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BIGCAT Sensitivity Calculator

Version: 2024-Nov-14 (Change Log)

Data

The BIGCAT central frequency to use. This frequency will be in the middle of the 1920 MHz BIGCAT window. This will be made up of 15 128 MHz subbands.

BIGCAT Freq:

The number of channels that each of the BIGCAT subbands is split into. This only considers the 128 MHz of bandwidth that is kept from each subband. This determines the frequency resolution of each subband.

# Subband Channels:

The central frequency of a zoom band that you want to observe. This frequency will be in the centre of the BIGCAT zoom band, with the zoom bandwidth specified below.

Zoom Freq:

The bandwidth of the zoom band you want to observe. This works with the frequency specified above, and the number of zoom channels supplied below, to characterise the zoom band.

Zoom Bandwidth:

The number of channels in the zoom band you want to observe. This works with the frequency and bandwidth of the zoom supplied above, to characterise the zoom band.

# Zoom Channels:

The array configuration that you want to use. Longer arrays will give better angular resolution, while shorter arrays will give better brightness sensitivity. Arrays prefixed with H are "hybrid" arrays, which allow imaging of sources near the celestial equator.

Array:

Select whether you will use data from antenna 6.

CA06:

The declination of the source. The calculator requires this parameter so it can determine the likely atmosphere the source will traverse during your observation, and so it can calculate the synthesised beam size.

Declination:

The lowest elevation that you will observe your source at. If you observe your source at lower elevations, you will be able to observe your source for longer on a single day, but the atmospheric conditions will deteriorate.

El Limit:

The hour-angle range you will observe your source over (an hour angle of 0 is at transit, when the source is at its highest elevation). Observing over a larger range of HA will result in improved uv-coverage, but may mean observing at lower elevations.

HA Limits:

The rest frequency of the spectral line you are trying to observe. If this parameter is specified, the calculator will determine the velocity range and resolution of your observations.

Rest Freq:

The weighting scheme used in the imaging process. The factors used by this calculator assume that Miriad's invert is used.

Weighting:

The weather conditions used to calculate the sensitivities are selected by using the season in which the observations will be made.

Season:

The number of frequency channels to average together, using simple averaging. Hanning smoothing is not required for CABB's polyphase filter bank. Smoothing can be changed for both the continuum and zoom bands separately here.

Smoothing:

Remove channels that are usually dominated by known, external sources of RFI. This has a varying effect, depending on the frequencies chosen.

Rem RFI:

This setting determines how the calculator operates. If you want to know the sensitivity achieved by a given amount of integration time, select "Integration". If you want to know the integration time required to reach a specified sensitivity, select "Sensitivity".

Supplied:

If you selected "Integration" above, fill in the amount of integration time in this box, in minutes.

Integration:

If you selected "Sensitivity" above, enter the required sensitivity in this box and select the appropriate units (mJy/beam or mK). You should then select whether you require this sensitivity for a continuum signal in the 2 GHz band ("Continuum"), for a spectral signal in the 2 GHz band ("Spectrum"), or for a spectral signal in the zoom band ("Zoom"). Finally, select the weather conditions to calculate for.

Sensitivity:
in:
with:

What type of observation are you considering?

The mode selected here will determine which panels will be shown during this process. If you are primarily interested in detecting a continuum signal in the 2 GHz BIGCAT band, select "Continuum". If you are primarily interested in detecting a line signal in either the 2 GHz BIGCAT band or the zoom bands, select "Spectral Line".



What will your central frequency be?

The centre of the 2 GHz BIGCAT band can be placed anywhere within the ranges listed in the table below. The available range is a combination of the receiver sensitivity and the capabilities of the local oscillators. The recommended frequencies provide the best available continuum sensitivity.
Band NameRange (MHz) Recommended (MHz)
16cm1728 - 24002100
4cm4928 - 109285500, 9000
15mm16000 - 2500017000, 19000
7mm30000 - 5000033000, 35000, 43000, 45000
3mm85000 - 10500093000, 95000
Repeatedly pressing the button for the recommended frequency in a band with more than one recommended frequency will cycle through those frequencies.

The recommended frequency for the band

OR

A specific frequency

 

What array do you require?

The array configuration you use will depend on your science requirements. If you require high angular resolution, then you should opt for a longer array, and include antenna 6. If you require sensitivity to extended structure, you should use a shorter array and omit antenna 6. If you need to image a source within 10 degrees of the celestial equator, or if you need to image a line that will be absorbed by the atmosphere at low elevation, you should select a hybrid array (those prefixed by "H").
Array:
Use CA06:

What BIGCAT configuration do you require?

The BIGCAT configuration determines:

  • Spectral resolution in each 128 MHz subband: Each 128 MHz subband is divided up into channels with the number specified by the configuration. For example, when there are 128 channels, each channel is 1 MHz wide.
  • The width of each zoom band: Each configuration may offer a different bandwidth for the zooms it produces.
  • The spectral resolution of each zoom band: Each configuration may split its zooms into a different number of channels.

At least the following modes should be available with BIGCAT, but you may enter any values in this calculator, since BIGCAT should be able to support whatever configuration you require. If you require non-standard modes, please reach out to the BIGCAT development team to discuss the possibility of adding your required mode.
  • Continuum: 128 channels per subband, no zooms
  • Spectral 74 kHz: 1728 channels per subband, no zooms
  • Spectral 37 kHz: 3456 channels per subband, no zooms
  • Spectral 18 kHz: 6912 channels per subband, no zooms
  • Spectral 9 kHz: 13824 channels per subband, no zooms
  • Zooms 2 MHz - 0.5 kHz: 128 channels per subband, 2 MHz wide zooms with 4096 channels
  • Zooms 4 MHz - 0.24 kHz: 1728 channels per subband, 4 MHz wide zooms with 16384 channels
  • Zooms 2 MHz - 0.06 kHz: 128 channels per subband, 2 MHz wide zooms with 32768 channels

If you want to use a different configuration, simply enter the number of channels per subband, the bandwidth of the zooms, and the number of channels per zoom in the data column at the left of the calculator and move on to the next question.
Standard BIGCAT Configuration

What is the source declination?

The source declination will determine both the path the source takes through the atmosphere and the uv coverage provided by the synthesis observation.
Declination:

What are your observation limits?

The antennas can track a source at any elevation above 12 degrees, but the atmosphere becomes thicker and more turbulent at lower elevations, which degrades the sensitivity. In the mm bands, it is often better to limit your observations to elevations above 30 degrees. You can also limit your observations to a specific hour-angle range, if you are observing for different times around transit, or are concerned about shadowing in the array you choose (shadowing diagrams can be found here). The calculator will use whichever of the two limits is more stringent.
Elevation Limit:
Hour-angle Limits:

What calculation do you require?

The calculator can be operated in one of two modes, depending on the information you provide:
  • By selecting "Integration", the calculator will return the sensitivity of an observation with the integration time you supply.
  • By selecting "Sensitivity", the calculator will return the integration time required to reach the sensitivity you supply.
Calculation Type:

How much integration time will you have?

Here you should specify, in minutes, the amount of integration time you will spend on your target source. The calculator will spread this time evenly over the hour-angle range you have allowed.
Integration Time:

What sensitivity do you require?

Here you need to provide the sensitivity you require your observations to have, in your required band, and under the conditions you specify.
Put the sensitivity in the entry box, and select the appropriate units (mJy/beam for a spectral or continuum signal, or milli-Kelvin for surface brightness).
Then select the band in which you require the sensitivity, from "Continuum" (a continuum signal in the 2 GHz band), "Spectrum" (a spectral signal in the 2 GHz band), or "Zoom" (a spectral signal in the zoom band).
Finally, choose the weather conditions to assume for the calculation, from "Best", "Typical" or "Worst".
Required Sensitivity:
Required Band:
Weather Conditions:

How much flagging will you do?

The calculator can estimate the likely amount of flagging that will need to be done to prevent external RFI from corrupting the images you make. You can disable this flagging here if you want. Only known emitters in the local area that corrupt the spectrum most of the time will be flagged. RFI that is only occasionally present (eg. weather radar) will not be counted.
RFI:

What is the frequency of the line you want to observe?

To observe a line in either the 128 MHz BIGCAT subbands or one of the zoom bands, it has to lie within 960 MHz of the BIGCAT central frequency, which in turn has to be within the range listed in the table below. A suitable BIGCAT central frequency will be chosen automatically once you specify your line frequency.
Band NameRange (MHz)
16cm1728 - 2400
4cm4928 - 10928
15mm16000 - 25000
7mm30000 - 50000
3mm85000 - 105000
If you specify the rest frequency of the line you are attempting to observe, the calculator will be able to calculate the velocity width and resolution of your observations.

You should also specify whether you expect to use the BIGCAT subbands to detect the line, or one of the zoom bands.

Observed Line frequency:
Line Frequency:
Detection band:

How will you make your image?

Assuming that you are making a multi-frequency-synthesis image from these data with Miriad's invert task, you will be asked to select a data weighting scheme. The choice of scheme will change the resolution and sensitivity of the resulting images. The choices are:

  • Natural: This gives an equal weight to each visibility (assuming each visibility has the same noise), and will give optimum sensitivity to point sources. The synthesised beam shape and sidelobe levels can be poor though, which makes deconvolution more difficult.
  • Uniform: This weights the visibilities proportionally to the number of visibilities in each resolution element, which minimises the sidelobe level in the synthesised beam, at the cost of a higher noise level.
  • Robust: This tries to give an optimal compromise between the noise levels obtainable with natural weighting, and the sidelobe levels obtainable with uniform weighting. A robust level of 2 minimises the noise only, while a level of -2 only minimises the sidelobe level.

More complete information about the available image weighting schemes can be found here.
Weighting scheme:

How will you make your image?

Assuming that you are making a cube from these data with Miriad's invert task, you will be asked to select a data weighting scheme and the number of channels to combine to form a single output plane. The choice of weighting scheme will change the resolution and sensitivity of the resulting images. The choices are:

  • Natural: This gives an equal weight to each visibility (assuming each visibility has the same noise), and will give optimum sensitivity to point sources. The synthesised beam shape and sidelobe levels can be poor though, which makes deconvolution more difficult.
  • Uniform: This weights the visibilities proportionally to the number of visibilities in each resolution element, which minimises the sidelobe level in the synthesised beam, at the cost of a higher noise level.
  • Robust: This tries to give an optimal compromise between the noise levels obtainable with natural weighting, and the sidelobe levels obtainable with uniform weighting. A robust level of 2 minimises the noise only, while a level of -2 only minimises the sidelobe level.

More complete information about the available image weighting schemes can be found here.

If you require a lower noise level in each output plane, and you don't require the resolution provided by the CABB channelisation, then you may want to choose to smooth your data in the imaging process. With CABB's polyphase filterbank design, Hanning smoothing is not required. You can smooth in either the continuum band or the zoom band, or both, with different levels of smoothing in each.
Weighting scheme:
Smoothing:

When will you observe?

The sensitivity calculator determines the best, typical and worst weather conditions based on the time of year you will observe. You should select the season below that your observations will be made in. The actual weather conditions that the calculator uses will displayed alongside the results.

The choices are:

  • Annual: choose this if you don't know when your observations may be scheduled, or you would like to know the absolute best and worst conditions that are seen at the ATCA.
  • APRS: choose this if you are proposing to observe in the April 1 - September 30 semester.
  • OCTS: choose this if you are proposing to observe in the October 1 - March 31 semester.
  • Summer: weather conditions present between December 1 and February 28.
  • Autumn: weather conditions present between March 1 and May 31.
  • Winter: weather conditions present between June 1 and August 31.
  • Spring: weather conditions present between September 1 and November 30.
  • Jan/Feb/Mar/Apr/May/Jun/Jul/Aug/Sep/Oct/Nov/Dec: weather conditions present in each particular month.

Season:

Ready to calculate!

You're now ready to get your results. Please check the data on the left to ensure that the settings are as you expect. If you need to change something, you can edit the data as necessary, or you can also go back to previous questions using the "Previous Question" link at the bottom of this panel.

Sensitivity Summary

Continuum Spectral Zoom
  • With of on-source integration time,
  • in typical weather (help?),
  • in the 2 GHz band centred at a frequency of ,
  • in a continuum image made with weighting (help?),

you will achieve

  • a brightness sensitivity of (help?),
  • and an RMS noise level of (help?).

To make a continuum image

  • in weather (help?),
  • in the 2 GHz band centred at a frequency of ,
  • with weighting (help?),
  • with a brightness sensitivity of (help?),
  • or an RMS noise level of (help?),

will require of on-source integration time.

  • With of on-source integration time,
  • in typical weather (help?),
  • in the 2 GHz band centred at a frequency of ,
  • in a cube made with weighting (help?),

each plane will have

  • a velocity width of (help?),
  • a brightness sensitivity of (help?),
  • and an RMS noise level of (help?).

To make a cube

  • in weather (help?),
  • using the 2 GHz band centred at a frequency of ,
  • with weighting (help?),

with each plane having a

  • a velocity width of (help?),
  • a brightness sensitivity of (help?),
  • or an RMS noise level of (help?),

will require of on-source integration time.

  • With of on-source integration time,
  • in typical weather (help?),
  • in the zoom band made up of individual zoom channels, and centred at a frequency of ,
  • in a cube made with weighting (help?),

each plane will have

  • a velocity width of (help?),
  • a brightness sensitivity of (help?),
  • and an RMS noise level of (help?).

To make a cube

  • in weather (help?),
  • using the zoom band made up of individual zoom bands, and centred at a frequency of ,
  • with weighting (help?),

with each plane having a

  • a velocity width of (help?),
  • a brightness sensitivity of (help?),
  • or an RMS noise level of (help?),

will require of on-source integration time.

<<< Restart questionnaire
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Array Information >>>
Continuum Information >>>
Spectral Information >>>
Zoom Information >>>

Array Information

Array Configuration
Number of Antenna:
Number of Baselines:
Longest Baseline:
Antenna Efficiency:
Array Sensitivity
Best Weather Typical Weather Worst Weather
System Temperature (?)
Antenna Sensitivity (?)
Array Sensitivity
Weather Conditions Summary (help?)
Best Weather Typical Weather Worst Weather
Temperature
Pressure
Humidity
<<< Restart questionnaire
<<< Reset questionnaire
<<< Sensitivity Summary
Continuum Information >>>
Spectral Information >>>
Zoom Information >>>

Continuum Information

Continuum Image Parameters
Weighting (?):
Weighting Factor: x Natural
Primary Beam FWHM (?):
Synthesised Beam FWHM (?):
Central Frequency:
Effective Bandwidth:
Continuum Image Sensitivity
Best Weather Typical Weather Worst Weather
RMS noise level (?)
Brightness Sensitivity (?)
Weather Conditions Summary (help?)
Best Weather Typical Weather Worst Weather
Temperature
Pressure
Humidity
<<< Restart questionnaire
<<< Reset questionnaire
<<< Sensitivity Summary
Array Information >>>
Spectral Information >>>
Zoom Information >>>

Spectral Information

Spectral Cube Parameters
Weighting (?):
Weighting Factor: x Natural
Primary Beam FWHM (?):
Synthesised Beam FWHM (?):
Central Frequency:
Effective Bandwidth:
Frequency Resolution:
Velocity Width (?):
Velocity Resolution:
Rest Frequency:
Spectral Cube Plane Sensitivity
Best Weather Typical Weather Worst Weather
RMS noise level (?)
Brightness Sensitivity (?)
The expected RMS noise varies across the spectral band as shown in this image. Click the image to expand it to full size. Red, cross-hatched frequency ranges in this plot would normally be flagged during the reduction process.
Weather Conditions Summary (help?)
Best Weather Typical Weather Worst Weather
Temperature
Pressure
Humidity
<<< Restart questionnaire
<<< Reset questionnaire
<<< Sensitivity Summary
Array Information >>>
Continuum Information >>>
Zoom Information >>>

Zoom Information

Zoom Band Cube Parameters
Weighting (?):
Weighting Factor: x Natural
Primary Beam FWHM (?):
Synthesised Beam FWHM (?):
Central Frequency:
Effective Bandwidth:
Frequency Resolution:
Cube planes:
Velocity Width (?):
Velocity Resolution:
Rest Frequency:
Zoom Band Cube Plane Sensitivity
Best Weather Typical Weather Worst Weather
RMS noise level (?)
Brightness Sensitivity (?)
Weather Conditions Summary (help?)
Best Weather Typical Weather Worst Weather
Temperature
Pressure
Humidity
<<< Restart questionnaire
<<< Reset questionnaire
<<< Sensitivity Summary
Array Information >>>
Continuum Information >>>
Spectral Information >>>