= Owl Processing Guide =

The Owl thermal hyperspectral sensor is new to the arsf and does not yet have a complete processing chain.  As this is developed this wiki page will be updated.  Details on the Owl sensor are available [https://arsf-dan.nerc.ac.uk/trac/wiki/Sensors/Owl here] and information on Owl testing is available [https://rsg.pml.ac.uk/intranet/trac/wiki/Projects/ARSF-DAN/Users/lah/OwlNotes here].

== Radiometric Calibration ==

Specim have provided a tool to process the Owl raw data into calibrated data.  Details on using this tool are located [https://arsf-dan.nerc.ac.uk/trac/wiki/Procedures/OwlProcessing/OwlTool here] if required.

To batch process the data use: processOWL.py -p <project directory>

To process individual lines use: process_OWL_line.py -p <project directory> -f <flightline>

Each flightline should have it's own calibration data in the form of additional files prefixed T1 and T2 in the capture directory.  If these are not present the script will produce a warning.  Run the script again with the option -c auto once the submitted flightlines have produced the required calibration files (Check the log has passed the "Writing calibration file..." step), or manually specify a calibration file with -c <flightline with calibration data_calibration.rad>.

All output files are written to the /processing/owl/calibration subdirectory of the project folder and logs written to /processing/owl/logs. The output files consist of the data (*_proc.data) and if not specified as inputs, the calibration (*_calibration.rad) and blinker files (*blinkers.dat), all with their own header file. Intermediate files are stored in /users/rsg/airborne/workspace/Owl/ and deleted on completion.

=== Blinking Pixels/Vertical Stripes ===

During the radiometric calibration blinking pixels are tested for and removed from the data.  It is likely that the default settings will not remove all the blinking pixels and the data will have vertical stripes.  To remove these reprocess with a lower value of pixstabi e.g.

process_OWL_line.py -p <project directory> -f <flightline> -m pixstabi=0.005

The pixstabi modifier defines the standard deviation of the time series allowed for a normal pixel, so reducing this removes more pixels above this range.  It is not expected that all blinking pixels can be removed as the blinking pixel routine does not yet appear to be optimal.  Do not make the value too low as this will remove too many pixels and result in thick vertical stripes where the data has been replaced.  It will also remove a considerable amount of spectral information, so check that the spectra still look reasonable. Somewhere between the first 2 images below is desirable.


|| [[Image(pixstabi238.png, align=centre, height=400)]] ||
|| Level 1b Owl data (2014 238) calibrated with different values of pixstabi (default 0.011, 0.005, 0.003, 0.0025, 0.002) ||

== Geocorrection ==

This is being incorporated into APL...