Observation and reduction methods of deep palomar 200 inch 4-shooter mosaics

We present deep contiguous CCD-mosaics in Gunn gri filters with the Palomar 200 inch 4-Shooter CCD array for two widely separated survey fields, each ∼0°.45 × 0°.145 in size. We used the FOCAS package to compile multicolor catalogs in each survey field that contain ∼23,000 galaxies and have 90% completeness limits of gri ≲ 24.5 mag (B₁≲ 25.2 mag). The purpose is to constrain the evolution of galaxy clustering by tracing w(θ) down to B₁ ∼ 25 mag. This paper describes the photometric and astrometric reduction methods of our 4-Shooter mosaics and the resulting faint galaxy catalogs. The accuracy of the global photometric zero points is determined from overlapping 4-Shooter frames and the known colors of field main-sequence stars, and amounts to ∼0.08 mag rms. Astrometric solutions are determined from 10-15 secondary standard stars for each CCD with accurately measured coordinates from recent-epoch Palomar 48 inch Schmidt plates. The CCD frame-to-frame overlap shows that the rms accuracy of each CCD's astrometry is ≲50.″5. Using ≲8 PSF stars in each CCD, we can distinguish stars from galaxies using object shape parameters down to gri ≲ 23 mag. We present the resulting galaxy counts down to Gunn gri ≲ 25 mag. The completeness of our galaxy catalogs is determined by comparing our galaxy counts with those from somewhat deeper surveys that cover much smaller areas. The multicolor two-point angular correlation functions for galaxies in these fields are presented in a companion (main journal) paper.