Subsections

• 14.9.1 Product PSDYNAMIC: PHT-S dynamic calibration - flux correction
• 14.9.2 Product PSDYNWT: PHT-S dynamic calibration - weighting function

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 $s(i,t)$ of detector pixel $i$ at time $t$ 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 $s(i,t)$ depending on the number of ramps in the measurement. For each value of $t$ a value of $F^t_{\nu}(i)$ can be determined. For small $t$, 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 $t$ a relatively higher weight when averaging the $f(t)$ 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 $s(i,t)$ and times $t$, the calibration tables use logarithmic axes for signal and time. The axes are tabulated as follows:

• signal axis:

  
  

  $$s(j) = -dex[-3.0202+(j-1)(\frac{3.0202-5.0}{28})] {\rm for} 1~{\leq}~j~{\leq}~29$$ (14.1)

  $$s(j) = 0~~~~~~~~~~~~~~~~~~~~~~~~~~~~ {\rm for} j=\,30$$ (14.2)

  $$s(j) = dex[-5+(j-31)(\frac{2.0+5.0}{99})]~~~ {\rm for} 31~{\leq}~j~{\leq}~130,$$ (14.3)

  
  

  where $j$ is the array index and signal $s(j)$ is in [V/s]. Note that negative signals can occur.

• time axis:

  
  

  $$t(j) = 2^j~~~{\rm [s]}~~~for~~0~{\leq}~j~{\leq}~12.$$ (14.4)

  
  

  As a consequence, times smaller than 1 s (and larger than 4096 s) are not handled by the calibration.

For both PSDYNAMIC and PSDYNWT the following FITS keywords are common:

NAXIS = 3
TYPE = REAL*4

14.9.1 Product PSDYNAMIC: PHT-S dynamic calibration - flux correction

AXIS	Length	Description 
1 	130 	signal 
2 	13 	time in ${\rm log_2}(t)$ 
3 	128 	pixels 

14.9.2 Product PSDYNWT: PHT-S dynamic calibration - weighting function

AXIS	Length	Description
1 	130 	signal 
2 	13 	time in ${\rm log_2}(t)$ 
3 	128 	pixels