# Compact Midwave Imaging System: Results from an Airborne Demonstration
###### Abstract  
The Compact Midwave Imaging System (CMIS) is a wide field of view, multi-angle, multi-spectral pushframe imager that relies on the forward motion of the satellite to create a two-dimensional (2D) image swath. An airborne demonstration of CMS was successfully completed in January-February 2021 on the NASA Langley Research Center Gulfstream III. The primary objective of the four-flight campaign was to demonstrate the capability of this unique instrument to perform stereo observations of clouds and other particulates (e.g., smoke) in the atmosphere. It is shown that the midwave infrared (MWIR) spectral bands of CMS provide a unique 24/7 capability with high resolution for accurate stereo sensing. The instrument relies on new focal plane array (FPA) technology, which provides excellent sensitivity at much warmer detector temperatures than traditional technologies. This capability enabled a compact, low-cost design that can provide atmospheric motion vectors and cloud heights to support requirements for atmospheric winds in the 2017-2027 Earth Science Decadal Survey. Applications include day/night observations of the planetary boundary layer, severe weather, and wildfires. A comparison with current space-based earth science instruments demonstrates that the SWIR/MWIR multi-spectral capability of CMS is competitive with larger, more expensive instrumentation. Imagery obtained over a controlled burn and operating nuclear power plant demonstrated the sensitivity of the instrument to temperature variations. The system relies on a mature stereoscopic imaging technique applied to the same scene from two independent platforms to unambiguously retrieve atmospheric motion vectors (AMVs) with accurate height assignment. This capability has been successfully applied to geostationary and low-earth orbit satellites to achieve excellent accuracy. When applied to a ground-point validation case, the accuracy for the CMS aircraft observations was 20 m and 0.3 m/s for cloud heights and motion vectors, respectively. This result was confirmed by a detailed error analysis with analytical and covariance models. The results for CMS cases with underflights of Aeolus, CALIPSO, and Aqua provided a good validation of expected accuracies. The paper also showed the feasibility of accommodating CMS on CubeSats to enable multiple instruments to be flown in a leader-follower mode. stereo winds; cloud motion vectors; midwave infrared; weather satellite 202214834. [[https://doi.org/10.3390/rs14040834](https://doi.org/10.3390/rs14040834)]([https://doi.org/10.3390/rs14040834](https://doi.org/10.3390/rs14040834))  
is essential to the understanding of cloud-climate and cloud-precipitation processes, as discussed in the recommendation: \"global measurements of the spatiotemporal (four-dimensional) evolution of large-scale horizontal wind vectors are urgently needed\" [3]. The Compact Midwave Imaging System (CMIS) project represents an effort to address these objectives with a compact, low-cost sensor that enables flexible accommodation on CubeSat or as hosted payloads on small satellites. CMS employs a robust stereo technique with accurate height assignment [4] to provide wide field of view (FOV), multi-angle observations of AMVs during the day and night over cloud-covered regions of the Earth (more than 60% coverage of the globe). This capability would produce vector winds resolved in 3D along each orbit, effectively complementing clear-air wind measurements yielded by LIDAR, to achieve a synergistic architecture for a global 3D wind characterization. Until recently, only cryogenically cooled detector technologies such as InSb and HgCdTe, which require detector temperatures < 80 K were available for midwave infrared (MWIR) sensing. The detectors from CMIS are made from the newly available and continually improving high-operating temperature (HOT) detector technology in the 2-5-\(\upmu\)m spectral range based on Type II Superlattice (T2 SL) detector structures.