Thursday, December 16, 2010

Rarotonga Airglow Photometer - 1968

Airglow image - NASA's Marshall Space Flight Centre photostream - FLICKR

What is airglow?

Airglow is a very weak light emission from the planetary atmosphere. The phenomenon was first identified in 1868 by Swedish scientist Anders Angstrom.

Airglow is caused by processes in the upper atmosphere such as ions and cosmic rays and chemicals reacting with the atmosphere to create light emissions.
It is not noticeable during the day because of the light from the sun. The above image shows airglow as blue.

Completed Airglow Photometer

A photometer is an instrument for measuring light intensity and in this case airglow.

We found a progress report for the Department of Scientific and Industrial Research (DSIR) New Zealand, contract 32 - Airglow Photometer to be used at Rarotonga during the period 30 August 1968 - 10 April 1969.

Data-recording equipment for the Photometer

The report contains a technical evaluation of the project and a financial report.

The University of Canterbury Industrial Development Department (UCIDD) completed its part of the construction work on the photometer and then the instrument was delivered to the Physics department with minor modifications to be done prior to packing and shipping to Rarotonga.

There were some initial problems encountered, including

  • A method of subtracting the background stellar noise from the signal. This background tended to obsure the desired airglow signal.

  • The need to move 3 filters in order to successfully measure the red signal, the red background and the green signal individually.

  • The need to greatly reduce the noise arising in the photomultiplier detection system, so as to significantly improve the signal noise ratio.

    A solution to all three problems was obtained.

Test jig

Side view of the Filter drive

Rear view of Filter Drive with the servo-motor

Front view of the Rim Drive with 3 filters

Figure 7 (above) represents a scan of the planet Mars and the star Antares. Both of these very red stellar objects are quite bright in the sky. As a result the scan was run on a rather insensitive setting of the photometer amplifiers.

Mr R.K. Malcolm worked on the project as a PhD student under the sponsorship of the DSIR Fellowship.

See letter of results here:

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