Two Decades of km-resolution Satellite- And Ground-based Measurements of the Precipitable Water Vapor in the Atacama Desert

Median (left panel) and mean (right panel) daytime PWV values in millimeters for all available years of MODIS Terra and Aqua NIR measurements. The mean PWV values are systematically higher than the median values due to the skewed, non-Gaussian distribution intrinsic to the data. The color scale is the same in both maps, and deep green values can exceed 5 mm. The borders, AAP+ALMA concession boundary, markers, and elevation contours are the same as in Figure 1, with the addition of red contours to denote locations with elevations higher than 5500 meters a.s.l.

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.

Pablo Gómez Toribio, Tony Mroczkowski, Anna Cabré, Carlos De Breuck

Comments: 19 pages, 14 figures + many more in the appendix
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2103.03917 [astro-ph.IM] (or arXiv:2103.03917v1 [astro-ph.IM] for this version)
Submission history
From: Tony Mroczkowski
[v1] Fri, 5 Mar 2021 19:54:55 UTC (36,529 KB)

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