Showing papers on "Scintillometer published in 2012"

Monin–Obukhov Similarity Functions for the Structure Parameters of Temperature and Humidity

Abstract: Monin–Obukhov similarity functions for the structure parameters of temperature and humidity are needed to derive surface heat and water vapour fluxes from scintillometer measurements and it is often assumed that the two functions are identical in the atmospheric surface layer. Nevertheless, this assumption has not yet been verified experimentally. This study investigates the dissimilarity between the turbulent transport of sensible heat and water vapour, with a specific focus on the difference between the Monin–Obukhov similarity functions for the structure parameters. Using two datasets collected over homogeneous surfaces where the surface sources of sensible heat and water vapour are well correlated, we observe that under stable and very unstable conditions, the two functions are similar. This similarity however breaks down under weakly unstable conditions; in that regime, the absolute values of the correlations between temperature and humidity are also observed to be low, most likely due to large-scale eddies that transport unsteadiness, advection or entrainment effects from the outer layer. We analyze and demonstrate how this reduction in the correlation leads to dissimilarity between the turbulent transport of these two scalars and the corresponding Monin–Obukhov similarity functions for their structure parameters. A model to derive sensible and latent heat fluxes from structure parameters without measuring the friction velocity is tested and found to work very well under moderately to strongly unstable conditions (−z/L > 0.5). Finally, we discuss the modelling of the cross-structure parameter over wet surfaces, which is crucial for correcting water vapour effects on optical scintillometer measurements and also for obtaining surface sensible and latent heat fluxes from the two-wavelength scintillometry.

Eddy-covariance flux measurements with a weight-shift microlight aircraft

Abstract: . The objective of this study is to assess the feasibility and quality of eddy-covariance flux measurements from a weight-shift microlight aircraft (WSMA). Firstly, we investigate the precision of the wind measurement (σu,v ≤ 0.09 m s−1, σw = 0.04 m s−1), the lynchpin of flux calculations from aircraft. From here, the smallest resolvable changes in friction velocity (0.02 m s−1), and sensible- (5 W m−2) and latent (3 W m−2) heat flux are estimated. Secondly, a seven-day flight campaign was performed near Lindenberg (Germany). Here we compare measurements of wind, temperature, humidity and respective fluxes between a tall tower and the WSMA. The maximum likelihood functional relationship (MLFR) between tower and WSMA measurements considers the random error in the data, and shows very good agreement of the scalar averages. The MLFRs for standard deviations (SDs, 2–34%) and fluxes (17–21%) indicate higher estimates of the airborne measurements compared to the tower. Considering the 99.5% confidence intervals, the observed differences are not significant, with exception of the temperature SD. The comparison with a large-aperture scintillometer reveals lower sensible heat flux estimates at both tower (−40 to −25%) and WSMA (−25–0%). We relate the observed differences to (i) inconsistencies in the temperature and wind measurement at the tower and (ii) the measurement platforms' differing abilities to capture contributions from non-propagating eddies. These findings encourage the use of WSMA as a low cost and highly versatile flux measurement platform.

Towards a Validation of Scintillometer Measurements: The LITFASS-2009 Experiment

Abstract: Scintillometry has been increasingly used over the last decade for the experimental determination of area-averaged turbulent fluxes at a horizontal scale of a few kilometres. Nevertheless, a number of assumptions in the scintillometer data processing and interpretation still call for a thorough evaluation, in particular over heterogeneous terrain. Moreover, a validation of the path-averaged structure parameters derived from scintillometer data (and forming the basis for the flux calculations) by independent measurements is still missing. To achieve this, the LITFASS-2009 field campaign has been performed around the Meteorological Observatory Lindenberg – Richard-Asmann-Observatory of the German Meteorological Service (DWD) in July 2009. The experiment combined tower-based in-situ turbulence measurements, field-scale laser scintillometers, long-range optical (large-aperture) and microwave scintillometers, and airborne turbulence measurements using an automatically operating unmanned aircraft. The paper describes the project design and strategy, and discusses first results. Daytime near-surface values of the temperature structure parameter, $${C_{T}^{2}}$$ , over different types of farmland differ by more than one order of magnitude in their dependence on the type and status of the vegetation. Considerable spatial variability in $${C_{T}^{2}}$$ was also found along the flight legs at heights between 50 and 100 m. However, it appeared difficult to separate the effects of heterogeneity from the temporal variability of the turbulence fields. Aircraft measurements and scintillometer data agreed in magnitude with respect to the temporal variation of the path-averaged $${C_{T}^{2}}$$ values during the diurnal cycle. The decrease of $${C_{T}^{2}}$$ with height found from the scintillometer measurements close to the surface and at 43 m under daytime convective conditions corresponds to free-convection scaling, whereas the aircraft measurements at 54 and 83 m suggest a different behaviour.

Consistency between hydrological model, large aperture scintillometer and remote sensing based evapotranspiration estimates for a heterogeneous catchment

Abstract: . The catchment averaged actual evapotranspiration rate is a hydrologic model variable that is difficult to quantify. Evapotranspiration rates – up till present – cannot be continuously observed at the catchment scale. The objective of this paper is to estimate the evapotranspiration rates (or its energy equivalent, the latent heat fluxes LE) for a heterogeneous catchment of 102.3 km2 in Belgium using three fundamentally different algorithms. One possible manner to observe this variable could be the continuous measurement of sensible heat fluxes (H) across large distances (in the order of kilometers) using a large aperture scintillometer (LAS), and converting these observations into evapotranspiration rates. Latent heat fluxes are obtained through the energy balance equation using a series of sensible heat fluxes measured with a LAS over a distance of 9.5 km in the catchment, and point measurements of net radiation (Rn) and ground heat flux (G) upscaled to catchment average through the use of TOPLATS, a physically based land surface model. The resulting LE-values are then compared to results from the remote sensing based surface energy balance algorithm ETLook and the land surface model. Firstly, the performance of ETLook for the energy balance terms has been assessed at the point scale and at the catchment scale. Secondly, consistency between daily evapotranspiration rates from ETLook, TOPLATS and LAS is shown.

Intensity fluctuations of flat-topped beam in non-Kolmogorov weak turbulence

Abstract: Results obtained on the intensity fluctuations of flat-topped Gaussian beams in weakly turbulent non-Kolmogorov horizontal atmospheric optics links are represented. Effects on the scintillation index of the power law α that describes the non-Kolmogorov spectrum are examined. Our results correctly reduce to the existing intensity fluctuations of flat-topped beams in Kolmogorov turbulence. Variation of the scintillation index against non-Kolmogorov power law α exhibits a peak at the worst power law αw, which happens to be smaller than the Kolmogorov power law of 11/3. If the power law is smaller (larger) than αw, increase in α will increase (decrease) the intensity fluctuations. Evaluation of the scintillation index at the worst power law results in smaller fluctuations for a Gaussian beam at short propagation distances; however, at long propagation distances flatter beams happen to possess smaller fluctuations. The scintillation change versus the source size follows a similar trend regardless whether the flat-topped beam propagates in a Kolmogorov or non-Kolmogorov medium.

Inner- and outer-scale effects on the scintillation index of an optical wave propagating through moderate-to-strong non-Kolmogorov turbulence

Abstract: By use of the generalized von Karman spectrum model that features both inner scale and outer scale parameters for non-Kolmogorov turbulence and the extended Rytov method that incorporates a modified amplitude spatial-frequency filter function under strong-fluctuation conditions, theoretical expressions are developed for the scintillation index of a horizontally propagating plane wave and spherical wave that are valid under moderate-to-strong irradiance fluctuations. Numerical results show that the obtained expressions also compare well with previous results in weak-fluctuation regimes. Based on these general models, the impacts of finite inner and outer scales on the scintillation index of an optical wave are examined under various non-Kolmogorov fluctuation conditions.

Comparison of Large Aperture Scintillometer and Satellite-based Energy Balance Models in Sensible Heat Flux and Crop Evapotranspiration Determination

Abstract: The estimation of crop water use or evapotranspiration (ET) is an important aspect of water management especially in arid and semi-arid regions. Various methods have been used in the estimation of ET including remote sensing (RS) based models, and these have an added advantage of estimating ET over a large area (e.g., regionally). This study looked at two models of estimating ET; Mapping evapotranspiration at high Resolution with Internalized Calibration (METRIC) and the Surface Energy Balance Algorithm for Land (SEBAL). Satellite images from Landsat 5 for 2010 for two alfalfa fields in Rocky Ford, Colorado, were processed and analyzed to obtain sensible heat flux (H). Both RS models employ the energy balance (EB) method and estimate net radiation (Rn) and soil heat flux (G) similarly. However they differ in the approach to calculate H. Since ET is determined as a residual in the EB equation, the accurate estimation of H becomes critical. The objective of the study was to assess the RS estimates of H with H measured using a Large Aperture Scintillometer (LAS). Further comparison was done for ET. Results indicated that METRIC more accurately estimated H and ET than SEBAL. For hourly ET, SEBAL showed a relative error up to 38% while METRIC resulted in a relative error up to 11%. Both models reported larger errors for dry fields depicting smaller fractional vegetation cover values. The results of this study indicate that there is an opportunity to improve the RS methods discussed by incorporating surface heterogeneity and perhaps the correction of radiometric surface temperature for atmospheric effects.

Continuous Time Series of Catchment-Averaged Sensible Heat Flux from a Large Aperture Scintillometer: Efficient Estimation of Stability Conditions and Importance of Fluxes under Stable Conditions

Abstract: A large aperture scintillometer (LAS) observes the intensity of the atmospheric turbulence across large distances, which is related to the path-averaged sensible heat flux H. In this paper, two problems in the derivation of continuous series of H from LAS data are investigated and the importance of nighttime H fluxes is assessed. First, as an LAS is unable to determine the sign of H, the transition from unstable to stable conditions is evaluated in order to make continuous H series. Therefore, different algorithms to judge the atmospheric stability for an LAS installed over a distance of 9.5 km have been tested. The diurnal cycle of the refractive index structure parameter, , results in the best suitable, operational algorithm. A second issue is the humidity correction for LAS data, which is performed by using the Bowen ratio (β). As β is taken from ground-based measurements with data gaps, the number of resulting H values is reduced. Not including this humidity correction results in a marginal er...

Verification of land surface evapotranspiration estimation from remote sensing spatial contextual information

Abstract: Estimation of evapotranspiration (ET) is of great significance in modeling the water and energy interactions between land and atmosphere. Negative correlation of surface temperature (Ts) versus vegetation index (VI) from remote sensing data provides diagnosis on the spatial pattern of surface soil moisture and ET. This study further examined the applicability of TsVI triangle method with a newly developed edges determination technique in estimating regional evaporative fraction (EF) and ET at MODIS pixel scale through comparison with large aperture scintillometer (LAS) and high-level eddy covariance measurements collected at Changwu agro-ecological experiment station from late June to late October, 2009. An algorithm with merely land and atmosphere products from MODIS onboard Terra satellite was used to estimate the surface net radiation (Rn) and soil heat flux. In most cases, the estimated instantaneous Rn was in good agreement with surface measurement with slight overestimation by 12 W/m2. Validation results from LAS measurement showed that the root mean square error is 0.097 for instantaneous EF, 48 W/m2 for instantaneous sensible heat flux, and 30 W/m2 for daily latent heat flux. This paper successfully presents a miniature of the overall capability of TsVI triangle in estimating regional EF and ET from limited number of data. For a thorough interpretation, further comprehensive investigation needs to be done with more integration of remote sensing data and in-situ surface measurements. Copyright (c) 2011 John Wiley & Sons, Ltd.

Creating a C n 2 profile as a function of altitude using scintillation measurements along a slant path

Abstract: Using a three-aperture scintillometer system (TASS) to measure irradiance fluctuations along a slant path, it is possible to create a C n 2 profile model as a function of altitude up to (and possibly beyond) the maximum altitude of a laser beam along the propagation slant path. This technique was demonstrated recently in June 2011 on a beacon beam transmitted between Hollister Airport in California and Fremont Peak at a slant range of 17 km. Although the primary experiment was to test a hybrid optical RF communication system (FOENEX), the beacon signal at the transmitter was intercepted by the TASS from which weighted path-average values of C n 2 , inner scale l 0 , and outer scale L 0 were determined. Path-average values were then entered into an algorithm that determines the parameters of the HAP C n 2 profile model (a variation of the HV profile model). In this paper we report on these recent measurements and how this method of constructing the HAP model can be used over other propagation paths.

Using Scintillometry to Estimate Sensible Heat Fluxes over Water: First Insights

Abstract: An extra large aperture scintillometer (XLAS) was used over several months across the Thau Lagoon (South of France) to retrieve one-wavelength scintillation and, thence, sensible heat flux. We present the experiment with the XLAS, an eddy-covariance station and meteorological stations measuring on or near the Thau Lagoon. Changes implemented to adapt the scintillometry processing schemes to the above water conditions are presented together with a full error budget, including sensitivity tests to the relevant parameters of the scintillometer processing scheme. The XLAS error budget amounts to 16% (systematic part) ±50% (random part). Sensible heat fluxes obtained using the XLAS under unstable atmospheric conditions are then compared to eddy-covariance estimates used as a reference. The scintillometry technique proved to perform satisfactorily in such a watery environment. Some discrepancies observed between the XLAS and eddy-covariance measurements were investigated according to the lagoon fraction of the source area, to discriminate whether they were related to deviations from the Monin–Obukhov similarity theory or to different atmospheric conditions at the respective instrument locations. Local atmospheric conditions agreed well with the Monin–Obukhov similarity theory, especially measurements with source areas largely composed of the lagoon surface. Retaining only the measurements with almost only the lagoon surface in the source area improved the agreement between the XLAS and eddy-covariance measurements. The remaining discrepancies are interpreted as being due to significant location differences between the two instruments, resulting in different atmospheric conditions, and to size differences in the source areas.

Two Experiments on Using a Scintillometer to Infer the Surface Fluxes of Momentum and Sensible Heat

Abstract: A traditional use of scintillometry is to infer path-averaged values of the turbulent surface fluxes of sensible heat Hs and momentum τ (, where ρ is air density and u* is the friction velocity). Many scintillometer setups, however, measure only the path-averaged refractive-index structure parameter ; the wind information necessary for inferring u* and Hs comes from point measurements or is absent. The Scintec AG SLS20 surface-layer scintillometer system, however, measures both and the inner scale of turbulence l0, where l0 is related to the dissipation rate of turbulent kinetic energy ɛ. The SLS20 is thus presumed to provide path-averaged estimates of both u* and Hs. This paper describes comparisons between SLS20-derived estimates of u* and Hs and simultaneous eddy-covariance measurements of these quantities during two experiments: one, over Arctic sea ice; and a second, over a midlatitude land site during spring. For both experiments, the correlation between scintillometer and eddy-covariance fl...

Direct evaluation of refractive-index structure functions from large-eddy simulation output for atmospheric convective boundary layers

Abstract: Fluctuations of the refractive index associated with atmospheric turbulence affect the propagation of electromagnetic and acoustic waves in the atmosphere In the reported study, the effects of turbulence on wave propagation in the atmospheric convective boundary layer (CBL) are considered in terms of the second-order refractive index structure function and related to its structure-function parameter Cn2 Two structure-function evaluation methods are compared The direct evaluation method involves calculating the refractive index at each point in the simulation domain with subsequent calculation of the structure function The second method is based on a parameterized linear relationship between the refractive-index structure function and temperature/humidity structure functions For each evaluation method, vertical profiles of Cn2 computed for separations along the three coordinate directions collapse together over a significant portion of the CBL Near-surface divergence of Cn2 values along the horizontal directions was noted and attributed to the influence of surface wind shear on the turbulent fluctuations of temperature and humidity The behavior of Cn2 near the surface was shown to agree favorably with similarity-theory predictions

Scintillometer-Based Estimates of Sensible Heat Flux Using Lidar-Derived Surface Roughness

Abstract: The estimation of sensible heat flux, H, using large aperture scintillometer (LAS) under varying surface heterogeneity conditions was investigated. Surface roughness features characterized by variable topography and vegetation height were represented using data derived from the highly accurate light detection and range (lidar) techniques as well as from traditional vegetation survey and topographic map methods. The study was conducted at the Cibola National Wildlife Refuge, Southern California, over a riparian zone covered with natural vegetation dominated by tamarisk trees interspersed with bare soil in a region characterized by arid to semiarid climatic conditions. Estimates of H were obtained using different representations of surface roughness features derived from both traditional and lidar methods to estimate LAS beam height [z(u)] at each increment u along its path, vegetation height (hc), displacement height (d), and roughness length (z0) combined with the LAS weighing function, W(u), alon...

Characterizing Optical Turbulence at the GMT Site with MooSci and MASS-DIMM

Abstract: .In order to guide the adaptive optics design and aid in performance predictions, optical turbulence at the site of the future Giant Magellan Telescope (GMT) is characterized using MooSci, a lunar scintillometer, and MASS-DIMM, a combination differential image motion monitor and multiaperture scintillation sensor. As a new instrument, MooSci, is verified as a reliable ground-layer turbulence profiler. The GMT can expect an improvement of approximately 0.1″ over the site testing results as measured with a DIMM. Turbulence below 30 m is horizontally nonhomogeneous, dependent on wind speed and direction, and on average accounts for 60% of the full ground-layer (up to 500 m) turbulence.

Scintillation of THz transmission by atmospheric turbulence near the ground

Abstract: Considering the two main factors which affect the terahertz band atmospheric refractive index structure parameter: temperature and humidity, this paper studies the influence on the refractive index structure parameter from temperature structure constant, humidity structure constant and joint structure constant of temperature and humidity by using the actual measured values in the infrared band, and shows the difference between the atmospheric refractive index structure parameter of THz band and that of optical band. Relationship between scintillation index and various parameters in the condition of zero-inner-scale or nonzero-inner-scale for plane wave and sphere wave is analyzed and discussed. Research shows that the THz scintillation effect is strong, and the scintillation index of plane wave is larger than the spherical wave; the inner scales of turbulence, frequency and transmission distance produces important influences on the scintillation index.

Radiometric Survey as a Useful Tool in Geological Mapping of Western Nigeria

Abstract: Gamma ray Spectrometer (DISA-300) and broadband gamma ray scintillometer (BGS-ISL) were used to evaluate the radiometric properties of rocks (Igneous, Sedimentary and Metamorphic) in parts of southwestern Nigeria. The study revealed that although the two instruments used recorded different gamma radiation value and the graphs generated by the instruments are quite similar. Based on the major peaks and troughs of the radioactivity graph, the different formations in the area were clearly delineated and these correspond approximately to the geological boundaries in the area. Lithologic characterization of the formations revealed that the concentration of radioactive elements in rock varies. Shale, clay and granites have the highest amount of gamma count (60-105) while amphibolites show the lowest gamma count (16-46). The gamma count is a function of the concentration of radioactive elements in the rock. The reading ranges from 65-85cps in the scintillometer while the spectrometer varies from 19.75-38.88cps. The difference in readings may be attributed to the higher sensitivity of the scintillometer to gamma radiation than the spectrometer. However, the two instruments display similar pattern of curves and good correlation.

Long-term measurements of atmospheric point-spread functions over littoral waters as determined by atmospheric turbulence

Abstract: During the FATMOSE trial, held over the False Bay (South Africa) from November 2009 until October 2010, day and night (24/7) high resolution images were collected of point sources at a range of 15.7 km. Simultaneously, data were collected on atmospheric parameters, as relevant for the turbulence conditions: air- and sea temperature, windspeed, relative humidity and the structure parameter for refractive index: Cn2. The data provide statistical information on the mean value and the variance of the atmospheric point spread function and the associated modulation transfer function during series of consecutive frames. This information allows the prediction of the range performance for a given sensor, target and atmospheric condition, which is of great importance for the user of optical sensors in related operational areas and for the developers of image processing algorithms. In addition the occurrence of “lucky shots” in series of frames is investigated: occasional frames with locally small blur spots. The simultaneously measured short exposure blur and the beam wander are compared with simultaneously collected scintillation data along the same path and the Cn2 data from a locally installed scintillometer. By using two vertically separated sources, the correlation is determined between the beam wander in their images, providing information on the spatial extension of the atmospheric turbulence (eddy size). Examples are shown of the appearance of the blur spot, including skewness and astigmatism effects, which manifest themselves in the third moment of the spot and its distortion. An example is given of an experiment for determining the range performance for a given camera and a bar target on an outgoing boat in the False Bay.

Measurement of the Structure Constant of Refractivity at Optical Wavelengths Using a Scintillometer

Abstract: The structure constant of the atmospheric re- fractive index is used for characterizing the turbulence strength and for predicting the scintillation of electromag- netic waves in atmosphere. It is measured continuously in Prague using an optical scintillometer. First monthly and seasonal statistics obtained from the data gathered in the summer 2011 are provided. Lognormal distribution pa- rameters are fitted to the empirical cumulative distribution. The hourly statistics of the structure constant show the typical evolution of turbulence strength during a day.

Measuring water-vapour and carbon-dioxide fluxes at field scales with scintillometry

Abstract: Scintillometry is a measurement technique that has proven itself to be of great value for measuring spatial-averaged fluxes of sensible heat, momentum, and evapotranspiration. Furthermore, for crop fields (field scales), scintillometry has been shown to accurately determine the sensible-heat and momentum flux over time intervals as short as 6 seconds. As a consequence, interests in scintillometry are growing and scintillometers that determine sensible-heat fluxes and momentum fluxes have become commercially available. This thesis deals with two aspects of scintillometry. First, after a general introduction of scintillometry, measurement errors that have been observed in the large-aperture scintillometer from Kipp&Zonen and in the SLS field-scale scintillometer from Scintec are evaluated. For both scintillometer types, we discuss the variability in the measurement errors among different instruments and, where possible, we give solutions to remove these errors. Furthermore, we present the results of a prototype scintillometer that was developed as part of the research project. With our proposed design, we aim to overcome the measurement errors in the Scintec scintillometer and extend the applicability of the field-scale scintillometer to paths that are longer than 200 m. Second, we extend the application of field-scale scintillometry to the flux measurements of latent-heat, carbon-dioxide, and other passive scalars. Until now, scintillometers could not be used for measuring passive-scalar fluxes over crop fields and we show that with our extended methodology these fluxes can be accurately determined over time intervals as short as 1 minute. The methodology is based on a combination of scintillometer measurements and additional high-frequency scalar measurements and works under conditions of homogeneous turbulence, i.e. single crop fields. We introduce four methods, notably the energy-balance method, the Bowen-variance method, the flux-variance method, and the structure-parameter method. Using several validation methods, we show that the energy-balance method is unsuitable for estimating scalar fluxes over 1-min averaging intervals. The Bowen-variance and flux-variance method perform better and the structure-parameter method accurately resolves 1-minute fluxes. Thus, with this methodology fluxes can be resolved with a high temporal resolution, making it possible to study vegetation in a natural environment under non-stationary conditions. This allows us to show that the wheat vegetation affects fluxes upon changes in solar radiation in time periods clearly shorter than 30 minutes and that the canopy resistance can change significantly within several minutes.

Fiber optical turbulence sensing system

Abstract: A novel fiber optical turbulence sensing system based on pha se generated carrier technique is developed for measuring the intensity and structure of local atmospheric optical turbulence. The turbulence-induced air refractive index fluctuations are detected through fiber optical turbulence sensor array and demodulated by the algorithm of correlation. The system’s dynamic range is 10 ~10 18 12 , which satisfies most of the sceneries in the boundary atmosphere. Time series of the measured refractive index fluctuations and its power spectrum up to the frequency of 500Hz in different conditions such as sealed box or free turbulent atmosphere are illuminated and analyzed. In the end, some of its applications are briefly outlined. Key words oFiber optical turbulence sensor, atmospheric optical tu rbulence, refractive index fl uctuation, power spectrum 1. INTRODUCTION When light propagates through turbulent atmosphere, it undergoes fluctuation in both amplitude and phase caused by random fluctuation of the refractive index, which affects the development of optoelectronic systems such as ground-based astronomical observation, free space laser communication systems and laser propagation systems

Turbulent Sensible Heat Flux in Łódź Obtained from Scintillometer Measuerments – Comparison of Free and Mix Algorithms

Abstract: Abstract The primary aim of this paper was to present the results of turbulent sensible heat flux (QH) measurements with Scintillometer Scintec BLS900 (LAS). The theoretical background of scintillation method has been presented as well as two different ways of sensible heat flux computation from LAS. The measurements presented here were conducted from April to December 2011. Diurnal and partially annual variability of QH has been analyzed, moreover the mean diurnal course of QH in considered months has been prepared. In order to choose the optimal method of QH computation from LAS the results obtained with three different Monin-Obuchov similarity theory functions as well as free convection assumption has been compared. In first case it has been proved that sensible heat flux differs significantly depending on chosen universal function. In turn in case of free convection assumptions it has been revealed that it is valid only for very unstable conditions. Therefore it does not apply to long-time heat flux measurement in case of Łódź. Nevertheless, this study has shown that scintillation method is valuable and reasonable source of path-averaged QH estimates in considered city. Abstrakt Głównym celem pracy była prezentacja wyników pomiarów turbulencyjnego strumienia ciepła jawnego (QH) w Łodzi za pomocą scyntylometru Scintec BLS900. Przedstawione zostały założenia teoretyczne metody scyntylacyjnej, jak również metody wyznaczania strumienia ciepła jawnego za pomocą scyntylometru. Pomiary obejmowały okres od kwietnia do grudnia 2011 roku. Przeanalizowano dobową oraz częściowo roczną zmienność QH, wyznaczając przy tym średnie dobowe jego przebiegi dla poszczególnych miesięcy. W celu wyznaczenia optymalnej metody estymacji QH z pomiarów scyntylometrycznych porównano wyniki uzyskane przy wykorzystaniu trzech różnych funkcji uniwersalnych teorii podobieństwa Monina- Obuchova, jak również przybliżenia dla swobodnej konwekcji. W pierwszym przypadku wykazano, iż strumieni ciepła jawnego w znacznym stopniu różni się, w zależności od zastosowanej funkcji uniwersalnej. Z kolei założenie swobodnej konwekcji w Łodzi sprawdza się jedynie w przypadku silnie chwiejnej warstwy granicznej. Ponadto wykazano, iż w przypadku Łodzi metoda scyntylacyjna stanowi wiarygodną alternatywę wyznaczania strumieni turbulencyjnych.

Refractive Index Compensation in Over-Determined

Abstract: We present an interferometric technique based on a differential interferometry setup for measurement under atmospheric conditions. The key limiting factor in any interferometric dimensional measurement are fluctuations of the refractive index of air representing a dominating source of uncertainty when evaluated indirectly from the physical parameters of the atmosphere. Our proposal is based on the concept of an over-determined interferometric setup where a reference length is derived from a mechanical frame made from a material with a very low thermal coefficient. The technique allows one to track the variations of the refractive index of air on-line directly in the line of the measuring beam and to compensate for the fluctuations. The optical setup consists of three interferometers sharing the same beam path where two measure differentially the displacement while the third evaluates the changes in the measuring range, acting as a tracking refractometer. The principle is demonstrated in an experimental setup.

Characteristics of long-range scintillation data over maritime coastal areas

Abstract: The knowledge on scintillation, caused by atmospheric turbulence, is of vital importance for the performance prediction of threat detection systems and for the development of associated detection algorithms. Additionally, scintillation data may support the knowledge on turbulence characteristics. Along these ideas, data have been analysed, collected during the FATMOSE trials, carried out over the False Bay (South Africa) over a range of 15.7 km from November 2009 until October 2010. The collected data include long-range scintillation measurements, taken with the MSRT radiometer and a modulated source and with a high resolution imager and static sources. In addition a standard scintillometer was used over a short range, 1.8 km parallel path and a mid-path sonic anemometer for direct measurement of windspeed and air temperature fluctuations. Indirectly, information on turbulence parameters is predicted from the weather data, collected at the mid-path station, by using our TARMOS code for the marine boundary layer. Details on the set-up and the method of analysis are given, including some relevant examples. Scintillation spectra between 0.1 and 100 Hz are shown for investigation of the validity of Kolmogorov's theory of turbulence. In addition, signal (irradiance) statistics are shown for testing the log-normality of their characteristics. In relation to this, attention is spent on the subject of saturation of scintillation, which may occur in conditions of strong turbulence, combined with small apertures and long ranges. Output from the various sensors is compared with TARMOS predictions and related to the simultaneously collected blur and beam wander data. Related to this, data on the signal correlations from the various MSRT apertures provide information on the transverse atmospheric coherence length n0, which parameter is directly linked to the blur. Examples are shown of the wavelength dependence of scintillation, predicted from the theory of weak turbulence, in comparison with the 3-band scintillation data from the MSRT sensor. In the comparison of the local and path-averaged scintillation, the effect of path inhomogeneities of the atmospheric conditions along the path is taken into account. Conditions with low scintillation are getting special attention, as they do not always correspond to conditions with small blur. © 2012 SPIE.

The use of large aperture scintillometer and eddy covariance system for monitoring energy and water vapour fluxes over different surfaces in the Heihe River Basin, China

Abstract: We analysed the seasonal variations of energy and water vapour fluxes, with a special focus on evapotranspiration (ET) over various surfaces: irrigated cropland (Yingke, YK), alpine meadow (A’rou, AR), and spruce forest (Guantan, GT). Energy and water vapour fluxes were measured using eddy covariance systems (EC) and a large aperture scintillometer (LAS) in the Heihe River Basin, China, in 2008 and 2009. We also determined the source areas of EC and LAS measurements for each site. The results show that the main EC source area was within a radius of 200 m at all sites. The main source area for the LAS (with a path length of 2390 m) stretched along a path line about 2000 m long and 700 m wide. The ground surface conditions in the source areas changed with season and site, and there were characteristic seasonal variations in energy and water vapour fluxes at all sites. The sensible heat flux was the main term of the energy budget during the dormant season. During the growing season, the latent heat flux dominated the energy budget, and an obvious “oasis effect” was observed at YK. The monthly ET reached its peak in July at YK and June at GT in both 2008 and 2009, while at AR it reached its peak in August in 2008 and June in 2009. ET at AR measured by different scales (kilometres scale, LAS; hundred metre scale, EC) had the similar monthly variations, presenting single peak patterns (appearing in August in 2008). There are also some differences between LAS and EC measurements because of the energy imbalance of EC system, the different source areas and surface heterogeneity.

Long-term measurements of refractive index structure constant in atmospheric boundary layer

Abstract: Results of long-term measurements of the refractive index structure constant in the boundary layer are introduced. The measurements were made on a 150-meter-high lattice mast equipped by nineteen meteorological sensors and one pressure sensor at the bottom of the mast. The Kolmogorov statistical theory of turbulence was used to calculate the refractive index structure constant C 2 n , allowing us to present annual cumulative distribution functions (CDFs) and seasonal quantiles. The quantiles of measured height dependence of the refractive index structure constant are also shown and compared with existing models (Hufnagel/Andrews/Phillips, SLC Day and Gurvich). Parameters of a linear model were calculated to fit the measured median height profile of the refractive index structure constant with the uncertainty of measurements also being addressed.