scholarly journals The polarized Sun and sky radiometer SSARA: design, calibration, and application for ground-based aerosol remote sensing

2020 ◽  
Vol 13 (1) ◽  
pp. 239-258 ◽  
Author(s):  
Hans Grob ◽  
Claudia Emde ◽  
Matthias Wiegner ◽  
Meinhard Seefeldner ◽  
Linda Forster ◽  
...  
Keyword(s):  
Polarized Light ◽  
Calibration Method ◽  
Saharan Dust ◽  
The Sun ◽  
Dust Layer ◽  
Additional Information ◽  
Clear Sky ◽  
Linearly Polarized ◽  
Aerosol Remote Sensing ◽  
Sky Conditions

Abstract. Recently, polarimetry has been used to enhance classical photometry to infer aerosol optical properties, as polarized radiation contains additional information about the particles. Therefore, we have equipped the Sun–sky automatic radiometer (SSARA) with polarizer filters to measure linearly polarized light at 501.5 nm. We describe an improved radiometric and polarimetric calibration method, which allows us to simultaneously determine the linear polarizers' diattenuation and relative orientation with high accuracy (0.002 and 0.1∘, respectively). Furthermore, we employed a new calibration method for the alt-azimuthal mount capable of correcting the instrument's pointing to within 32 arcmin. So far, this is limited by the accuracy of the Sun tracker. Both these methods are applicable to other Sun and sky radiometers, such as the Cimel CE318-DP instruments used in the AErosol RObotic NETwork (AERONET). During the A-LIFE (Absorbing aerosol layers in a changing climate: aging, LIFEtime and dynamics) field campaign in April 2017, SSARA collected 22 d of data. Here, we present two case studies. The first demonstrates the performance of an aerosol retrieval from SSARA observations under partially cloudy conditions. In the other case, a high aerosol load due to a Saharan dust layer was present during otherwise clear-sky conditions.

scholarly journals The polarized sun and sky radiometer SSARA: design, calibration, and application for ground based aerosol remote sensing

2019 ◽  
Author(s):  
Hans Grob ◽  
Claudia Emde ◽  
Matthias Wiegner ◽  
Meinhard Seefeldner ◽  
Bernhard Mayer
Keyword(s):  
Polarized Light ◽  
Calibration Method ◽  
Saharan Dust ◽  
Dust Layer ◽  
Additional Information ◽  
Clear Sky ◽  
Aerosol Retrieval ◽  
Linearly Polarized ◽  
Aerosol Remote Sensing ◽  
Sky Conditions

Abstract. Recently, polarimetry has been used to enhance classical photometry to infer aerosol optical properties, as polarized radiation contains additional information about the particles. Therefore, we have equipped the SSARA sun and sky photometer with polarizer filters to measure linearly polarized light at 501.5 nm. We have developed a novel radiometric and polarimetric calibration method, which allows us to simultaneously determine the linear polarizers' diattenuation and relative orientation with high accuracy (0.002 and 0.1°, respectively). Furthermore, we employed a new calibration method for the azimuthal mount capable of correcting the instrument's pointing to within 32 arcmin. So far, this is limited by the accuracy of the sun-tracker. Both these methods are applicable to other sun and sky radiometers, such as Cimel CE318-DP instruments used in AERONET. During the A-LIFE field campaign in April 2017, SSARA collected 22 days of data. Here, we present two case studies: The first demonstrates the performance of an aerosol retrieval from SSARA observations under partially cloudy conditions. In the other case, a high aerosol load due to a Saharan dust layer was present during otherwise perfect clear sky conditions.

scholarly journals Problems of Menotactic Orientation According to the Polarized Light of the Sky

1975 ◽  
Vol 30 (1-2) ◽  
pp. 88-90 ◽  
Author(s):  
Kuno Kirschfeld ◽  
M. Lindauer ◽  
H. Martin
Keyword(s):  
Infinite Number ◽  
Polarized Light ◽  
The Sun ◽  
Number Of Solutions ◽  
Special Cases ◽  
Linearly Polarized ◽  
Vector Direction

Abstract It is shown that the knowledge of the E-vector direction of the linearly polarized light at any point of the sky alone is insufficient for the determination of the position of the sun. If the E-vector direction of a second point is not known the knowledge of at least one other parameter is necessary. This parameter might be the height of the sun over the horizon. With the knowledge of the height the infinite number of solutions for the sun’s position becomes reduced to two, or in special cases to one. These cases are derived.

scholarly journals Celestial polarization patterns sufficient for Viking navigation with the naked eye: detectability of Haidinger's brushes on the sky versus meteorological conditions

2017 ◽  
Vol 4 (2) ◽  
pp. 160688 ◽  
Author(s):  
Gábor Horváth ◽  
Péter Takács ◽  
Balázs Kretzer ◽  
Szilvia Szilasi ◽  
Dénes Száz ◽  
...  
Keyword(s):  
Meteorological Conditions ◽  
Degree Of Polarization ◽  
The Sun ◽  
Polarization Pattern ◽  
Clear Sky ◽  
Solar Elevation ◽  
Cloud Coverage ◽  
Open Sea ◽  
Imaging Polarimetry ◽  
Sky Conditions

If a human looks at the clear blue sky from which light with high enough degree of polarization d originates, an 8-shaped bowtie-like figure, the yellow Haidinger's brush can be perceived, the long axis of which points towards the sun. A band of high d arcs across the sky at 90° from the sun. A person can pick two points on that band, observe the yellow brushes and triangulate the position of the sun based on the orientation of the two observed brushes. This method has been suggested to have been used on the open sea by Viking navigators to determine the position of the invisible sun occluded by cloud or fog. Furthermore, Haidinger's brushes can also be used to locate the sun when it is below the horizon or occluded by objects on the horizon. To determine the position of the sun using the celestial polarization pattern, the d of the portion of the sky used must be greater than the viewer's degree of polarization threshold d * for perception of Haidinger's brushes. We studied under which sky conditions the prerequisite d  >  d * is satisfied. Using full-sky imaging polarimetry, we measured the d -pattern of skylight in the blue (450 nm) spectral range for 1296 different meteorological conditions with different solar elevation angles θ and per cent cloud cover ρ . From the measured d -patterns of a given sky we determined the proportion P of the sky for which d  >  d *. We obtained that P is the largest at low solar elevations θ  ≈ 0° and under totally or nearly clear skies with cloud coverage ρ  = 0%, when the sun's position is already easily determined. If the sun is below the horizon (−5° ≤  θ  < 0°) during twilight, P  = 76.17 ± 4.18% for d min ∗ = 23 % under clear sky conditions. Consequently, the sky-polarimetric Viking navigation based on Haidinger's brushes is most useful after sunset and prior to sunrise, when the sun is not visible and large sky regions are bright, clear and polarized enough for perception of Haidinger's brushes.

scholarly journals Atmospheric effect on the ground-based measurements of broadband surface albedo

2012 ◽  
Vol 5 (1) ◽  
pp. 385-409 ◽  
Author(s):  
T. Manninen ◽  
A. Riihelä ◽  
G. de Leeuw
Keyword(s):  
Optical Depth ◽  
Zenith Angle ◽  
Surface Albedo ◽  
New Method ◽  
Test Case ◽  
The Sun ◽  
Atmospheric Conditions ◽  
Atmospheric Effect ◽  
Clear Sky ◽  
Sky Conditions

Abstract. Ground-based pyranometer measurements of broadband surface albedo values are affected by the atmospheric conditions. A new method for estimating the magnitude of this effect in clear sky conditions is presented. Global and reflected radiation values and AOD values at two wavelengths are needed to apply the method. Depending on the atmospheric optical depth and the sun zenith angle values the effect can be as large as 20%. For the test case of Cabauw the atmosphere caused typically 5% higher surface albedo values than the corresponding black-sky surface albedo values.

scholarly journals Polarized Light and the Orientation of Two Marine Crustacea

1957 ◽  
Vol 34 (3) ◽  
pp. 342-364
Author(s):  
RICHARD BAINBRIDGE ◽  
TALBOT H. WATERMAN
Keyword(s):  
Polarized Light ◽  
Longitudinal Axis ◽  
The Sun ◽  
Visual Contact ◽  
General Direction ◽  
Terrestrial Arthropods ◽  
Linearly Polarized ◽  
Vertical Beam ◽  
Celestial Compass ◽  
The Mean

1. Quantitative experiments are described, designed to test the hypothesis that underwater polarized light is used for orientation by aquatic animals as that of the blue sky is by terrestrial arthropods. 2. Studied in the laboratory the littoral mysid, mysidium gracile, was found capable of orientation relative to the e vector in a vertical beam of linearly polarized light. 3. Statistically significant preference was shown by this animal for aligning its longitudinal axis at right angles to the plane of polarization. 4. A secondary slight preference was shown for swimming parallel with the plane and the degree of random orientation was often high (4% mean). 5. The littoral prawn, Palaemon northropi, when released in quiet water far enough from the bottom and the shore to prevent visual contact, was found to swim on relatively straight horizontal courses for appreciable distances in forty-one out of sixty-one tests. 6. The mean length of these runs was 24.5 m., the maximum 119 m. ; swimming velocities up to about 1 km./hr. were measured. 7. The sun's position seems to be the only directional clue not controlled in these tests, and the general direction of the runs is significantly correlated with the direction of the sun, being at right anglea to it. 8. It is thus concluded that this animar can use the sun, either directly or through the polarization pattern, as a celestial compass.

Evaluation of net shortwave radiation over China with a regional climate model

2020 ◽  
Vol 80 (2) ◽  
pp. 147-163
Author(s):  
X Liu ◽  
Y Kang ◽  
Q Liu ◽  
Z Guo ◽  
Y Chen ◽  
...  
Keyword(s):  
Regional Climate Model ◽  
Climate Model ◽  
Regional Climate ◽  
Radiant Energy ◽  
Energy System ◽  
Radiation Budget ◽  
Shortwave Radiation ◽  
Monsoon Region ◽  
Clear Sky ◽  
Sky Conditions

The regional climate model RegCM version 4.6, developed by the European Centre for Medium-Range Weather Forecasts Reanalysis, was used to simulate the radiation budget over China. Clouds and the Earth’s Radiant Energy System (CERES) satellite data were utilized to evaluate the simulation results based on 4 radiative components: net shortwave (NSW) radiation at the surface of the earth and top of the atmosphere (TOA) under all-sky and clear-sky conditions. The performance of the model for low-value areas of NSW was superior to that for high-value areas. NSW at the surface and TOA under all-sky conditions was significantly underestimated; the spatial distribution of the bias was negative in the north and positive in the south, bounded by 25°N for the annual and seasonal averaged difference maps. Compared with the all-sky condition, the simulation effect under clear-sky conditions was significantly better, which indicates that the cloud fraction is the key factor affecting the accuracy of the simulation. In particular, the bias of the TOA NSW under the clear-sky condition was <±10 W m-2 in the eastern areas. The performance of the model was better over the eastern monsoon region in winter and autumn for surface NSW under clear-sky conditions, which may be related to different levels of air pollution during each season. Among the 3 areas, the regional average biases overall were largest (negative) over the Qinghai-Tibet alpine region and smallest over the eastern monsoon region.

Airborne measurements of dust layer properties, particle size distribution and mixing state of Saharan dust during SAMUM 2006

Tellus B ◽  
2009 ◽  
Vol 61 (1) ◽  
Author(s):  
Bernadett Weinzierl ◽  
Andreas Petzold ◽  
Michael Esselborn ◽  
Martin Wirth ◽  
Katharina Rasp ◽  
...  
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Saharan Dust ◽  
Mixing State ◽  
Dust Layer ◽  
Airborne Measurements

Efficient downscaling of satellite oceanographic data with convolutional neural networks

2021 ◽  
Vol 12 (3) ◽  
pp. 46-47
Author(s):  
Nikita Saxena
Keyword(s):  
Neural Networks ◽  
Deep Learning ◽  
Convolutional Neural Networks ◽  
Super Resolution ◽  
Sea Surface ◽  
Clear Sky ◽  
Oceanographic Data ◽  
Computationally Expensive ◽  
Sky Conditions ◽  
Data Inference

Space-borne satellite radiometers measure Sea Surface Temperature (SST), which is pivotal to studies of air-sea interactions and ocean features. Under clear sky conditions, high resolution measurements are obtainable. But under cloudy conditions, data analysis is constrained to the available low resolution measurements. We assess the efficiency of Deep Learning (DL) architectures, particularly Convolutional Neural Networks (CNN) to downscale oceanographic data from low spatial resolution (SR) to high SR. With a focus on SST Fields of Bay of Bengal, this study proves that Very Deep Super Resolution CNN can successfully reconstruct SST observations from 15 km SR to 5km SR, and 5km SR to 1km SR. This outcome calls attention to the significance of DL models explicitly trained for the reconstruction of high SR SST fields by using low SR data. Inference on DL models can act as a substitute to the existing computationally expensive downscaling technique: Dynamical Downsampling. The complete code is available on this Github Repository.

scholarly journals Radiative Effect and Mixing Processes of a Long-Lasting Dust Event over Athens, Greece, during the COVID-19 Period

Atmosphere ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 318
Author(s):  
Panagiotis Kokkalis ◽  
Ourania Soupiona ◽  
Christina-Anna Papanikolaou ◽  
Romanos Foskinis ◽  
Maria Mylonaki ◽  
...  
Keyword(s):  
Atmospheric Pollutants ◽  
Saharan Dust ◽  
Radiative Effect ◽  
Atmospheric Conditions ◽  
Dust Event ◽  
Mixing Processes ◽  
Hysplit Model ◽  
European Continent ◽  
Dust Layer ◽  
Ground Based Lidar

We report on a long-lasting (10 days) Saharan dust event affecting large sections of South-Eastern Europe by using a synergy of lidar, satellite, in-situ observations and model simulations over Athens, Greece. The dust measurements (11–20 May 2020), performed during the confinement period due to the COVID-19 pandemic, revealed interesting features of the aerosol dust properties in the absence of important air pollution sources over the European continent. During the event, moderate aerosol optical depth (AOD) values (0.3–0.4) were observed inside the dust layer by the ground-based lidar measurements (at 532 nm). Vertical profiles of the lidar ratio and the particle linear depolarization ratio (at 355 nm) showed mean layer values of the order of 47 ± 9 sr and 28 ± 5%, respectively, revealing the coarse non-spherical mode of the probed plume. The values reported here are very close to pure dust measurements performed during dedicated campaigns in the African continent. By utilizing Libradtran simulations for two scenarios (one for typical midlatitude atmospheric conditions and one having reduced atmospheric pollutants due to COVID-19 restrictions, both affected by a free tropospheric dust layer), we revealed negligible differences in terms of radiative effect, of the order of +2.6% (SWBOA, cooling behavior) and +1.9% (LWBOA, heating behavior). Moreover, the net heating rate (HR) at the bottom of the atmosphere (BOA) was equal to +0.156 K/d and equal to +2.543 K/d within 1–6 km due to the presence of the dust layer at that height. On the contrary, the reduction in atmospheric pollutants could lead to a negative HR (−0.036 K/d) at the bottom of the atmosphere (BOA) if dust aerosols were absent, while typical atmospheric conditions are estimated to have an almost zero net HR value (+0.006 K/d). The NMMB-BSC forecast model provided the dust mass concentration over Athens, while the air mass advection from the African to the European continent was simulated by the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model.

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