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simulator.setnoise - Function

2.4.1 Set the noise level fixed sigma (mode=simplenoise) or Brown’s equation using the ATM model for frequency-dependent atmospheric opacity (mode=tsys-atm) or Brown’s equation, manually specifying the zenith opacity (constant across the band) and atmospheric temperature (mode=tsys-manual)


Description

Set various system parameters from which the thermal (ie, random additive) noise level will be calculated.

For mode=simplenoise, one specifies the standard deviation ”sigma” for the noise to be added to real and imaginary parts of the visibility. The noise in amplitude per visibility is approximately ”sigma” although it is not Gaussian (see Thompson, Moran, and Swenson fig. 6.9) and the point source noise in a Stokes I image will be ~sigma/sqrt(n_pol)/sqrt(n_baselines)/sqrt(n_integrations), where n_pol are the number of polarizations in the MS (typically 2), and n_integrations are the number of correlator integration times in the MS (~ track time / int. time)

For mode=tsys-atm or tsys-atm, the noise will vary with dish diameter, antenna efficiency, system temperature, opacity, sky temperature, etc. The noise will increase with the airmass if tau is greater than zero. The noise is calculated according to the Brown Equation (ie, R.L. Brown’s calculation of MMA sensitivity, 3Oct95): dS = 4*sqrt(2) *( T_rx*exp(-tau_atm) + T_atm*( exp(tau_atm) - epsilon_l + T_cmb) ) *epsilon_q *epsilon_a *pi *Dˆ2 *sqrt(dnu*dt)

For mode=tsys-atm, the sky brightness temperature is calculated using an atmospheric model created for the user-input PWV. For mode=tsys-manual, the user specifies the sky brightness temperature manually.

Arguments

Inputs

mode

Mode of operation.

allowed:

string

Default:

simplenoise

’simplenoise’

’tsys-atm’

’tsys-manual’

table

Name of optional cal table to write (if OTF=False)

allowed:

string

Default:

”

simplenoise

Level of noise if not calculated by amt

allowed:

any

Default:

variant 0.1Jy

pground

Ground pressure for ATM model (if tsys-atm)

allowed:

any

Default:

variant 560mbar

relhum

ground relative humidity for ATM model (if tsys-atm)

allowed:

double

Default:

20.0
altitude

site altitude for ATM model (if tsys-atm)

allowed:

any

Default:

variant 5000m

waterheight

Height of water layer for ATM model (if tsys-atm)

allowed:

any

Default:

variant 200m

pwv

Precipitable Water Vapor ATM model (if tsys-atm)

allowed:

any

Default:

variant 1mm

tatmos

Temperature of atmosphere [K] (if tsys-manual)

allowed:

double

Default:

250.0
tau

Zenith Atmospheric Opacity (if tsys-manual)

allowed:

double

Default:

0.1

antefficiency

Antenna efficiency

allowed:

double

Default:

0.8

spillefficiency

Forward spillover efficiency

allowed:

double

Default:

0.85

correfficiency

Correlation efficiency

allowed:

double

Default:

0.88

trx

Receiver temp (ie, all non-atmospheric Tsys contributions) [K]

allowed:

double

Default:

50

tground

Temperature of ground/spill [K]

allowed:

double

Default:

270.0

tcmb

Temperature of cosmic microwave background [K]

allowed:

double

Default:

2.73

OTF

calculate noise on-the-fly (WARNING: only experts with high-RAM machines should use False)

allowed:

bool

Default:

true

senscoeff

sensitivity constant (1./sqrt(2) for interferometer [default]; 1. for total power)

allowed:

double

Default:

0.

rxtype

Receiver type; 0=2SB, 1=DSB e.g. ALMA B9

allowed:

int

Default:

0

Returns
bool
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