UIST – Corrections for Non-Linearity

UIST – Corrections for Non-Linearity

Corrections for non-linearity 

The currently distributed version of the ORACDR does not correct for non-linearity. Hence a small script is provided here which will do the corrections. For applying the corrections, please copy the script to any directory, and set the environment variable “ORAC_PRIMITIVE_DIR” to the path of the directory where the script is placed. 

Click here to download the script.

Note that this correction applies only to the data collected using the ARC (formerly SDSU) controller commissioned with UIST in December 2006. For numbers specific to the old Edict system, please contact the instrument scientist.

For non-thermal data, the correction “y” is: 
y = ( 1.7929E-14 * x3 ) – ( 1.9544E-10 * x2 ) + ( 6.5558E-6 * x ) + 0.98657 
for data where the counts are between 750 and 20000 ADUs. 

For thermal data, the correction “y” is : 
y = ( 3.6058E-27 * x6 ) – (4.1373E-22* x5) + ( 1.8632E-17 * x4 ) – ( 4.1209E-13 * x3 ) + ( 4.762E-9 * x2 ) – ( 2.353E-5 * x ) + 1.0294 
for data where the counts are between 890 and 36000 ADUs. 

“x” is the observed counts on the raw data (in ADUs). “y” is the correction factor to be multiplied to “x” to derive the linearized images. 

Note that for thermal images, the lower limit of 890 ADUs is adequate. We will always be above this level when we work in the thermal regime. However, for non-thermal images, a lower limit of 750 ADUs is not always sufficient. Improved corrections extending well below 750 ADUs will be available soon.

How do we tell ORACDR to use this script? 

You can copy the lines given below to a file, remove the square brackets and replace the fields within the square brackets with the appropreate UTdate, directory names and file numbers, and execute it as a shell program from cshell. 

oracdr_uist [UTdate]
setenv ORAC_PRIMITIVE_DIR [path of the directory where the script is located]
setenv ORAC_DATA_IN [path of the directory containing the raw data]
setenv ORAC_DATA_OUT [path of the directory where the reduced data need to be put]
oracdr -list [from_frame_number:to_frame_number]