The talk at JAO/Santiago

Here is a link to the talk I presented here in Santiago:

http://www.mrao.cam.ac.uk/~bn204/publications/2009/ALMAAugust2009.pdf

Memo on inference of phase correction coefficients

This is the second memo in the series.

Abstract:

By observing bright and compact astronomical sources while also taking data with the 183 GHz Water Vapour Radiometers, ALMA will be able to measure the `empirical' relationship between fluctuations in the phase of the astronomical signal and the fluctuations of sky brightness around 183 GHz. Simulations of such measurements assuming only thermal noise in the astronomical and WVR receivers are presented and it is shown that accurate determination of the empirical relationship should be possible in a relatively short time. It is then proposed that the best way of using these empirical coefficients is to include them as a constraint on a physical model of the atmosphere -- this allows them to be used for longer period of time, increasing the efficiency of observing. This approach fits naturally into the analysis framework presented in the previous memo, which has now been extended to implement it. The technique is illustrated via simulations and on a short data set collected at
the SMA.


Full text:

http://www.mrao.cam.ac.uk/~bn204/publications/2009/ALMAMemo588.pdf

Visiting ALMA Santiago office and the ALMA Site

For the next two weeks I'm in Chile visiting the ALMA offices in Santiago as well as the ALMA site itself where we will be doing some experiments with the ALMA Water Vapour Radiometers.

My talk at JAO/ALMA FP6 Enhancement meeting

Is available at:

http://www.mrao.cam.ac.uk/~bn204/publications/2009/ESOJuly2009.pdf

JAO/EU FP6 ALMA Enhancement meeting

I will be at this meeting in Munich on 24th July... See you maybe there.

European Union FP6 ALMA Enhancement at Cambridge

We have put together a small number web-pages that summarise the work that we are doing on advanced phase correction for ALMA through a grant by the European Union Framework Programme 6. The address is:

http://www.mrao.cam.ac.uk/projects/alma/fp6/

Talk on OOF holography at Cambridge

I gave a talk here in Cambridge this week on the OOF holography technique, link and screen shot below

Title: The OOF Holography Technique: Correcting the Effects of Gravity and Thermal Gradients on Large Filled-Aperture Telescopes

http://www.mrao.cam.ac.uk/~bn204/publications/2009/MRAOApril09.pdf

Abstract:

The maximum practical size of large single-dish telescopes is mainly defined by the effects three forces: gravity, thermal gradients, and wind. All of these can in principle be corrected by the new generation of active surfaces on telescopes if we knew the actual deformations that are caused by them. At current cm, mm and sub-mm telescopes, measuring these deformations corresponds to measurement of one part in a million which is challenging for conventional survey techniques. In this talk I will introduce the phase-retrieval holography technique based on Out-Of-Focus (OOF) beam maps that is particularly suited to measuring these deformations. I will also present the application of this technique to the 100m-diameter Green Bank Telescope where we have been able to eliminate residual gain variation due to gravity and open up the daytime for efficient observations at mm-wavelengths.