National Radio Astronomy Observatory
Site Studies
Atacama Large Millimeter Array/US

Chajnantor Test Instruments

After initial reconnaisance in 1994, NRAO started quantitative studies of atmospheric conditions on Chajnantor in 1995 April by deploying a suite of autonomous test instruments. These include a 225 GHz tipping radiometer that measures atmospheric transparency and temporal emission fluctuations, a simple weather station, and a two element, 12 GHz interferometer that measures atmospheric phase fluctuations. Since then, a seismometer and a surveillance camera (1997 June) have been added. A submillimeter tipping photometer, which measures the atmospheric transparency at 350 micron wavelength, was deployed in 1997 October. A submillimeter Fourier transform spectrometer, developed by the Smithsonian Astrophysical Observatory Submillimeter Receiver Lab, was deployed at Chajnantor 1997 October through 1999 December. A campaign of radiosonde launches was begun in 1998 October.

The test equipment is powered by a solar panel array that charges a battery bank. A small windmill to the east of the container provides a backup power source. The power system can supply 500 W continuously (5 kW for short intervals) and has enough storage capacity to continue running for a few days even without sunlight. The solar panels are mounted on the north side of a standard 20 ft shipping container. This container houses the battery bank and the instrument computers and electronics. It also provides a sheltered workshop for site maintainance. An Inmarsat-A satellite telephone provides voice and data (9600 baud) communications. The satellite telephone antenna is mounted on top of the container's east end. Masts attatched to the northeast and soutwest corners of the container support a ground cable that provides some lightning protection. The weather station is mounted on the northeast mast the top of one of the masts.

The 225 GHz tipping radiometer is mounted on the east end of the container's south wall. The scanning mirror sticks out through an opening in the wall.

The two interferometer antennae are arranged on a 300 m east-west baseline with the container in the middle. The interferometer cables were buried when the site was set up. The antennae themselves are 1.8 m in diameter and are mounted on concrete foundations.

The seismometer is mounted on a concrete pad in a hole about 50 cm deep on the south side of the container.

The surveillance camera views the soutwest horizon from the top of the container.

The submm tipper is mounted on the roof of the container on the east end.

The submm Fourier transform spectrometer is located at ground level on the east end of the container.

The Nobeyama Radio Observatory also operates an independent weather station at Chajnantor. This is installed to the west of the container.

In 1998 June, the LSA project installed a container with a suite of instruments about 30 m north of the MMA container.

Radiosondes are launched from a container about 1 km west of the other instruments.

View of container looking northeast. Cerro Chascon in background.
Photo: S. Radford, 1995 May.

View of container looking southeast. Moonrise over Cerro Chascon in background.
Photo: S. Radford, 1995 May.

Container setup, 1995 April.

Interferometer antenna.
Photo: S. Radford, 1995 May.

Last modified 2001 January 18
Simon Radford