A quick look at the other wavelengths shows that the long wavelengths (18a, Soifer) are totally not worth doing unless we cut down on the light or really speed up the frame time (partial array readout).
The BP14100 wasn't that good, either. The N07904 with slit 1 and 0.5mm FCLS was brilliant, but no interesting atmospheric lines.
The rotation and shifting used at 6.6 worked well at 7.9, which is probably because the grating angle is the same for both. The continuum in the 6.6 is spatially offset from in the 7.9. The FCLS parameters are: 6.6) X,Z = 43,26 and 29,14.5 with 2mm aperture, slit 6. 7.9) X,Z = 43,26 and 29,14.75 with 0.5mm aperture and slit 1. The offset could be due to the different aperture and EXES slit. The separation between the continua is different between the two filters -- and in the wrong sense from what the FCLS coordinates suggest -- but I'm doubtful the data are good enough to make conclusions.
There was very strange fringing in the raw files (upper left, below). Saw enhanced DN in relatively thin bands that look like wavey lines across the detector. They are not evenly spaced in frequency, which basically means they can not be caused by an optic before dispersion (filter, window). Best theory is that they are from the detector. See same basic pattern at 6.6 and 7.9, although fewer fringes at longer wavelength.
I reduced the data by taking difference of the "nod" pair with greatest extent along the slit (upper right). I then rotated the frame using IDL new_frame = ROT(old_frame,12.0) where the rotation angle was not what made the slit vertical in imaging mode, but 1.4 degrees more than that. This probably depends on grating angle. With atmospheric absorption lines in the 6.6 difference, I judged the rotation by eye. At this point the continua still ran diagonally across the detector and the spatial dimension was correct. I then shifted the continua at each spatial position so the spectra ran along rows. I then took a box around where all the data were good (see lower left), summed the spectral information to create a spatial weighting, and made a weighted extraction of the spectrum (lower right).
The spectrum, I later noticed, has some variation with integration time. Not too surprising since I didn't correct for non-linearity. We will need to look at how to do that best before continuum. The displayed data comes from analyzing the second samples in each ramp.
The final extracted spectrum was compared with the HITRAN emission strengths for H2O at room temperature using the hitran_exes IDL procedure that lets you specify a wavenumber, a grating angle, a mode, and a grating angle (many other things possible) and get a predicted output spectrum. I ended up using 51.885 degrees as the echelle angle - Curtis later told me there is an offset between hi-med and med mode spectra of about 100 pixels - and overplotted the results in the lower right. It's not perfect, but it is pretty darn close. I don't know what causes the additional absorption near 6.51 microns. I have since found that CH4 has a couple lines there, but don't know that we have enough CH4 to cause that. Also, it looks more like a tight band to me at 6.51 microns, so it could be a hot band that I don't know about or just haven't stumbled across.
Below I show the impact of integrating longer. The data had four samples in each ramp. The black line is for the first sample, green - second, red - third, and blue - fourth. There could be an impact due to non-linearity, but there could also be an impact in the absorbers changed. I have trouble believing the air in the TAAS changed substantially, but the line near 1537 cm-1 really looks like a line and not a non-linearity.
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