Amount Of Precipitable Water Vapor Research Articles

Retrieval of high spatial resolution precipitable water vapor maps using heterogeneous earth observation data

The determination of the amount of precipitable water vapor (PWV) from global navigation satellite system (GNSS) is restricted to a limited number of ground-based stations with low spatial resolution. The PWV obtained by the multi-source data fusion method has a low spatial resolution because of the low spatial resolution of the data used. Therefore, it is difficult to retrieve PWV maps with sub-km resolution. Therefore, retrieving PWV with high spatial resolution becomes the focus of this study. A dual-scale method for retrieving PWV maps, based on heterogeneous earth data, is proposed, which can obtain sub-kilometer resolution PWV, while maintaining accuracy. First, an approach for analyzing the spatial correlation between land cover types (LCT) and ground-based PWV was proposed, and the meteorological, ecological, topographic, and LCT variables affecting changes in PWV in the near-earth atmosphere were determine, Subsequently, three different regression models, including multiple linear regression (MLR), random forest (RF), and a generalized regression neural network (GRNN), were used to construct the functional model linking heterogeneous earth observation data and ground-based GNSS-derived PWV. Finally, the PWV map with sub-kilometer resolution was generated based on the dual-scale method. Unlike the PWV obtained by data fusion and remote sensing technology, the proposed dual-scale retrieval method can generate PWV maps at 300 m spatial resolution. Statistical analyses demonstrated that the RMS of the PWV derived from the proposed method was less than 2.2 mm, and the bias was close to 0, thereby filling the gap in the sub-kilometer high-precision PWV products.

Water Vapour Assessment Using GNSS and Radiosondes over Polar Regions and Estimation of Climatological Trends from Long-Term Time Series Analysis

The atmospheric humidity in the Polar Regions is an important factor for the global budget of water vapour, which is a significant indicator of Earth’s climate state and evolution. The Global Navigation Satellite System (GNSS) can make a valuable contribution in the calculation of the amount of Precipitable Water Vapour (PW). The PW values retrieved from Global Positioning System (GPS), hereafter PWGPS, refer to 20-year observations acquired by more than 40 GNSS geodetic stations located in the polar regions. For GNSS stations co-located with radio-sounding stations (RS), which operate Vaisala radiosondes, we estimated the PW from RS observations (PWRS). The PW values from the ERA-Interim global atmospheric reanalysis were used for validation and comparison of the results for all the selected GPS and RS stations. The correlation coefficients between times series are very high: 0.96 for RS and GPS, 0.98 for RS and ERA in the Arctic; 0.89 for RS and GPS, 0.97 for RS and ERA in Antarctica. The Root-Mean-Square of the Error (RMSE) is 0.9 mm on average for both RS vs. GPS and RS vs. ERA in the Arctic, and 0.6 mm for RS vs. GPS and 0.4 mm for RS vs. ERA in Antarctica. After validation, long-term trends, both for Arctic and Antarctic regions, were estimated using Hector scientific software. Positive PWGPS trends dominate at Arctic sites near the borders of the Atlantic Ocean. Sites located at higher latitudes show no significant values (at 1σ level). Negative PWGPS trends were observed in the Arctic region of Greenland and North America. A similar behaviour was found in the Arctic for PWRS trends. The stations in the West Antarctic sector show a general positive PWGPS trend, while the sites on the coastal area of East Antarctica exhibit some significant negative PWGPS trends, but in most cases, no significant PWRS trends were found. The present work confirms that GPS is able to provide reliable estimates of water vapour content in Arctic and Antarctic regions too, where data are sparse and not easy to collect. These preliminary results can give a valid contribution to climate change studies.

Machine learning methods for Precipitable Water Vapor estimation by radiometric data in millimetre wavelength

This work deals with the first try to calculate the amount of Precipitable Water Vapor (PWV) in atmosphere by using machine learning and AI methods. We use the detector voltages series measured by radiometric system “MIAP-2” as the initial data for machine learning. The radiometer MIAP-2 works by “atmospheric dip method” in 2mm and 3mm atmospheric transparency windows. We also have PWV data series collected by Water Vapor Radiometer and GNSS receiver for data validation. The best convergence results were demonstrated by the independent component analysis (ICA) method with coefficient of determination R2= 0.53 and artificial neural network method (ANN) with R2= 0.8. These methods allow to reduce the systematic errors due to direct PWV calculation from raw radiometric data avoiding unnecessary steps opacity calculation.

Monitoring precipitable water vapour in near real-time to correct near-infrared observations using satellite remote sensing

Context. In the search for small exoplanets orbiting cool stars whose spectral energy distributions peak in the near infrared, the strong absorption of radiation in this region due to water vapour in the atmosphere is a particularly adverse effect for ground-based observations of cool stars. Aims. To achieve the photometric precision required to detect exoplanets in the near infrared, it is necessary to mitigate the effect of variable precipitable water vapour (PWV) on radial-velocity and photometric measurements. The aim is to enable global PWV correction by monitoring the amount of precipitable water vapour at zenith and along the line of sight of any visible target. Methods. We developed an open-source Python package that uses imagery data obtained with the Geostationary Operational Environmental Satellites (GOES), which provide temperature and relative humidity at different pressure levels to compute the near real-time PWV above any ground-based observatory that is covered by GOES every 5 min or 10 min, depending on the location. Results. We computed PWV values on selected days above Cerro Paranal (Chile) and San Pedro Mártir (Mexico) to benchmark the procedure. We also simulated different pointing at test targets as observed from the sites to compute the PWV along the line of sight. To asses the accuracy of our method, we compared our results with the on-site radiometer measurements obtained from Cerro Paranal. Conclusions. Our results show that our publicly available code proves to be a good supporting tool for measuring the local PWV for any ground-based facility within the GOES coverage, which will help to reduce correlated noise contributions in near-infrared ground-based observations that do not benefit from on-site PWV measurements.

Precipitable Water Vapor Variation in the Clear-Cloud Transition Zone From the ARM Shortwave Spectrometer

A new technique to retrieve precipitable water vapor (PWV) amount in the clear-cloud transition zone using ground-based zenith spectral radiance is developed. The method uses zenith radiances at the water vapor band at 720 nm and at the adjacent nonadsorbing band at 750 nm. Radiative transfer calculations show that the relative difference in zenith radiance between the two bands depends on PWV and the variations in cloud optical depth introduce a small change in the relative difference which is independent of PWV amount. This allows us to retrieve PWV variations in the clear-cloud transition zone for clouds over dark ocean surface. We applied this method to a Cu cloud case with zenith radiance observations by Shortwave Array Spectroradiometer-Zenith (SASZe) during the Marine ARM GPCI Investigation of Clouds (MAGIC) field campaign. We found that there is about 10% change in PWV amount from the known-cloudy region to known-clear sky in the cloud edges.

Water vapor retrieval using the Airborne Multiangle SpectroPolarimetric Imager

The Airborne Multiangle SpectroPolarimetric Imager (AirMSPI) acquires radiance measurements in eight spectral bands centered at 355, 380, 445, 470*, 555, 660*, 865*, and 935 nm, three of which also measure linear polarization (denoted by asterisks). A two-step retrieval approach is developed to retrieve total precipitable water vapor (PWV) abundance: a) the first step is a fast estimate of water vapor obtained by comparing the ratio of observed radiance in the near-infrared (NIR) bands L935nm/L865nm at multiple view angles against pre-calculated lookup table values as a function of PWV abundance, on the assumption of no aerosols and a moderately bright land surface; (b) the second step refines the estimated solution by accounting for aerosol loading, particle properties, and surface reflection, which are retrieved from AirMSPI measurements in its ultraviolet to NIR aerosol bands. Our retrieval is tested using 27 AirMSPI datasets with low to moderately high aerosol loadings and PWV up to about 3.5 cm, acquired during four NASA field campaigns plus one AirMSPI engineering test flight. Comparison of the retrieved total PWV amount against AERONET reference data shows a mean percentage difference 8.6%. The quantities that inform the second step of the PWV retrieval—namely, aerosol optical depth (AOD), aerosol single scattering albedo (SSA), and aerosol effective radius—are also compared to the AERONET reference data. The mean absolute differences (MADs) are less than 0.0253 and less than 0.036 for AOD and SSA in the visible, respectively. The MADs are 0.036 μm and 1.232 μm for the effective radius of fine and coarse mode aerosols, respectively. Comparison to data from the Cloud Physics Lidar places the MAD of aerosol layer height at about 360 m.

An overview of and issues with sky radiometer technology and SKYNET

Abstract. This paper is an overview of the progress in sky radiometer technology and the development of the network called SKYNET. It is found that the technology has produced useful on-site calibration methods, retrieval algorithms, and data analyses from sky radiometer observations of aerosol, cloud, water vapor, and ozone. A formula was proposed for estimating the accuracy of the sky radiometer calibration constant F0 using the improved Langley (IL) method, which was found to be a good approximation to observed monthly mean uncertainty in F0, around 0.5 % to 2.4 % at the Tokyo and Rome sites and smaller values of around 0.3 % to 0.5 % at the mountain sites at Mt. Saraswati and Davos. A new cross IL (XIL) method was also developed to correct an underestimation by the IL method in cases with large aerosol retrieval errors. The root-mean-square difference (RMSD) in aerosol optical thickness (AOT) comparisons with other networks took values of less than 0.02 for λ≥500 nm and a larger value of about 0.03 for shorter wavelengths in city areas and smaller values of less than 0.01 in mountain comparisons. Accuracies of single-scattering albedo (SSA) and size distribution retrievals are affected by the propagation of errors in measurement, calibrations for direct solar and diffuse sky radiation, ground albedo, cloud screening, and the version of the analysis software called the Skyrad pack. SSA values from SKYNET were up to 0.07 larger than those from AERONET, and the major error sources were identified as an underestimation of solid viewing angle (SVA) and cloud contamination. Correction of these known error factors reduced the SSA difference to less than 0.03. Retrievals of other atmospheric constituents by the sky radiometer were also reviewed. Retrieval accuracies were found to be about 0.2 cm for precipitable water vapor amount and 13 DU (Dobson Unit) for column ozone amount. Retrieved cloud optical properties still showed large deviations from validation data, suggesting a need to study the causes of the differences. It is important that these recent studies on improvements presented in the present paper are introduced into the existing operational systems and future systems of the International SKYNET Data Center.

Method for retrieval of atmospheric water vapor using OH airglow for correction of astronomical observations

Context. Water vapor in the atmosphere undergoes quick spatial and temporal variations. This has a serious impact on ground-based astronomical observations from the visible band to the infrared band resulting from water vapor attenuation and emission. Aims. We seek to show how the sky spectrum of an astronomical observation can be used to determine the amount of precipitable water vapor (PWV) along the line of sight toward the science target. Methods. In this work, we discuss a method to retrieve the PWV from the OH(8-3) band airglow spectrum. We analyzed the influences of the pressure and temperature of the atmosphere and the different water vapor vertical distributions on the PWV retrieval method in detail. Meanwhile, the accuracy of the method was analyzed via Monte Carlo simulations. To further verify the method of PWV retrieval, we carried out cross comparisons between the PWV retrieved from OH airglow and PWV from the standard star spectra of UVES using equivalent widths of telluric absorption lines observed from 2000 to 2016 at Cerro Paranal in Chile. Results. The Monte Carlo tests and the comparison between the two different methods prove the availability the PWV retrieval method from OH airglow. These results show that using OH airglow spectra in astronomical observations, PWVs along the same line of sight as the astronomical observations can be retrieved in real time. Conclusions. We provide a quick and economical method for retrieving the water vapor along the same line of sight of astronomical observation in the real time. This is especially helpful to correcting the effect of water vapor on astronomical observations.

An Empirical Model for Estimating Precipitable Water Vapor on the Tibetan Plateau

Using the ground meteorological and radiosonde data of 122 atmospheric stations from 1958 to 2008 all over China, excellent numerical correlations between precipitable water vapor (PWV) and ground humidity parameters such as ground water vapor pressure (e) have been derived; by introducing two parameters, latitude φ and altitude H, we establish an empirical model for estimating the total amount of PWV from e in different climatic areas in China, especially on the vast Tibetan Plateau with complex topography. In the validation, we make use of the ground meteorological data of the atmospheric weather station from 2016 July 12 to December 22 at the Ali observatory (32.°30N, 80.°05E, 5050 m above sea level), which is located in the most western part of the Tibetan Plateau, to obtain the total amount of PWV by the empirical model; compared with the PWV derived from radiosonde observations at Ali, the model shows a very good performance estimating PWV, and presents very well the seasonal and diurnal variations of PWV. The total amount of PWV derived from the empirical model at the observatory agree with that from radiosonde observations very well, with the correction coefficient R = 0.958 and the root mean square error RMSE = 1.04 mm; the errors between the model and observations are a bit larger in summer when PWV is rich, and small in winter when PWV values are usually less than 2.0 mm. Based on the empirical model, the median PWV value in 2017 at the Ali observatory was about 2.9 mm, and the values were less than 2.0 mm for half the 2017. Overall, the total amount of PWV derived from the empirical model is proved to be reliable, and the empirical model is excellent and accurate, allowing it to be implemented as an operational tool for estimating PWV at an astronomical site.

Observations of Precipitable Water Vapor along the Maritime Continent Associated with El Niño-Southern Oscillation Activity

The effect of El Nino and La Nina events is a major issue in the regional climate of Southeast Asia. This study uses the Precipitable Wa- ter Vapor (PWV) values estimated from Global Navigation Satellite System (GNSS; in particular Global Positioning System, GPS) to in- vestigate the El Nino-Southern Oscillation (ENSO) activity in the Southern coast of the South China Sea (SCS). For this study, GPS and meteorological systems are installed at the Universiti Malaysia Sabah, Kota Kinabalu (UMSK), which is located on the coast of the mar- itime continent. Subsequently, PWV from GPS and PWV obtained from Radiosonde, prior to the investigation of ENSO activity, are com- pared. To further investigate the relationship between PWV and ENSO activities, data from three additional GPS stations located along the coast of SCS during the 3-year period 2009-2011 were analyzed. The selection period considers the availability of GPS data. The obtained results show that during the increased intensity of El Nino in 2009/2010, PWV decreases and drops about 10-week later, i.e., after the sea surface temperature anomaly (SSTa) has peaked. PWV has a negative correlation with the El Nino index, which is comparable with pre- cipitation data obtained from NASA’s Tropical Rainfall Measuring Mission (TRMM). In contrast, the amount of PWV was increased dur- ing the La Nina event of 2010/2011. This observation suggests the GPS is a suitable technique for studying the ENSO activity.

Precipitable water vapor (PWV) estimations from the site of the Eastern Anatolia Observatory∗ (DAG), a new astronomical observatory in Turkey

We present preliminary statistics on the precipitable water vapor (PWV) content over the Karakaya Hills in Erzurum city, where the largest optical and near-infrared astronomical telescope in Turkey will be operated. Since the observatory will observe in the near-infrared (NIR), it is intended to perform PWV measurements of the atmosphere above the site by using signal delays in Global Positioning System (GPS) communication. The analysis of the GPS data recorded on the summit for almost one year shows that the atmosphere over the site of the observatory, which has an altitude of 3170 m, has favorable conditions for NIR observations. From GPS measurements, we report that the site had an average PWV of 3.2 mm and a median PWV of 2.7 mm between October 6, 2016, and June 15, 2017. We also present the time dependency of the PWV content and the correlations between the amount of PWV and the other meteorological records gathered from radiosonde flights and ground-based measurements.

Numerical study and experimental validation of a combined diurnal solar heating and nocturnal radiative cooling collector

Neither solar collectors nor nocturnal radiative cooling units could work all day. A novel combined diurnal solar heating and nocturnal radiative cooling (SH-RC) collector was proposed and investigated in this study. The collector can obtain heat at daytime and gather cooling energy at nighttime, therefore offering multi-functionality and enhancing its time utilization ratio. A spatial distributed parameter mathematic model that considers the spectral radiant distribution was established to evaluate the performance of the collector. Besides, the precipitable water vapor amount was introduced to predict the spectral emissivity of atmosphere. Experiments were conducted to validate results obtained from the numerical simulation. The root-mean-square deviations between the experimental and simulation results are only 4.59% for thermal efficiency and 4.90% for cooling power. Based on the validated models, the thermal performance of the collector was investigated under different insulation thicknesses, wind velocities, ambient and inlet temperatures, water flow rates, precipitable water vapor amounts and solar irradiance. Annual performances of four Chinese cities were also conducted. The annual heat gains of the SH-RC collector in Beijing, Hefei, Fuzhou and Urumqi are 3328.76, 2423.53, 2543.31 and 3313.46 MJ/m2, respectively. The annual net radiative cooling gains of the collector in the four cities are 862.44, 831.54, 741.63 and 775.34 MJ/m2, respectively.

Comparison of precipitable water vapor derived from AIRS and SPM measurements and its correlation with surface temperature of 29 synoptic stations over Iran

Distribution of atmospheric water vapor is highly variable in time and space across the Earth; the knowledge of its distribution is essential in climate studies. In Iran, atmospheric water vapor measurements using conventional ground-based methods such as radiosondes are limited. In this paper, a comparison of precipitable water vapor (PWV) estimated by a ground-based sunphotometer (SPM) with atmospheric infrared sounder (AIRS) satellite sensor is presented over Zanjan, a city in northwest Iran for a period from December 2009 to December 2013. The PWV of SPM and AIRS have a good agreement (R2 = 93%). The seasonal bias between PWV estimated by SPM and AIRS (PWV SPM - PWV AIRS) over Zanjan city is −3.35, −5.15, −2.27, −0.95 mm during spring, summer, autumn, and winter, respectively. Average of AIRS PWV over Iran shows that the largest amount of PWV occurs along the seas (Caspian Sea, Oman Sea, and the Persian Gulf) and its lowest value happens in high altitude mountainous regions of the country. Also, correlation coefficients between AIRS PWV and surface temperature of 29 synoptic stations are calculated over Iran from September 2002 to December 2016. The average of correlation coefficients over the stations is 0.73.

Conceptual development of a building-integrated photovoltaic–radiative cooling system and preliminary performance analysis in Eastern China

Building-integrated photovoltaic/thermal (BIPV/T) technology has been receiving considerable research attention because of its ability to generate electricity and thermal energy simultaneously. However, space cooling is crucial for buildings in hot regions where space heating is of little use. This study proposed a building-integrated photovoltaic–radiative cooling system (BIPV–RC) that can generate electricity via photovoltaic (PV) conversion during daytime and generate cooling energy via radiative cooling (RC) during nighttime to satisfy the demand in such areas. The selective plate, which is the main component of the BIPV–RC system, exhibits high spectral absorptivity (emissivity) in the PV conversion band of crystalline silicon solar cells and in the atmospheric window band (i.e., 0.3–1.1μm and 8–13μm), as well as low spectral absorptivity (emissivity) in other bands. A quasi-steady-state mathematical model was built, and its performance under realistic ambient conditions was analyzed. The electrical efficiencies of the BIPV–RC and conventional BIPV systems were then compared under different solar radiations. Comparison results show that the annual electricity production and cooling energy gain of the BIPV–RC system in Hefei reached 156.74kWhm−2 (equivalent to 564.26MJm−2) and 579.91MJm−2, respectively. The total electricity production and cooling energy gain of this system are 96.96% higher than those of the BIPV system. Parametric studies show that the precipitable water vapor amount has remarkable effects on the nocturnal RC performance of the BIPV–RC system. A small precipitable water vapor amount corresponds to a high nocturnal RC power, thereby implying that a dry climate condition benefits the nocturnal RC of this system.

Effect of Precipitable Water Vapor Amount on Radiative Cooling Performance

A radiative cooler based on aluminum-evaporated polyvinyl-fluoride surface was employed to investigate the effect of precipitable water vapor amount on its radiative cooling performance. A mathematic model of steady heat transfer that considers the spectral radiant distribution of the sky, the transparent cover and the collecting surface was established. The results indicate that the amount of precipitable water vapor shows a remarkable and negative effect on radiative cooling performance of the radiative cooler. Both the temperature difference between the cooler and surroundings and the net radiative cooling power decrease as the precipitable water vapor amount increases. The net radiative cooling power drops by about 41.0% as the the precipitable water vapor amount changes from 1.0 cm to 7.0 cm. Besides, the radiative cooler shows better cooling performance in winter than in summer. The net radiative cooling power in summer of Hefei is about 82.2% of that in winter.

Preliminary thermal analysis of a combined photovoltaic–photothermic–nocturnal radiative cooling system

A novel combined photovoltaic–photothermic–nocturnal radiative cooling (PV–PT–RC) system was proposed to achieve multifunctional and all-weather operation. The proposed system collects electricity and heat energy at daytime through PV and PT conversions and cooling energy at nighttime through RC. A quasi-steady-state mathematical model that considers the spectral radiant distribution was established. A sensitivity analysis of the model to key inputs was carried out as well. An experimental apparatus was used to test the daily solar heating and nocturnal RC performance of the system, as well as verify the correctness of the mathematical model. The equilibrium temperature of the collecting plate showed root-mean-square deviation results of 2.8% and 1.8% in daily and nocturnal operation modes respectively, thereby validating the mathematical model. Simulation studies were performed to investigate the cooling performance of the PV–PT–RC system using the validated model. Results showed that insulation thickness and ambient temperature positively affects cooling performance, whereas wind velocity and precipitable water vapor amount negatively affects cooling performance. The RC performances of the PV–PT–RC system in different Chinese cities were investigated. The system exhibited optimal cooling performance during winter in northwestern China and the weakest cooling performance during summer in southeastern China.

ALMA Long Baseline Campaigns: Phase Characteristics of Atmosphere at Long Baselines in the Millimeter and Submillimeter Wavelengths

We present millimeter- and submillimeter-wave phase characteristics measured between 2012 and 2014 of Atacama Large Millimeter/submillimeter Array long baseline campaigns. This paper presents the first detailed investigation of the characteristics of phase fluctuation and phase correction methods obtained with baseline lengths up to ∼15 km. The basic phase fluctuation characteristics can be expressed with the spatial structure function (SSF). Most of the SSFs show that the phase fluctuation increases as a function of baseline length, with a power-law slope of ∼0.6. In many cases, we find that the slope becomes shallower (average of ∼0.2–0.3) at baseline lengths longer than ∼1 km, namely showing a turn-over in SSF. These power law slopes do not change with the amount of precipitable water vapor (PWV), but the fitted constants have a weak correlation with PWV, so that the phase fluctuation at a baseline length of 10 km also increases as a function of PWV. The phase correction method using water vapor radiometers (WVRs) works well, especially for the cases where PWV , which reduces the degree of phase fluctuations by a factor of two in many cases. However, phase fluctuations still remain after the WVR phase correction, suggesting the existence of other turbulent constituent that cause the phase fluctuation. This is supported by occasional SSFs that do not exhibit any turn-over; these are only seen when the PWV is low (i.e., when the WVR phase correction works less effectively) or after WVR phase correction. This means that the phase fluctuation caused by this turbulent constituent is inherently smaller than that caused by water vapor. Since in these rare cases there is no turn-over in the SSF up to the maximum baseline length of ∼15 km, this turbulent constituent must have scale height of 10 km or more, and thus cannot be water vapor, whose scale height is around 1 km. Based on the characteristics, this large scale height turbulent constituent is likely to be water ice or a dry component. Excess path length fluctuation after the WVR phase correction at a baseline length of 10 km is large (), which is significant for high frequency ( or ) observations. These results suggest the need for an additional phase correction method to reduce the degree of phase fluctuation, such as fast switching, in addition to the WVR phase correction. We simulated the fast switching phase correction method using observations of single quasars, and the result suggests that it works well, with shorter cycle times linearly improving the coherence.

Modelling and validation of the weighted mean temperature for Turkey

ABSTRACTWater vapour is involved in many atmospheric processes. Precipitation specifically relies on the amount of precipitable water vapour (PWV) or the water vapour content suspended in the atmosphere.Opportunities with regard to the conversion of existing continuous Global Navigation Satellite System (GNSS) stations to GNSS meteorology stations (GNSS MET) with very little cost and acquisition of near real‐time water vapour have become popular in studies of the estimation of water vapour using GNSSs. In order to convert the GNSS observables into meteorological assets, one has to account for the extremely important conversion parameters between zenith wet delay and PWV in GNSS meteorology: Tm or Q. They are estimated by analysis of radiosonde profile observations of a radiosonde station (RS).In this study, linear Tm models were estimated from 4103 profile observations of eight Turkish RSs for the year 2011. The verification of these models was tested by using 1 year of observations at the Ankara and Istanbul RS‐GNSS stations. A Tm = 48.55 + 0.80Ts model was computed for Turkey with a root mean square error of ±2.57 K. The accuracies of PWV derived from the developed Tm model and the GNSS observations at the Ankara and Istanbul stations in 2013 and 2014 were found to be ±1.7 and ±1.8 mm, respectively.

Experimental investigation of simple solar radiation spectral model performances under a Mediterranean Algerian's climate

In this work, models are presented that, under cloudless atmosphere conditions, calculate solar spectral normal direct and horizontal diffuse irradiance. Based on different monochromatic transmission factors related to the main constituents of the atmosphere, the models evaluate the spectral irradiance between 0.29 and 4.0 μm. Absorption by water vapor, uniformly mixed gas, and ozone are considered as well as scattering by the atmospheric aerosols. Based on the equations relative to each one of the two retained models, a MATLAB program is developed to evaluate the spectral distribution of each solar irradiance component. Hence, the geographical coordinates of the site, and the monochromatic distribution of the extraterrestrial irradiance are used as input data. From three-year data measurement records made in Bouzareah site (temperate climate), thirty eight days characterized by a clear sky state have been selected from over different months of the year and the corresponding main meteorological parameters used as input parameters. So, because only the five-minute broadband data measurements are available, the modified numerical trapeze method is used to integrate the monochromatic curve values related to each solar irradiance component. Consequently, the precipitable water vapor amount, the Angstrom and Linke turbidity factors are evaluated and a multi-linear correlation relating the Linke turbidity factor to the precipitable water vapor and the Angstrom turbidity coefficient is established. Hence, according to the mean values of Linke and Angstrom turbidity factors and those of the precipitable water vapor, the site of Bouzareah is classified as a rural site. So, the effect of the main constituents of the atmosphere on the spectral distribution of solar irradiance is discussed and, it is also observed that the aerosol amount contained in the atmosphere affects most both of the diffuse and direct solar irradiance amount than that of the horizontal and inclined solar global components. Conversely, it is observed that it is less efficient in evaluating the horizontal diffuse components and its accuracy depends on several scattering phenomena, which are represented by scientists by means of constant values or expressions. The reasonable accuracy of the model and for it's simplicity make it for a number of solar applications.

Modeling beam attenuation in solar tower plants using common DNI measurements

Solar radiation reflected by concentrating mirrors is attenuated due to atmospheric extinction as it travels to the receiver of a solar tower plant. The lack of information on the magnitude of extinction increases the uncertainties in yield analysis and tower plant design. In-situ measurements of atmospheric extinction as well as measurement correction methods have been recently performed and developed (Hanrieder et al., 2012, 2015), but specific information is unavailable for individual plant projects. It is well known though that the extinction varies significantly with site and time.To overcome this absence of information a model to derive the attenuation loss between heliostat and receiver from common direct normal irradiance (DNI) measurements was developed by Sengupta and Wagner (2011) (SW2011 model). We present an updated version of that model and a comparison between the performance of the models using extinction measurements.In the new approach presented here, different precipitable water vapor (PWV) amounts are considered and the model is adjusted to the elevation of the investigated site.The strongest assumption in this approach is the assumption about the aerosol extinction height profile. Three different height profiles are tested for the Plataforma Solar de Almería (PSA) resulting in three different new transmittance models.The SW2011 as well as the three new models are evaluated with one year of corrected extinction data derived with the ABC (absorption and broadband correction) method of Hanrieder et al. (2015) and a Vaisala FS11 scatterometer at PSA. The new models show a mean difference to the reference data set of 0.01, 0.05 and 0.03 and a root mean square error (RMSE) of 0.052, 0.056 and 0.049 (compared to a mean bias of −0.08 and RMSE of 0.095 for the SW2011 model for transmittances through a 1km slant range). These results indicate the importance of adequate assumptions for the aerosol height profile. Testing the developed TM with the LIVAS height profile (Amiridis et al., 2015) for PSA shows satisfying results and this motivates testing the approach for other sites. By applying an additional correction for the Linke turbidity (TL) derived as in Ineichen and Perez (2002) the mean bias can be further lowered.An uncertainty analysis shows that the absolute uncertainty coincide with the RMSE levels of the evaluation. Performing the additional TL correction promises an improvement of the overall performance of the model.The new models outperform the SW2011 model due to the PWV and elevation adjustments. The approach can be applied for different sites and incorporated in already existing ray-tracing or plant optimization tools. It is expected to be valuable for reducing uncertainty in power tower design and operations.