Ronald Dobosy

A sensitive fast-response probe to measure turbulence and heat flux from any airplane

The theory, configuration, and accuracy of an inexpensive probe to measure turbulence from a small airplane are presented. The probe employs a nine-hole pressure-sphere design along with inprobe high-frequency pressure, temperature, and acceleration sensors. This sensor suite is specifically designed to extend mass, momentum and energy eddy-flux measurement to the higher frequencies characteristic of marine and nocturnal boundary layers. The probe is part of a mobile flux system, independent of the conveyance, which does not require a separate Inertial Navigation System.The new nine-port pressure sphere turbulence probe allows accurate turbulent velocity measurement with proper probe installation and appropriate computation technique for dynamic pressure. A thermistor in the central pressure port provides simultaneous temperature measurement, at a location symmetrical with respect to the flow, for accurate determination of true airspeed and heat flux. The probemounted temperature sensor gives heat fluxes with variance 5% of the mean in a weakly-turbulent marine boundary layer.

A Pressure-Sphere Anemometer for Measuring Turbulence and Fluxes in Hurricanes

Abstract Turbulence and air-surface exchange are important factors throughout the life cycle of a tropical cyclone. Conventional turbulence instruments are not designed to function in the extreme environment encountered in such storms. A new instrument called the Extreme Turbulence (ET) probe has been developed specifically for measuring turbulence on a fixed tower in hurricane conditions. Although the probe is designed for surface deployment, it is based on the same pressure-sphere technology used for aircraft gust probes. The ET probe is designed around a 43-cm-diameter sphere with 30 pressure ports distributed over its surface. A major obstacle during development was finding a method to prevent water from fouling the pressure ports. Two approaches were investigated: a passive approach using gravity drainage and an active approach using an air pump to flush water from the ports. The probes were tested in both dry and wet conditions by mounting them on a vehicle side by side with more conventional instru...

Calibration and Quality Assurance of an Airborne Turbulence Probe in an Aeronautical Wind Tunnel

AbstractThe Best Aircraft Turbulence (BAT) probe is used by multiple research groups worldwide. To promote an accurate interpretation of the data obtained from the probe’s unusual nine-port design, a detailed understanding of the BAT probe’s function along with a characterization and minimization of its systematic anomalies is necessary. This paper describes recent tests to enhance understanding of the probe’s behavior. The tests completed in the Wright Brothers Wind Tunnel at the Massachusetts Institute of Technology (MIT) built on earlier findings at Purdue University. Overall the true-vertical wind relative to the probe was found to have a systematic anomaly of about 10%–15%, an acceptable value borne out by considerable field experience and further reducible by modeling and removing. However, significant departure from theoretical behavior was found, making detailed generalization to other BAT probes still inadvisable. Based on these discoveries, recommendations are made for further experiments to exp...

Estimating Random Uncertainty in Airborne Flux Measurements over Alaskan Tundra: Update on the Flux Fragment Method

AbstractAirborne turbulence measurement gives a spatial distribution of air–surface fluxes that networks of fixed surface sites typically cannot capture. Much work has improved the accuracy of such measurements and the estimation of the uncertainty peculiar to streams of turbulence data measured from the air. A particularly significant challenge and opportunity is to distinguish fluxes from different surface types, especially those occurring in patches smaller than the necessary averaging length. The flux fragment method (FFM), a conditional-sampling variant of eddy covariance in the space–time domain, was presented in 2008. It was shown capable of segregating the mean flux density (CO2, H2O, sensible heat) in maize from that in soybeans over the patchwork farmlands of Illinois. This was, however, an ideal surface for the method, and the random-error estimate used a relatively rudimentary bootstrap resampling. The present paper describes an upgraded random-error estimate that accounts for the serial corre...

Accuracy and Utility of Aircraft Flux Measurements

Strategies to assess long-term atmosphere-ecosystem exchange of CO2 and H2O must deal not only with time trends but also with spatial variability. Flux-towers, always limited in number, efficiently measure time trends but the representativeness of a tower site — or the significance of spatial Variation between sites — is best addressed through flux measurements from small aircraft (see Fig. B.10). Recent technological advances in aircraft and instruments allow airborne flux measurements to be made with enhanced precision, greater ease and lower cost. Challenges remain, however, in all aspects of the activity: instrumentation, data processing, and data interpretation.

Permafrost Nitrous Oxide Emissions Observed on a Landscape Scale Using Airborne Eddy Covariance Method

The microbial by-product nitrous oxide (N2O), a potent greenhouse gas and ozone depleting substance, has conventionally been assumed to have minimal emissions in permafrost regions. This assumption has been questioned by recent in situ studies demonstrating that, in fact, some geologic features in permafrost may have elevated emissions comparable to those of tropical soils. These recent studies, however, along with every known in situ study focused on permafrost N2O fluxes, have used chambers to examine small areas (< 50 m). Using the airborne eddy covariance technique, we made in situ N2O 15 flux measurements from a low-flying aircraft spanning a much larger area: around 310 km. We observed a daily mean averaged over our flight campaign of 3.8 (2.2-4.7) mg N2O m d with 90% confidence interval in parentheses. If these measurements are representative of the whole month, then the permafrost areas we observed emitted a total of around 0.040.09 g m for August, comparable to what is typically assumed to be the maximum yearly emissions for these regions.