Radiation calibration is a necessary part in making camera. In fact, the essential of radiometric calibration is not only used in visible light and infrared light. The calibration is also needed in many measurement and exploration process. The essential of calibration accurately is to confirm the relationship of measurement values and physical quantity. The task of radiometric calibration of TDI CCD camera is to make certain the relationship between the input radiance parameters and the output gray values. The radiometric calibration of TDI CCD camera is done in the State Key Laboratory of Applied Optics. An integration sphere is used for simulating different radiance, which is decided by the sun vertex angle and reflectivity of ground. The linearity of TDI CCD response and the relationships between the response and the gain and stage separately are tested. According to test results, we get the parameters including gains and stages, which are sent to the camera. The errors are discussed after the experiments terminate.
The interleaver component, which enables very-high-channel-count Dense Wavelength division multiplexed (DWDM) systems and is widely applied in mux/demux system, is a kind of photon-component without source. One type of them is a fused-fiber Mach-Zehnder interferometer. Because of its all-fiber design, it has very low loss, uniform response over a wide wavelength range, very low dispersion, and minimal polarization-dependence effects. In this paper, we put forward and study a novel approach to fabric an interleaver. The method enables real-time measurement and control, and it obtains more flexibility and reduces the cost in procedure. Analysis and numerical simulation results in the paper have some directive significance for practical fabrication of interleaver.
The radiometric calibration of the Time delay and integration Charge-coupled Device (TDI CCD) imaging system is a necessary part in the manufacturing TDI CCD camera. The radiometric calibration of the TDI CCD remote sensing camera is done in the State Key Laboratory of Applied Optics. The integration sphere is used for simulating different radiance, which is decided by the different sun vertex angle and different reflectivity of the ground. The parameters of the gain and stage of the TDI CCD remote sensing camera are given through the analyzing of outcome of the experiment. The outcomes are used in the practice and the errors are discussed in the end of the experiments.
Many applications, such as industrial inspection and overhead reconnaissance benefit from line scanning architectures where time delay integration (TDI) significantly improves sensitivity. Images with linear response have become the backbone of the imaging industry. But each pixel of the TDI CCD has unique light sensitivity characteristics. Because these characteristics and the lens of the optical system affect camera’s linearization and its performance, they must be removed through calibration. The process by which a CCD image is calibrated is known as nonuniformity correction. This paper discusses several methods of nonuniformity correction. The first is one-point correction technique, which requires only one calibration point. This approach is to shift each curve toward the nominal curve by subtracting the offset from or adding the offset to the average. The second is two-point correction technique, which requires two calibration points. Each point is rotated and aligned so that all the detectors have the same response under the same radiance. The third is multipoint correction. It is recommended that more calibration points be implemented at appropriate regions of the response curve. Depend on the linear photoelectric response of the TDI CCD, we use two-point calibration and the standard deviations for the images are given before and after the correction.
The gain of a TDI CCD camera is the conversion between the number of electrons recorded by the TDI CCD and the number of digital units (counts) contained in the CCD image. TDI CCD camera has been a main technical approach for meeting the requirements of high-resolution and lightweight of remote sensing equipment. It is useful to know this conversion for evaluating the performance of the TDI CCD camera. In general, a lower gain is better. However, this is only true as long as the total well depth (number of electrons that a pixel can hold) of the pixels can be represented. High gains result in higher digitization noise. System gains are designed to be a compromise between the extremes of high digitization noise and loss of well depth. In this paper, the mathematical theory is given behind the gain calculation on a TDI CCD camera and shows how the mathematics suggests ways to measure the gain accurately according to the Axiom Tech. The gains were computed using the mean-variance method, also known as the method of photon transfer curves. This method uses the effect of quantization on the variance in the measured counts over a uniformly illuminated patch of the detector. This derivation uses the concepts of signal and noise. A linear fit is done of variance vs. mean; the resulting slope is the gain of the TDI CCD. We did the experiments using the Integration Sphere in order to get a flat field effects. We calculated the gain of the four IT-EI-2048 TDI CCD. The results and figures of the four TDI CCD are given.
Small satellites are capable of performing space explore missions that require accurate attitude determination and control. However, low weight, size, power and cost requirements limit the types of attitude sensor of small craft, such as CCD, are not practical for small satellites. CMOS APS is a good substitute for attitude sensors of small craft. Some of the technical advantages of CMOS APS are no blooming, single power, low power consumption, small size and little support circuitry, direct digital output, simple to system design, in particular, radiation-hard characteristic compare with CCD. This paper discusses the application probability of CMOS APS in star tracker for small satellites, further more, a prototype ground-based star camera based on STAR250 CMOS image sensor has been built. In order to extract stars positions coordinates, subpixel accuracy centroiding algorithm has been developed and tested on some ground-based images. Moreover, the camera system star sensitivity and noise model are analyzed, and the system accuracy is been evaluated. Experimental results indicate that a star camera based on CMOS APS is a viable practical attitude sensor appropriate for space small satellites.