Data and software for "Correcting Turbulence-induced Errors in Fiber Positioning for the Dark Energy Spectroscopic Instrument"

Supplementary material to the DESI publication "Correcting Turbulence-induced Errors in Fiber Positioning for the Dark Energy Spectroscopic Instrument".

The main "turbfigures.py" script generates the figures in the paper from the included data files.

Contents:

Software files

• turbfigures.py: Turbulence plotting and analysis plotting routines.
• turbulence.py: Analysis routines called by turbfigures.py.  The live version of this code in production for desi is in the desimeter package (https://github.com/desihub/desimeter/blob/main/py/desimeter/turbulence.py)

Data files

• coord-summary-20240124-pm.fits
  • Measured centroids of fibers in for 400 consecutive images of the focal plane while at zenith.  File contains the following columns:
    • expid - exposure ID
    • location - "location" of fiber in focal plane; ranges from 0 - 10000.  Fibers on petal 0 have numbers between 0 and 1000, etc.  There are only 500 positioners per petal, so most locations are not populated.
    • move - in real data, this indexes over the moves in a DESI positioning loop; garbage information here.
    • fpa_{x,y} - measured position of the fiber in this exposure
    • req_{x,y} - requested position of the fiber in this exposure; not used for this data set where positioners are fixed in location
    • {x,y}turb - empty in this file; gets filled in by turbfigures.py with measured turbulence
    • flags_cor - flags indicating that a positioner or fiber may be problematic
    • postype - flags indicating that a location corresponds to a real positioner vs. a fiducial
    • expected_{x,y} - empty in this file; gets filled in by turbfigures.py with "expected" positions of each fiber, so that fpa_{x,y} - expected_{x,y} is a noisy estimate of the turbulence seen by the fiber.
  • Note that this file has an awkward structure.  It has 10000 rows, one for each possible location.  Most fields are then 400 element arrays that gives the corresponding values, corresponding to the 400 exposures present in the file.
• coordinates-stats.ecsv
  • statistics of positioning accuracy and turbulence amplitude in DESI positioning loops.  Measured RMSes are the 5-sigma clipped root-mean-square positioning offset in 2D: sqrt(mean(dx^2 + dy^2)).  Measured medians are median(sqrt(dx^2 + dy^2)).
  • Contents:
    • coord_filename - file name of DESI coordinates file statistics were drawn from
    • rms_turbulence - RMS for the turbulent contribution to the positioning error
    • rms_positioning - RMS for positioning after removing turbulence
    • rms_total - Total RMS
    • med_turbulence - median turbulence in exposure
    • med_positioning - median positioning error in exposure
    • med_total - median total turbulence + positioning error in exposure
    • expid - exposure id number

Dependencies: The included software uses the DESI software stack and otherwise the usual python astronomy packages: numpy scipy matplotlib astropy.  Alternatively, people with access to NERSC can load the default DESI environment and pull in all needed dependencies.