Mauna Kea Observatory

11-01-2019

The Submillimeter Array (SMA) is an 8-element radio interferometer located at top Mauna Kea in Hawaii. Operating at frequencies from 180 GHz to 700 GHz, the 6m dishes may be arranged into configurations with baselines as long as 509m, producing a synthesized beam of sub-arcsecond width. Each element can observe with two receivers simultaneously, with 2 GHz bandwidth each. The digital correlator backend allows flexible allocation of thousands of spectral channels to each receiver. The Submillimeter Array is a joint venture of the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics.

The installation of antenna specific weather data collection was in response to a request to mount pressure, temperature and humidity sensor on each of the eight antennas in in our array to obtain atmospheric weather measurements for refraction correction data, especially when we are in extended and very extended configurations. The atmospheric conditions can be quite variable across the entire area the array is occupying, and using the data only from the roof of the Observation Building might not be representative in all conditions.

We are prohibited from using wireless networking to gather data at the summit, due to the risk of interference with our, or neighboring observatories', equipment. However, each of our antennas does have a network hub to communicate with the on-board equipment from our observation facilities on the summit of Mauna Kea, or from our other base facilities around the world. The T7511 units fulfilled our requirements, and after the two units we purchased for testing proved their capability, we ordered eight more to outfit the array. They have been gathering data for us 24-hours a day, 365 days a year, in frequently very challenging circumstances (sleet, snow, 90 mph winds, etc.) ever since.

Below, a photo of the mounting of the weather station's radiation shield outside of the antenna, taken while the antenna was inside the maintenance hangar. The rest of the electronics are mounted in the large wide rectangular enclosure immediately behind it. Shading from the dish was not considered a major problem, as humidity and pressure were of greater concern, due to their impact on atmospheric refraction.