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 T_sys 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 T_sys 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:

c = 2.998 × 10⁸ [m/s]                       Speed of light
k_B = 1.38 × 10⁻²³ [J/K]                      Boltzmann Constant
η_c = 0.98                                            Correlator efficiency
n_pol = 2.                                             Number of polarizations
η_Q =  0.9625                                     Digitizer quantization efficiency
D = 18.  [m]                                       Diameter of the antenna
Nant                                                   Total number of antennas in subarray
T_sys  [K]                                              System Temperature
t_int [s]                                                 Integration (or observation) time
A  [m²]                                               Geometric area of single antenna
η_A                                                       Aperture (antenna) efficiency (from table)
SEFD  [Jy]                                           System Equivalent flux Density  of an antenna
Δν [Hz]                                               Correlated bandwidth
b_max  [m]                                           Physical length of longest baseline in subarray

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 weigthed point source sensitivity is defined as:

where  η_weight is an inneficiency 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).