Journal articles: 'Skynet'

1

Jethva, Hiren, and Omar Torres. "A comparative evaluation of Aura-OMI and SKYNET near-UV single-scattering albedo products." Atmospheric Measurement Techniques 12, no. 12 (December 9, 2019): 6489–503. http://dx.doi.org/10.5194/amt-12-6489-2019.

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Abstract. The aerosol single-scattering albedo (SSA) retrieved by the near-UV algorithm applied to the Aura Ozone Monitoring Instrument (OMI) measurements (OMAERUV) is compared with an independent inversion product derived from the sky radiometer network SKYNET – a ground-based radiation observation network with sites in Asia and Europe. The present work continues previous efforts to evaluate the consistency between the retrieved SSA from satellite and ground sensors. The automated spectral measurements of direct downwelling solar flux and sky radiances made by the SKYNET Sun-sky radiometer are used as input to an inversion algorithm that derives spectral aerosol optical depth (AOD) and single-scattering albedo (SSA) in the near-UV to near-IR spectral range. The availability of SKYNET SSA measurements in the ultraviolet region of the spectrum allows, for the first time, a direct comparison with OMI SSA retrievals eliminating the need of extrapolating the satellite retrievals to the visible wavelengths as is the case in the evaluation against the Aerosol Robotic Network (AERONET). An analysis of the collocated retrievals from over 25 SKYNET sites reveals that about 61 % (84 %) of OMI–SKYNET matchups agree within the absolute difference of ±0.03 (±0.05) for carbonaceous aerosols, 50 % (72 %) for dust aerosols, and 45 % (75 %) for urban–industrial aerosol types. Regionally, the agreement between the two inversion products is robust over several sites in Japan influenced by carbonaceous and urban–industrial aerosols; at the biomass burning site Phimai in Thailand; and the polluted urban site in New Delhi, India. The collocated dataset yields fewer matchups identified as dust aerosols mostly over the site Dunhuang with more than half of the matchup points confined to within ±0.03 limits. Altogether, the OMI–SKYNET retrievals agree within ±0.03 when SKYNET AOD (388 or 400 nm) is larger than 0.5 and the OMI UV Aerosol Index is larger than 0.2. The remaining uncertainties in both inversion products can be attributed to specific assumptions made in the retrieval algorithms, i.e., the uncertain calibration constant, assumption of spectral surface albedo and particle shape, and subpixel cloud contamination. The assumption of fixed and spectrally neutral surface albedo (0.1) in the SKYNET inversion appears to be unrealistic, leading to underestimated SSA, especially under lower aerosol load conditions. At higher AOD values for carbonaceous and dust aerosols, however, retrieved SSA values by the two independent inversion methods are generally consistent in spite of the differences in retrieval approaches.

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2

Hashimoto, M., T. Nakajima, O. Dubovik, M. Campanelli, H. Che, P. Khatri, T. Takamura, and G. Pandithurai. "Development of a new data-processing method for SKYNET sky radiometer observations." Atmospheric Measurement Techniques Discussions 5, no. 3 (June 25, 2012): 4361–407. http://dx.doi.org/10.5194/amtd-5-4361-2012.

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Abstract. In order to reduce uncertainty in the estimation of aerosol direct radiative forcing (DARF), it is important to improve the estimation of the single scattering albedo (SSA). In this study, we propose a new data-processing method to improve SSA retrievals for the SKYNET sky radiometer network, which is one of the growing number of networks of sun-sky photometers, such as NASA AERONET and others. There are several reports that SSA values from SKYNET have a bias compared to those from AERONET, which is regarded to be the most accurate due to its rigorous calibration routines. We investigated possible causes of errors in SSA that might explain the known biases through sensitivity experiments using a numerical model, and also using real data at the SKYNET sites at Pune (18.616° N/73.800° E) in India and Beijing (39.586° N/116.229° E) in China. Sensitivity experiments showed that an uncertainty of the order of ±0.03 in the SSA value can be caused by a possible error in the ground surface albedo or solid view angle assumed for each observation site. Another candidate for possible error in the SSA was found in cirrus contamination generated by imperfect cloud screening in the SKYNET data processing. Therefore, we developed a new data quality control method that eliminates these error sources, and we applied this method to the real observation data at the Pune site in SKYNET. After applying this method to the observation data, we were able to screen out a large amount of cirrus-contaminated data and to reduce the deviation in the SSA value from that of AERONET. We then estimated DARF using data screened by our new method. The result showed that the method significantly reduced the difference of 5 W m−2 that existed between the SKYNET and AERONET values of DARF before screening. The present study also suggests the necessity of preparing suitable a priori information on the distribution of coarse particles ranging in radius between 10 μm and 30 μm for the analysis of heavily dust-laden atmospheric cases.

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3

Mok, Jungbin, Nickolay A. Krotkov, Omar Torres, Hiren Jethva, Zhanqing Li, Jhoon Kim, Ja-Ho Koo, et al. "Comparisons of spectral aerosol single scattering albedo in Seoul, South Korea." Atmospheric Measurement Techniques 11, no. 4 (April 23, 2018): 2295–311. http://dx.doi.org/10.5194/amt-11-2295-2018.

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Abstract. Quantifying aerosol absorption at ultraviolet (UV) wavelengths is important for monitoring air pollution and aerosol amounts using current (e.g., Aura/OMI) and future (e.g., TROPOMI, TEMPO, GEMS, and Sentinel-4) satellite measurements. Measurements of column average atmospheric aerosol single scattering albedo (SSA) are performed on the ground by the NASA AERONET in the visible (VIS) and near-infrared (NIR) wavelengths and in the UV-VIS-NIR by the SKYNET networks. Previous comparison studies have focused on VIS and NIR wavelengths due to the lack of co-incident measurements of aerosol and gaseous absorption properties in the UV. This study compares the SKYNET-retrieved SSA in the UV with the SSA derived from a combination of AERONET, MFRSR, and Pandora (AMP) retrievals in Seoul, South Korea, in spring and summer 2016. The results show that the spectrally invariant surface albedo assumed in the SKYNET SSA retrievals leads to underestimated SSA compared to AMP values at near UV wavelengths. Re-processed SKYNET inversions using spectrally varying surface albedo, consistent with the AERONET retrieval improve agreement with AMP SSA. The combined AMP inversions allow for separating aerosol and gaseous (NO2 and O3) absorption and provide aerosol retrievals from the shortest UVB (305 nm) through VIS to NIR wavelengths (870 nm).

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4

Hashimoto, M., T. Nakajima, O. Dubovik, M. Campanelli, H. Che, P. Khatri, T. Takamura, and G. Pandithurai. "Development of a new data-processing method for SKYNET sky radiometer observations." Atmospheric Measurement Techniques 5, no. 11 (November 15, 2012): 2723–37. http://dx.doi.org/10.5194/amt-5-2723-2012.

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Abstract. In order to reduce uncertainty in the estimation of Direct Aerosol Radiative Forcing (DARF), it is important to improve the estimation of the single scattering albedo (SSA). In this study, we propose a new data processing method to improve SSA retrievals for the SKYNET sky radiometer network, which is one of the growing number of networks of sun-sky photometers, such as NASA AERONET and others. There are several reports that SSA values from SKYNET have a bias compared to those from AERONET, which is regarded to be the most accurate due to its rigorous calibration routines and data quality and cloud screening algorithms. We investigated possible causes of errors in SSA that might explain the known biases through sensitivity experiments using a numerical model, and also using real data at the SKYNET sites at Pune (18.616° N/73.800° E) in India and Beijing (39.586° N/116.229° E) in China. Sensitivity experiments showed that an uncertainty of the order of ±0.03 in the SSA value can be caused by a possible error in the ground surface albedo or solid view angle assumed for each observation site. Another candidate for possible error in the SSA was found in cirrus contamination generated by imperfect cloud screening in the SKYNET data processing. Therefore, we developed a new data quality control method to get rid of low quality or cloud contamination data, and we applied this method to the real observation data at the Pune site in SKYNET. After applying this method to the observation data, we were able to screen out a large amount of cirrus-contaminated data and to reduce the deviation in the SSA value from that of AERONET. We then estimated DARF using data screened by our new method. The result showed that the method significantly reduced the difference of 5 W m−2 that existed between the SKYNET and AERONET values of DARF before screening. The present study also suggests the necessity of preparing suitable a priori information on the distribution of coarse particles ranging in radius between 10 μm and 30 μm for the analysis of heavily dust-laden atmospheric cases.

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5

Estellés, V., M. Campanelli, T. J. Smyth, M. P. Utrillas, and J. A. Martínez-Lozano. "AERONET and ESR sun direct products comparison performed on Cimel CE318 and Prede POM01 solar radiometers." Atmospheric Chemistry and Physics Discussions 12, no. 2 (February 7, 2012): 4341–71. http://dx.doi.org/10.5194/acpd-12-4341-2012.

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Abstract. The European Skynet Radiometers network (EuroSkyRad or ESR) has been recently established as a research network of European Prede POM sun – sky radiometers. Moreover, ESR is federated with SKYNET (SKYrad NETwork), an international network mostly present in East Asia. In contrast to SKYNET, the European network also integrates users of the Cimel CE318 sunphotometer. Keeping instrumental duality in mind, a set of open source algorithms has been developed consisting of two modules for: (1) the retrieval of direct sun products from the sun extinction measurements; and (2) the inversion of the sky radiance to derive aerosol optical properties. In this study we evaluate the ESR direct sun products (spectral aerosol optical depth, Angström wavelength exponent and columnar content of water vapour) in comparison with the AERosol RObotic NETwork (AERONET) products. Specifically, we have applied the ESR algorithm to a Cimel CE318 and Prede POM01L simultaneously for a 4 yr database measured at the Burjassot site (Valencia, Spain), and compared the resultant products with the AERONET direct sun retrievals obtained with the same Cimel CE318 instrument. The comparison show that aerosol optical depth differences are mostly within the nominal uncertainty of 0.003 for a standard calibration instrument, and fall within the nominal AERONET uncertainty of 0.01–0.02 for a field instrument. Therefore, we present an open source code that can be used for both radiometers and whose results are comparable to those of AERONET and SKYNET.

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6

Lippuner, Jonas, and Luke F. Roberts. "SkyNet: A Modular Nuclear Reaction Network Library." Astrophysical Journal Supplement Series 233, no. 2 (December 5, 2017): 18. http://dx.doi.org/10.3847/1538-4365/aa94cb.

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7

Davison, Iain, and Ian Miles. "A SPAR Modelling Platform Case Study: Skynet 5." Procedia CIRP 11 (2013): 431–34. http://dx.doi.org/10.1016/j.procir.2013.07.001.

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8

Davison, lain, and Ian Miles. "A Spar Modelling Platform Case Study: Skynet 5." Safety and Reliability 32, no. 4 (December 2012): 5–12. http://dx.doi.org/10.1080/09617353.2012.11716244.

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9

Estellés, V., M. Campanelli, T. J. Smyth, M. P. Utrillas, and J. A. Martínez-Lozano. "Evaluation of the new ESR network software for the retrieval of direct sun products from CIMEL CE318 and PREDE POM01 sun-sky radiometers." Atmospheric Chemistry and Physics 12, no. 23 (December 5, 2012): 11619–30. http://dx.doi.org/10.5194/acp-12-11619-2012.

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Abstract. The European Skynet Radiometers network (EuroSkyRad or ESR) has been recently established as a research network of European PREDE sun-sky radiometers. Moreover, ESR is federated with SKYNET, an international network of PREDE sun-sky radiometers mostly present in East Asia. In contrast to SKYNET, the European network also integrates users of the CIMEL CE318 sky–sun photometer. Keeping instrumental duality in mind, a set of open source algorithms has been developed consisting of two modules for (1) the retrieval of direct sun products (aerosol optical depth, wavelength exponent and water vapor) from the sun extinction measurements; and (2) the inversion of the sky radiance to derive other aerosol optical properties such as size distribution, single scattering albedo or refractive index. In this study we evaluate the ESR direct sun products in comparison with the AERosol RObotic NETwork (AERONET) products. Specifically, we have applied the ESR algorithm to a CIMEL CE318 and PREDE POM simultaneously for a 4-yr database measured at the Burjassot site (Valencia, Spain), and compared the resultant products with the AERONET direct sun measurements obtained with the same CIMEL CE318 sky–sun photometer. The comparison shows that aerosol optical depth differences are mostly within the nominal uncertainty of 0.003 for a standard calibration instrument, and fall within the nominal AERONET uncertainty of 0.01–0.02 for a field instrument in the spectral range 340 to 1020 nm. In the cases of the Ångström exponent and the columnar water vapor, the differences are lower than 0.02 and 0.15 cm, respectively. Therefore, we present an open source code program that can be used with both CIMEL and PREDE sky radiometers and whose results are equivalent to AERONET and SKYNET retrievals.

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10

Smith, Adam B., Daniel B. Caton, and R. Lee Hawkins. "Implementation and Operation of a Robotic Telescope on Skynet." Publications of the Astronomical Society of the Pacific 128, no. 963 (March 30, 2016): 055002. http://dx.doi.org/10.1088/1538-3873/128/963/055002.

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11

Jang, Hyun-Sung, Hwan-Jin Song, Hyoung-Wook Chun, Byung-Ju Sohn, and Tamio Takamura. "Validation of MODIS-derived Aerosol Optical Thickness Using SKYNET Measurements over East Asia." Journal of the Korean earth science society 32, no. 1 (February 28, 2011): 21–32. http://dx.doi.org/10.5467/jkess.2011.32.1.21.

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12

Westman, A., M. Sjoling, A. Lindberg, and U. Bjornstig. "The SKYNET data: demography and injury reporting in Swedish skydiving." Injury Prevention 16, Supplement 1 (September 1, 2010): A120. http://dx.doi.org/10.1136/ip.2010.029215.432.

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13

Westman, Anton, Mats Sjöling, Ann Lindberg, and Ulf Björnstig. "The SKYNET data: Demography and injury reporting in Swedish skydiving." Accident Analysis & Prevention 42, no. 2 (March 2010): 778–83. http://dx.doi.org/10.1016/j.aap.2009.11.013.

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14

Nakajima, Teruyuki, Monica Campanelli, Huizheng Che, Victor Estellés, Hitoshi Irie, Sang-Woo Kim, Jhoon Kim, et al. "An overview of and issues with sky radiometer technology and SKYNET." Atmospheric Measurement Techniques 13, no. 8 (August 10, 2020): 4195–218. http://dx.doi.org/10.5194/amt-13-4195-2020.

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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.

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Wang, Yingjian, Lu Sun, Dong Liu, Zhien Wang, Zhenzhu Wang, and Chenbo Xie. "Cloud and Aerosol Interaction Observed in SKYNET Hefei Site in China." EPJ Web of Conferences 119 (2016): 16013. http://dx.doi.org/10.1051/epjconf/201611916013.

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16

Miller, Isaac, Mark Campbell, Dan Huttenlocher, Frank-Robert Kline, Aaron Nathan, Sergei Lupashin, Jason Catlin, et al. "Team Cornell's Skynet: Robust perception and planning in an urban environment." Journal of Field Robotics 25, no. 8 (August 2008): 493–527. http://dx.doi.org/10.1002/rob.20253.

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Khatri, P., T. Takamura, T. Nakajima, V. Estellés, H. Irie, H. Kuze, M. Campanelli, et al. "Factors for inconsistent aerosol single scattering albedo between SKYNET and AERONET." Journal of Geophysical Research: Atmospheres 121, no. 4 (February 27, 2016): 1859–77. http://dx.doi.org/10.1002/2015jd023976.

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18

Sano, I., S. Mukai, M. Yamano, T. Takamura, T. Nakajima, and B. Holben. "Calibration and validation of retrieved aerosol properties based on AERONET and SKYNET." Advances in Space Research 32, no. 11 (December 2003): 2159–64. http://dx.doi.org/10.1016/s0273-1177(03)90538-2.

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19

Teixeira, Filipe, and Ben Derudder. "SKYNET: An R package for generating air passenger networks for urban studies." Urban Studies 56, no. 14 (December 11, 2018): 3030–44. http://dx.doi.org/10.1177/0042098018803258.

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There is a long tradition of urban studies invoking air transport data either for tackling the city/air transport-nexus head on (e.g. in research on the causality between urban-economic development and air transport connectivity) or as a secondary data source (e.g. in research mapping city networks). However, air transport statistics rarely come in a format that allows for their immediate scrutiny in light of the research questions at hand, so that handling and transforming these data often involves both practical challenges and considerable effort. Against this backdrop, this article introduces ‘SKYNET’, a flexible R package that allows generating bespoke air transport statistics for urban studies based on publicly available data from the Bureau of Transport Statistics (BTS) in the United States. The basic elements of the package are explained, after which we demonstrate its usefulness by showing its potential for addressing research questions emerging in the literatures on 1) evolving urban landscapes of air travel accessibility, and 2) differences in intercity air transport networks by scale, types and season. We argue that this R package has the potential to become the backbone of a range of easily navigable tools overcoming some of the main methodological challenges researchers face when handling complex airline data in an urban context.

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Campanelli, M., V. Estelles, T. Smyth, C. Tomasi, M. P. Martìnez-Lozano, B. Claxton, P. Muller, et al. "Monitoring of Eyjafjallajökull volcanic aerosol by the new European Skynet Radiometers (ESR) network." Atmospheric Environment 48 (March 2012): 33–45. http://dx.doi.org/10.1016/j.atmosenv.2011.09.070.

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21

Estellés, V., M. Campanelli, M. P. Utrillas, F. Expósito, and J. A. Martínez-Lozano. "Comparison of AERONET and SKYRAD4.2 inversion products retrieved from a Cimel CE318 sunphotometer." Atmospheric Measurement Techniques 5, no. 3 (March 13, 2012): 569–79. http://dx.doi.org/10.5194/amt-5-569-2012.

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Abstract. SKYNET is an international research network of ground based sky – sunphotometers for the observation and monitoring of columnar aerosol properties. The algorithm developed by SKYNET is called SKYRAD.pack, and it is used on Prede instruments only. In this study, we have modified the SKYRAD.pack software in order to adapt it to Cimel sunphotometers. A one month database of Cimel data obtained at Burjassot (Valencia, Spain) has been processed with this program and the obtained inversion products have been compared with AERONET retrievals. In general, the differences found were consistent with the individual error assessments for both algorithms. Although the aerosol optical depth compared well for any aerosol burden situation (rmsd of 0.002–0.013 for all wavelengths), inversion products such as the single scattering albedo, refractive index and asymmetry parameter compared better for higher turbidity situations. The comparison performed for cases with an aerosol optical depth at 440 nm over 0.2 showed rms differences of 0.025–0.049 for single scattering albedo, 0.005–0.034 for the real part of refractive index, 0.004–0.007 for the imaginary part of the refractive index and 0.006–0.009 for the asymmetry parameter. With respect to the volume distributions, the comparison also showed a good agreement for high turbidity cases (mainly within the 0.01–7 μm interval) although the already known discrepancy in the extremes of the distribution was still found in 40% of the cases, in spite of eliminating data and instrumental differences present in previous studies.

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22

Estellés, V., M. Campanelli, M. P. Utrillas, F. Expósito, and J. A. Martínez-Lozano. "Comparison of AERONET and SKYRAD4.2 inversion products retrieved from a Cimel CE318 sunphotometer." Atmospheric Measurement Techniques Discussions 4, no. 6 (November 18, 2011): 6883–913. http://dx.doi.org/10.5194/amtd-4-6883-2011.

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Abstract. SKYNET is an international research network of ground based sky-sunphotometers for the observation and monitoring of columnar aerosol properties. The algorithm developed by SKYNET is called SKYRAD.pack, and so far it has been used on Prede instruments only. In this study we have modified the SKYRAD.pack software in order to adapt it to Cimel sunphotometers. A one month database of Cimel data obtained at Burjassot (Valencia, Spain) has been processed with this program and the obtained inversion products have been compared with AERONET retrievals. In general, the differences found were consistent with the individual error assessments for both algorithms. Although the aerosol optical depth compared well for any aerosol burden situation (rmsd of 0.002–0.013 for all wavelengths), inversion products such as the single scattering albedo, refractive index and asymmetry parameter compared better for higher turbidity situations. The comparison performed for cases with an aerosol optical depth at 440 nm over 0.2 showed rms differences of 0.025–0.049 for single scattering albedo, 0.005–0.034 for the real part of refractive index, 0.004–0.007 for the imaginary part of the refractive index, and 0.006–0.009 for the asymmetry parameter. In respect to the volume distributions, the comparison also showed a good agreement for high turbidity cases (mainly within the 0.01–7 μm interval) although the already known discrepancy in the extremes of the distribution was still found in 40% of cases, in spite of eliminating data and instrumental differences present in previous studies.

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23

Graff, Philip, Farhan Feroz, Michael P. Hobson, and Anthony Lasenby. "SkyNet: an efficient and robust neural network training tool for machine learning in astronomy." Monthly Notices of the Royal Astronomical Society 441, no. 2 (May 12, 2014): 1741–59. http://dx.doi.org/10.1093/mnras/stu642.

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24

Buisson, Lise du, Navin Sivanandam, Bruce A. Bassett, and Mathew Smith. "Machine Classification of Transient Images." Proceedings of the International Astronomical Union 10, S306 (May 2014): 288–91. http://dx.doi.org/10.1017/s1743921314013842.

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AbstractUsing transient imaging data from the 2nd and 3rd years of the SDSS supernova survey, we apply various machine learning techniques to the problem of classifying transients (e.g. SNe) from artefacts, one of the first steps in any transient detection pipeline, and one that is often still carried out by human scanners. Using features mostly obtained from PCA, we show that we can match human levels of classification success, and find that a K-nearest neighbours algorithm and SkyNet perform best, while the Naive Bayes, SVM and minimum error classifier have performances varying from slightly to significantly worse.

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Xue, Zixuan, Hiroaki Kuze, and Hitoshi Irie. "Retrieval of Aerosol Optical Thickness with Custom Aerosol Model Using SKYNET Data over the Chiba Area." Atmosphere 12, no. 9 (September 5, 2021): 1144. http://dx.doi.org/10.3390/atmos12091144.

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The retrieval of the aerosol optical thickness (AOT) from remotely-sensed data relies on the adopted aerosol model. However, the method of this technique has been rather limited because of the high variability of the surface albedo, in addition to the spatial variability in the aerosol properties over the land surfaces. To overcome unsolved problems, we proposed a method for the visibility-derived AOT estimation from SKYNET-based measurement and daytime satellite images with a custom aerosol model over the Chiba area (35.62° N, 140.10° E), which is located in the greater Tokyo metropolitan area in Japan. Different from conventionally-used aerosol models for the boundary layer, we created a custom aerosol model by using sky-radiometer observation data of aerosol volume size distribution and refractive indices, coupled with spectral response functions (SPFs) of satellite visible bands to alleviate the wide range of path-scattered radiance. We utilized the radiative transfer code 6S to implement the radiative transfer calculation based on the created custom aerosol model. The concurrent data from ground-based measurement are used in the radiative analysis, namely the temporal variation of AOT from SKYNET. The radiative estimation conducted under clear-sky conditions with minimum aerosol loading is used for the determination of the surface albedo, so that the 6S simulation yields a well-defined relation between total radiance and surface albedo. We made look-up tables (LUTs) pixel-by-pixel over the Chiba area for the custom aerosol model to retrieve the satellite AOT distribution based on the surface albedo. Therefore, such a reference of surface albedo generated from clear-sky conditions, in turn, can be employed to retrieve the spatial distribution of AOT on both clear and relatively turbid days. The value for the AOTs retrieved using the custom aerosol model is found to be stable than conventionally-used typical aerosol models, indicating that our method yields substantially better performance.

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Martin, J. R., D. E. Reichart, D. A. Dutton, M. P. Maples, T. A. Berger, F. D. Ghigo, J. B. Haislip, et al. "Skynet Algorithm for Single-dish Radio Mapping. I. Contaminant-cleaning, Mapping, and Photometering Small-scale Structures." Astrophysical Journal Supplement Series 240, no. 1 (January 21, 2019): 12. http://dx.doi.org/10.3847/1538-4365/aad7c1.

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Jones, C. H. "The development of a multi-access traffic simulator for the testing of the SKYNET 4 system." Journal of the Institution of Electronic and Radio Engineers 56, no. 2 (1986): 62. http://dx.doi.org/10.1049/jiere.1986.0021.

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KITAKOGA, Shiho, Yoko INOUE, Makoto KUJI, and Tadahiro HAYASAKA. "Characteristics of Aerosol Properties of Haze and Yellow Sand Examined from SKYNET Measurements over East China Sea." Journal of the Meteorological Society of Japan. Ser. II 92A (2014): 57–69. http://dx.doi.org/10.2151/jmsj.2014-a04.

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Wang, Zhenzhu, Dong Liu, Chenbo Xie, Bangxin Wang, Zhiqing Zhong, Yingjian Wang, and Bin Chen. "Long-term ground-based microwave radiometric measurements of atmospheric brightness temperature in SKYNET Hefei (31.90N, 117.17E) site." Journal of Quantitative Spectroscopy and Radiative Transfer 188 (February 2017): 181–87. http://dx.doi.org/10.1016/j.jqsrt.2016.07.005.

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30

Ong, Prane Mariel, Nofel Lagrosas, Tatsuo Shiina, and Hiroaki Kuze. "Diurnal Behavior of Aerosol Optical Properties Studied with Lidar and Ground-Based Instruments." EPJ Web of Conferences 237 (2020): 02011. http://dx.doi.org/10.1051/epjconf/202023702011.

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The combined use of remote sensing and in-situ monitoring instruments could help improve the assessment of near-surface aerosol properties. In this paper, we analyze the diurnal behavior of aerosol extinction coefficients, αExt(λ), at λ=349 and 550 nm using a lidar and a present weather detector, respectively. We utilize the aerosol optical thickness (AOT), single scattering albedo (SSA), and Ångström exponent (AE) from SKYNET sky radiometer, and AE from aethalometer, and the number distribution from optical particle counter to evaluate the effect of relative humidity (RH) on aerosol extinction coefficients. It is found that although αExt(λ) often exhibits a positive correlation with the ambient RH, this relation is obscured when both the number distribution and particle size change simultaneously. Moreover, αExt at 349 nm is more sensitive to this change than at 550 nm.

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Golpayegani, Golnoosh, Duncan R. Lorimer, Steven W. Ellingson, Devansh Agarwal, Olivia Young, Frank Ghigo, Richard Prestage, Kaustubh Rajwade, Maura A. McLaughlin, and Michael Mingyar. "GBTrans: a commensal search for radio pulses with the Green Bank 20-m telescope." Monthly Notices of the Royal Astronomical Society 489, no. 3 (September 2, 2019): 4001–6. http://dx.doi.org/10.1093/mnras/stz2424.

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ABSTRACT We describe GBTrans, a real-time search system designed to find fast radio bursts (FRBs) using the 20-m radio telescope at the Green Bank Observatory. The telescope has been part of the Skynet educational programme since 2015. We give details of the observing system and report on the non-detection of FRBs from a total observing time of 503 d. Single pulses from four known pulsars were detected as part of the commensal observing. The system is sensitive enough to detect approximately half of all currently known FRBs and we estimate that our survey probed redshifts out to about 0.3 corresponding to an effective survey volume of around 124 000 Mpc3. Modelling the FRB rate as a function of fluence, ${\cal F}$, as a power law with ${\cal F}^{-\alpha }$, we constrain the index α < 2.5 at the 90 per cent confidence level. We discuss the implications of this result in the context of constraints from other FRB surveys.

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Wang, Zhenzhu, Dong Liu, Zhien Wang, Yingjian Wang, Pradeep Khatri, Jun Zhou, Tamio Takamura, and Guangyu Shi. "Seasonal characteristics of aerosol optical properties at the SKYNET Hefei site (31.90°N, 117.17°E) from 2007 to 2013." Journal of Geophysical Research: Atmospheres 119, no. 10 (May 27, 2014): 6128–39. http://dx.doi.org/10.1002/2014jd021500.

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Jiang, Zhe, Minzheng Duan, Huizheng Che, Wenxing Zhang, Teruyuki Nakajima, Makiko Hashimoto, Bin Chen, and Akihiro Yamazaki. "Intercomparison between the aerosol optical properties retrieved by different inversion methods from SKYNET sky radiometer observations over Qionghai and Yucheng in China." Atmospheric Measurement Techniques 13, no. 3 (March 11, 2020): 1195–212. http://dx.doi.org/10.5194/amt-13-1195-2020.

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Abstract. This study analyzed the aerosol optical properties derived by SKYRAD.pack versions 5.0 and 4.2 (referred to as V5.0 and V4.2) using the radiometer measurements over Qionghai and Yucheng in China, two new sites of the sky radiometer network (SKYNET). As V5.0 uses an a priori size distribution function (SDF) of a bimodal log-normal function, the volume size distribution retrieved by V5.0 presented bimodal patterns with a 0.1–0.2 µm fine particle mode and a 3.0–6.0 µm coarse particle mode both over Qionghai and Yucheng. The differences in the volume size distributions between the two versions were very large for the coarse mode with a radius of over 5 µm. The single scattering albedos (SSAs) by V5.0 correlated with SSAs by V4.2 with R=0.88, 0.87, 0.90, 0.88, and 0.92 at wavelengths of 400, 500, 670, 870, and 1020 nm over Qionghai, respectively. The correlation coefficients were around 0.95, 0.95, 0.96, 0.94, and 0.91 at the five channels in Yucheng. An error of ±5 % for the solid view angle (SVA) introduced about ±2 % differences in retrieved SSA values both by V4.2 and V5.0. An error of ±50 % for ground surface albedo (Ag) caused about 1 % averaged differences in retrieved SSA values by the two versions. With the atmospheric pressure (PRS) increased by 1 %, 2 %, 3 %, and 4 %, the averaged changes in SSAs did not exceed 0.8 % both by V4.2 and V5.0. The SSA differences at 500 nm between the two versions decreased, while aerosol optical depths (AODs) increased over both sites. The seasonal variability of the aerosol properties over Qionghai and Yucheng was investigated based on SKYRAD.pack V5.0. The seasonal averaged AOD over Qionghai had higher values in spring, winter, and autumn and lower values in summer. The AOD averages were commonly higher in summer and spring than in winter and autumn in Yucheng. The lowest seasonal averaged SSAs were both observed in winter at the two sites. The fraction of the fine aerosol particles was much smaller in summer than in other seasons over Qionghai; the volume fraction of the coarse-mode particle in Yucheng had much larger values compared to the fine-mode particle in all seasons. The validation results provide valuable references for continued improvement of the retrieval algorithms of SKYNET and other aerosol observational networks.

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Ningombam, Shantikumar S., E. J. L. Larson, U. C. Dumka, Victor Estellés, M. Campanelli, and Colwell Steve. "Long-term (1995–2018) aerosol optical depth derived using ground based AERONET and SKYNET measurements from aerosol aged-background sites." Atmospheric Pollution Research 10, no. 2 (March 2019): 608–20. http://dx.doi.org/10.1016/j.apr.2018.10.008.

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Dim, Jules R., Tamio Takamura, Akiko Higurashi, Pradeep Kathri, Nobuyuki Kikuchi, and Takahashi Y. Nakajima. "Validation of Two MODIS Aerosols Algorithms with SKYNET and Prospects for Future Climate Satellites Such as the GCOM-C/SGLI." Advances in Meteorology 2013 (2013): 1–16. http://dx.doi.org/10.1155/2013/508064.

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Potential improvements of aerosols algorithms for future climate-oriented satellites such as the coming Global Change Observation Mission Climate/Second generation Global Imager (GCOM-C/SGLI) are discussed based on a validation study of three years’ (2008–2010) daily aerosols properties, that is, the aerosol optical thickness (AOT) and the Ångström exponent (AE) retrieved from two MODIS algorithms. The ground-truth data used for this validation study are aerosols measurements from 3 SKYNET ground sites. The results obtained show a good agreement between the ground-truth data AOT and that of one of the satellites’ algorithms, then a systematic overestimation (around 0.2) by the other satellites’ algorithm. The examination of the AE shows a clear underestimation (by around 0.2–0.3) by both satellites’ algorithms. The uncertainties explaining these ground-satellites’ algorithms discrepancies are examined: the cloud contamination affects differently the aerosols properties (AOT and AE) of both satellites’ algorithms due to the retrieval scale differences between these algorithms. The deviation of the real part of the refractive index values assumed by the satellites’ algorithms from that of the ground tends to decrease the accuracy of the AOT of both satellites’ algorithms. The asymmetry factor (AF) of the ground tends to increase the AE ground-satellites discrepancies as well.

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36

Che, H., G. Shi, A. Uchiyama, A. Yamazaki, H. Chen, P. Goloub, and X. Zhang. "Intercomparison between aerosol optical properties by a PREDE skyradiometer and CIMEL sunphotometer over Beijing, China." Atmospheric Chemistry and Physics 8, no. 12 (June 25, 2008): 3199–214. http://dx.doi.org/10.5194/acp-8-3199-2008.

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Abstract. This study compares the aerosol optical and physical properties simultaneously measured by a SKYNET PREDE skyradiometer and AERONET/PHOTONS CIMEL sunphotometer at a location in Beijing, China. Aerosol optical properties (AOP) including the Aerosol Optical Depth (AOD), Angstrom exponent (α), volume size distribution, single scattering albedo (ω) and the complex refractive index were compared. The difference between the two types of instruments was less than 1.3% for the AOD and less than 4% for the single scattering albedo below the wavelength of 670 nm. There is a difference between the volume size distribution patterns derived from two instruments, which is probably due to difference of measurement protocols and inversion algorithms for the respective instruments. AOP under three distinct weather conditions (background, haze, and dust days) over Beijing were compared by using the retrieved skyradiometer and sunphotometer data combined with MODIS satellite results, pyranometer measurements, PM10 measurements, and backtrajectory analysis. The results show that the significant difference of AOP under background, haze, and dust days over Beijing is probably due to different aerosol components under distinct weather conditions.

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Che, H., G. Shi, A. Uchiyama, A. Yamazaki, H. Chen, P. Goloub, and X. Zhang. "Intercomparison between aerosol optical properties by a PREDE skyradiometer and CIMEL sunphotometer over Beijing, China." Atmospheric Chemistry and Physics Discussions 7, no. 6 (November 14, 2007): 16023–53. http://dx.doi.org/10.5194/acpd-7-16023-2007.

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Abstract. This study compares the aerosol optical and physical properties simultaneously measured by a SKYNET PREDE skyradiometer and AERONET/PHOTONS CIMEL sunphotometer at a location in Beijing, China. Aerosol optical properties (AOP) including the Aerosol Optical Depth (AOD), Angstrom exponent (α), volume size distribution, single scattering albedo (ω) and the complex refractive index were compared. The difference between the two types of instruments was less than 1.3% for the AOD and less than 4% for the single scattering albedo below the wavelength of 670 nm. There is a difference between the volume size distribution patterns derived from two instruments, which is probablely due to difference of measurement protocols and inversion algorithms for the respective instruments. AOP under three distinct weather conditions (background, haze, and dust days) over Beijing were compared by using the retrieved skyradiometer and sunphotometer data combined with MODIS satellite results, pyranometer measurements, PM10 measurements, and backtrajectory analysis. The results show that the significant difference of AOP under background, haze, and dust days over Beijing is probablely due to different aerosol components under distinct weather conditions.

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Schutgens, N. A. J., T. Miyoshi, T. Takemura, and T. Nakajima. "Applying an ensemble Kalman filter to the assimilation of AERONET observations in a global aerosol transport model." Atmospheric Chemistry and Physics Discussions 9, no. 6 (November 11, 2009): 23835–73. http://dx.doi.org/10.5194/acpd-9-23835-2009.

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Abstract. We present a global aerosol assimilation system based on an ensemble Kalman filter, which we believe leads to a significant improvement in aerosol fields. The ensemble allows realistic, spatially and temporally variable model covariances (unlike other assimilation schemes). As the analyzed variables are mixing ratios (prognostic variables of the aerosol transport model), there is no need for the extra assumptions required by previous assimilation schemes analyzing aerosol optical thickness (AOT). We describe the implementation of this assimilation system and in particular the construction of the ensemble. This ensemble should represent our estimate of current model uncertainties. Consequently, we construct the ensemble around randomly modified emission scenarios. The system is tested with AERONET observations of AOT and Angström exponent (AE). Particular care is taken in the prescribing the observational errors. The assimilated fields (AOT and AE) are validated through independent AERONET, SKYNET and MODIS Aqua observations. We show that, in general, assimilation of AOT observations leads to improved modelling of global AOT, while assimilation of AE only improves modelling when the AOT is high.

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Schutgens, N. A. J., T. Miyoshi, T. Takemura, and T. Nakajima. "Applying an ensemble Kalman filter to the assimilation of AERONET observations in a global aerosol transport model." Atmospheric Chemistry and Physics 10, no. 5 (March 12, 2010): 2561–76. http://dx.doi.org/10.5194/acp-10-2561-2010.

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Abstract. We present a global aerosol assimilation system based on an Ensemble Kalman filter, which we believe leads to a significant improvement in aerosol fields. The ensemble allows realistic, spatially and temporally variable model covariances (unlike other assimilation schemes). As the analyzed variables are mixing ratios (prognostic variables of the aerosol transport model), there is no need for the extra assumptions required by previous assimilation schemes analyzing aerosol optical thickness (AOT). We describe the implementation of this assimilation system and in particular the construction of the ensemble. This ensemble should represent our estimate of current model uncertainties. Consequently, we construct the ensemble around randomly modified emission scenarios. The system is tested with AERONET observations of AOT and Angström exponent (AE). Particular care is taken in prescribing the observational errors. The assimilated fields (AOT and AE) are validated through independent AERONET, SKYNET and MODIS Aqua observations. We show that, in general, assimilation of AOT observations leads to improved modelling of global AOT, while assimilation of AE only improves modelling when the AOT is high.

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Wang, Z., D. Liu, Y. Wang, Z. Wang, and G. Shi. "Diurnal aerosol variations do affect daily averaged radiative forcing under heavy aerosol loading observed in Hefei, China." Atmospheric Measurement Techniques Discussions 8, no. 2 (February 23, 2015): 2123–41. http://dx.doi.org/10.5194/amtd-8-2123-2015.

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Abstract. Strong diurnal variation of aerosol has been observed in many heavy polluted regions in China. This variation could alter the distribution of the direct aerosol radiative forcing (DARF) during the whole daytime that could increase the uncertainty of the normally used averaged values. To quantify the effect of using the daily averaged DARF, 196 days of high temporal resolution ground-based data collected in SKYNET Hefei site during the period from 2007 to 2013 is used to perform an assessment. We demonstrate that strong diurnal changes of heavy aerosol loading have an impact on the 24 h averaged DARF when daily averaged optical properties are used to retrieve this quantity. Though there is a high temporal sampling of aerosol properties to be used for calculation of daily averaged ones, statistical errors (up to 5.3 Wm−2 absolutely and 14.6% relatively) in the computed DARF still occur. These errors increase with increasing daily aerosol optical depth (AOD) is also found which indicated the high temporal resolution DARF dataset should be used in the model instead of the normal daily-averaged one, especially under heavy aerosol loading condition.

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Campanelli, Monica, Alessandra Mascitelli, Paolo Sanò, Henri Diémoz, Victor Estellés, Stefano Federico, Anna Maria Iannarelli, et al. "Precipitable water vapour content from ESR/SKYNET sun–sky radiometers: validation against GNSS/GPS and AERONET over three different sites in Europe." Atmospheric Measurement Techniques 11, no. 1 (January 9, 2018): 81–94. http://dx.doi.org/10.5194/amt-11-81-2018.

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Abstract. The estimation of the precipitable water vapour content (W) with high temporal and spatial resolution is of great interest to both meteorological and climatological studies. Several methodologies based on remote sensing techniques have been recently developed in order to obtain accurate and frequent measurements of this atmospheric parameter. Among them, the relative low cost and easy deployment of sun–sky radiometers, or sun photometers, operating in several international networks, allowed the development of automatic estimations of W from these instruments with high temporal resolution. However, the great problem of this methodology is the estimation of the sun-photometric calibration parameters. The objective of this paper is to validate a new methodology based on the hypothesis that the calibration parameters characterizing the atmospheric transmittance at 940 nm are dependent on vertical profiles of temperature, air pressure and moisture typical of each measurement site. To obtain the calibration parameters some simultaneously seasonal measurements of W, from independent sources, taken over a large range of solar zenith angle and covering a wide range of W, are needed. In this work yearly GNSS/GPS datasets were used for obtaining a table of photometric calibration constants and the methodology was applied and validated in three European ESR-SKYNET network sites, characterized by different atmospheric and climatic conditions: Rome, Valencia and Aosta. Results were validated against the GNSS/GPS and AErosol RObotic NETwork (AERONET) W estimations. In both the validations the agreement was very high, with a percentage RMSD of about 6, 13 and 8 % in the case of GPS intercomparison at Rome, Aosta and Valencia, respectively, and of 8 % in the case of AERONET comparison in Valencia. Analysing the results by W classes, the present methodology was found to clearly improve W estimation at low W content when compared against AERONET in terms of % bias, bringing the agreement with the GPS (considered the reference one) from a % bias of 5.76 to 0.52.

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Choi, Yongjoo, and Young Sung Ghim. "Variations in major aerosol components from long-term measurement of columnar aerosol optical properties at a SKYNET site downwind of Seoul, Korea." Atmospheric Environment 245 (January 2021): 117991. http://dx.doi.org/10.1016/j.atmosenv.2020.117991.

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43

Irie, Hitoshi, Hossain Mohammed Syedul Hoque, Alessandro Damiani, Hiroshi Okamoto, Al Mashroor Fatmi, Pradeep Khatri, Tamio Takamura, and Thanawat Jarupongsakul. "Simultaneous observations by sky radiometer and MAX-DOAS for characterization of biomass burning plumes in central Thailand in January–April 2016." Atmospheric Measurement Techniques 12, no. 1 (January 29, 2019): 599–606. http://dx.doi.org/10.5194/amt-12-599-2019.

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Abstract. The first intensive multicomponent ground-based remote-sensing observations by sky radiometer and multi-axis differential optical absorption spectroscopy (MAX-DOAS) were performed simultaneously at the SKYNET Phimai site located in central Thailand (15.18∘ N, 102.56∘ E) from January to April 2016. The period corresponds to the dry season associated with intense biomass burning (BB) activity around the site. The near-surface concentration of formaldehyde (HCHO) retrieved from MAX-DOAS was found to be a useful tracer for absorption aerosols from BB plumes, when BB was the dominant source of HCHO and absorption aerosols over other sources. As the HCHO concentration tripled from 3 to 9 ppbv, the ratio of gaseous glyoxal to HCHO concentrations in daytime decreased from ∼0.04 to ∼0.03, responding presumably to the increased contribution of volatile organic compound emissions from BB. In addition, clear increases in aerosol absorption optical depths (AAODs) retrieved from sky radiometer observations were seen with the HCHO enhancement. At a HCHO of 9 ppbv, AAOD at a wavelength of 340 nm reached as high as ∼0.15±0.03. The wavelength dependence of AAODs at 340–870 nm was quantified by the absorption Ångström exponent (AAE), providing evidence for the presence of brown carbon aerosols at an AAE of 1.5±0.2. Thus, our multicomponent observations around central Thailand are expected to provide unique constraints for understanding physical–chemical–optical properties of BB plumes.

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Mazurczyk, Wojciech, Maciej Karaś, and Krzysztof Szczypiorski. "SkyDe: a Skype-based Steganographic Method." International Journal of Computers Communications & Control 8, no. 3 (June 2, 2013): 432. http://dx.doi.org/10.15837/ijccc.2013.3.469.

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Wang, Z., D. Liu, Y. Wang, Z. Wang, and G. Shi. "Diurnal aerosol variations do affect daily averaged radiative forcing under heavy aerosol loading observed in Hefei, China." Atmospheric Measurement Techniques 8, no. 7 (July 20, 2015): 2901–7. http://dx.doi.org/10.5194/amt-8-2901-2015.

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Abstract. A strong diurnal variation of aerosol has been observed in many heavily polluted regions in China. This variation could affect the direct aerosol radiative forcing (DARF) evaluation if the daily averaged value is used as normal rather than the time-resolved values. To quantify the effect of using the daily averaged DARF, 196 days of high temporal resolution ground-based data collected in SKYNET Hefei site during the period from 2007 to 2013 is used to perform an assessment. We demonstrate that strong diurnal changes of heavy aerosol loading have an impact on the 24-h averaged DARF when daily averaged optical properties are used to retrieve this quantity. The DARF errors varying from −7.6 to 15.6 W m−2 absolutely and from 0.1 to 28.5 % relatively were found between the calculations using daily average aerosol properties, and those using time-resolved aerosol observations. These errors increase with increasing daily aerosol optical depth (AOD) and decreasing daily single-scattering albedo (SSA), indicating that the high temporal resolution DARF data set should be used in the model instead of the normal daily-averaged one, especially under heavy aerosol loading conditions for regional campaign studies. We also found that statistical errors (0.3 W m−2 absolutely and 11.8 % relatively) will be less, which means that the effect of using the daily averaged DARF can be weakened by using a long-term observational data set.

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Lobban, A. P., S. Zola, U. Pajdosz-Śmierciak, V. Braito, E. Nardini, G. Bhatta, A. Markowitz, et al. "X-ray, UV, and optical time delays in the bright Seyfert galaxy Ark 120 with co-ordinated Swift and ground-based observations." Monthly Notices of the Royal Astronomical Society 494, no. 1 (March 4, 2020): 1165–79. http://dx.doi.org/10.1093/mnras/staa630.

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ABSTRACT We report on the results of a multiwavelength monitoring campaign of the bright, nearby Seyfert galaxy Ark 120, using a ∼50-d observing programme with Swift and a ∼4-month co-ordinated ground-based observing campaign, pre-dominantly using the Skynet Robotic Telescope Network. We find Ark 120 to be variable at all optical, UV, and X-ray wavelengths, with the variability observed to be well correlated between wavelength bands on short time-scales. We perform cross-correlation analysis across all available wavelength bands, detecting time delays between emission in the X-ray band and the Swift V, B, and UVW1 bands. In each case, we find that the longer wavelength emission is delayed with respect to the shorter wavelength emission. Within our measurement uncertainties, the time delays are consistent with the τ ∼ λ4/3 relation, as predicted by a disc reprocessing scenario. The measured lag centroids are τcent = 11.90 ± 7.33, 10.80 ± 4.08, and 10.60 ± 2.87 d between the X-ray and V, B, and UVW1 bands, respectively. These time delays are longer than those expected from standard accretion theory and, as such, Ark 120 may be another example of an active galaxy whose accretion disc appears to exist on a larger scale than predicted by the standard thin-disc model. Additionally, we detect further inter-band time delays: most notably between the ground-based I and B bands (τcent = 3.46 ± 0.86 d), and between both the Swift XRT and UVW1 bands and the I band (τcent = 12.34 ± 4.83 and 2.69 ± 2.05 d, respectively), highlighting the importance of co-ordinated ground-based optical observations.

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Hoque, Hossain Mohammed Syedul, Hitoshi Irie, Alessandro Damiani, and Masahiro Momoi. "Primary Evaluation of the GCOM-C Aerosol Products at 380 nm Using Ground-Based Sky Radiometer Observations." Remote Sensing 12, no. 16 (August 18, 2020): 2661. http://dx.doi.org/10.3390/rs12162661.

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The Global Change Observation Mission-Climate (GCOM-C) is currently the only satellite sensor providing aerosol optical thickness (AOT) in the ultraviolet (UV) region during the morning overpass time. The observations in the UV region are important to detect the presence of absorbing aerosols in the atmosphere. The recently available GCOM-C dataset of AOT at 380 nm for January to September 2019 were evaluated using ground-based SKYNET sky radiometer measurements at Chiba, Japan (35.62° N, 140.10° E) and Phimai, central Thailand (15.18° N, 102.56° E), representing urban and rural sites, respectively. AOT retrieved from sky radiometer observations in Chiba and Phimai was compared with coincident AERONET and multi-axis differential optical absorption spectroscopy (MAX-DOAS) AOT values, respectively. Under clear sky conditions, the datasets showed good agreement. The sky radiometer and GCOM-C AOT values showed a positive correlation (R) of ~0.73 for both sites, and agreement between the datasets was mostly within ±0.2 (the number of coincident points at both sites was less than 50 for the coincidence criterion of ≤30 km). At Chiba, greater differences in the AOT values were primarily related to cloud screening in the datasets. The mean bias error (MBE) (GCOM-C – sky radiometer) for the Chiba site was −0.02 for a coincidence criterion of ≤10 km. For a similar coincidence criterion, the MBE values were higher for observations at the Phimai site. This difference was potentially related to the strong influence of biomass burning during the dry season (Jan–Apr). The diurnal variations in AOT, inferred from the combination of GCOM-C and ozone monitoring instrument (OMI) observations, showed good agreement with the sky radiometer data, despite the differences in the absolute AOT values. Over Phimai, the AOT diurnal variations from the satellite and sky radiometer observations were different, likely due to the large differences in the AOT values during the dry season.

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Damiani, Alessandro, Hitoshi Irie, Takashi Horio, Tamio Takamura, Pradeep Khatri, Hideaki Takenaka, Takashi Nagao, Takashi Y. Nakajima, and Raul R. Cordero. "Evaluation of Himawari-8 surface downwelling solar radiation by ground-based measurements." Atmospheric Measurement Techniques 11, no. 4 (April 27, 2018): 2501–21. http://dx.doi.org/10.5194/amt-11-2501-2018.

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Abstract. Observations from the new Japanese geostationary satellite Himawari-8 permit quasi-real-time estimation of global shortwave radiation at an unprecedented temporal resolution. However, accurate comparisons with ground-truthing observations are essential to assess their uncertainty. In this study, we evaluated the Himawari-8 global radiation product AMATERASS using observations recorded at four SKYNET stations in Japan and, for certain analyses, from the surface network of the Japanese Meteorological Agency in 2016. We found that the spatiotemporal variability of the satellite estimates was smaller than that of the ground observations; variability decreased with increases in the time step and spatial domain. Cloud variability was the main source of uncertainty in the satellite radiation estimates, followed by direct effects caused by aerosols and bright albedo. Under all-sky conditions, good agreement was found between satellite and ground-based data, with a mean bias in the range of 20–30 W m−2 (i.e., AMATERASS overestimated ground observations) and a root mean square error (RMSE) of approximately 70–80 W m−2. However, results depended on the time step used in the validation exercise, on the spatial domain, and on the different climatological regions. In particular, the validation performed at 2.5 min showed largest deviations and RMSE values ranging from about 110 W m−2 for the mainland to a maximum of 150 W m−2 in the subtropical region. We also detected a limited overestimation in the number of clear-sky episodes, particularly at the pixel level. Overall, satellite-based estimates were higher under overcast conditions, whereas frequent episodes of cloud-induced enhanced surface radiation (i.e., measured radiation was greater than expected clear-sky radiation) tended to reduce this difference. Finally, the total mean bias was approximately 10–15 W m−2 under clear-sky conditions, mainly because of overall instantaneous direct aerosol forcing efficiency in the range of 120–150 W m−2 per unit of aerosol optical depth (AOD). A seasonal anticorrelation between AOD and global radiation differences was evident at all stations and was also observed within the diurnal cycle.

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Uchiyama, Akihiro, Tsuneo Matsunaga, and Akihiro Yamazaki. "The instrument constant of sky radiometers (POM-02) – Part 2: Solid view angle." Atmospheric Measurement Techniques 11, no. 9 (September 26, 2018): 5389–402. http://dx.doi.org/10.5194/amt-11-5389-2018.

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Abstract. Ground-based networks have been developed to determine the spatiotemporal distribution of aerosols using sky radiometers. In this study, errors related to the solid view angle (SVA) of sky radiometers, which are used by SKYNET, were investigated. The SVA is calculated using solar disk scan data, the measured radiances around the solar direction in 0.1×0.1∘ increments. These measurements include the scattered light from aerosol and air molecules, as well as the direct solar irradiance, causing errors in the SVA calculation. The influence of these errors was evaluated with simulations. From the results of these simulations if the aerosol optical depth (optical path length) is less than 0.5 (0.58) at 550 nm and the aerosol does not include large particles, such as desert dust particles, then its influence on the SVA calculation was less than 0.5 %. Problems with the software for the SVA calculation were also investigated. First, the data processing does not consider the change of airmass (solar zenith angle) during the solar disk scan measurement. In practice if a measurement is made in the period when the change in airmass is small, then the error is small. Second, before starting data processing, the minimum measured value is subtracted from the measured values, resulting in underestimation of the SVA by 1 % to 4 %. Thirdly, the values between 1.4 and 2.5∘ are not properly extrapolated, resulting in overestimation of the SVA by 0.6 % to 2.1 %. The second and third error sources partially cancel each other out, and the total error is an underestimation of 0.5 % to 1.9 % of the actual value. Furthermore, the annual trend in the SVA was examined. In both the visible and near-infrared regions (Si photodiode region) and in the shortwave-infrared region (InGaAs photodiode region), this trend cannot be seen in 4 and 8 years of data, respectively. The seasonal variation of the SVA was also examined, but no clear seasonal variation could be detected.

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Kudo, Rei, Tomoaki Nishizawa, and Toshinori Aoyagi. "Vertical profiles of aerosol optical properties and the solar heating rate estimated by combining sky radiometer and lidar measurements." Atmospheric Measurement Techniques 9, no. 7 (July 22, 2016): 3223–43. http://dx.doi.org/10.5194/amt-9-3223-2016.

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Abstract. The SKYLIDAR algorithm was developed to estimate vertical profiles of aerosol optical properties from sky radiometer (SKYNET) and lidar (AD-Net) measurements. The solar heating rate was also estimated from the SKYLIDAR retrievals. The algorithm consists of two retrieval steps: (1) columnar properties are retrieved from the sky radiometer measurements and the vertically mean depolarization ratio obtained from the lidar measurements and (2) vertical profiles are retrieved from the lidar measurements and the results of the first step. The derived parameters are the vertical profiles of the size distribution, refractive index (real and imaginary parts), extinction coefficient, single-scattering albedo, and asymmetry factor. Sensitivity tests were conducted by applying the SKYLIDAR algorithm to the simulated sky radiometer and lidar data for vertical profiles of three different aerosols, continental average, transported dust, and pollution aerosols. The vertical profiles of the size distribution, extinction coefficient, and asymmetry factor were well estimated in all cases. The vertical profiles of the refractive index and single-scattering albedo of transported dust, but not those of transported pollution aerosol, were well estimated. To demonstrate the performance and validity of the SKYLIDAR algorithm, we applied the SKYLIDAR algorithm to the actual measurements at Tsukuba, Japan. The detailed vertical structures of the aerosol optical properties and solar heating rate of transported dust and smoke were investigated. Examination of the relationship between the solar heating rate and the aerosol optical properties showed that the vertical profile of the asymmetry factor played an important role in creating vertical variation in the solar heating rate. We then compared the columnar optical properties retrieved with the SKYLIDAR algorithm to those produced with the more established scheme SKYRAD.PACK, and the surface solar irradiance calculated from the SKYLIDAR retrievals was compared with pyranometer measurement. The results showed good agreements: the columnar values of the SKYLIDAR retrievals agreed with reliable SKYRAD.PACK retrievals, and the SKYLIDAR retrievals were sufficiently accurate to evaluate the surface solar irradiance.

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Journal articles on the topic 'Skynet'

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