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3. HOW DOES SWS TAKE DATA?
As photons fall onto the detectors the current generated charges up a capacitor. The voltage across this capacitor is read-out and digitised into a bit value 24 times a second. At a set interval the capacitor is discharged. The time interval between two detector resets is automatically determined from the user's input data (flux and SNR, or execution speed) and is either 1, 2 or 4 seconds. To observe faint sources, integrations over several reset intervals are used. Raw data is saved in an Edited Raw Data (ERD) file, with an ERD record for one second consisting of an array of 52 ramps of 24 read-out's each. The Standard Processed Data (SPD) and Auto-Analysis Results (AAR) files contain for each detector a single flux estimate for each reset interval.
Example of ERD data can be seen in figures 2 and 4, of SPD can be seen in figure 3, and of AAR can be seen in figure 5.
When observing, the spectrometers scan the wavelength ranges of interest at least twice, once with the grating moving in one direction, then with it moving in another. This is known as an up-down scan. The grating only moves in one direction when observing with the FPs.
A. Salama et al.