[X] My Assistant

[ugordan]

I've made some progress with the IR channel on VIMS, have managed to do partial calibration of the cubes. It's still buggy, but at least it's something. Here's a couple of rough results, all using R=5um, G=2um, B=1.26um.


In case of Saturn the green and blue channels were scaled up to match the intense thermal radiation. The cubes were flatfielded, quantum efficiency corrected and divided by solar spectrum, though I don't know if all the steps were carried out correctly. Dark current subtraction remains to be done - it's possibly the reason why the lower left Titan insets have banding in the red channel. I'm actually pretty satisfied with the way these two turned out, they are reminiscent of official VIMS surface composites, including the "blue" material.

Hopefully I'll be able to put something out to convert cubes to PNGs before long. A better solution would be a GUI but that's the tedious part for me.

[ugordan]

Preliminary, test release of QUB2PNG which dumps the entire cube to PNG files.
It expects the following files to be located in a directory named "calib" which should be in the same directory as QUB2PNG.EXE:

vis_flatfield.qub
vis_hires_flatfield.qub
vis_lowres_dark_model.tab
vis_hires_dark_model.tab
vis_perf.qub
ir_flatfield.qub
ir_hires_flatfield.qub
ir_perf.qub
solar.qub

These calibration files can be located on every VIMS PDS DVD, for example http://pdsimg.jpl.nasa.gov/data/cassini/ca...ims_0015/calib/

At the moment there are a number of limitations to the program - it doesn't correctly work on spectrally summed cubes nor ones where either VIS or IR part of the instrument is turned off. It also doesn't yet work with IR sampling mode "UNDER" a.k.a. NYQUIST mode.

When searching the PDS you want cubes where the mode is IMAGE, not LINE or OCCULTATION.
By default, running the program with just the name of the VIMS cube it will dump the 352 wavelengths into the same folder - not a very good idea, read on.
The second parameter is a scaling factor, useful for tweaking the brightness of various targets and managing underexposure/overexposure. Note that due to significant detector quantum efficiency variation over the spectral range, raw data that was saturated at certain wavelengths doesn't necessarily appear saturated (maxed-out brightness) in the output PNG data.
The third parameter is the output directory.
An example: qub2png v1356762057_2.qub 10 output\

The resulting filenames are as follows:
v1356762057_2 - [072] 0.87863.png

Where 072 is the channel number, 0-95 is VIS channel, 96-351 is IR channel. 0.87863 is the wavelength in microns. In general you do not want to mix the VIS and IR channel data in your processings, they aren't compatible currently (different scale factors, not entirely calibrated), have slightly different boresights, FOVs and distortions depending on mode. You'll notice the last few VIS channels and the first few IR channels overlap.

VIS HI-RES mode is 3x spatial resolution of NORMAL mode on both axes, IR HI-RES mode is 2x spatial resolution in the horizontal axis while the vertical axis is the same as in NORMAL so it "squashes" the images.
VIS and IR NORMAL modes are almost identical in FOV, but the boresights are slightly shifted a pixel or two in both axes.

Looking forward to any feedback.

 QUB2PNGv01.zip ( 43.96K ) Number of downloads: 690

[ugordan]

In the meantime, a few more "results":


Airglow in Titan's atmosphere extending to huge altitudes. Note the "reddish" cloud just peeking over the limb at 1 o'clock in the surface view. Another shot of the airglow, 3.316 um is mapped to red, 3.283 um to green and 3.213 um to blue:



Jupiter with Europa (seen in natural color composite) and the green splotch in IR at the left edge is Ganymede.

Finally, a scan through the 256 IR wavelengths in a Quicktime movie, just for fun:
 titan_vims.mov ( 534.98K ) Number of downloads: 672