scholarly journals How the clear-sky angle of polarization pattern continues underneath clouds: full-sky measurements and implications for animal orientation

2001 ◽  
Vol 204 (17) ◽  
pp. 2933-2942 ◽  
Author(s):  
István Pomozi ◽  
Gábor Horváth ◽  
Rüdiger Wehner
Keyword(s):  
Single Scattering ◽  
Degree Of Polarization ◽  
Polarization Pattern ◽  
Clear Sky ◽  
Animal Navigation ◽  
Imaging Polarimetry ◽  
Polarization Compass ◽  
Sky Conditions ◽  
Perceptual Threshold ◽  
Animal Orientation

SUMMARY One of the biologically most important parameters of the cloudy sky is the proportion P of the celestial polarization pattern available for use in animal navigation. We evaluated this parameter by measuring the polarization patterns of clear and cloudy skies using 180° (full-sky) imaging polarimetry in the red (650nm), green (550nm) and blue (450nm) ranges of the spectrum under clear and partly cloudy conditions. The resulting data were compared with the corresponding celestial polarization patterns calculated using the single-scattering Rayleigh model. We show convincingly that the pattern of the angle of polarization (e-vectors) in a clear sky continues underneath clouds if regions of the clouds and parts of the airspace between the clouds and the earth surface (being shady at the position of the observer) are directly lit by the sun. The scattering and polarization of direct sunlight on the cloud particles and in the air columns underneath the clouds result in the same e-vector pattern as that present in clear sky. This phenomenon can be exploited for animal navigation if the degree of polarization is higher than the perceptual threshold of the visual system, because the angle rather than the degree of polarization is the most important optical cue used in the polarization compass. Hence, the clouds reduce the extent of sky polarization pattern that is useful for animal orientation much less than has hitherto been assumed. We further demonstrate quantitatively that the shorter the wavelength, the greater the proportion of celestial polarization that can be used by animals under cloudy-sky conditions. As has already been suggested by others, this phenomenon may solve the ultraviolet paradox of polarization vision in insects such as hymenopterans and dipterans. The present study extends previous findings by using the technique of 180° imaging polarimetry to measure and analyse celestial polarization patterns.

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 Direct Aerosol Radiative Forcing Uncertainty Based on a Radiative Perturbation Analysis

2010 ◽  
Vol 23 (19) ◽  
pp. 5288-5293 ◽  
Author(s):  
Norman G. Loeb ◽  
Wenying Su
Keyword(s):  
Radiative Forcing ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Aerosol Radiative Forcing ◽  
Clear Sky ◽  
Radiative Perturbation ◽  
Sky Conditions ◽  
Global Mean ◽  
Aerosol Properties ◽  
Aerosol Radiative

Abstract To provide a lower bound for the uncertainty in measurement-based clear- and all-sky direct aerosol radiative forcing (DARF), a radiative perturbation analysis is performed for the ideal case in which the perturbations in global mean aerosol properties are given by published values of systematic uncertainty in Aerosol Robotic Network (AERONET) aerosol measurements. DARF calculations for base-state climatological cloud and aerosol properties over ocean and land are performed, and then repeated after perturbing individual aerosol optical properties (aerosol optical depth, single-scattering albedo, asymmetry parameter, scale height, and anthropogenic fraction) from their base values, keeping all other parameters fixed. The total DARF uncertainty from all aerosol parameters combined is 0.5–1.0 W m−2, a factor of 2–4 greater than the value cited in the Intergovernmental Panel on Climate Change’s (IPCC’s) Fourth Assessment Report. Most of the total DARF uncertainty in this analysis is associated with single-scattering albedo uncertainty. Owing to the greater sensitivity to single-scattering albedo in cloudy columns, DARF uncertainty in all-sky conditions is greater than in clear-sky conditions, even though the global mean clear-sky DARF is more than twice as large as the all-sky DARF.

scholarly journals Clear Night Sky Polarization Patterns Under the Super Blue Blood Moon

Atmosphere ◽  
2020 ◽  
Vol 11 (4) ◽  
pp. 372
Author(s):  
Yueting Yang ◽  
Pengwei Hu ◽  
Jian Yang ◽  
Shanpeng Wang ◽  
Qingyun Zhang ◽  
...  
Keyword(s):  
Atmospheric Model ◽  
Single Scattering ◽  
Degree Of Polarization ◽  
Polarization Distribution ◽  
Clear Sky ◽  
Polarization Characteristics ◽  
Symmetric Line ◽  
Atmospheric Radiative Transfer ◽  
Navigation Information ◽  
The Ideal

Investigating celestial polarization patterns in the case of different environments is important for exploring the atmospheric radiative transfer mechanism. Although intensive studies on clear sky, foggy sky, and even total solar eclipse sky have been conducted, the polarization distribution generated by the moonlight has not been well investigated. This study analyzes celestial polarization patterns generated by the Super Blue Blood Moon (SBBM) through several comparative studies. The polarization patterns under the SBBM are collected, analyzed, and compared with both those generated by the ideal single-scattering Rayleigh model and those in the normal sky. From the analysis of the relative variation of the celestial polarization characteristics including the Degree of Polarization (DoP) and Angle of Polarization (AoP), the changes of the extremum, frequency, symmetric line, and neutral points are discussed. As a result, SBBM polarization patterns change at the beginning of the partial eclipse, and the neutral points vary from traditional neutral points. The value of DoP gradually decreases as the obscuration ratio of the Moon increases. The AoP is no longer symmetrical about the celestial meridian. As a conclusion, it is suggested that the variation of the polarized skylight during the SBBM should be considered in atmospheric model calculation for nocturnal biological activity and navigation information computation.

scholarly journals Impact of Aerosol on the Estimation Accuracy of Solar Radiation

2018 ◽  
Vol 60 (1) ◽  
pp. 97-103
Author(s):  
Calinoiu Delia-Gabriela ◽  
Paulescu Marius
Keyword(s):  
Solar Irradiance ◽  
Single Scattering ◽  
Empirical Models ◽  
Parametric Models ◽  
Surface Radiation ◽  
Estimation Accuracy ◽  
Asymmetry Factor ◽  
Clear Sky ◽  
Sky Conditions ◽  
Aerosol Properties

AbstractThe paper is focused on the solar irradiance estimation in clear-sky conditions and an aerosol-loaded atmosphere. Two parametric models developed by our group and three empirical models are tested. The estimates of the parametric models are based on three atmospheric parameters (ozone, nitrogen dioxide and water vapor column content) and the aerosol properties quantified by means of several specific parameters (Ångström turbidity coefficient, single scattering albedo, asymmetry factor). The empirical models contain no inputs for aerosol properties. Data collected from 10 stations were used to test the models. The inputs for the parametric models were retrieved from Aerosol Robotic Network - AERONET. Global and diffuse solar irradiance data at high-quality standards were retrieved from the Baseline Surface Radiation Network BSRN. A comparative analysis of the models’ accuracy in estimating clear-sky solar irradiance is discussed from the perspective of aerosol proprieties.

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.

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 Bionic Integrated Positioning Mechanism Based on Bioinspired Polarization Compass and Inertial Navigation System

Sensors ◽  
2021 ◽  
Vol 21 (4) ◽  
pp. 1055
Author(s):  
Qingyun Zhang ◽  
Jian Yang ◽  
Panpan Huang ◽  
Xin Liu ◽  
Shanpeng Wang ◽  
...  
Keyword(s):  
Navigation System ◽  
Inertial Navigation System ◽  
Inertial Navigation ◽  
System Model ◽  
Degree Of Polarization ◽  
Positioning System ◽  
Integration Model ◽  
Position Errors ◽  
Model Combining ◽  
Polarization Compass

In this paper, to address the problem of positioning accumulative errors of the inertial navigation system (INS), a bionic autonomous positioning mechanism integrating INS with a bioinspired polarization compass is proposed. In addition, the bioinspired positioning system hardware and the integration model are also presented. Concerned with the technical issue of the accuracy and environmental adaptability of the integrated positioning system, the sun elevation calculating method based on the degree of polarization (DoP) and direction of polarization (E-vector) is presented. Moreover, to compensate for the latitude and longitude errors of INS, the bioinspired positioning system model combining the polarization compass and INS is established. Finally, the positioning performance of the proposed bioinspired positioning system model was validated via outdoor experiments. The results indicate that the proposed system can compensate for the position errors of INS with satisfactory performance.

Intra-Day DNI Forecasting Under Clear Sky Conditions Using ANFIS

2014 ◽  
Vol 47 (3) ◽  
pp. 10361-10366 ◽  
Author(s):  
Rémi Chauvin ◽  
Julien Nou ◽  
Stéphane Thil ◽  
Stéphane Grieu
Keyword(s):  
Clear Sky ◽  
Sky Conditions

scholarly journals How dim is dim? Precision of the celestial compass in moonlight and sunlight

2011 ◽  
Vol 366 (1565) ◽  
pp. 697-702 ◽  
Author(s):  
M. Dacke ◽  
M. J. Byrne ◽  
E. Baird ◽  
C. H. Scholtz ◽  
E. J. Warrant
Keyword(s):  
Dung Beetle ◽  
The Sun ◽  
The Moon ◽  
Polarization Pattern ◽  
Animal Group ◽  
Straight Line ◽  
Celestial Orientation ◽  
Polarization Compass ◽  
Celestial Compass ◽  
Diurnal Species

Prominent in the sky, but not visible to humans, is a pattern of polarized skylight formed around both the Sun and the Moon. Dung beetles are, at present, the only animal group known to use the much dimmer polarization pattern formed around the Moon as a compass cue for maintaining travel direction. However, the Moon is not visible every night and the intensity of the celestial polarization pattern gradually declines as the Moon wanes. Therefore, for nocturnal orientation on all moonlit nights, the absolute sensitivity of the dung beetle's polarization detector may limit the precision of this behaviour. To test this, we studied the straight-line foraging behaviour of the nocturnal ball-rolling dung beetle Scarabaeus satyrus to establish when the Moon is too dim—and the polarization pattern too weak—to provide a reliable cue for orientation. Our results show that celestial orientation is as accurate during crescent Moon as it is during full Moon. Moreover, this orientation accuracy is equal to that measured for diurnal species that orient under the 100 million times brighter polarization pattern formed around the Sun. This indicates that, in nocturnal species, the sensitivity of the optical polarization compass can be greatly increased without any loss of precision.

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