Optimal designing of digitalizing bits for remote sensing camera with photo-electric sensor

The photo-electric sensors of CCD and CMOS are used in many space-borne remote sensing missions. The digitalizing bit is a key parameter of signal processing circuit (SPC) system with photoelectric sensors, and it determined the dynamic range of the digital signals transferred by the photo-electric effect in semi-conductor sensor. It is closely related with imaging performance and image quality. For imaging performance, big digitalizing bits brought high signal to noise ratio (SNR) with low noise in chips, giving camera system the capability to detect the weak signals. For image quality, big digitalizing bit meant broad gray scale range and high sensitivity to unveil more details for very dark and bright objects. This paper utilized two methods to analyze the relation between digitalizing bits with imaging performance prediction and image quality evaluation of CCD and CMOS remote sensing camera. 1) Firstly, based on the imaging theory of photoelectric camera to analyze the effect of digitalizing bits in SPC on imaging performance, the typical radiance was used as input in front of the optical system to compute digitalizing noise and system SNR for remote sensing cameras. The noise efficient reflectance (NEΔρ) is introduced to dissect the function of digitalizing bits on detecting the weak signal for the imaging system. Secondly, this paper used image quality parameters of MSE and clarity to comparing the differences in dark and bright image aeras and calculated the image entropy with bits varying. Comparing with computation results of imaging performance and image quality with 8 to 14 digitalizing bits with both SPC and image, it concludes that: 1) bigger digitalizing bits correspond to better imaging performance and higher image quality from 8 to 14bits; 2) the improving effects are not obvious from 12 to 14 bits; 3) bigger digitalizing bits have strong effects on weak signals for both imaging performance and image quality. The conclusion of this paper can be a theoretical suggestion for the choice of CCD and CMOS digitalizing bits used in new generation remote sensing satellite.