3.3 RESPCAL : Responsivity Calibration

To aid understanding and to help maintain the pipeline code pipeline modules are named where calculations happen.

aas_read_conv_factors:

First the AOT band related calibration file 25 is read in. Calfile 25 contains the data of the RSRF (resfac) for several wavelength of an AOT band. Every calfile 25 entry is associated with a related error (reserr). How this error is computed is subject of the related CAP.
For a given key wavelength the related calfile 25 RSRF-factor (resfac_kw) is determined by searching in the array of data. Then a linear interpolation conserving the flux is applied to the calfile 25 data.

aas_fc_intpol:

The flux at key wavelength (resfac_kw) is the total integral of fluxes (obtained using the trapezoid rule) between flux at key wavelength minus FWHM and flux at key wavelength plus FWHM divided by FWHM. For AOT1 the FWHM is obtained from Cal-G file 19, for all other AOTs it is set to 0 and no division takes place

It is assumed that the error follows the same integration formulae as the fluxes (reserr_kw), except that the error is divided by the square root of a dilution factor being the ratio between the FWHM and the local stepsize in wavelength. Integrating over more wavelength's yields a smaller error while interpolating over a small part one wavelength interval a larger error.

aas_read_conv_factors:

Every array entry (resfac) is normalized to the computed factor at key wavelength (resfac_kw):

The errors of the normalized calfile 25 data are calculated in OLP V5 as:

The current IA3 system (and future OLP V6) computes the error differently:

aas_det_conv_factor:

For every wavelength the related table of resfac_n (equation 23) is searched and the actual value at the wavelength of interest is determined by linear interpolation, to produce resfac_ni. For AOT1 data calfile 19 is accessed and a special FWHM value is extracted. This value goes into the interpolation conserving the flux algorithm as above (err_ni). Errors are treated as before (aas_fc_intpol). For the simple linear interpolation (non AOT1 data), the error is also computed by linear interpolation (err_ni). Now the calfile 25 data are prepared to be applied.

aas_resp_cal:

Finally the new flux is computed:

 flux_out    : new computed flux

flux_in     		 : 		 flux input from equation 21

err_out     		 : 		 new error computed

err_in      		 : 		 error input from equation 22

The current IA3 implementation (and OLP V6) computes the error as:

And the new error: