Sierra Negra (SN) is the site of the 50-m diameter Large Millimeter Telescope (LMT) at an elevation of 4600 m.a.s.l. located in the state of Puebla in central México. The LMT hosts several heterodyne and continuum instruments in the bands from 3 mm to 1 mm wavelength, thus making it necessary to have continuous opacity measurements at the millimeter wavelengths. The site has been monitored in the past using a commercial 225 GHz opacity radiometer. The 210 GHz Survey radiometer is an instrument previously used to search for the best Mexican site for the LMT. The Survey radiometer is a compact and portable instrument that has proven its reliability in remote sites. Due to its low cost and compact architecture the Survey radiometer has the potential to be reproduced and taken to other candidate radio astronomical sites in particular, locations for ngVLA antennas in northern México. In this paper we present the results of the measurements taken with the 225 GHz radiometer. The statistical data are consistent and within the dispersion measurements taken in the past. We also present a review of the Survey radiometer and recent data taken at the LMT site with this instrument. Furthermore, we compare current Survey data with data set taken by the 225 GHz radiometer at SN.
KEYWORDS: Radiometry, Embedded systems, Telecommunications, Radio astronomy, Observatories, Opacity, Radio telescopes, Computer programming, Microcontrollers, Control systems
We present the refurbishment of a 23.8/31.5 GHz tipping radiometer (WVR-III) to characterize atmospheric opacity for astronomical sites. The mid-life upgrade will bring new life to the 20-year-old WVR-III with most control functions now embedded on a Raspberry PI 3B+ (RPi-3B+). The radiometer will be installed alongside the 225 GHz radiometer at the Large Millimeter Telescope site in Mexico and in 2021 it will be taken to the Hartebeesthoek Radio Astronomy Observatory in South Africa. Later, it will be deployed to Mt Gamsberg, Namibia to perform PWV site surveying for potential future radio astronomy telescopes. This paper describes the new control and data acquisition sub-systems that are controlled by the RPi-3B+.
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