Flat field calibration

Fig. 3.10. Examples of an artifacts related to the flat field procedure, (a) not corrected defective column on a homogeneity test image, (b) artifact caused by the movement of an object in the X-ray beam after the flat field calibration on a...

Standard data reduction, i.e. bias and flat field correction, has been performed with Iraf. The Iraf task APEXTRACT/APALL was used to extract the spectra, with interactively selected background sampling, in order to avoid contamination for the star spectrum. The wavelength calibration has been done using daily He, Ne, HgCd arcs, and, in order to improve the calibration, wavelengths values for the transitions used were taken from http //physics.nist.gov/. 

An example of the effect of a flat-fielding correction is shown in Fig. 2.8. The interval between calibrations... 

The flat-fielding correction is generally based on an assumption that the detector responds linearly to radiation exposure. If some or all of the dels have nonlinear response, then a two-constant (slope and intercept) correction will only operate properly under exactiy the exposure conditions used to obtain the calibration constants. Under other signal levels, different nonlinearities of the del responses will result in image nonuniformities (Fig. 2.7d). 

Two integrating spheres, illuminated throng small holes by black body sources, are mounted on the selection wheel, for flat fielding and calibration purposes. 

Figure I Simulation of a transducer calibration test, a) Calibration configuration T45° transducer and 6 flat bottom holes at various depths b) Predicted field by Champ-Sons c) Simulated Bscan d) Echodynamic curve.

Fig. 3.5 Fabrication of pp specimens for SPM calibration. The first step (1) comprises soft-lithography of appropriate SAM molecules onto a planar substrate. A composite stamp, which has both flat and corrugated areas, allows printing of the comb-patterned strip with the adjacent solid calibration field. Next, a graded UV-ozonolysis (UVO) systematically modifies the chemistry of the patterned SAM (and calibration field) along one direction (3). For example, methyl-terminated alkyl chain SAMs (hydrophobic) can be gradually converted into carboxylic acid terminated (hydrophilic) chains. Subsequent filling with a hydrophilic SAM completes the matrix of the specimen (2fA...

Twin Cond is a conductivity meter, available from HORIBA Jobin Yvon, which features a waterproof flat sensor. Twin Cond can measure the conductivity of a solution from a single drop of sample and is therefore very suitable for both field measurements in rivers and lakes and for rain samples. It features a measurement range from 1 p,S/cm to 19.9 mS/cm. It also has one-touch auto-calibration, automatic temperature conversion and a salinity conversion function (from 0-1.1 %). Multiparameter meters can test for pH, conductivity, total dissolved solids and temperature in the one device. 

Two limiting electrostatic conditions of interest in potential measurement are constant voltage and constant charge flat surfaces. In both cases a uniform electric field is desired between the source and the sensing electrode so that the calibration of the instrument is retained over a wider range of separation distances (Blitshteyn, 1984). 

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