map Carrington Rotation Map

The calibrated magnetogram images (the mag product) input to MAGMAP are processed into a magnetogram synoptic map. First, a weight image is created for each magnetogram by replacing the pixel values with ones. The weighting images are apodized about the limb and processed using the same steps as described. The mag product is converted into Carrington coordinates by first running EPHEMINTERP on the images to calculate the value of L0, the center of the image in heliographic coordinates. The images are then processed through CAMOFFSET to calculate the camera offset angle and are then processed through HGREMAP with the proper plm_trim file to produce images registered in heliographic coordinates with a size of 180x180 pixels. The images produced by HGREMAP are registered in heliographic coordinates and represent the surface of the sun from -90° to 90°. The template image is zeroed and the image produced by HGREMAP is then placed in the center of the the grid. The image is shifted using SHIFTLINES and the value of L0, to the proper place in the template image. All the individual images are then multiplied by their corresponding gaussian window function and added together. The composite image is then divided by the sum of the weighting images. The header of the image is edited to include the start date and time, the end date and time, and a list of unused images of the Carrington rotation cycle.

A map FITS image file consists of 360x180 16-bit integer pixels containing magnetic field strength in arbitrary units. A map image is of the form: 

        mrmapYYMMDD.fits  

where YYMMDD corresponds to the center of the Carrington rotation cycle.
The heliographic longitude is 
        ix - 181
where ix is the one-indexed pixel address. The sin of the heliographic latitude is 
        (1/90)*iy - 1.0
where iy is the one-indexed pixel address.

The heliographic longitude varies from 0° to 360° along the x-axis with a sampling interval of 1° per pixel. The sin(heliographic latitude) varies from -1 to 1 with a sampling interval of 0.01111 per pixel.

MAGMAP adds the following parameters to the FITS header: 

        TIME    : the time of the center of the Carrington rotation cycle
        DATE    : the date of the center of the Carrington rotation cycle
        GHIST   : the processing history including tasks used, polarity
                  adjustments, number of images, and images discarded.
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