# Compact Midwave Imaging System: Results from an Airborne Demonstration
## 3 Results
### Aeolus Under-Flight  
The Hold J flight was designed to fly along the track of Aeolus on 8 February 2021 at night. The Atmospheric Dynamics Mission (ADM-Aeolus) Doppler Wind Lidar (DWL) measures the atmospheric wind profile in a horizontal line-of-sight (HLOS) direction 35\({}^{\circ}\) from nadir and 90\({}^{\circ}\) from the spacecraft velocity. Therefore, the Aeolus measurements are single-component wind profiles along the HLOS. Because of the 35\({}^{\circ}\) slant view, each height level of the HLOS wind profile corresponds to a different geographic location, with the  
Figure 16: (**a**) Joint distribution of U-V winds and (**b**) speed-height from the MODIS-GOES stereo run corroborate the CMIS winds. Figure 15: CMIS winds over Hold D1 where the mean wind height is constrained to approximate the CALIOP layer-1 top are shown with (**a**) winds resolved AT-XT and (**b**) U-V.  
higher levels closer to the satellite ground track. This height-dependent geolocation of HLOS winds is evident in Figures 17 and 18. The Hold J flight is also within the coverage of both GOES-16 and -17. We use the stereo winds from GOES-16 and -17 [8] to set the _a priori_ value of the AT wind for the CMIS retrievals and compare against Aeolus. The first pass (J1) was the most simultaneous to the Aeolus Mie wind retrievals. CMIS was 5 min ahead of Aeolus over Hold J, which was completely cloud covered. Sites for the three sets of retrievals are shown in Figure 17. The sampling scales are quite different, with CMIS densely sampling over a very small patch due to the low altitude of the aircraft (compared to satellites). The GOES stereo winds used a triplet of CONUS scenes centered on 23:36Z from GOES-16 and a doublet of contemporaneous Full Disk scenes from GOES-17. The GOES stereo winds as shown in Figure 17 reveal a cloud layer at 4813 m median height and with median winds resolved along and across the direction of the CMIS flight of 2.76 m/s (AT) and \(-\)35.07 m/s (XT). We use 2.76 m/s for the prior value of the AT wind in the CMIS retrieval code and solve for XT wind and CTH at each CMIS retrieval site. Figure 17: Retrieval sites for Aeolus, GOES stereo, and CMIS wind retrievals are indicated, showing a vast difference in sampling densities between the aircraft and satellite observations. GOES stereo wind statistics are computed over a larger domain (1.5\({}^{\circ}\) latitude \(\times\) 1\({}^{\circ}\) longitude) containing 32 GOES stereo retrievals, compared to several thousand CMIS retrievals. Figure 18: Comparison between Aeolus, G16-G17 stereo, and CMIS stereo for (**a**) XT winds and (**b**) stereo heights over Michigan on 8 February 2021. Figure 18 compares AMVs and CTHs from GOES and CMIS against Aeolus Mie winds. There is broad agreement for all three estimates, although Aeolus wind retrievals are biased about 5 ms\({}^{-1}\) lower than those retrieved using GOES and CMIS. The XT winds for CMIS match fairly well with G16-G17 stereo winds. We see a local minimum (in magnitude) for both GOES and CMIS near 42.6\({}^{\circ}\)N. A similar local minimum appears for Aeolus near 42.7\({}^{\circ}\)N. The height retrievals for CMIS (Figure 18b) match the overall shape of those for G16-G17 stereo. We see decreasing CTH between 42.3\({}^{\circ}\) and 42.5\({}^{\circ}\) for both GOES and CMIS, although the decrease is steeper for CMIS. This may be due to the very fine GSD for the CMIS aircraft payload. CMIS demonstrated good sensitivity to small-scale variability. The retrieval histograms are shown in Figure 19. The XT wind distribution is quite narrow, and its median value of \(-\)35.83 m/s is a good match with the median GOES stereo wind of \(-\)35.07 m/s (XT). The distribution of CMIS heights is broader, but the GOES stereo-wind median is in the range toward the upper end. There are six Aeolus Mie winds in the relevant atmospheric layer. Because the flight line was nearly parallel to the Aeolus track, Aeolus HLOS wind components are opposite in direction to the XT winds from CMIS.