Ridge uses the output file from the Profile module to find the peak in the spatial profile. The peak is represented as a percent value and can be a user-specified input.
INPUTS
Percent setting(Default or Manual): If the Default option is chosen, the percent that represents the peak flux will be computed by SPICE. If the Manual option is chosen instead, the user-input field is activated.
PERCENT: This is the input field for a Manual Ridge location; it is only active if the Manual option is selected. The user may enter the peak of interest directly or use the slider bar on the Profile plot to determine the exact value. The peak is defined in a percent across the slit from x = 0.
OUTPUTS
Ridge Output Table (*.ridge.tbl): A table containing the x,y position of the peak for each order and each wavelength is output. This output table will become the input table for the next module, Extract. An overlay appears on the input image. An ASCII version of the file is seen by clicking the View button. The spatial position (percent) of the Ridge is drawn on the Profile plot.
Ridge Overlay (*.overlay.tbl): A table containing the order, wavelength, and x,y pixel positions of the trace determined by the module, together with the x,y pixel positions of the extraction aperture defined by the current settings of the Extract module. This file is updated if the extraction aperture is changed later. The overlay is plotted on top of the BCD image in the FITS window. An ASCII version of the file is seen by clicking the View button.
DISCUSSION
The Ridge module defines the spectral trace of the source to be extracted. The module takes as input the output of the Profile module, *profile.tbl, and two calibration files, the wavsamp.tbl file, and the fov.tbl file. It can either search for the location of the peak, or can be given a manual position. In either case, it produces an output file describing the computed ridge line. SPICE also produces a file that gives the pixel position of the ridge line and extraction window for overlaying on the BCD image.
If a manual ridge position is specified (as a percentage along the slit), then that value is used to create the output file. Otherwise, the Ridge module searches for the peak in the input *profile.tbl file. The search is performed within PCT_RANGE of the position expected based upon the FOV. In SPICE and the pipeline, PCT_RANGE = 25%. The search algorithm is as follows:
For each region R as specified in the profile table file:
· Read in the data for region R: yorig
· Calculate a linear fit to yorig, and subtract it from the data to obtain yh
· Perform median filtering of this flattened yh data, using MEDIAN_PTS points to get yf. In both SPICE and the pipeline, MEDIAN_PTS = 5.
· Calculate the new mean, μf, and sigma, σf, for the median-filtered data yf
· Find the max peak value μh of the not filtered, flattened data, yh
· Region R has a candidate peak if
In both SPICE and the pipeline, NUM_SIGMA = 3.0.
The final cut percentage P is then set to the maximum of the candidate peaks from all the regions. But if no candidate peaks were found, P is set to the expected position of the field of view as defined by the DFRAC column of the fov.tbl file.
Once the peak is determined, the Ridge module computes the ridge line, defined to be the two or more vertices which comprise the group of line segments located at the percentage P from the leftmost edge of the pseudo-rectangles. It outputs a table containing most of the wavsamp.tbl data, plus the newly computed ridge line.
