characterized by ultra-lightweight and low cost. Figuring membrane mirror's surface by electrostatic field is one of the most promising methods. This method is based on the elastic mechanics and electrostatic theories. Membrane mirror is deformed by applying electrostatic voltage between membrane and electrodes behind the membrane. A Φ200mm membrane mirror with electrostatic deformation system has been built and this membrane mirror can be pulled from flat mirror to a 17m radius of curvature. It consists of membrane mounting device, electrode pad and high direct current (DC) voltage control system. The deformation of membrane mirror was observed with ZYGO interferometer and the radius of curvature of membrane mirror was measured by Moiré deflectometry.

After alignment of an imaging spectrometer, the image of a special wavelength should in theory strictly meet with the design value and is focused on a certain column of the CCD focal plane. Since the imaging spectrometer is usually used in spatial or aerial environment, the optical components and the detector will departure from the regulated place and leads to focusing the image onto the deflected position of the focal plane in the spectral direction. Since the onboard readjustment of an inaccurate imaging spectrometer is usually unavailable, the equivalent task should be performed by certain post processing method. In this paper, we present a wavelength calibration method based on a fitting algorithm. Because of the linear diffraction feature of a grating, first order fit is adopted for the calibration. Using a standard mercury lamp as the light source during the calibration, the experimental imaging data collected from the whole CCD focal plane is used for the wavelength calibration to construct the actual wavelength distributing curve. Because of spectral line bending (smiling) of the imaging spectrometer, the wavelength calibration result of each row of the CCD plane differs so that a row-by-row calibration work should be carried out. The total row-by-row calibration result not only provides a full-scale and high-precision calibration effort, but also brings forward a smiling evaluation method for the whole imaging spectrometer. Using a standard Hg-Cd lamp as both the illuminating light source and the object, the spectroscopic image of the slit focusing onto the CCD focal plane of a calibrated imaging spectrometer is collected. In certain rows of the image, the center position of every spectral line is recorded. Through the comparison of recorded positions of different rows, the smiling of the calibrated imaging spectrometer is worked out, which meets with the design value.

The requirement for low distortion in either spatial or spectral direction of a push-broom imaging spectrometer has been recently recognized. Though distortion scale of as much as 1 or 2 pixels have been accepted in previous spectrometer designs, it is suggested to be limited to the order of hundredth of a pixel to preserve the validity and integrity of the spectral imaging data. The developed push-broom imaging spectrometer adopts a reflective Offner relay structure and provides good optical correction and compact size. The spectral and spatial distortion measurement is of significance for instrument performance evaluation and alignment guidance. In this paper, two easy-to-implement and effective measurement methods for both spatial and spectral distortion are presented. By using a standard Hg-Cd lamp as both the illuminating source and the object, the spectroscopic image of the slit focusing onto the CCD focal plane is collected. In certain rows of the image, the center positions of every spectral line are recorded. Through the comparison of recorded positions of different rows, the spectral line bending of the calibrated imaging spectrometer is worked out. In the continuous spectrum illumination condition and by using a self-made mask as the object, the entrance slit image is cut into tens of tiny rows that correspond to different image heights. The center positions of 5 typical rows are calculated and five chromatic distortion curves are worked out with certain interpolation method.

Frame transfer area-array CCD camera is the perfect solution for high-end real-time medical, scientific and industrial applications because it has characteristics of high fill factor, low dark current, high resolving power, high sensitivity, high linear dynamic range and electronic shutter capability. Time sequences of frame transfer area-array CCD camera have two compact segments: CCD driving sequences and CCD signal processing sequences. Proper working of CCD sensor lies on good driving sequences while accurate CCD signal processing sequences ensures high quality of CCD image. The relationship among CCD camera time sequences is complex and precise. The conventional methods are uneasy to implement time sequences of Frame transfer area-array CCD. Embedded designing method is introduced in this paper and field programmable gate array device is chosen as the hardware design platform. Phase-locked loops are used for precise phase shifting and embedded logic analyzer for waveform verification. CCD driving clocks, electronic shutter signal, A/D and black pixels clamp clocks and double correlation sampling clocks have been attained on the hardware platform and this timing generator can control exposure time flexibly. High quality images have been acquired through using this timing generator on the CCD circuit system board which has been designed by our team.