Abstract:We demonstrate compact, low power, lightweight laser-based sensors for measuring trace gas species in the atmosphere designed specifically for electronic unmanned aerial vehicle (UAV) platforms. The sensors utilize non-intrusive optical sensing techniques to measure atmospheric greenhouse gas concentrations with unprecedented vertical and horizontal resolution (~1 m) within the planetary boundary layer. The sensors are developed to measure greenhouse gas species including carbon dioxide, water vapor and methane in the atmosphere. Key innovations are the coupling of very low power vertical cavity surface emitting lasers (VCSELs) to low power drive electronics and sensitive multi-harmonic wavelength modulation spectroscopic techniques. The overall mass of each sensor is between 1-2 kg including batteries and each one consumes less than 2 W of electrical power. In the initial field testing, the sensors flew successfully onboard a T-Rex Align 700E robotic helicopter and showed a precision of 1% or less for all three trace gas species. The sensors are battery operated and capable of fully automated operation for long periods of time in diverse sensing environments. Laser-based trace gas sensors for UAVs allow for high spatial mapping of local greenhouse gas OPEN ACCESSRemote Sens. 2012, 4 1356 concentrations in the atmospheric boundary layer where land/atmosphere fluxes occur. The high-precision sensors, coupled to the ease-of-deployment and cost effectiveness of UAVs, provide unprecedented measurement capabilities that are not possible with existing satellite-based and suborbital aircraft platforms.

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In this work, eleven protic ionic liquids (PILs) containing different cations and anions were prepared and their physicochemical properties were measured. All PILs's structures were confirmed by NMR and elemental analysis (CHNS) were carried out. The physicochemical properties such as density, surface tension, viscosity and thermal degradation behaviour were measured, and the effect of cation/anion was investigated. The density and viscosity were measured within the temperature range of 293.15-373.15 K at atmospheric pressure. The thermal expansion coefficient values were calculated from the density data. Surface tensions were measured in the temperature range of 293.15 to 353.15 K and further the values were used to estimate the surface entropy and enthalpy of the ionic liquids at 303.15 K. The boiling and critical temperature were also estimated according to the Eötvos and Rebelo methods.The refractive indices were measured within the temperature range of 293.15 to 323.15 K.The thermal gravimetric analysis was performed in the temperature range of 373.15-773.15 K.

New cyano-based ionic liquids with thiocyanate anion and nitrile, ally, benzyl, and hydroxyl functionalized imidazolium cations were prepared, and some of their important thermophysical properties were measured. Properties such as density, viscosity, and refractive index were measured over various temperature ranges. From the experimental density values, the molecular volume, standard molar entropy, lattice energy, and thermal expansion coefficient of the ionic liquids were calculated. The thermal stabilities of the ionic liquids were investigated using thermogravimetric analysis. The effects of functionalized imidazolium side chains on the thermophysical properties of the ionic liquids were investigated. Density functional theory calculations were performed to study the effect of the structural variation of the imidazolium cation on properties of the ionic liquids.