ngECT Documentation
The ngECT allows the calculation of the estimated sensitivity for continuum and spectral line modes. Specifically:
1. Continuum:
- continuum point source sensitivity in units of µJy/beam
- continuum brightness sensitivity in units of K
2. Line
- line point source sensitivity in units of µJy/beam
- line brightness sensitivity in units of K
Alternatively you can request the calculation of the on-source integration time needed to reach the input image sensitivity.
Note: the ngECT only does natural + outer uv-taper. The capability of including robust values is being developed. This version of the ngECT uses Tsys and aperture efficiency values that are frequency dependent. For the continuum it has the option to use the maximum receiver bandwidth when the receiver bandwidth is smaller than the correlator bandwidth, and calculates the Tsys and efficiency at the band center. At band 6 it tries to center the 20 GHz of instantaneous bandwidth on the desired frequency instead of using the band average. Also, it calculates the line sensitivity and brightness temperature at the desired frequency instead of the band center.
The ngECT uses the following parameters:
| Parameter | Units | Value | Description |
|---|---|---|---|
| c | m/s | 2.998 × 108 | Speed of light |
| kB | J/K | 1.38 × 10−23 | Boltzmann constant |
| ηc | — | 0.98 | Correlator efficiency |
| npol | — | 2 | Number of polarizations |
| ηQ | — | 0.9625 | Digitizer quantization efficiency |
| Nant | — | [determined based on the subarry selected] | Number of antennas |
| Tsys | K | [determined based on the representative frequency and correlated bandwidth] | System temperature |
| tint | s | [entered by the user or computed to in order to achive the user-requested RMS] | Integration (or observation) time |
| A | m2 | 254.47 (for the 18m antennas) | Geometric area of single antenna |
| ηA | — | [determined based on the representative frequency and correlated bandwidth] | Aperture (antenna) efficiency |
| bmax | m | [determined based on the subarry selected] | Physical length of longest baseline in subarray |
| Δν | Hz | [entered by the user] | Correlated bandwidth |
| SEFD | Jy | [calculated following the relevant equation below] | System Equivalent Flux Density of an antenna |
The theoretical thermal noise or point-source rms expected for an image using natural weighting of the uv data is:
where SEFD is defined as:
The weighted point source sensitivity is defined as:
where ηweight is an inefficiency factor that is estimated through the taperability analysis which takes into account the change in sensitivity due to using an outer uv taper (see more in ngVLA memo #106).
If you have further questions or encounter an issue with the ngECT, please contact us.
