Bias Vector

File Format: FITS image

Name:, where rrrrrr is the imaging run number (of the calibration run which produced the vector), b is the filter used (u, g, r, i, or z), and c is the column location in the Imaging Array of the CCD which acquired the data (1-6).

Produced by: bias

Used by: ps, frames

Size: 8640 bytes per file. For a single calibration of all photometric chips, there are 30 files created for a total of 259.2 Kb.

Archived? Yes


There is one bias vector per chip. Bias vectors are determined from calibration runs, separate from the actual data run being processed. A bias calibration run is just a normal drift scan with the "shutter" closed. The bias vector is just the median over all rows in the run; i.e., each pixel value in the bias vector is the median value of all pixel values along its associated column. Overscan columns are included, and medianed the same way as the data columns. No other processing is done.

When processing the data from an imaging run, the bias vectors from the most recent bias calibration run are used.

The pixel values are stored as unsigned integers. The TSCALE keyword gives the amount by which each pixel value has been multiplied; e.g., if TSCALE = 32, then each pixel value in the image is 32 times larger than the true value. This scaling allows us to calculate precise values while maintaining pure integers.

Primary Header

SIMPLE  =                    T
BITPIX  =                   16
NAXIS   =                    2
NAXIS1  =                 2128
NAXIS2  =                    1
BSCALE  =                    1
BZERO   =                32768
VERSION = 'XXX     '           / Software version used.
TSCALE  =                  XXX / Scale factor to increase precision
CAMCOL  =                  XXX / Column in the imaging camera.
CAMROW  =                  XXX / Row in the imaging camera.
RUN     =                  XXX / Run which produced the vector.
BIAS_ID = 'XXX     '           / Bias pipeline run identifier.