# Compact Midwave Imaging System: Results from an Airborne Demonstration
## 2 Materials and Methods
### Instrument
#### 2.1.1 Focal Plane Array (FPA)  
The FPA has the capability to operate at a frame rate synchronized to the ground advance of one pixel, \(\sim\)13 Hz for a 415-km orbit. Full 640 \(\times\) 512-pixel image frames are acquired by the camera electronics, which then selects five lines for output, one for each filter stripe. The epoxy that holds the filter stripes together creates low optical transmission zones near the margin of the stripes, leaving 32 unobstructed lines available for processing by the camera electronics. The test flights demonstrated that the calibration for the CMIS detector is very stable with time. Gain coefficients measured more than a year prior yielded brightness temperatures accurate to \(\pm\)1 K.  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Parameter** & **Requirement** \\ \hline \multirow{5}{*}{Payload accommodation} & Mass & 3 kg \\  & & Optical Unit \\  & Size & 20 \(\times\) 10 \(\times\) 10 cm \\  & & Electronics: \\  & & 9 \(\times\) 9 \(\times\) 9 cm \\  & Power & 20 W peak for initial cool-down \\  & & 8 W average \\ \hline \multirow{3}{*}{Position/attitude} & Position knowledge & 4 m \\  & Pointing accuracy & \(\pm\)0.005\({}^{\circ}\) \\  & Pointing stability & 36 arc-s/1-s \\ \hline \multirow{3}{*}{Data} & Data transfer rate & 600 kbps \\  & Data storage & 10.4 GBits \\ \cline{1-1}  & Data downlink & 5.2 Cbits/day \\ \hline \hline \end{tabular}
\end{table}
Table 2: Spacecraft accommodation.  
Figure 4: Depictions of the CMIS instrument. (**a**) Cutout of the CMIS instrument highlighting the locations of the ceramic pallet, filter over the FPA and lens assembly. The rays (in blue) entering the lens depict the 50\({}^{\circ}\)\(\times\) 40\({}^{\circ}\) field of view. (**b**) Five-zone stripe filter and light shield installed over the FPA on the ceramic pallet.  
The focus of the current paper is to demonstrate multi-angle observations from the 3.75 \(\upmu\)m bands for retrieving stereo cloud heights and AMVs. The stereo imaging technique requires only relative intensity measurements from a cloudy scene, as the algorithm tracks and matches the cloud patterns to determine their disparity with respect to the ground. However, calibrated radiances from the CMS channels will enable additional retrievals of cloud and surface properties, such as temperature and fire intensity. A multispectral analysis of collocated 2.25, 3.75, and 4.05 \(\upmu\)m measurements can determine the relative contribution between the reflected solar and thermal blackbody emissions from the atmosphere. A future effort will be devoted to evaluate a solar-corrected brightness temperature at 3.75 \(\upmu\)m. During daytime collections, the radiance in the 2.25-\(\upmu\)m band will be used to separate the reflected and thermally emitted component of the incident light at 3.75 \(\upmu\)m [7]. We can also take advantage of the fact that each temperature has a unique ratio of blackbody radiance at different wavelengths. The ratio of the signals in the 4.05-\(\upmu\)m and 3.75-\(\upmu\)m bands can thus be used to further refine the temperature measurement. Temperature estimation will be the focus of a future study.