The increasing data rates of two dimensional SAXS and WAXS detectors (hundreds of gigabytes of raw data per day) enforce the need for online data treatment. Moreover, it is unavoidable to pre-process and check the data during an ongoing experiment to assure high data quality. For that reason, a data analysis package has been developed which can operate simultaneously with several detectors. The program is embedded into the SPEC data acquisition macros and allows a transparent way of data processing during the experiment via a graphical user interface. After an acquisition the data correction program is automatically called for each activated detector (SAXS, WAXS or both). At the end, azimuthally averaged scattering intensities can be plotted against the modulus of the scattering vector as shown the figure. This possibility is especially useful during time resolved scattering experiments and to check the correct functioning of the experiment. The detector data is saved together with a set of parameters that describe all the experimental conditions which can later be used for data reprocessing.

Without azimuthal regrouping, the correction time is of the order of 0.5 seconds per image (1024 x 1024 pixels, 16 bit) on a 750MHz UltraSPARC III workstation. During experiments where multiple fast acquisitions are triggered by the TFG (e.g. 100 frames with alternating dead and live frames of 0.1 s duration), the images are corrected after the end of the last frame. In this case the delay is acceptable because the whole experiment takes only a few seconds. During less rapid experiments single frames are repeatedly acquired and corrected. The data correction is split into several steps. The raw data is first corrected for detector artifacts (subtraction of dark current and readout noise, division by flatfield, and spatial distortion correction). In the second step, the data is normalized to absolute scattering intensities. The output data is given in number of scattered photons per sterad divided by the number of incoming photons. After this step all detector and beamline dependent features are corrected. The corrected data is written onto the disk. To get the absolute scattering cross section per volume the user need only to divide the corrected SAXS data by the sample thickness.

 

 

Available data analysis package

 

 

 

 

Further Information