Pixel Response Non-uniformity Research Articles

Modeling the Wavelength Dependence of Pixel Response Nonuniformity of a CCD Sensor

Precision measurements in astronomy require stringent control of systematics such as those arising from imperfect correction of sensor effects. In this work, we develop a parametric method to model the wavelength dependence of pixel response nonuniformity (PRNU) for a laser-annealed backside-illuminated charge-coupled device. The model accurately reproduces the PRNU patterns of flat-field images taken at nine wavelengths from 290 to 950 nm, leaving the rms residuals no more than 0.2% in most cases. By removing the large-scale nonuniformity in the flat fields, the rms residuals are further reduced. This model fitting approach gives more accurate predictions of the PRNU than cubic-spline interpolation does with fewer free parameters. It can be applied to make PRNU corrections for individual objects according to their spectral energy distribution to reduce the photometry errors caused by the wavelength-dependent PRNU, if sub-percent level precision is required.

Design and data processing of TDICCD real-time radiation correction system

In order to increase the lifetime of the TDICCD imaging system in space and decrease the impact on the imaging quality for a long-time working in orbit, a system of real-time radiation correction in space is designed. It generates real-time correction parameters of multi-TDICCD channels and pixels in-channel by rotating the focus plane before the calculation of the real-time calibration images, and improves the adaptability and PRNU (pixel response non-uniformity) values of the TDICCD mosaic camera imaging system. FPGA is used to calculate and save the parameters, and an optimization design is implemented to improve the system stability and reliability. This method can calculate the real-time PRNU correction parameters of the TDICCD mosaic camera in-orbit, and the PRNU value of TDICCD mosaic camera in-channel reaches 2.01% after real-time calibration. This method is potentially used in real-time radiation calibration, and has got a better result.

Tearing and related field distortions in deep-depletion charge-coupled devices

Tearing patterns affecting flat field frames in CCDs are a visually striking obstacle to performing Pixel Response Non-Uniformity corrections. These patterns can be explained by lateral field distortions, caused by the non-uniform distribution of holes in the channel stops between sensor columns. Over the course of LSST camera development, a number of practical fixes have been suggested to get rid of tearing. But applying these fixes to our 16-channel Teledyne-e2v sensors leaves at best a distortion pattern at the vertical edges of every segment. Our working hypothesis is that the origin of the tearing is the parallel clocking itself, which moves the holes that are present in the channel stops regions. The efficiency of these transfers depends strongly on the details of the clocking operations, resulting in the observed variety of distortion patterns. Removal of most of the distortion patterns can therefore be achieved by executing a purge operation, which flattens back the hole distribution in the channel stops, immediately before acquiring a frame. A more effective solution is to switch all clocking operations to use a bipolar voltage set.

Is Flat Fielding Safe for Precision CCD Astronomy?

The ambitious goals of precision cosmology with wide-field optical surveys such as the Dark Energy Survey (DES) and the Large Synoptic Survey Telescope (LSST) demand precision CCD astronomy as their foundation. This in turn requires an understanding of previously uncharacterized sources of systematic error in CCD sensors, many of which manifest themselves as static effective variations in pixel area. Such variation renders a critical assumption behind the traditional procedure of flat fielding—that a sensor’s pixels comprise a uniform grid—invalid. In this work, we present a method to infer a curl-free model of a sensor’s underlying pixel grid from flat-field images, incorporating the superposition of all electrostatic sensor effects—both known and unknown—present in flat-field data. We use these pixel grid models to estimate the overall impact of sensor systematics on photometry, astrometry, and PSF shape measurements in a representative sensor from the Dark Energy Camera (DECam) and a prototype LSST sensor. Applying the method to DECam data recovers known significant sensor effects for which corrections are currently being developed within DES. For an LSST prototype CCD with pixel-response non-uniformity (PRNU) of 0.4%, we find the impact of “improper” flat fielding on these observables is negligible in nominal .7″ seeing conditions. These errors scale linearly with the PRNU, so for future LSST production sensors, which may have larger PRNU, our method provides a way to assess whether pixel-level calibration beyond flat fielding will be required.

Radiometric Calibration of dual Sensor Camera System, a Comparison of classical and low cost Calibration

Abstract. Several identical dual camera systems with two different spectral sensitivities have to be calibrated radiometrically and geometrically. The aim of this project is to build up a calibration laboratory for the calibration of a set of identical cameras using low cost equipment and to compare the results to classical/professional equipment. The main goal of this paper is to demonstrate how to use a low cost, inhomogeneous LED-backlight to measure the Pixel Response Non-Uniformity (PRNU) of the investigated cameras.

TDICCD拼接相机的像元响应非均匀性校正方法

To improve the Pixel Response Non-uniformity(PRNU) in a TDICCD mosaic camera,an algorithm was proposed to correct the PRNU between the channels and among the pixels in channels at different gains,deviations and integrated time.Then,a design method was given to implement the algorithm on a Field Programmable Gate Array(FPGA) platform.The experimental results indicate that the problems of PRNU could be solved at different gains,deviations and integrated time in the TDICCD mosaic camera.The PRNU of a single TDICCD could be decreased from 4.72% to 0.27%.In bad circumstance,the PRNU of the single TDICCD could be decreased from 4.68% to 2.13%.The actual image also proves that the pixel correction algorithm has high real time performance,high reliability and stability,and a satisfied result to the requirements of space-projects.It solves the real-time pixel correction problem of the PRNU in TDICCD mosaic cameras.

Influence of nonuniform charge-coupled device pixel response on aperture photometry

The extensive use of charge-coupled devices (CCDs) in astronomical imaging and spectroscopic applications has resulted in techniques being developed to correct for sensitivity variations attributable to the focal plane array detector. One normally overlooked effect is that these sensitivity variations also include intrapixel spatial effects that can influence measurements made with CCDs in certain circumstances. We demonstrate the influence of CCD pixel response nonuniformity on photometric measurements. An investigation is presented of how the relation between pixel size and the image size affects the photometric accuracy. Results are presented for a front-illuminated CCD array using an experimentally measured pixel sensitivity functions.