The Statistics Menu

The Statistics menu allows the user to define windows and perform statistical operations on data within these windows. These include cross sections in X and Y, made by collapsing a window onto the X or Y axis. These functions perform differently depending upon whether they are operating on IPCS data or CCD data, for IPCS data they sum the data in the perpendicular direction, whereas for CCD data they average them. This difference must be borne in mind when, for instance, estimating count rates per pixel for IPCS data, and estimating atmospheric transparency from a CCD spectrum of a spectrophotometric standard. At present only two windows are available for all data screens and all buffers, these remain in place until adjusted with the SET WINDOW options, even when the user switches between IPCS and CCD data. A future enhancement will provide separately defined windows for each data buffer.

With the X-CUT and Y-CUT functions it is possible to perform a preliminary sky subtraction. To do this Window 1 is placed on the object spectrum, and Window 2 on a suitable sky area. It is not necessary to make Window 2 exactly the same width as Window 1, as appropriate scaling is applied. It is not necessary to place Window 2 precisely in the spectral direction, as the limits in this direction of the sky region are changed to those of Window 1.

Options available from the Statistics menu are:-

• SET WINDOW1 - After selecting this option with the user can adjust the size of Window 1 by moving the mouse on the reflective pad. After then pressing the user can adjust the position of the window by moving the mouse. The user can return to adjusting the size with and the position with as many times as necessary. returns to the Statistics menu.
• SET WINDOW2 - This allows the user to adjust the size and position of Window 2, and the function of the keys is exactly the same as for SET WINDOW1.
• CALCULATE - This calculates, and displays near the bottom right hand corner of the display: the location and size in X and Y of the window selected with one of the SET WINDOW options or the WINDOW USE option; and the mean, maximum, minimum and standard deviation of all the pixel values within that window. It leaves the user in the Statistics menu.
• PIXEL - After selecting this function with the user can move the cursor around in the image display area, and read out individual pixel values with . toggles between a zoomed and unzoomed display. returns to the unzoomed display and returns the user to the Statistics menu.
• X-CUT - This option collapses the selected window onto the X-axis, and plots the result. For IPCS data it sums the pixels in Y, and for CCD data it averages them. If the WINDOW1-WINDOW2 option is selected with WINDOW USE then the left and right boundaries of WINDOW2 will be changed to match those of WINDOW1, and the data from WINDOW2 will be scaled by the ratio of the window widths before subtraction. The plot will remain displayed until is pressed, when the user will be returned to the Statistics menu.
• Y-CUT - This option collapses the selected window onto the Y-axis, and plots the result. For IPCS data it sums the pixels in X, and for CCD data it averages them. If the WINDOW1-WINDOW2 option is selected with WINDOW USE then the upper and lower boundaries of WINDOW2 will be changed to match those of WINDOW1, and the data from WINDOW2 will be scaled by the ratio of the window widths before subtraction. The plot will remain displayed until is pressed, when the user will be returned to the Statistics menu.
• Z-CUT - This option is not applicable to any of the current ISIS data taking modes.
• WINDOW USE - This option selects the window to which X-CUT, Y-CUT or CALCULATE will be applied. After selecting this option with further presses of will cycle between: WINDOW1; WINDOW2; and WINDOW1-WINDOW2. The current selection is displayed just below the menu. returns the user to the Statistics menu.