Airborne Field Calibration System for LWIR HSI Vapor Quantification

Passive Long Wave Infrared (LWIR) Hyperspectral Imagers (HSI) are among the best sensors for quantifying dangerous gas clouds from weapons of mass destruction (WMD), counter-WMD operations, and fugitive emissions from industry and agriculture. LWIR HSI is very sensitive for detecting chemical vapors, but quantification of concentrations can be ambiguous as the observed signals have a complicated dependence on atmospheric conditions and temperatures. Much progress has been made in quantifying concentration using sophisticated retrieval algorithms, but truth data is required for calibration.   We propose an airborne calibration system that removes all ambiguity from concentration measurements using a dual-temperature blackbody source mounted on a Class1 UAS to make a simple and direct absorption measurement of the chemical in the glass cloud. A ground station compiles HSI data from the sensor under test with position and temperature information from the UAS to make transmission measurements of the atmosphere with and without the chemical cloud.  Absolute concentrations determined for the pixel viewing the UAS-mounted source can be compared directly to the retrieved concentrations in neighboring pixels to provide calibration for the sensor under test and its retrieval algorithm.