In section 5 the validation results are presented and discussed, and their implications are presented in section 6. Estimation of the UV reaching the Earth's surface is divided in two parts. The surface albedo information required for modeling of the surface UV irradiance is not pointwise surface albedo but rather a regional quantity, referred to as effective albedo, that describes the overall effect of the surface albedo of the surrounding area on the surface UV irradiance. Krotkov et al.
We have used two different methods for determination of CMF. The details of the PPC model based cloud correction method are described by Krotkov et al. LER is determined by solving a simple form of the radiative transfer equation that assumes a pure Rayleigh scattering atmosphere bounded by an isotropically scattering Lambertian surface [e. This enabled comparison of the performance of the two alternative cloud correction methods. Estimation of the CMF for mountainous regions is difficult because mountain peaks often rise above the clouds.
Greatest overestimations are anticipated for regions affected by urban pollution and for major natural aerosol episodes. However, the UV irradiances are calculated for local solar noon. Corrections are not made for possible changes in cloudiness or total column ozone between the local noon and satellite overpass time. The erythemal daily dose is determined by applying the trapezoidal integration method to the hourly erythemal dose rates calculated assuming the total column ozone and cloud optical depth corresponding to a single OMI measurement. Bugliaro et al. Martin et al. This finding, however, applies only for sites with no systematic diurnal course cycle of cloudiness.
Formation of convective clouds causes increased afternoon cloudiness [e. The occurrence of convective clouds depends on latitude and climate being common at lowlatitudes and midlatitudes in summer. Among the validation sites included in this study, the role of the convective clouds was considered to be the most significant for Mauna Loa and Boulder.
This kind of fog, that has a clear diurnal cycle, can be formed by radiational cooling during the night. However, the radiation fog usually disappears soon after sunrise and has hardly any effect on the accumulated daily dose. The primary contents of the OMUVB granules are erythemally weighted daily dose and erythemal dose rate at local solar noon. Additionally, the product includes spectral irradiances at The spectral irradiances assume triangular slit function with full width half maximum of 0.
The overpass data files include all the OMI data whose center of the ground pixel is within 50 km from the measurement site. For high latitudes, OMI provides more than one overpass per day. In this validation study we used the OMI data that were recorded closest to the solar noon minimum solar zenith angle.
The first OMI data correspond to late August , but the instrument started to provide data on a more regular basis in September The measurement sites, which are summarized in Table 1 , represent different latitudes, elevations, and climatic conditions. More detailed description of local conditions at each validation site is included in the discussion of the validation results. All the instruments are well maintained, calibrated regularly, and their data are corrected for major error sources.
The following subsections provide more detailed information on the instruments deployed within each network. In Finland, routine spectral UV measurements are performed at two sites. They are scheduled to perform spectral scans at fixed solar zenith angles, and, additionally, at solar noon each day. This yields a typical scan frequency of once or twice an hour.
The data processing includes corrections for dark current, spikes [ Meinander et al. The method is assessed to result in erythemal dose rates that are accurate within a few percents.
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Both Finnish instruments have participated actively in international intercomparison campaigns [e. In addition, a national comparison is arranged annually. Spectral scans are normally taken every 12 min from sunrise to sunset. More details are found in the work of den Outer et al.
The data are corrected for dark current, spikes, temperature dependence and angular response errors. More details on the instrument performance, quality control, corrections and data retrieval can be found in the work of Bais et al. Spectral scans are normally performed from one to four times an hour throughout the day from sunrise to sunset [ McArthur et al. This estimate includes a small contribution from not correcting for the temperature dependence of the instruments [ Weatherhead et al.
From the short single monochromator Brewer spectra the erythemal dose rates are calculated using an empirically derived, increased weighting value for the measured nm irradiance. The instrument setup has been described by McKenzie et al. The measurements are corrected for stray light, dark current, nonlinearities in the wavelength drive, temperature dependence of the diffuser [ McKenzie et al.
Previous measurement intercomparison campaigns [e. The instruments are designed and manufactured by Biospherical Instruments Inc.
Materials and Methods
Spectral scans are taken every 15 min. These additional data were used for interpretation of the validation results. The data sets were combined to form a paired daily dose time series. For sites experiencing snow cover, the data pairs were treated separately for high and low surface albedo cases; when the UV surface albedo according to the climatology [ Tanskanen , ] was higher than 0.
Hereafter the terms wintertime and summertime refer to the two separate classes of data pairs for sites where snow cover changes seasonally.
It should be noted that because the true snow conditions may diverge from the surface albedo climatology, part of the data pairs were not classified correctly. According to the surface albedo climatology in Summit and McMurdo, the climatological surface albedo was above 0. Therefore prior to statistical analysis, a threshold filter of 0. The two different cloud correction methods show some systematic features. The PPC model tends to give somewhat higher values of the erythemal daily dose, and for many validation sites the PPC doses differed more from the reference data than the doses obtained with the LER method.
The results are in accordance with previous findings of Krotkov et al. However, it should be remembered that because the current surface UV algorithm does not account for tropospheric extinction, a positive bias is anticipated for sites affected by absorbing aerosols or trace gases. Both cloud correction methods were affected by errors in assumed surface albedo, but the PPC model performed somewhat better in these cases. In the following subsection the validation results are examined site by site starting from simple cases and working towards the more complex cases.
The analysis is focused on validation results for the PPC model, but most of the findings are valid also for the LER model. The algorithm does not apply any cloud correction for sites above 2. The plot illustrates the role of clouds on UV doses at a high elevation measurement site: satellite algorithm performs well at cloud free conditions, but clouds lead to underestimation of the surface UV dose at Mauna Loa.
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The channel does not freeze, but according to the NSF surface albedo data, snow cover increases the effective albedo up to 0. In Churchill, snow begins accumulating in November, lasts through April, and is melted by June. The maximum climatological wintertime surface albedo used by the OMI surface UV algorithm is of the order of 0. The summertime positive bias may be caused by aerosols originating from forest fires [ Holben et al. Forest fires are episodic events and show large variation in their extent, and thus it is difficult to account for their effect on surface UV irradiance.
The number of snow cover days is typically about , and snow cover can increase the effective surface UV albedo up to 0. The causes of biases are likely similar to those identified for Churchill. However, the possible sources of aerosols and trace gases include urban pollution and smoke from agricultural and forest fires [ Stohl et al. The average number of snow cover days is 75, and snow cover elevates the effective albedo of the urban area to about 0.
Formation of convective clouds may partly explain the observed difference in bias. The Chukchi Sea is typically covered by ice from November to July, while the flat tundra around the site is usually covered by snow from October to June. Arctic aerosol loadings peak in winter and spring, and as the aerosol mixture includes absorbing components the amount of UV radiation reaching the surface is decreased [ Wetzel et al.
The number of summertime data pairs is too small to make conclusive remarks, which is partly caused by the surface albedo climatology that likely overestimates the surface albedo in late summer. At Eureka snow cover typically starts to accumulate in September and lasts till the end of April. There are no local sources of pollution in Eureka, but the site is affected by Arctic haze [ Ishii et al. The area is subarctic, and the average number of snow cover days is more than The effective surface albedo ranges from a few percents in summer up to 0.
According to the validation results, the OMI surface UV algorithm performs well both in summer and winter in spite of the seasonal variation of the surface albedo due to snow cover.
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McMurdo Station is located at Ross Island and surrounded by ice shelves and glaciers. The surface in the immediate vicinity of the instrument is typically covered by snow, but dark volcanic rock may be exposed during summer months January to March , leading to a drop in effective UV albedo to about 0. Palmer Station is situated at Anvers Island, west of the Antarctic peninsula. The ocean surrounding the glaciated island is frozen during winter and open during summer, leading to an annual cycle in albedo with values of about 0.
The Antarctic atmosphere is the cleanest globally [ Shaw , ; Herber et al. The modeling error is caused by the climatological surface albedo that deviates substantially from the NSF surface albedo data, which leads to overestimation of cloudiness.
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Table 3. In the group of fattening pigs, we found the highest concordance over all evaluated production groups in the benchmarking of farms overall similarity We observed Table 4. Figure 3 shows the distribution of the calculated weight for broilers A , suckling piglets B and fattening pigs C based on the ADFs considered in this current evaluation.
The median of the estimated weight of the broilers was 0. Figure 3. Distribution of the estimated weights of broiler A , suckling piglets B and fattening pigs C at the time of treatment. The present work compares two different methods to calculate antibiotic usage in livestock, demonstrating the differences between applying the Used Daily Dose UDD and Defined Daily Dose DDD and their consequences for individual farmers as well as at the general population level.
Both TF calculations are generally in line with the incidence density concept for presenting new events within a given time period In this evaluation, we used the number of livestock places as a proxy for the animal population at risk 23 , 24 , The number of livestock places is not exactly equal to the number of animals stabled and maintained during the fattening period, which could vary slightly due to mortality or temporary overcrowding.
Those differences between livestock places and the exact number of animas stabled or present at the farm at any time can lead to an over- or underestimation of the TF at some point, but we consider that bias to be negligible and compensated by the observation that the number of barn places remains stable over time.