Showing papers on "Scintillometer published in 2010"

The impact of in-canopy wind profile formulations on heat flux estimation in an open orchard using the remote sensing-based two-source model

Abstract: . For open orchard and vineyard canopies containing significant fractions of exposed soil (>50%), typical of Mediterranean agricultural regions, the energy balance of the vegetation elements is strongly influenced by heat exchange with the bare soil/substrate. For these agricultural systems a "two-source" approach, where radiation and turbulent exchange between the soil and canopy elements are explicitly modelled, appears to be the only suitable methodology for reliably assessing energy fluxes. In strongly clumped canopies, the effective wind speed profile inside and below the canopy layer can strongly influence the partitioning of energy fluxes between the soil and vegetation components. To assess the impact of in-canopy wind profile on model flux estimates, an analysis of three different formulations is presented, including algorithms from Goudriaan (1977), Massman (1987) and Lalic et al. (2003). The in-canopy wind profile formulations are applied to the thermal-based two-source energy balance (TSEB) model developed by Norman et al. (1995) and modified by Kustas and Norman (1999). High resolution airborne remote sensing images, collected over an agricultural area located in the western part of Sicily (Italy) comprised primarily of vineyards, olive and citrus orchards, are used to derive all the input parameters needed to apply the TSEB. The images were acquired from June to October 2008 and include a relatively wide range of meteorological and soil moisture conditions. A preliminary sensitivity analysis of the three wind profile algorithms highlights the dependence of wind speed just above the soil/substrate to leaf area index and canopy height over the typical range of canopy properties encountered in these agricultural areas. It is found that differences among the models in wind just above the soil surface are most significant under sparse and medium fractional cover conditions (15–50%). The TSEB model heat flux estimates are compared with micro-meteorological measurements from a small aperture scintillometer and an eddy covariance tower collected over an olive orchard characterized by moderate fractional vegetation cover (≈35%) and relatively tall crop (≈3.5 m). TSEB fluxes for the 7 image acquisition dates generated using both the Massman and Goudriaan in-canopy wind profile formulations give close agreement with measured fluxes, while the Lalic et al. equations yield poor results. The Massman wind profile scheme slightly outperforms that of Goudriaan, but it requires an additional parameter accounting for the roughness sub-layer of the underlying vegetative surface. The analysis also suggests that within-canopy wind profile model discrepancies become important, in terms of impact on modelled sensible heat flux, only for sparse canopies with moderate vegetation coverage.

Intercomparison of sensible heat flux from large aperture scintillometer and eddy covariance methods: Field experiment over a homogeneous semi-arid region

Abstract: Scintillometers are becoming increasingly popular for the validation of satellite remote sensing sensible heat-flux estimates due to the comparable spatial resolutions. However, it is important to gain confidence in the accuracy of the sensible heat-flux measurements obtained by the scintillometer. Large aperture scintillometer (LAS) and eddy-covariance (EC) measurements were collected over a homogeneous, dry and semi-arid region near Las Cruces, New Mexico, USA, where the homogeneity allowed direct comparison of the two instruments despite their differences in footprint sizes. The differences between the sensible heat-flux measured by both LAS and EC systems fall within the differences between two EC systems. We conclude that the large aperture scintillometer is a reliable system for measuring sensible heat flux in a dry semiarid region.

Near-ground turbulence profiles from lunar scintillometer

Abstract: A simple and inexpensive 6-channel array of photo-diodes, LuSci, can measure weak moon- light scintillation produced by optical turbulence within few hundred meters above the ground. We describe the instrument, its operation, and data reduction. Measured covariances of lunar scintillation are fitted to a smooth turbulence profile model with few parameters. Complete recipe for calculating the instrument response (including the effects of Moon's phases) is given. The robustness of the results relative to various exp erimental factors and model as- sumptions is investigated. We give examples of the data and compare LuSci with other turbu- lence profilers. LuSci finds numerous applications in night- time site testing and monitoring.

Measurement of grassland evaporation using a surface-layer scintillometer

Abstract: A dual-beam surface-layer scintillometer (SLS) was used to estimate sensible heat flux (H) every 2 min for a path length of either 50 or 101 m, for more than 30 months in a mesic grassland in eastern South Africa. The SLS method relies on Monin-Obukhov similarity theory, the correlation between the laser beam signal amplitude variances and the covariance of the logarithm of the beam signal amplitude measured using 2 laser detectors. Procedures for checking SLS data integrity in real-time are highlighted as are the post-data collection rejection procedures. From the H estimates, using SLS and measurements of soil heat flux and net irradiance, evaporation rates were calculated as a residual of the shortened energy balance equation and compared with grass reference evaporation rates (ETo). Inconsistent hourly ETo values occur in the late afternoon due to the incorrect assumption that the soil heat flux is 10% of net irradiance. The SLS estimates of H and the estimates of evaporation rate as a residual compared favourably with those obtained using the Bowen ratio and eddy covariance methods for cloudless days, cloudy days and days with variable cloud. There was no evidence for the eddy covariance measurements of H being underestimated in comparison to the Bowen ratio and SLS measurements. On many days, the diurnal variation in SLS H was asymmetrical, peaking before noon. Keywords: energy balance, Bowen ratio, eddy covariance, grass reference evaporation, rejection criteria

Test of Scintillometer Saturation Correction Methods Using Field Experimental Data

Abstract: Boundary Layer Meteorology manuscript No. (will be inserted by the editor) Test of scintillometer saturation correction methods using field experimental data J. Kleissl, O.K. Hartogensis, J.D. Gomez Received: Aug. 11, 2009 / Accepted: date Abstract Saturation of large aperture scintillometer (LAS) signals can result in sen- sible heat flux measurements that are biased low. A field study with LASs of different aperture sizes and path lengths was performed to investigate the onset of and correc- tions for signal saturation. Saturation already occurs at C n 2 ≈ 0.074D 5/3 λ 1/3 L −8/3 , where C n 2 is the structure parameter of the refractive index, D is the aperture size, λ is the wavelength, L is the transect length, which is smaller than theoretically de- rived saturation limits. At a transect length of 1 km, a height of 2.5 m, and aperture ≈ 0.15 m the correction factor exceeds 5% already at C n 2 = 2 × 10 −12 m −2/3 , which will affect many practical applications of scintillometry. The Clifford correction method, which only depends on C n 2 and transect geometry, provides good saturation corrections over the range of conditions observed in our study. The saturation correction proposed by Ochs and Hill results in correction factors that are too small in large saturation regimes. An inner length scale dependence of the sat- uration correction factor was not observed. Thus for practical applications the Clifford correction method should be applied. Keywords Large aperture scintillometer · Sensible heat flux · Signal saturation · Wave propagation 1 Introduction A major challenge for the validation of surface energy balance fluxes from remote sens- ing images is the ground measurement at a scale similar to their spatial resolution. While the pixel size of daily thermal remote sensing images is on the order of km, J. Kleissl Dept. of Mechanical and Aerospace Engineering, University of California, San Diego, USA Tel.: +1-443-527-2740 E-mail: jkleissl@ucsd.edu J.D. Gomez Dept. of Earth and Environmental Sciences, New Mexico Tech, Socorro, New Mexico, USA O.K. Hartogensis Dept of Meteorology and Air Quality, Wageningen University, Wageningen, The Netherlands

Surface layer scintillometry for estimating the sensible heat flux component of the surface energy balance

Abstract: The relatively recently developed scintillometry method, with a focus on the dual-beam surface layer scintillometer (SLS), allows boundary layer atmospheric turbulence, surface sensible heat and momentum flux to be estimated in real-time. Much of the previous research using the scintillometer method has involved the large aperture scintillometer method, with only a few studies using the SLS method. The SLS method has been mainly used by agrometeorologists, hydrologists and micrometeorologists for atmospheric stability and surface energy balance studies to obtain estimates of sensible heat from which evaporation estimates representing areas of one hectare or larger are possible. Other applications include the use of the SLS method in obtaining crucial input parameters for atmospheric dispersion and turbulence models. The SLS method relies upon optical scintillation of a horizontal laser beam between transmitter and receiver for a separation distance typically between 50 and 250 m caused by refractive index inhomogeneities in the atmosphere that arise from turbulence fluctuations in air temperature and to a much lesser extent the fluctuations in water vapour pressure. Measurements of SLS beam transmission allow turbulence of the atmosphere to be determined, from which sub-hourly, real-time and in situ path-weighted fluxes of sensible heat and momentum may be calculated by application of the Monin-Obukhov similarity theory. Unlike the eddy covariance (EC) method for which corrections for flow distortion and coordinate rotation are applied, no corrections to the SLS measurements, apart from a correction for water vapour pressure, are applied. Also, path-weighted SLS estimates over the propagation path are obtained. The SLS method also offers high temporal measurement resolution and usually greater spatial coverage compared to EC, Bowen ratio energy balance, surface renewal and other sensible heat measurement methods. Applying the shortened surface energy balance, measurements of net irradiance and soil heat as well as SLS estimates of sensible heat allows path-weighted evaporation from the surface to be estimated. Research applications involving the use of the SLS method, as well as the theory on which the method is based, are presented.

EOSTAR Pro: a flexible extensive library to assess EO sensor performance

Abstract: The FATMOSE trial (FAlse-bay ATMOSpheric Experiment) running over a period from November 2009 to July 2010, was a continuation of the cooperation between TNO and IMT on atmospheric propagation and point target detection and identification in a maritime environment. Instruments were installed for measuring scintillation, blurring- and refraction effects over a 15.7 km path over sea. Simultaneously, a set of instruments was installed on a mid-path lighthouse for collecting local meteorological data, including scintillation, sea surface temperature and visibility. The measurements covered summer and winter conditions with a prevailing high wind speed from the South East, bringing in maritime air masses. The weather conditions included variations in the Air-Sea Temperature Difference (ASTD), that may affect the vertical temperature gradient in the atmospheric boundary layer, causing refraction effects in the lightpath. This was measured with a theodolite camera, providing absolute Angles of Arrival (AOA). Blur data were collected with a high resolution camera system with 10 bits dynamic range. Specially designed image analysis software allows determination of the atmospheric blur, while simultaneously providing information on the Scintillation Index (S.I.). This S.I. was also measured by using the Multiband Spectral Radiometer Transmissometer (MSRT). The ratio of the transmission levels of this instrument contains information on the size distribution of the aerosols along the path. In the paper, experimental details on the set-up and the instrumentation are given as well as the methods of analysis. Preliminary results are shown, including a comparison of measured blur and scintillation data with Cn2 data from the scintillometer, correlation between AOA and ASTD and comparison of transmission data with data from the visibility meter. Blur and scintillation data are compared with predictions from standard turbulence model predictions, using Cn2. In future studies the data will be used for validation of propagation models such as EOSTAR.

Boundary layer seeing measurements in the Canadian High Arctic.

Abstract: As part of a program to measure and evaluate atmospheric turbulence on mountains at the most northerly tip of North America, we have deployed two SODARs and a lunar scintillometer at the Polar Environment Atmospheric Research Lab (PEARL) located on a 600m-high ridge near Eureka on Ellesmere Island, at 80° latitude. This paper discusses the program and presents a summary of ground-layer turbulence and seeing measurements from the 2009-10 observing season.

Scintillometer measurements above the urban area of London

Abstract: The spatial heterogeneity of urban surfaces presents a particular challenge to the measurement of turbulent fluxes. This is particularly true close to the urban surface (in the roughness sub-layer (RSL)) where the mosaic of roof top and street canyon surfaces present a complex three dimensional source area. Scintillometery, which offers the ability to make path-averaged measurements of turbulent fluxes of heat and momentum, provides an alternative approach to obtaining more spatially representative data sets in the RSL.

Preliminary results of the FATMOSE atmospheric propagation trials in the False Bay, South Africa, November 2009-July 2010

Abstract: The FATMOSE trial (FAlse-bay ATMOSpheric Experiment) running over a period from November 2009 to July 2010,was a continuation of the cooperation between TNO and IMT on atmospheric propagation and point target detection and identification in a maritime environment. Instruments were installed for measuring scintillation, blurring- and refraction effects over a 15.7 km path over sea. Simultaneously, a set of instruments was installed on a mid-path lighthouse for collecting local meteorological data, including scintillation, sea surface temperature and visibility. The measurements covered summer and winter conditions with a prevailing high wind speed from the South East, bringing in maritime air masses. The weather conditions included variations in the Air-Sea Temperature Difference (ASTD), that may affect the vertical temperature gradient in the atmospheric boundary layer, causing refraction effects in the lightpath. This was measured with a theodolite camera, providing absolute Angles of Arrival (AOA). Blur data were collected with a high resolution camera system with 10 bits dynamic range. Specially designed image analysis software allows determination of the atmospheric blur, while simultaneously providing information on the Scintillation Index (S.I.). This S.I. was also measured by using the Multiband Spectral Radiometer Transmissometer (MSRT). The ratio of the transmission levels of this instrument contains information on the size distribution of the aerosols along the path. In the paper, experimental details on the set-up and the instrumentation are given as well as the methods of analysis. Preliminary results are shown, including a comparison of measured blur and scintillation data with Cn 2 data from the scintillometer, correlation between AOA and ASTD and comparison of transmission data with data from the visibility meter. Blur and scintillation data are compared with predictions from standard turbulence model predictions, using Cn 2. In future studies the data will be used for validation of propagation models such as EOSTAR.

Prediction of the ground-level refractive index structure parameter from the measurement of atmospheric conditions

Abstract: Evaluation of the methods developed by Bendersky, Kopeika, and Blaunstein1 to predict the refractive index structure parameter from the direct measurement of macroscopic atmospheric conditions were investigated. Measurements of ground-level temperature, relative humidity, wind speed, solar flux, and aerosol loading taken by the University of Central Florida weather station were compared against concurrent measurements of the refractive index structure parameter made by Scintec SLS-20 scintillometers positioned near the weather station. Wind measurements were obtained by three, three-axis sonic anemometers (capable of resolving a three-dimensional wind vector) positioned at heights of 1, 1.5, and 2.5 meters above the ground. Temperature measurements were taken at ground level, and at heights of 1 and 1.5 meters. Data were collected for two days atop Antelope Peak, NV. Collection times covered both daytime and nighttime measurements.

Atmospheric cross-wind and turbulence measurements using turbulence-induced scintillations

Abstract: We report on remote measurements of cross-wind and atmospheric turbulence, using a one-station scheme. As most remote wind-sensing methods, our method is based on observing the drift of the scintillation pattern across the line of sight. The scintillations are caused by naturally-occurring turbulence-induced refractive index irregularities in the atmosphere, which drift at wind speed. Analyzing spatial-temporal cross-correlation function of the signals of two elements in the array, it is possible to obtain the cross-wind speed. We use the zero-crossings technique for measuring the cross-wind value, while the cross-wind direction is determined by comparing areas from both sides of the peak of the cross-correlation function. Here we present results obtained using these techniques in comparison to independent measurements of the anemometers. The experiments were performed along a uniform path over a flat beach parallel to the Mediterranean Sea shore. Four white-screen diffusive targets were placed at distances of 300, 600, 850 and 1200m. Five anemometers were placed along the laser beam path, one near each target and at the measurement station. Each target was illuminated with a beam from a glass fiber pulsed infrared laser with a repetition rate of several thousand Hz, and a sub-microsecond pulse-length, and output beam divergence of ~300 μrad. The receiver has an entrance aperture of 80mm, and the incoming radiation is focused onto an array of four 50×250um InGaAs detectors by a lens with f=500mm. The results show good agreement. From the fluctuations of the signal on the detector array, our system also measures the turbulence structure parameter Cn 2, using the angle-of arrival technique. The obtained results show reasonable agreement with independent scintillometer measurements of C n 2 , performed with a CW He-Ne laser in a two-station setup with a detector at a distance of 60m from the laser.

Measurement, Analysis and Application of Surface Energy and Water Vapor Fluxes at Large Scale

Abstract: The measurements of surface energy and water vapor fluxes at large scale are crucial for solving the area-averaging problem from local in situ measurements to area-integrated information,validating hydrological and meteorological models,and verifying remote sensing products etc.This paper reviews the worldwide progress in surface energy and water vapor fluxes at large scale using scintillometer,from these aspects of observation instruments and experiments,and processing,analysis and application of observational data.A brief outlook about scintillometer is given.

MooSci: a lunar scintillometer

Abstract: MooSci is a linear array of photodiodes that measures time varying intensities of light reflected from the Moon, lunar scintillation. The covariance between all possible pairs of photodiodes can be used to reconstruct the ground layer turbulence profile from the ground up to a maximum height roughly determined by the distance between the furthest pair of detectors. This technique of profile restoration will be used for site testing at various locations. This paper describes the design of a lunar scintillometer and preliminary results from Las Campanas Peak.

Estimation of catchment averaged sensible heat fluxes using a Large Aperture Scintillometer

Abstract: [1] Evapotranspiration rates at the catchment scale are very difficult to quantify. One possible manner to continuously observe this variable could be the estimation of sensible heat fluxes (H) across large distances (in the order of kilometers) using a large aperture scintillometer (LAS), and inverting these observations into evapotranspiration rates, under the assumption that the LAS observations are representative for the entire catchment. The objective of this paper is to assess whether measured sensible heat fluxes from a LAS over a long distance (9.5 km) can be assumed to be valid for a 102.3 km2 heterogeneous catchment. Therefore, a fully process-based water and energy balance model with a spatial resolution of 50 m has been thoroughly calibrated and validated for the Bellebeek catchment in Belgium. A footprint analysis has been performed. In general, the sensible heat fluxes from the LAS compared well with the modeled sensible heat fluxes within the footprint. Moreover, as the modeled H within the footprint has been found to be almost equal to the modeled catchment averaged H, it can be concluded that the scintillometer measurements over a distance of 9.5 km and an effective height of 68 m are representative for the entire catchment.

A Study of the Observation Method of Large Aperture Scintillometer

Abstract: At present,Large Aperture Scintillometer(LAS) is widely used in regional water and heat flux measurements.Thus,the study of its observation method is very necessary.In this paper,the guideline of LAS is systematically summarized,including observation site selection,instrument installation,instrument adjusting and maintenance,as well as data collection.This work may facilitate better performance of experiment and assure the quality of data.

The Scale Relationship of Sensible Heat Flux Measured by Large Aperture Scintillometer and Eddy Covariance System

Abstract: With the flux data observed by Eddy Covariance system(EC) and Large Aperture Scintillometer(LAS) at Xiaotangshan(Changping district,Beijing) in 2002 and 2004,and based on an analytical footprint model,the scale relationship of sensible heat flux between EC and LAS measurement was analyzed.The results showed that the level of surface homogeneity or heterogeneity had a direct influence on the sensible heat flux difference measured by eddy covariance system and large aperture scintillometer.After analyzing the relationship between flux differences of EC and LAS observation and the footprint ratio and size ratio of overlap zone of source areas of the two sensors over homogeneous and heterogeneous surfaces,a scale transfer equation was constructed to composite the sensible heat flux measured by eddy covariance system at each patch into the area-averaged sensible heat flux.

Flux Footprint Analysis and Application for the Large Aperture Scintillometer

Abstract: Mean flux footprints were analyzed for long-term measurements of a large aperture scintillometer(LAS) in Miyun county,Beijing.A set of half-hourly mean,full-year turbulence data in 2008 was used for the analysis.As a quality control,one of the integral turbulent characteristics,σw/u*,was used to exclude that part of data which may violate the Monin-Obukhov similarity,in combining with other reasonability assessments.We yielded a sub-set data of 6 806 available from the total of 8 152 in the year.A footprint model based on an analytical solution was applied to calculate the 2-dimenasional footprints for the LAS measurements.Accordingly,seasonal mean footprints,as well as the mean footprints for 12 types of meteorological conditions at this site,were calculated.Wind direction,wind speed and atmospheric stability were used to determine the meteorological type.Finally,as an example,footprint climatology for sensible heat flux was derived,by averaging the footprints with the real flux measurements as the weight function.Results showed that: the mean footprint at this site varied little seasonally,stability and wind direction influenced the footprint size and location significantly while the wind speed played a relatively weak role in it.Long-term mean turbulent fluxes and their spatial representativeness can be expressed better by the flux-weighted mean footprint,which differed from the simple mean footprint slightly at this site,for the case of sensible heat flux.

Global predictions of the optical sensing through turbulence

Abstract: Electro-optical sensors are affected by the atmospheric turbulence, as quantified by the refractive index structure parameter. The present study introduces a method to predict the meteorological-scale variations of this quantity near the surface. The predictions are evaluated against long-term scintillometry measurements. The essential aspects of the meteorological variability of the optical turbulence rate are captured. The method is illustrated to provide a global and predictive assessment of the optical turbulence rate. It can also be used to analyze the corresponding climatological distributions. Existing relationships can further be incorporated to form predictions of the mean optical sensing performance.

A Study of Applications of Large Aperture Scintillometer in the Heihe River Basin

Abstract: As a new flux measuring instrument,Large Aperture Scintillometer(LAS),which can measure sensible heat flux in large scales,has developed rapidly in recent years.A great number of ground stations were established over different surfaces in the upper and middle reaches of Heihe river basin,supported by the project "Watershed Airborne Telemetry Experimental Research(WATER)".In addition to conventional meteorological parameters,radiation components,soil temperature/soil moisture,soil heat flux and Eddy Covariance system(EC),large aperture scintillometers were erected in the Arou freeze/thawing observation station(upper reaches) and Linze grassland station(middle reaches).This paper focused on the analysis of the diurnal and seasonal variations of sensible heat flux measured by LAS,and used the observation data from March,2008 to December,2009 at Arou station and from May to August,2008 at Linze grassland station.In order to improve the overall quality of LAS measurements,analyzing carefully not only the difference of EC and LAS source area(based on analytical models) and the relevant influences,but also the quality control of LAS measurement data under different atmosphere stabilities and the calculation methods of sensible heat flux by the relative analysis with EC data were analyzed carefully.Long-term data analysis showed that: There were good correlations in sensible heat flux and its time variation between LAS and EC measurements.There were also significant differences in part time,which was caused mainly by the different underlying surfaces in their source areas.In most cases,the LAS measurements were on average larger than the EC′s.The reason seems that EC has a smaller source area than LAS,whose measurement has the effect of a natural area averaged fluxes.

Remote Sensing ET of Alfalfa Using a Surface Aerodynamic Temperature Model

Abstract: Accurate estimates of spatially distributed evapotranspiration (ET) using remote sensing algorithms could potentially improve crop water management. In addition, seasonal ET values could be used in assessing irrigation project efficiency, water use efficiency, ground water depletion, and the use of water rights over large irrigated areas. In this study, ET was mapped using airborne remote sensing model (SAT_ET) which uses inputs such as surface reflectance and radiometric surface temperature (Ts), and a surface aerodynamic temperature (To) sub-model. The SAT_ET model for irrigated alfalfa in Colorado was developed using surface temperature, horizontal wind speed and air temperature profile measurements, and with measurements of turbulent sensible heat fluxes (H) acquired with a Large Aperture Scintillometer (LAS). Estimates of the remote sensing-based ET for a 4.0 hectare alfalfa field, during the 2009 cropping season, were evaluated using a large weighing lysimeter (3.0 x 3.0 x 2.4 m) located at the Colorado State University (CSU) Arkansas Valley Research Center (AVRC) in Rocky Ford, CO. Hourly alfalfa ET was very well estimated with small errors of -5.8 to 1.1% while larger errors were found for estimates of daily ET (-13.5 to 17.8%). The To sub-model is very promising; however it needs to be further developed incorporating a wider range of crops and environmental and atmospheric conditions. Furthermore, the mechanism to extrapolate hourly to daily ET values needs to be investigated as well as the method to calculate reference ET for the conditions encountered in eastern Colorado.

The Uncertainty of Sensible Heat Flux Measurement over Cropland Using Large Aperture Scintillometer(LAS)

Abstract: Sensible heat flux is an important index for reflecting exchange intensity at surface-atmosphere interfaceWith the fast development of Eddy Covariance(EC) technique,the local sensible heat flux measurement becomes easier and more reliableTo study regional or global exchanges,the pixel-size flux measurement becomes an important and key step for up-scalingLarge Aperture Scintillometer(LAS) is the best instrument for measuring pixel-size sensible heat fluxTo evaluate its accuracy and uncertainty,in this paper,the sensible heat fluxes over cropland measured by LAS and EC methods were compared,especially the reasons for errors and uncertainties were analyzedIt shows that: ①No matter in daytime or nighttime,the changing trends of the sensible heat flexes by two methods are the sameThe relationship between them is very good,especially during strong exchange periods②There are still differences between two sensible heat fluxesThe mean abstract difference is less than 50 W/m2Generally,when daytime flux is weak(about less than 70 W/m2),the flux measured by LAS(H LAS) is larger than that by EC(HEC),and when flux is strong,HLAS is smaller than HEC③Due to the heterogeneous surface,the LAS footprint will be affected by the wind speed and wind directionAdvection may induce the uncertainty for LAS sensible heat fluxIn addition,based on all the variables and parameters for LAS equations,the possible sources of the uncertainty,including the uncertainty of EC method and its effect on Bowen ratio,the inaccuracy and changeable parameters(egzero plane displacement and surface roughness etc) were analyzed

A Study of the Processing Method of Large Aperture Scintillometer Observation Data

Abstract: Sensible/latent heat fluxes can be obtained by Large Aperture Scintillometer(LAS) over several kilometers,which play an significant role in the analysis of and application to agricultural and forestry,hydrology and meteorology research.Take LAS observations in Miyun and Guantao stations over Hai River Basin in 2008 as an example.The way of data screening and quality control under unstable conditions as well as the effect of different calculation method on sensible heat flux have been discussed.The results showed: the structure parameter of the refractive index(C2n) should be calculated with the variance of the voltage of structure parameter of the refractive index;Humidity correction can be done with daily Bowen ratio;The effective height of LAS can be calculated with spatial averaged function;The Andreas(1988) function is used to get reliable sensible heat flux.Meanwhile,the nonlinear regression method and dynamic linear regression method have been used to fill the 30min and daily missing data while the 30 min missing data under stable conditions can be set to zero.The correlation relationship between daily ET measured by LAS and EC has been constructed to estimate daily ET when daily Rn50 W/m2.Based on the above analysis,a set of LAS data processing scheme has been set up,which ensures continuous and high quality sensible/latent data can be obtained over various surfaces and weather conditions.

The Feasibility of Using LAS Measurements of the Sensible Heat Flux from a Mixed Plantation in the Hilly Zone of the North China

Abstract: In this study,by use of the Large Aperture Scintillometer(LAS) method and the Eddy Covariance(EC) method respectively,the sensible heat flux under unstable stratification conditions was calculated over a mixed plantation in the hilly zone of the north China from May to September in 2009,which was called HLAS and HEC for short respectivelyHEC in the source area for LAS method(HfEC) was corrected and estimated with the application of footprint modelThe result showed that the correlation coefficient between HfEC and HLAS was 093It proved the feasibility of using LAS measurements to estimate H over the mixed plantations in the hilly zone,based on the analysis of the footprint and source area

Intercomparison of Sensible Heat Flux Measurement based on Eddy Covariance and Small Aperture Scintillometer above the Forest Canopy

Abstract: Eddy covariance and scintillometer techniques are effective ways to measure the sensible heat flux at local and regional scales.As part of ChinaFLUX,continuous sensible heat flux was measured by using the Eddy Covariance(EC) technique at two and three canopy heights of a subtropical pinus plantation on the red earth hilly region in southeastern China.Meanwhile,continuous sensible heat flux was also measured by Small Aperture Scintillometer(SAS),which was installed in the direction of east by south,with about 70m distance between the laser emitter and receiver.There were consistence between the EC systems at two and three canopy heights and SAS system.At the diurnal and seasonal scales,sensible heat flux by SAS was higher than that by the EC systems at two and three canopy heights.However,sensible heat flux by SAS was lower than that by the EC systems at two and three canopy heights.There showed the strongest correlation in the direction of from south to south by west and from north by east to east by north,which were perpendicular to the dominating wind direction.During the daytime,the correlation of sensible heat flux between the EC systems at two and three canopy heights and SAS system were higher than that during the nighttime.The difference of sensible heat flux between the EC systems at two and three canopy heights and SAS system were related with the disparity in their footprint and disadvantages.

Comparison of MODIS derived Evapotranspiration with las measurements at Changwu agro-ecological experimental station

Abstract: Significance of Evapotranspiration (ET) has been realized in disciplines of hydrology, meteorology and agriculture from a number of studies. A parameterization based on the spatially contextual information of surface temperature-vegetation index, namely T s -VI triangle method, is applied to estimate regional ET from remotely sensed data acquired at the Changwu agro-ecological experiment station. Surface net radiation (R n ) is estimated also from MODIS/Terra products. Ratio of soil heat flux (G) to R n is determined using a linear combination of G/R n at bare soil and fully vegetated surface. Reasonably good agreement between estimated and measured sensible heart flux from Large Aperture Scintillometer is observed with RMSD about 48 W/m2.

n fluctuations observed durin ga5k m communication link experiment

Abstract: The path-integrated turbulence strength is usually thought of as a parameter that varies slowly with time. In a recent free-space communications experiment the C 2 n value over a 5-km horizontal path was monitored almost continuously for a period of nearly a month. In addition to well defined and repeatable diurnal fluctuations, strong short-term fluctuations were observed in which the turbulence strength changed by an order of magnitude within a period of minutes. These rapid changes were independently measured by a commercial scintillometer and the high-rate output from the communications transceiver. The characteristics and probable causes for these dynamic atmospheric events and their impact on the design of free-space communication systems are discussed in this article.

Design and characterization analysis of turbulence chamber for optical propagation experiments

Abstract: Since the refractive index fluctuations in the atmosphere are caused mainly by random variations in temperature,turbulence can be artificially generated and its strength can be controlled via changing the temperature and velocity of air flow.Based on this principle,a turbulence chamber was designed and built for performing optical propagation experiments.The refractive index structure constant Cn2 of atmosphere and inner scale l0 of turbulence along the optical propagation path inside the chamber were obtained from the simultaneous measurement of angle-of-arrival fluctuations and scintillation of the propagating light-wave.The experimental results show that the Cn2 and l0 of the generated turbulence are mainly influenced by the temperature and wind velocity inside the chamber,respectively.Cn2=1.58×10-11 m-2/3 is obtained at 45 ℃ with wind velocity 0.48 m/s and l0=2.33 mm at 25 ℃ with wind velocity 1.04 m/s.And the temporal power spectrum analysis of log-intensity indicates that the generated turbulence is suitable for performing optical propagation experiments.