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.

Early high-z Science with ALMA

Next Monday I will be at the "Early high-z Science with ALMA" in
Oxford:

http://www-astro.physics.ox.ac.uk/~ianh/alma/

Maybe see you there....

New Memo on inference of phase coefficients

I've just posted the completed version of the first memo on the
inference of phase correction coefficients. This the link to the memo:

http://www.mrao.cam.ac.uk/~bn204/publications/2009/ALMAMemo587.pdf

All of the software and data is available for download from here:

http://www.mrao.cam.ac.uk/~bn204/alma/memo-infer.html

And all the other publications are as usual available from:

http://www.mrao.cam.ac.uk/~bn204/publications/publicationlist.html

A note on using 183 GHz Water Vapour Radiometers to correct total power observations

I've posted a short note on using 183 GHz Radiometers to correct for
the atmospheric emission fluctuations that can limit total power
observations. The note is available at:

http://www.mrao.cam.ac.uk/~bn204/publications/2009/tpower-v01.pdf

The attached graph is a summary of how well the correction would is
expected to work -- see the article for the detail.

OOF software

I've released a new version of the OOF analysis software which you can
get from:

http://www.mrao.cam.ac.uk/~bn204/oof/software.html#Current+version%3A+V1.3

The main improvements have been in the configuration and building of
the packages which should be more adaptable now. For details see the
NEWS files in each of the constituent packages.

Turbulent 3d fields and bnlib-1.3

I've uploaded a new version the "bnlib" library that amongst other items contains the code to generate very large simulations of turbulent fields. The library can be downloaded at:

http://www.mrao.cam.ac.uk/~bn204/alma/memo-turb.html#Current+version+of+library%3A+V1.3

An illustration of the sorts of effects you can investigate with such
fields here is a slide from a presentation I gave a while back. You
can get the whole presentation at
http://www.mrao.cam.ac.uk/~bn204/publications/2008/ALMASim08.pdf