14.9 PHT-S Dynamic Calibration for Staring Observations

Description Parameter: Section 5.2.6 Processing Level: SPD Usage in processing: Section 7.4 in particular Section 7.4.2 File Type: FITS Image Units: Jy for PSDYNAMIC, dimensionless for PSDYNWT File names: PSDYNAMIC, PSDYNWT

The dynamic calibration for staring observations with PHT-S is based on the assumption that point sources with similar flux densities will produce identical signal variations as a function of time for each PHT-S detector array element. With a sufficient number of calibration stars spanning a large range of flux densities for each detector pixel, it has been possible to construct two dimensional surfaces where for any signal

of detector pixel

at time

a flux density $F^t_{\nu}(i)=\varphi(i,s(i,t),t)$ in Jy can be assigned (see Section 5.2.6). The calibration data are tabulated in PSDYNAMIC.

The SPD processing subdivides a staring measurement into a number of

depending on the number of ramps in the measurement. For each value of

a value of $F^t_{\nu}(i)$ can be determined. For small

, the corrections are largest because of the steep initial rise of the signal transient curve. The flux calibration becomes more accurate by giving the signals at larger

a relatively higher weight when averaging the

to obtain the average flux density for a measurement. The weights are stored in a separate calibration file PSDYNWT.

Due to the high dynamic range in possible signals

and times

, the calibration tables use logarithmic axes for signal and time. The axes are tabulated as follows:

signal axis:

$\displaystyle s(j) = -dex[-3.0202+(j-1)(\frac{3.0202-5.0}{28})]$	$\textstyle {\rm for}$	$\displaystyle 1~{\leq}~j~{\leq}~29$	(14.1)
$\displaystyle s(j) = 0~~~~~~~~~~~~~~~~~~~~~~~~~~~~$	$\textstyle {\rm for}$	$\displaystyle j=\,30$	(14.2)
$\displaystyle s(j) = dex[-5+(j-31)(\frac{2.0+5.0}{99})]~~~$	$\textstyle {\rm for}$	$\displaystyle 31~{\leq}~j~{\leq}~130,$	(14.3)