Production of Alternate Realizations of DESI Fiber Assignment for Unbiased Clustering Measurement in Data and Simulations

A critical requirement of spectroscopic large scale structure analyses iscorrecting for selection of which galaxies to observe from an isotropic targetlist. This selection is often limited by the hardware used to perform thesurvey which will impose angular constraints of simultaneously observabletargets, requiring multiple passes to observe all of them. In SDSS thismanifested solely as the collision of physical fibers and plugs placed inplates. In DESI, there is the additional constraint of the robotic positionerwhich controls each fiber being limited to a finite patrol radius. A number ofapproximate methods have previously been proposed to correct the galaxyclustering statistics for these effects, but these generally fail on smallscales. To accurately correct the clustering we need to upweight pairs ofgalaxies based on the inverse probability that those pairs would be observed(Bianchi & Percival 2017). This paper details an implementation of that methodto correct the Dark Energy Spectroscopic Instrument (DESI) survey forincompleteness. To calculate the required probabilitites, we need a set ofalternate realizations of DESI where we vary the relative priority of otherwiseidentical targets. These realizations take the form of alternate Merged TargetLedgers (AMTL), the files that link DESI observations and targets. We presentthe method used to generate these alternate realizations and how they aretracked forward in time using the real observational record and hardwarestatus, propagating the survey as though the alternate orderings had beenadopted. We detail the first applications of this method to the DESIOne-Percent Survey (SV3) and the DESI year 1 data. We include evaluations ofthe pipeline outputs, estimation of survey completeness from this and othermethods, and validation of the method using mock galaxy catalogs.