collection for Figure 4 shows the corresponding spectral image of the no- 
hen back to sunglint case, of Figure 3. The TIMS imagery vertical axis is 
Field spatial in content, while the horizontal axis is spectral in 
content. This spectral image is identical with the zero level of 
the TIMS instrument used in calibration. 
  
Raw spectral image AV401 shown for glint-vith-no-ceil, spectral 
lines & spatial variation easily discernable 
Figure 6. Spectral image used in radiometric calibration 
spectral dimension is horizontal, while the spatial 
dimension of the split is along the vertical axis. 
(vertical axis) is 30.48 m from the airship’s 457.2 m height. The 
spectral range of the TIMS sensor (horizontal axis) in Figure 6 
  
Raw spectral image AV302 shown for water-ro-qiint, no light is is 2.3200 to 2.3421 um from left to right, with a spectral 
reflected from surface & no spectra are seen resolution of 0.08 nm. The curvature of the spectral lines is a 
; feature of the off axis optical design, which is accounted for in 
Figure 4. TIMS spectral image (spatial on vertical axis, the radiometric calibration. To simulate the presence of a 
spectral on horizontal axis) over no sun-glint. known amount of methane over the water a cell with methane 
: à : was placed in front of the aperture of the TIMS instrument. 
Figure 5 shows the camera image for the mirror rotated to look Measurements were taken multiple times with and without the 
into the ~45° forward sunglint, limited by the airship floor cell of methane in place. 
viewport size. The TIMS clear field of view extends to the 
green line due to a 10 cm offset. The entire length of the slitis ^ For radiometric calibration there were initial concerns of 
fully illuminated by the sunglint region. variable sunglint spectral reflectance. However the behavior of 
reflectance over sunglint in the ShortWave Infrared (SWIR) was 
constant, so this was not an issue, allowing spectra in the image 
to be normalized by reflectance ratios. For this analysis two of 
the 512 spectra available have been analyzed, with one spectra 
used in the retrieval; this processing may be automated to use 
more of the spectra to improve the accuracy, and by dwelling 
upon a location accuracy may be further improved. 
  
1 during this 
by a grating 
spectrometer 
jeving high 
2.4 Lockheed Martin Methane Retrieval Processing 
ip over the 
the image 
ng reflection 
The LM Methane Retrieval Algorithm uses the UMBC 
kCARTA (Desouza-Machado et al, 1997). Along with the 
TIMS calibrated radiometric input the retrieval algorithm uses 
n beam and for optical depths computed using kCARTA code. This KCARTA 
mately as shown package uses a table of precompressed optical depths, generated 
using the HITRAN 2008 lineshape parameters, to rapidly 
compute the actual optical depths for a realistic Earth 
atmosphere, at a high spectral resolution. 
  
video frame for fini 
spectral image AV401 © 
    
: appr 
Figure 5. Spectral image region outline over the camera image 
over sunglint 
The corresponding spectral image to the previous image (Figure The LM Methane Retrieval Algorithm as a first guess uses the 
3) is shown in Figure 6. There are 512 pixels along the spatial ^ (o.located National Oceanic Atmospheric Association (NOAA) 
extent of the slit (vertical in this image). A 1024 pixel spectrum National Centers for Environmental Prediction Global Forecast 
is laid out horizontal in this image for each of the 512 pixels System (NCEP GFS) forecast profiles for temperature, pressure, 
along the slit. These are atmospheric absorption spectra of CHy, humidity and ozone fields, as well as the US Standard gas 
H;O and CO in the sunlight that has passed through the profiles for the rest of the atmospheric gases. The retrieval first 
atmosphere and reflected nearly specular (the sunglint) off the eg radiances with no gas cell present. The window channels 
  
s 
AV302 surface water back up to the TIM. The slits spatial range are used to estimate the surface reflectivity, followed by using 
; the water lines to adjust the column water amount, and the CH, 
"gon of no lines to adjust the CH; column. Having determined the 
OTS Imaging atmospheric parameters, the retrieval then uses the TIMS 
radiance spectra with the gas cell present, to first determine a 
new surface reflectance, followed by a multiplier for the amount 
nd the view of gas present in the cell. The measured and computed radiances 
is no light are converted to effective brightness temperatures during the 
retrieval process. Currently the water and CH4 multipliers are 
determined using a simple scaling adjustment. Incorporation of 
an Optimal Estimation retrieval scheme in the future could