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Weight array

MRTCAL offers the possibility to associate a weight array (Associated Array W) together with the spectrum intensities ( RY). This weight varies in frequency. The weight at channel $i$ is:

\begin{displaymath}
W(i) = \frac{t \times \vert \delta f \vert}{(T_{sys}(i) \times e^{A \tau (i)})^2}
\end{displaymath} (1)

where $t$, $\delta f$ and $A$ are respectively the integration time (seconds), the frequency resolution (MHz) and the airmass (same scalar values shared by all channels), and $\tau (i)$ is the opacity at channel $i$. $T_{sys}(i)$ is the zenithal system temperature, which can be found in the calibration products from a calibration scan (see subsection [*]).

By default, MRTCAL does not save the weight array. This is activated by the command:

MRTCAL> MSET OUTPUT WEIGHT YES
Beware that if enabled, this writes twice more data per spectrum, which typically doubles the CLASS file size! An example of a weight array is plotted in the Figure [*], produced with the following commands:
LAS> file in 09054                                                        
I-CONVERT,  File is  [Native]                                             
I-INPUT,  09054.30m successfully opened                                   
LAS> find /source controld                                                
I-FIND,  12 observations found                                            
LAS> get first                                                               
I-GET,  Observation 3; Vers 1 Scan 201
LAS> plot w

Figure: Weight array associated to a spectrum produced from the file iram30m-4mhz-20100930s200-imb.fits.


next up previous contents
Next: Exploring IMB-FITS files (no Up: Calibrating Previous: Calibration products   Contents
Gildas manager 2023-06-01