  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.
