Effect of spectral resolution on the measurement of monoaromatic hydrocarbons by DOAS.
The excellent response characteristics and detection sensitivity with much lower operational cost and the capability to discriminate between the isomer of some monoaromatic hydrocarbons (MAHCs) make differential optical absorption spectroscopy (DOAS) a powerful tool to trace concentration variation of MAHCs. But due to the similarity in chemical structure, those MAHCs have the similar overlapped characteristic absorption structures, which make the selection of instrumental parameter critical to the accurate detection of MAHCs. Firstly, the spectral resolution used in DOAS system determines the nonlinear absorption of O2 and the mass dependence of characteristic absorption structure; thereby it determines the effect of elimination error of O2 absorption in the atmospheric spectra for the detection of MAHCs. Secondly, spectral resolution determines the differential absorption characteristics of twelve MAHCs representing major constituents in technical solvents used in the automobile industry and the interference of spectral overlapping. Thirdly, the spectral resolution determines the sensitivity, time resolution and linear range. So the spectral resolution range with the best ratio of signal to noise is used to determine the most suitable spectral resolution range, as well as the spectral resolution range that ensure the characteristic absorption structure of MAHCs and the minimization of O2 absorption interference. Finally, 0.15-0.16 nm (FWHM: full width at half maximum) is assumed to be closest to the optimum spectral resolution and it is confirmed by the results of practical measurement of MAHCs by DOAS.
Development and use of compact instruments for tropospheric investigations based on optical spectroscopy from mobile platforms
This thesis presents the development of four different remote-sensing instruments dedicated to atmospheric research and their use in field campaigns between 2008 and 2012. The instruments are based on uv-visible spectrometers and installed respectively on a scientific aircraft (Safire ATR-42), ultralight aircraft, and cars. One of the instruments is targeted to operate from an Unmanned Aerial Vehicle (UAV). The Differential Optical Absorption Spectroscopy (DOAS) technique is used to quantify the molecular absorption in the spectra of scattered sky light. These absorptions are then interpreted by modeling the radiative transfer in the atmosphere. Depending on the instrument, different information on trace gases and aerosols are retrieved: vertical distributions, tropospheric columns, or maps of surface abundances. Airborne platforms enable new measurement geometries, leading for instance to a high sensitivity in the free troposphere. On the other hand, a miniaturization effort is required, especially for the instruments on board ultralight aircraft and UAV. Reaching the limited size, weight, and power consumption is possible through the use of compact spectrometers and computers, together with custom built electronics circuits and housings. The inversion strategies are optimized for each instrument with proper error budgets and the results are compared with other datasets when available. In April 2008, the Airborne Limb Scanning DOAS (ALS-DOAS) was first used on the ATR-42 to derive NO2 and aerosol extinction profiles during the POLar study using Aircraft, Remote sensing, surface measurements and models, of Climate chemistry, Aerosols and Transport (POLARCAT). It revealed in particular that NO2, despite its typical lifetime of a few hours, may be transported from mid-latitude Europe to the Arctic. This is not visible in satellite data since the involved concentrations are under the detection limit. The Ultralight Motorized-DOAS (ULM-DOAS) was operated during the Earth Challenge expedition in April, October, and December 2009. This expedition provided an opportunity to perform measurements from an ultralight between Australia and Belgium, crossing areas were few local measurements have been reported, such as Bangladesh, Rajasthan, Saudi Arabia, and Libya. The ULM-DOAS measurements of tropospheric NO2 columns mostly fall within the confidence interval of satellite data but indicate that the NO2 columns over Riyadh may be underestimated by the Ozone Monitoring Instrument (OMI). In addition, the ULM-DOAS data provided a confirmation for the recent finding of a soil signature in the spectra recorded above desert. The Mobile-DOAS, operated from a car, was developed and first operated during the Cabauw Intercomparison Campaign of Nitrogen Dioxide measuring Instruments (CINDI) in the Netherlands during June and July 2009. Routine measurements in 2010 and 2011, mostly across Belgium yielded a large database of measurements which was compared with a chemical transport model (CHIMERE). The geometric approximation was not used to evaluate the database, since air mass factors calculations indicate that the associated uncertainties are larger than expected from previous studies. Finally, the UAV payload, the Small Whiskbroom Imager for trace gases monitoriNG (SWING) was tested from an ultralight aircraft in July and October 2012. One major objective of the UAV measurements is the mapping of NO2 columns at high spatial resolution allowing to subsample satellite measurements within the extent of a typical ground pixel. This has yet to be achieved.
Training and maintaining the performance of dogs (Canis familiaris) on an increasing number of odor discriminations in a controlled setting
Abstract The number of substances detector dogs are trained to detect varies depending on the mission of the agency they serve. No studies have been conducted concerning how training multiple odor discriminations affects detection performance and refresher training requirements. This study used a controlled field setting to examine the effects of training dogs to detect multiple substances on their subsequent detection performance and refresher training requirements. Dogs were first trained to detect a single odor. Their detection performance was tested 10 days later and refresher training was then given to bring their performance back up to a predetermined standard. Following refresher training, detection of a new substance was trained, and approximately 10 days later the detection of both trained substances was tested. This sequence of testing, refresher training, and new odor training continued every 10 days until the dogs had been trained and tested on 10 odors. The detection of previously learned odors did not decrease as the number of substances trained increased. In fact, the amount of training required to refresh detection performance and to train new odor discriminations tended to decrease as more odor discriminations were trained.