Leiden Observatory
The survey designation "P-L" stands for "Palomar–Leiden", named after the fruitful Palomar–Leiden survey, a collaboration between the Palomar and Leiden Observatory in the 1960s. Gehrels used Palomar's Samuel Oschin telescope (also known as the 48-inch Schmidt Telescope), and shipped the photographic plates to Ingrid and Cornelis van Houten at Leiden Observatory where astrometry was carried out. The trio are credited with the discovery of several thousand minor planets.