A52C-01 INVITED
Miniaturized aerosol, cloud and radiometric payloads for small unmanned aerial vehicles
Miniaturized aerosol, cloud and radiometric payloads were developed to advance atmospheric observations using small autonomous unmanned aerial vehicles (AUAVs). The observing system consisted of three vertically- stacked AUAVs to allow simultaneous sampling of the earth's atmosphere – offering new insights to radiation budgets and aerosol-cloud interactions. To accomplish this campaign, aerosol, cloud, radiometric instruments, and an integrated data acquisition system have been miniaturized with a total payload weight less than 4 kg and power less than 30 W. Due to size and weight limitations of the lightweight AUAV platform, the payloads are mission-specific and outfitted to perform a defined set of measurements depending on the scientific goals. These measurements include aerosol concentration, aerosol size distribution, aerosol absorption, cloud drop concentration and size distribution, solar radiation fluxes (visible and broadband), temperature, pressure, and relative humidity. The data integrity has been validated using standard calibration routines in conjunction with ground-based and laboratory instruments, as well as inter-aircraft comparisons. The instrument suite includes commercially-available instruments that have been repackaged or redesigned to minimize weight and volume and improve their performance. Several instruments have been completely redesigned including an aerosol inlet, absorption photometer based on an aethelometer and cloud condensation nucleus (CCN) counter. Re-engineering of the absorption photometer's optics and electronics improved its performance at three wavelengths. The CCN instrument has been reduced to less than 2kg (compared to 28 kg) without compromising performance utilizing theory and model simulations to optimize design and define operating limits. A shrouded aerosol inlet was specifically designed for the AUAVs to minimize sample biases in aerosol number and size distributions. The radiometric sensors perform well during straight and level portions of the flight as the autopilot maintains a level platform (pitch and roll) to within a degree. An integrated data acquisition system connects to the instruments via a common interface that supplies power and distributes the data signals to the onboard computer. Several integrated circuits are embedded into the interface to increase its functionality as the central data system, including a GPS for time stamping and spatial coordination. The importance of miniaturization, in light of current research needs, will also be discussed.
A52C-02
New Miniaturized Cloud Microphysical Instrumentation for Small UAV's
A new micro-sensor and data acquisition system that measures the cloud particle size distribution from 1 to 50 microns and records high-resolution (2.3 micron pixel) digital images of cloud particles has been developed. The new sensor, called a micro-CPI (cloud particle imager) weighs less than 2 kg and consumes about 10 W of electrical power. A single-board Linux processor controls a large field programmable gate array (FPGA) and stores data on a flash disk. A forward scattering optical system that sizes particles from 1 to 50 microns is also part of the particle detection system used to pulse the high-power imaging laser diode. Test flights on an Aerosonde UAV are scheduled for the spring of 2008. A new miniaturized version of a dual-wavelength in situ lidar (ISL) is also being developed for application on small UAV's. The micro-ISL pulses two high-power laser diodes, one at a wavelength that is non-absorbing and a second at a wavelength that is slightly absorbing in water clouds. The time of flight of multiply-scattered photons is measured by off-axis photo detectors. The micro-ISL measures the volumetric extinction, liquid water content and effective drop radius of water clouds within several tens of meters around the UAV. The micro-ISL is based on a principle that has been successfully documented using a large, high-power Nd:YAG laser on a Learjet. http://www.specinc.com
A52C-03
Development of Miniaturized Difference Frequency Generation, Fiber Optic, and Quantum Cascade Laser Systems in Conjunction With Integrated Electronics for Global Studies of Atmospheric Tracers Using UAVs.
In order to harness the power of UAVs (Unmanned Aerial Vehicles) for in situ atmospheric monitoring of tracers such as CO2, N2O, CH4, and H2O, we have developed small, lightweight, single mode laser systems with co- developed integrated electronics. The laser sources are of various types including newly developed cavity- enhanced difference frequency generation (CE DFG), distributed feedback quantum cascade lasers (DFB QCLs), and new types of commercially available DFB diode lasers. All are continuous wave (cw) and thermo-electrically cooled, ensuring a high instrument duty cycle in a compact, low maintenance package. The light sources are collimated with miniature aspherical lenses and coupled into a home-built astigmatic Herriott cell for detection of the various targets using direct absorption. In parallel with the optical components, we have developed integrated electrical systems for laser control, data processing, and acquisition. A prototype instrument suite is described that illustrates the importance of parallel development of optical and electrical components in achieving an apparatus that is compact, fully automated, and highly capable scientifically. Although the emphasis here is on atmospheric tracers, this technology could be applied to spectroscopic measurements of other atmospheric species such as isotopes, free radicals, and reactive intermediates.
A52C-04
Fast in situ gas chromatographic analysis of important atmospheric trace gases for both manned and unmanned aircraft.
Atmospheric trace gases play an important role in climate change, stratospheric ozone depletion, and air quality. Observations of the vertical profiles of these gases over a wide range of latitudes are extremely useful for testing climate models, estimating atmospheric lifetimes, and making estimates of emissions. Measuring the vertical and horizontal distributions from fast moving airborne platforms requires high sampling frequency. Traditional measurement technologies have included gas chromatography and mass spectroscopy. These methods can require massive size, "off the shelf" laboratory equipment along with long times (10-60 minutes) to perform the separation of gases on chromatographic adsorption columns and/or to concentrate part-per-trillion levels of these gases on adsorption traps. We have used a combination of heart-cutting chromatography, fold-back chromatography, and dual channel trapping to improve our sampling frequency. Our team also has been involved in reducing the size of the airborne instrumentation. We developed a two-channel gas chromatograph (GC) that flew during the NOAA Unmanned Aircraft Systems (UAS) Demo in 2005 and the NASA Fire Mission in 2006 on the NASA UAS Altair (General Atomics Aeronautical Systems Predator B type). It measured carbon monoxide, methane, and hydrogen on one GC channel and nitrous oxide and sulfur hexafluoride on the other channel. Customized versions of commercially available instruments for ambient temperature, relative humidity, ozone and water vapor also were incorporated into the UAS GC for the Fire mission. The ultimate goal is to further reduce the size of these instruments to suit smaller size UAS. The past successes and possibilities for the future will be addressed in this talk. http://uas.noaa.gov
A52C-05
Development of a Fast Time-Tagged Aerosol Collector (Fast TRAC)
The Time-Resolved Aerosol Collector (TRAC) was developed for sampling atmospheric aerosols in 2000, and is small and very convenient for collecting as many as 500 field samples with times per sample from about 1 minute to hours. It has been successfully used to collect field samples for subsequent laboratory characterization such as hygroscopicity, morphology, and composition, including single particle methods. We will present the development of a "Fast Time-Resolved Aerosol Collector", or Fast-TRAC, that is particularly well suited for airplane studies of cloud microstructures. The Fast TRAC tags each particle with its individual collection time, within milliseconds, for tens of thousands of particles or more. In addition, near real-time particle size and number information will be provided. The feasibility of the Fast TRAC will be demonstrated and evidence of its performance will be provided.
A52C-06
Single Scatter Albedo Monitor for Airborne Particulates
We describe an instrument that simultaneously incorporates measurements of both airborne particle extinction and scattering coefficients and thus single scatter albedo. Based on a cavity enhanced detection technique, cavity attenuated phase shift spectroscopy, the sensor comprises a light emitting diode (LED), an enclosed measurement cell (25 cm in length) incorporating a resonant optical cavity of near-confocal design (which provides a pathlength of ~ 1km) and a vacuum photodiode to detect extinction and a photomultiplier tube to detect scattering. An extinction coefficient noise floor of approximately 0.3 Mm-1 with 60 seconds integration time was established measuring Rayleigh scattering of nitrogen. In order to minimize the possibility of measurement bias as a function of particle size, the optical cavity is enclosed in an integrating volume, ensuring reasonably efficient collection of scattered light from all angles. To verify this, simultaneous measurements of extinction and scattering using polystyrene latex (PSL) particles of diameters ranging from 0.1 to 8 μm were performed. The results indicated that the monitor response to scattering as a function of particle size is flat from 0.1 to 2 μm and falls off to 75% of full response at 8 μm. Extensive modeling indicates that this performance is likely limited by the relatively crude construction of the integrating volume and can readily be improved.
A52C-07
Applications of Spectroscopy to Studying Atmospheric Chemistry
Spectroscopic techniques are finding increased applications in studies of atmospheric chemistry because of inherent advantages in the techniques and technological improvements in optical and computer components. There are many advantages of using spectroscopy for study of chemistry. Spectroscopy is absolutely calibrated and thus requires only validation, reducing the need for consumable standards and reducing size and weight. Generally, spectroscopic instruments can be built from inexpensive solid-state components with few or no moving parts, improving long-term reliability. Huge advances in optoelectronic components, such as availability of diode lasers, cheap imaging detectors, light emitting diodes, have widened the breadth of applications and reduced costs. In this presentation, we discuss two recent applications of atmospheric spectroscopy that exploit these advantages. In the first application, our group has used off-axis Cavity Ring-Down Spectroscopy (oaCRDS) to make a small and inexpensive detector for nitrate radicals (NO3) and dinitrogen pentoxide (N2O5), which are atmospherically important nitrogen oxides the dominate reactivity during nighttime. This instrument fits in a small waterproof case that is (98cm x 40cm x 15cm), weighs less than 25kg, and uses an inexpensive diode laser. The instrument was recently incompared to a number of other techniques for measuring these gases and showed excellent performance. In a second application, we have used multiple-axis Differential Optical Absorption Spectroscopy (MAXDOAS) to measure halogen oxides and other UV-absorbing gases at remote locations. This instrument will be a part of an autonomous chemical-measuring buoy that will be deployed on the Arctic Ice. The instrument will make measurements and telemeter the data back via an iridium satellite modem. Our MAXDOAS instrument is very small, inexpensive, and uses only 2 watts of power, allowing long life when operating on batteries. Many features were built into the instrument to ensure long-term reliability without physical access the the instrument. http://www.uaf.edu/chem/simpson