Impact Of Cloudiness Research Articles

Combination of Sentinel-1 and Sentinel-2 Data for Tree Species Classification in a Central European Biosphere Reserve

Microwave and optical imaging methods react differently to different land surface parameters and, thus, provide highly complementary information. However, the contribution of individual features from these two domains of the electromagnetic spectrum for tree species classification is still unclear. For large-scale forest assessments, it is moreover important to better understand the domain-specific limitations of the two sensor families, such as the impact of cloudiness and low signal-to-noise-ratio, respectively. In this study, seven deciduous and five coniferous tree species of the Austrian Biosphere Reserve Wienerwald (105,000 ha) were classified using Breiman’s random forest classifier, labeled with help of forest enterprise data. In nine test cases, variations of Sentinel-1 and Sentinel-2 imagery were passed to the classifier to evaluate their respective contributions. By solely using a high number of Sentinel-2 scenes well spread over the growing season, an overall accuracy of 83.2% was achieved. With ample Sentinel-2 scenes available, the additional use of Sentinel-1 data improved the results by 0.5 percentage points. This changed when only a single Sentinel-2 scene was supposedly available. In this case, the full set of Sentinel-1-derived features increased the overall accuracy on average by 4.7 percentage points. The same level of accuracy could be obtained using three Sentinel-2 scenes spread over the vegetation period. On the other hand, the sole use of Sentinel-1 including phenological indicators and additional features derived from the time series did not yield satisfactory overall classification accuracies (55.7%), as only coniferous species were well separated.

The impact of cloudiness and cloud type on the atmospheric heating rate of black and brown carbon in the Po Valley

Abstract. We experimentally quantified the impact of cloud fraction and cloud type on the heating rate (HR) of black and brown carbon (HRBC and HRBrC). In particular, we examined in more detail the cloud effect on the HR detected in a previous study (Ferrero et al., 2018). High-time-resolution measurements of the aerosol absorption coefficient at multiple wavelengths were coupled with spectral measurements of the direct, diffuse and surface reflected irradiance and with lidar–ceilometer data during a field campaign in Milan, Po Valley (Italy). The experimental set-up allowed for a direct determination of the total HR (and its speciation: HRBC and HRBrC) in all-sky conditions (from clear-sky conditions to cloudy). The highest total HR values were found in the middle of winter (1.43 ± 0.05 K d−1), and the lowest were in spring (0.54 ± 0.02 K d−1). Overall, the HRBrC accounted for 13.7 ± 0.2 % of the total HR, with the BrC being characterized by an absorption Ångström exponent (AAE) of 3.49 ± 0.01. To investigate the role of clouds, sky conditions were classified in terms of cloudiness (fraction of the sky covered by clouds: oktas) and cloud type (stratus, St; cumulus, Cu; stratocumulus, Sc; altostratus, As; altocumulus, Ac; cirrus, Ci; and cirrocumulus–cirrostratus, Cc–Cs). During the campaign, clear-sky conditions were present 23 % of the time, with the remaining time (77 %) being characterized by cloudy conditions. The average cloudiness was 3.58 ± 0.04 oktas (highest in February at 4.56 ± 0.07 oktas and lowest in November at 2.91 ± 0.06 oktas). St clouds were mostly responsible for overcast conditions (7–8 oktas, frequency of 87 % and 96 %); Sc clouds dominated the intermediate cloudiness conditions (5–6 oktas, frequency of 47 % and 66 %); and the transition from Cc–Cs to Sc determined moderate cloudiness (3–4 oktas); finally, low cloudiness (1–2 oktas) was mostly dominated by Ci and Cu (frequency of 59 % and 40 %, respectively). HR measurements showed a constant decrease with increasing cloudiness of the atmosphere, enabling us to quantify for the first time the bias (in %) of the aerosol HR introduced by the simplified assumption of clear-sky conditions in radiative-transfer model calculations. Our results showed that the HR of light-absorbing aerosol was ∼ 20 %–30 % lower in low cloudiness (1–2 oktas) and up to 80 % lower in completely overcast conditions (i.e. 7–8 oktas) compared to clear-sky ones. This means that, in the simplified assumption of clear-sky conditions, the HR of light-absorbing aerosol can be largely overestimated (by 50 % in low cloudiness, 1–2 oktas, and up to 500 % in completely overcast conditions, 7–8 oktas). The impact of different cloud types on the HR was also investigated. Cirrus clouds were found to have a modest impact, decreasing the HRBC and HRBrC by −5 % at most. Cumulus clouds decreased the HRBC and HRBrC by −31 ± 12 % and −26 ± 7 %, respectively; cirrocumulus–cirrostratus clouds decreased the HRBC and HRBrC by −60 ± 8 % and −54 ± 4 %, which was comparable to the impact of altocumulus (−60 ± 6 % and −46 ± 4 %). A higher impact on the HRBC and HRBrC suppression was found for stratocumulus (−63 ± 6 % and −58 ± 4 %, respectively) and altostratus (−78 ± 5 % and −73 ± 4 %, respectively). The highest impact was associated with stratus, suppressing the HRBC and HRBrC by −85 ± 5 % and −83 ± 3 %, respectively. The presence of clouds caused a decrease of both the HRBC and HRBrC (normalized to the absorption coefficient of the respective species) of −11.8 ± 1.2 % and −12.6 ± 1.4 % per okta. This study highlights the need to take into account the role of both cloudiness and different cloud types when estimating the HR caused by both BC and BrC and in turn decrease the uncertainties associated with the quantification of their impact on the climate.

The impact of clouds on the brightness of the night sky

Clouds are a kind of atmospheric factor that most effectively scatters the artificial light coming from the ground. Therefore, they have the most significant impact on the brightness of the night sky. The paper analyses the influence of both the level of cloudiness, as well as the genera of clouds and altitude of its base, on amplifying of the light pollution. The impact of cloudiness on the brightness of the night sky in places with different levels of light pollution was researched. Measurements of meteorological elements were used together with clouds genera assessments. The introduction of an innovative method of identifying some genera of clouds on the base of the all-night continuous measurements of the sky's brightness allowed for a similar analysis in the absence of observational data specifying the genera of clouds.A linear correlation between the cloudiness and the brightness of the night sky was found. The determined linear correlation parameters allow for specifying the three types of light-polluted areas, possibly related to the density of population. It was found that among the nine genera of the identified night clouds, the Altocumulus, Cirrocumulus, and Cumulonimbus ones are responsible for this correlation. No dependence of the brightness of the night sky on the clouds’ albedo was found. In case of overcast sky, there was a clear relationship between the average altitude of the individual genus of clouds and the brightness of the night sky. Most of the night sky brightness comes from the light scattered on the lowest altitude clouds genera, while the least contribution comes from the light scattered on the high-level clouds. It was also found that at the freezing temperatures, the layer of aerosols forms below the level of the genera Nimbostratus or Stratus. This layer, thickening with the decreasing temperature, additionally scatters the artificial light.

Assessment of the Energy Gain of Photovoltaic Systems by Using Solar Tracking in Equatorial Regions

Solar tracking is a major alternative to increase the electric output of a photovoltaic (PV) module, and therefore, improves the global energy collected by PV systems. Nonetheless, solar-tracking PV systems require more resources and energy than static systems. Additionally, the presence of cloudiness and shadows from near buildings may reduce the profitability of these systems. Therefore, their feasibility must be assessed in order to justify their application. In equatorial latitudes, the sun's movement through the sky is in the zenith East–West axis. It may be advantageous, since the best tilt in such latitudes is the horizontal. In these terms, the main objective of this research is to numerically assess the performance of a PV array with solar tracking and under typical operation conditions in equatorial latitudes. For this, the assessment of the solar resource in Quito was analyzed in first place. Then, the comparison between three solar arrays was studied to evaluate the feasibility of solar tracking (two-axes tracking, horizontal one-axis tracking, and horizontal fixed). Additionally, the impact of cloudiness and shadows in the system was analyzed. The results showed that the horizontal one-axis tracking is the most beneficial option for equatorial latitudes as the two-axes tracking system only surpasses the gains of the one-axis tracking marginally. Furthermore, the use of a strategy to place the PV modules horizontally in cloudy conditions seems to be marginally advantageous. Finally, the shadows created from neighboring buildings in the East and West of the system may reduce considerably the solar irradiation on the PV-array (not the ones in the north and south).

Method for estimating admixture content in seawater using operative spectrophotometry

The paper discusses spectra of the radiance coefficient of the sea surface measured in the open ocean and in coastal waters, and different kinds of these spectra corresponding to the water types are revealed. The focus is the method of measuring the radiance coefficient from a moving ship with a hyperspectral spectrophotometer. The results of studying a water area of Russia’s Black Sea coast at river mouths are presented. A new calibration method that can process measurement results taking into account the impact of cloudiness and wind has been proposed and tested. The concentrations of the main admixtures in natural seawater in the studied water area are estimated according to the obtained spectra; these estimates are compared to the results of direct analysis of water samples. It has been shown that the method of remote measurement of the sea radiance coefficient from on board a ship makes it possible to obtain operative maps of the spatial distribution of the main seawater admixtures.

Appraisement of geographic information systems as tool supporting energy management in the cities

Polish international obligations, in particular the European Union and European Commission directives, pose a real challenge for Poland to radically reduce emissions of atmospheric pollutions and significantly increase the usage of energy coming from renewable sources in the overall energy balance of the country. These goals seem to be difficult to achieve, nevertheless the development and implementation of innovative concepts is always a step forward. Nowadays the renewable energy sources seem to be the panacea for the problems of pollutions and energy saving. Many inventors and scientists work on concept of smart grid technology. The basic concept of this technology is producing energy directly in the cities. It seems to be a good idea but often in urban areas there is no place for new installations or cost of land is the barrier. Therefore to produce and manage energy directly in the cities, we have to take into account many aspects such as cost of land, location, available renewable energy sources, number of inhabitants, electrical network, terrain obstacles, and local plans. Here is the good place to use geographic information system technology which can help us to analyze all these issues and combine spatial, satellite, and statistical data to create one coherent concept of managing various sources of energy in the cities. The aim of this study is to consider opportunities of using geographic information systems in supporting process of energy management in the cities. It was taken into account many important elements: solar conditions, impact of cloudiness on value of solar radiation, spatial data, buildings and electrical network, obstacles, and number of inhabitants. It is all for identify the advantages and disadvantages of geographic information system in the analysis of solar energy potential in the city.

Impact of cloudiness on net ecosystem exchange of carbon dioxide in different types of forest ecosystems in China

Abstract. Clouds can significantly affect carbon exchange process between forest ecosystems and the atmosphere by influencing the quantity and quality of solar radiation received by ecosystem's surface and other environmental factors. In this study, we analyzed the effects of cloudiness on net ecosystem exchange of carbon dioxide (NEE) in a temperate broad-leaved Korean pine mixed forest at Changbaishan (CBS) and a subtropical evergreen broad-leaved forest at Dinghushan (DHS), based on the flux data obtained during June–August from 2003 to 2006. The results showed that the response of NEE of forest ecosystems to photosynthetically active radiation (PAR) differed under clear skies and cloudy skies. Compared with clear skies, the light-saturated maximum photosynthetic rate (Pec,max) at CBS under cloudy skies during mid-growing season (from June to August) increased by 34%, 25%, 4% and 11% in 2003, 2004, 2005 and 2006, respectively. In contrast, Pec,max of the forest ecosystem at DHS was higher under clear skies than under cloudy skies from 2004 to 2006. When the clearness index (kt) ranged between 0.4 and 0.6, the NEE reached its maximum at both CBS and DHS. However, the NEE decreased more dramatically at CBS than at DHS when kt exceeded 0.6. The results indicate that cloudy sky conditions are beneficial to net carbon uptake in the temperate forest ecosystem and the subtropical forest ecosystem. Under clear skies, vapor pressure deficit (VPD) and air temperature increased due to strong light. These environmental conditions led to greater decrease in gross ecosystem photosynthesis (GEP) and greater increase in ecosystem respiration (Re) at CBS than at DHS. As a result, clear sky conditions caused more reduction of NEE in the temperate forest ecosystem than in the subtropical forest ecosystem. The response of NEE of different forest ecosystems to the changes in cloudiness is an important factor that should be included in evaluating regional carbon budgets under climate change conditions.

Enhanced solar global irradiance during cloudy sky conditions

The impact of cloudiness on the shortwave downwelling radiation (SDR) at the surface is investigated by means of collocated pyranometer radiation measurements and all-sky imager observations. The measurements have been performed in Westerland, a seaside resort on the North Sea island of Sylt, Germany, during summer 2004 and 2005. A main improvement to previous studies on this subject resulted from the very high temporal resolution of cloud images and radiation measurements and, therefore, a more robust statistical analysis of the occurrence of this effect. It was possible to observe an excess of solar irradiation compared to clear sky irradiation by more than 500 W/m 2 , the largest observed excess irradiation to our knowledge so far. Camera images reveal that largest excess radiation is reached close to overcast situations with altocumulus clouds partly obscuring the solar disk, and preferably with cumulus clouds in lower levels. The maximum duration of the enhancements depends on its strength and ranges from 20 seconds (enhancements > 400 W/m 2 ) up to 140 seconds (enhancements > 200 W/m 2 ).

Assessment of smoke aerosol impact on surface solar irradiance measured in the Rondônia region of Brazil during Smoke, Clouds, and Radiation ‐ Brazil

The impact of smoke aerosols on the surface solar irradiance in the Rondônia region of Brazil is examined. The climate of this region is subequatorial with two distinct seasons. There is a sharp decline of the precipitation and cloudiness during the dry season which lasts from June to September accompanied by anthropogenic burning of savanna and forest in August and September with the resultant strong emission of smoke into the troposphere. Thus the magnitude of the column aerosol optical depth increases in these months while both precipitable water and cloud amount decrease in accordance with the seasonal cycle of humidity. All these atmospheric constituents influence the magnitude of the solar irradiance at the surface. In order to assess the aerosol and gaseous effects on the surface irradiance as compared with impact of cloudiness, we performed the clear‐sky radiative transfer model calculations by employing a broadband radiation code and both aerosol optical depth and precipitable water retrieved from Sun photometer measurements. Calculation results show that the elevated aerosol optical depth observed in Rondônia during August and September causes a negative trend in the daily mean clear‐sky surface solar irradiance during this period. Since the daily mean solar irradiance measured at the surface under all‐sky conditions demonstrates a similar negative trend, it can be explained by the aerosol influence while the effect of clouds appears in the daily variations of the irradiance. It was also shown that smoke aerosols cause a decrease of the monthly mean values of all‐sky surface irradiance in August and September as compared with July and October. Corresponding decreases in the near surface air temperature due to the smoke aerosols were not found.

On the impact of cloudiness on the characteristics of nocturnal downslope flows

The effects of cloud cover amount and the height of cloud base on nighttime thermally induced downslope flow were investigated using analytical and numerical model approaches. The conclusions obtained with the analytical and the numerical model evaluations agreed. It was concluded that, (i) as cloud cover increases and/or the height of cloud base decreases, the depth and the intensity of nighttime thermally-induced downslope flows may decrease by a factor reaching one sixth and one tenth, respectively, in the case of overcast low cloud; (ii) when skies suddenly cloud over around midnight, the development of the downslope flow is altered in different ways: a reduction in intensity; or a cessation of further development, depending on the fraction of cloud coverage, and (iii) with a sudden clearing of overcast low cloud around midnight, the depth and the intensity of the downslope flow increases significantly.

The influence of satellite spectral sensor response on the analysis of satellite imagery at high latitudes

Abstract Many polar-orbiting satellites used in high-latitude work employ instruments which sense only narrow regions of the solar spectrum. A radiative transfer scheme is used to illustrate the differences between broad-band albedos and those calculated using the spectral response of the NOAA-6 AVHRR channel 1 and DMSP visible sensors. The albedo contrast between snow/no snow is shown to be exaggerated by the satellite sensors and the impact of cloudiness over snow on the albedo is drastically reduced, by a factor of 10 in the case of the NOAA-6 sensor. A significant solar zenith angle dependence is also shown for the NOAA-6 sensor