Models for the Directional Distribution of the Diffuse Sky Radiance

1990 ◽  
Vol 112 (2) ◽  
pp. 102-109 ◽  
Author(s):  
F. M. F. Siala ◽  
M. A. Rosen ◽  
F. C. Hooper
Keyword(s):  
Angular Distribution ◽  
Stochastic Models ◽  
Continuous Distribution ◽  
Time Dependent ◽  
Distribution Models ◽  
Directional Distribution ◽  
Sky Radiance ◽  
Semi Empirical ◽  
Sky Type

Both traditional and recently proposed models for the angular distribution of diffuse sky radiance are reviewed and compared. The models considered include basic models, sky-type-specific models, empirical and semi-empirical continuous distribution models, models which account for time-dependent cloud effects and stochastic models.

scholarly journals Predictive Ecosystem Mapping of South-Eastern Australian Temperate Forests Using Lidar-Derived Structural Profiles and Species Distribution Models

2019 ◽  
Vol 11 (1) ◽  
pp. 93 ◽  
Author(s):  
Melissa Fedrigo ◽  
Stephen B. Stewart ◽  
Stephen H. Roxburgh ◽  
Sabine Kasel ◽  
Lauren T. Bennett ◽  
...  
Keyword(s):  
Species Distribution ◽  
Vegetation Structure ◽  
Species Distribution Models ◽  
Sustainable Forest Management ◽  
Continuous Distribution ◽  
Forest Monitoring ◽  
Distribution Models ◽  
Study Region ◽  
South Eastern ◽  
Eastern Australia

Modern approaches to predictive ecosystem mapping (PEM) have not thoroughly explored the use of ‘characteristic’ gradients, which describe vegetation structure (e.g., light detection and ranging (lidar)-derived structural profiles). In this study, we apply a PEM approach by classifying the dominant stand types within the Central Highlands region of south-eastern Australia using both lidar and species distribution models (SDMs). Similarity percentages analysis (SIMPER) was applied to comprehensive floristic surveys to identify five species which best separated stand types. The predicted distributions of these species, modelled using random forests with environmental (i.e., climate, topography) and optical characteristic gradients (Landsat-derived seasonal fractional cover), provided an ecological basis for refining stand type classifications based only on lidar-derived structural profiles. The resulting PEM model represents the first continuous distribution map of stand types across the study region that delineates ecotone stands, which are seral communities comprised of species typical of both rainforest and eucalypt forests. The spatial variability of vegetation structure incorporated into the PEM model suggests that many stand types are not as continuous in cover as represented by current ecological vegetation class distributions that describe the region. Improved PEM models can facilitate sustainable forest management, enhanced forest monitoring, and informed decision making at landscape scales.

Queue-Based Headway Distribution Models at Signal Controlled Intersection under Mixed Traffic

2020 ◽  
Vol 2674 (11) ◽  
pp. 768-778
Author(s):  
Satyajit Mondal ◽  
Ankit Gupta
Keyword(s):  
Traffic Flow ◽  
Statistical Significance ◽  
Flow Analysis ◽  
Continuous Distribution ◽  
Statistical Investigation ◽  
Generation Process ◽  
Mixed Traffic ◽  
Distribution Models ◽  
Headway Distribution ◽  
Vehicle Position

Headway of vehicles during platoon dispersion at signalized intersection is one of the critical microscopic traffic characteristics in traffic flow theory. The distribution of the discharge headways of vehicles also has a significant impact on the traffic generation process in most of the microsimulation approaches. However, few studies have investigated the vehicle discharge headway for interrupted flow at signalized intersections under mixed traffic conditions. The present study uses data collected from 20 intersections in six cities for comprehensive analysis of discharge headway. A box-and-whiskers plot is generated for discharge headway to quantify its reasonable profile. The diagram shows that headway of vehicles decreases with the queue dispersion. A stable headway can be observed after the fifth vehicle position of a queue, giving a saturation headway of 2.05 s per vehicle. Six types of continuous distribution are tested to model the discharge headway distribution. A statistical investigation is also performed to verify the best-fitted model for each vehicle position in a queue. The ranking of a best-fitted distribution is done for each vehicle position as per the statistical significance. This study demonstrates the discharge headway characteristics and distribution at each vehicle position, which can be useful for traffic flow analysis and especially for improving microsimulation models.

scholarly journals Angular Distribution Models for Top-of-Atmosphere Radiative Flux Estimation from the Clouds and the Earth’s Radiant Energy System Instrument on the Terra Satellite. Part I: Methodology

2005 ◽  
Vol 22 (4) ◽  
pp. 338-351 ◽  
Author(s):  
Norman G. Loeb ◽  
Seiji Kato ◽  
Konstantin Loukachine ◽  
Natividad Manalo-Smith
Keyword(s):  
Angular Distribution ◽  
Radiant Energy ◽  
Tropical Rainfall Measuring Mission ◽  
Energy System ◽  
Distribution Models ◽  
Radiative Fluxes ◽  
Earth Observing System ◽  
Moderate Resolution ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Terra Satellite

Abstract The Clouds and Earth’s Radiant Energy System (CERES) provides coincident global cloud and aerosol properties together with reflected solar, emitted terrestrial longwave, and infrared window radiative fluxes. These data are needed to improve the understanding and modeling of the interaction between clouds, aerosols, and radiation at the top of the atmosphere, surface, and within the atmosphere. This paper describes the approach used to estimate top-of-atmosphere (TOA) radiative fluxes from instantaneous CERES radiance measurements on the Terra satellite. A key component involves the development of empirical angular distribution models (ADMs) that account for the angular dependence of the earth’s radiation field at the TOA. The CERES Terra ADMs are developed using 24 months of CERES radiances, coincident cloud and aerosol retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS), and meteorological parameters from the Global Modeling and Assimilation Office (GMAO)’s Goddard Earth Observing System (GEOS) Data Assimilation System (DAS) V4.0.3 product. Scene information for the ADMs is from MODIS retrievals and GEOS DAS V4.0.3 properties over the ocean, land, desert, and snow for both clear and cloudy conditions. Because the CERES Terra ADMs are global, and far more CERES data are available on Terra than were available from CERES on the Tropical Rainfall Measuring Mission (TRMM), the methodology used to define CERES Terra ADMs is different in many respects from that used to develop CERES TRMM ADMs, particularly over snow/sea ice, under cloudy conditions, and for clear scenes over land and desert.

Continuous-time stochastic models of a multigrade population

1978 ◽  
Vol 15 (1) ◽  
pp. 26-37 ◽  
Author(s):  
Sally I. McClean
Keyword(s):  
Markov Model ◽  
Exponential Distribution ◽  
Stochastic Models ◽  
Continuous Time ◽  
Time Dependent ◽  
Poisson Arrival ◽  
Mixed Exponential Distribution ◽  
Previous Assumption

The continuous-time Markov model of a multigrade organization is extended in several ways. Firstly the internal transitions and the leaving process are generalized to a semi-Markov formulation which allows for the inclusion of well-authenticated leaving distributions such as the mixed exponential distribution. The previous assumption of Poisson recruitment is then generalized to allow for a time-dependent Poisson arrival distribution in which the instantaneous probability of an arrival is a mixture of exponential terms. Finally we extend the capital-related manpower model to describe a multigrade organization.

The Angular Distribution of Diffuse Sky Radiance: An Assessment of the Effects of Haze

1991 ◽  
Vol 113 (3) ◽  
pp. 200-205 ◽  
Author(s):  
M. A. Rosen
Keyword(s):  
Angular Distribution ◽  
Complex Relationship ◽  
Distribution Shape ◽  
The Absolute ◽  
Sky Radiance

The effects of haze on the angular distribution of the diffuse sky radiance are investigated by examining and comparing data for individual clear skies with and without haze, and for other selected sky types, and by modeling and comparing data for such skies. It is found that haze appears to affect the radiance distributions only for clear, partly cloudy, and lightly overcast skies, and that for clear skies, increasing haze increases the absolute sky radiance values. In addition, the radiance distributions for clear skies with haze are found to exhibit characteristics generally similar to those for the nonopaque overcast skies. However, it is also found that the normalized radiance distributions for clear skies with haze, which generally provide clearer illustrations of distribution shape than the absolute radiance distributions, exhibit slightly less intense circumsolar and horizon brightening components than do the normalized distributions for clear skies without haze. In general, a systematic, but complex, relationship appears to exist between haze and the distribution of the diffuse sky radiance. The results may prove useful to several disciplines, including the design of solar technologies.

scholarly journals Next-generation angular distribution models for top-of-atmosphere radiative flux calculation from CERES instruments: methodology

2015 ◽  
Vol 8 (2) ◽  
pp. 611-632 ◽  
Author(s):  
W. Su ◽  
J. Corbett ◽  
Z. Eitzen ◽  
L. Liang
Keyword(s):  
Angular Distribution ◽  
Sea Ice ◽  
Regional Scale ◽  
Radiant Energy ◽  
Energy System ◽  
Continuous Functions ◽  
Climate Feedback ◽  
Radiative Energy ◽  
Next Generation ◽  
Distribution Models

Abstract. The top-of-atmosphere (TOA) radiative fluxes are critical components to advancing our understanding of the Earth's radiative energy balance, radiative effects of clouds and aerosols, and climate feedback. The Clouds and the Earth's Radiant Energy System (CERES) instruments provide broadband shortwave and longwave radiance measurements. These radiances are converted to fluxes by using scene-type-dependent angular distribution models (ADMs). This paper describes the next-generation ADMs that are developed for Terra and Aqua using all available CERES rotating azimuth plane radiance measurements. Coincident cloud and aerosol retrievals, and radiance measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS), and meteorological parameters from Goddard Earth Observing System (GEOS) data assimilation version 5.4.1 are used to define scene type. CERES radiance measurements are stratified by scene type and by other parameters that are important for determining the anisotropy of the given scene type. Anisotropic factors are then defined either for discrete intervals of relevant parameters or as a continuous functions of combined parameters, depending on the scene type. Significant differences between the ADMs described in this paper and the existing ADMs are over clear-sky scene types and polar scene types. Over clear ocean, we developed a set of shortwave (SW) ADMs that explicitly account for aerosols. Over clear land, the SW ADMs are developed for every 1° latitude × 1° longitude region for every calendar month using a kernel-based bidirectional reflectance model. Over clear Antarctic scenes, SW ADMs are developed by accounting the effects of sastrugi on anisotropy. Over sea ice, a sea-ice brightness index is used to classify the scene type. Under cloudy conditions over all surface types, the longwave (LW) and window (WN) ADMs are developed by combining surface and cloud-top temperature, surface and cloud emissivity, cloud fraction, and precipitable water. Compared to the existing ADMs, the new ADMs change the monthly mean instantaneous fluxes by up to 5 W m−2 on a regional scale of 1° latitude × 1° longitude, but the flux changes are less than 0.5 W m−2 on a global scale.

Sign in / Sign up

Export Citation Format

Share Document