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Gaofen-3 is the first C-band fully polarimetric SAR satellite in China, which is widely used in various fields such as ocean monitoring, disaster reduction and so on. In this paper, a new satellite constellation is proposed based on the orbit of Gaofen-3 satellite. The constellation includes Gaofen-3 and other two duplicates. It is able to do repeat-pass interferometry, repeat-pass differential interferometry, along-track interferometry and stereo measurement. With these abilities, it can generate the earth DEM without ground control points and have better performance in moving target identification and monitoring. The performance and the system requirements are analysed, which provides a good reference for the design of spaceborne SAR constellation.

Optical polyimide (PI) membranes have been increasingly attractive in optoelectronic substrate and optical element material applications. Controlled stress distribution is very important to optical PI membrane-based optics. However, nondestructive absolute stress measurement inside optical PI membranes remains challenging. In this letter, we adopted the stress birefringence method to experimentally investigate the correlation between stress and retardation in uniaxially, biaxially, and circularly stretched PI membranes. The calculated value of the photoelastic coefficient was found to be around 400 nm/Mpa·cm. A theoretical model was established where the retardation angle is the negative arctan of the principal stress ratio in the biaxially stretched membrane. We also found that the average retardation angle is an important parameter for evaluating the uniformity of stretching force in the circularly stretched membrane. This work provides a better understanding of the stress birefringence measurement of membrane materials.