Unmanned Aircraft bistatic LIDAR for CO₂ column density determination

A novel technique for laser remote sensing of aviation-related atmospheric pollutants from Unmanned Aircraft (UA) platforms is presented. In particular, the paper focuses on Carbon Dioxide (CO₂), which is the most important aviation greenhouse gas, and whose column density data can be used for environmental monitoring purposes and to support the development and validation of aircraft engines and Systems for Green Operations (SGO). The proposed measurement techniques are based on a near-infrared bistatic Light Detection and Ranging (LIDAR) system using a modified version of the Integrated Path Differential Absorption (IPDA) technique currently adopted in state-of-the-art (monostatic) remote sensing LIDARs. Target surfaces of known spectral reflectance and Bidirectional Reflectance Distribution Function (BRDF) are irradiated with two laser beams of appropriate wavelengths. The first wavelength is selected in coincidence with one vibrational band of the CO₂ molecule, exhibiting significant absorption phenomena (absorption line). The second wavelength is selected in the same transmission window but outside the absorption line. By measuring the difference in incident energy between the two beams, and inverting the differential transmittance models, it is possible to determine the pollutant column density. Parasite effects include haze, precipitation and dust particulate, which can be modelled as well. In addition to the bistatic LIDAR technique, a monostatic control technique is also proposed in this paper for experimental and calibration purposes.