The Atacama Desert has long been established as an excellent site for submillimeter observations. Yet identifying potentially optimal locations for a new facility within this region can require long field campaigns that rely on the construction of weather stations and radiometer facilities to take data over sufficiently long timescales. Meanwhile, high-level remote sensing data products from satellites have generally only been available at >25 km resolution, limiting their utility for astronomical site selection. We aim to improve and expedite the process of site characterization and selection through the use of km-resolution satellite data. We analyze the daytime precipitable water vapor (PWV) values inferred using near-IR measurements from the MODIS Aqua and Terra satellites, comparing the level-2 satellite products to those from existing ground-based measurements from the radiometer at the Atacama Pathfinder Experiment (APEX) site. Since the APEX radiometer data has been extensively tested and compared to atmospheric transmission models, particularly in low-PWV conditions of interest for astronomy, we use these data to re-calibrate the MODIS data for the entire region, reducing systematic errors to a level of < 3%. After re-calibration, the satellite data allow mapping of the PWV across the region, and we identify several promising sites. Our findings confirm previous results, but provide a more complete and higher resolution picture, filling in key spatial and temporal information often missing from dedicated field campaigns. We also examine the seasonal trends in the ground-based data from APEX and surrounding region, finding that both data sets indicate that PWV has increased moderately over the past two decades. We demonstrate a potentially powerful method for siting new facilities such as AtLAST and extensions to global very long baseline interferometry networks like the EHT.
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