V.R.I. - Virtual Radio Interferometer

The Virtual Radio Interferometer (VRI) is an experimental Java applet written by Nuria McKay, Derek McKay and Mark Wieringa, from the Nuffield Radio Astronomy Laboratories, Jodrell Bank and the Australia Telescope Compact Array .

It simulates various radio interferometers, and allows users to conduct a number of "what-if" experiments. It extends the prototype version ( uvTest ) by allowing accumulation of arrays, improved control and fourier transforms.

Basic UV operation

The VRI appletis divided into four panels, (clockwise from top right) the observatory map, the UV coverage plot, the UV plane and the image plane. Each of these panels can be scaled (using the Zoom buttons or the PGUP or PGDN keys) and scrolled (using the arrow keys). The observatory map and UV coverage panels will show the scale by means of a scale bar. Configurations can be selected from the configuration menu.

The Plot button forces the current array layout to be plotted in the UV coverage panel. The UV coverage is also affected by the Hour Angle, Declination and Frequency selection at the bottom of the applet.

UV coverage from different arrays can be accumulated, byt pressing the Add button after each array has been selected. Old arrays can be plotted in blue or red and can be hidden, by selecting the appropriate option out of the Accumulate menu. The Clear button will remove any stored arrays.

Image and UV plane control

VRI allows the user to also experiment with test images. The Source menu will allow the selection of different test sources. By selecting file:, alternative test sources can be entered. These should be .GIF files, no greater that 256x256 pixels.

Clicking on the FFT will casue the fourier transform of the current image to be displayed in the UV plane panel. Conversely, clicking on the FFT-1 button will cause the inverse fourier transform of the UV plane to be displayed in the image panel.

The UV plane, comprising complex numbers, can be displayed in various forms. Choose the appropriate Display from the menu and wait a few seconds for the UV plane to be replotted.

Applying UV coverage

By pressing the Apply button, the current UV plane is masked by the current and accumulated UV coverage. By inverse transforming the masked UV plane, a simulation of the image, as if observed by such a synthesised aperture, can be obtained. As the scale of the images is arbitrary, the masking is down at the scaled level, allowing vastly difference arrays to be simulated (e.g. VSOP vs. ATCA). To compare arrays, make sure the UV plane and coverage displays are set at the scale for each application.

Other observatories

The Obs: menu and fields allow the user to control which observatory is used. Arbitrary observatories can be created, by adjusting the values in the various fields and pressing return for each alteration. It is also possible to drag the antennas about the observatory map, using the mouse, to simulate any configuration. New antennas are always "piled up" at the centre of the array, and will need to be moved. Don't use too many antennas, it will take forever to plot!

The authors can add additional observatories if there is enough demand. The required information we need is:


The FFT, FFT-1, Plot and Display options all deal with a lot of data (especially for an interpretted language).

While the authors hope that this applet will be useful, it is not a definative scientific tool. For more detailed analysis of UV coverage, etc. use Miriad, in particular, the UVGEN task.

There is a bug in some versions of NetScape, which prevents recognition of keyboard keys like PGUP, PGDN, etc.

Sometimes, because of slow links, the test source images don't fully load. Just select them again. Also, the download time is fairly long, owing to the large amounts of code - an added incentive to visit the ATCA!


We would greatly appreciate any comments you may have on this documentation, or the VRI java applet. Please e-mail them to Nuria McKay (nm@jb.man.ac.uk).

Return to the NRAL - Jodrell Bank Home page

Return to the Merlin Home Page

Original: dmckay@atnf.csiro.au (4-FEB-1997)
Modified: nm@jb.man.ac.uk (10-Sep-1997)