scholarly journals Shortwave Spectral Radiative Signatures and Their Physical Controls

2019 ◽  
Vol 32 (15) ◽  
pp. 4805-4828 ◽  
Author(s):  
Jake J. Gristey ◽  
J. Christine Chiu ◽  
Robert J. Gurney ◽  
Keith P. Shine ◽  
Stephan Havemann ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Physical Properties ◽  
Spectral Reflectance ◽  
Spatial Scales ◽  
Monsoon Season ◽  
Spectral Characteristics ◽  
Great Promise ◽  
Earth System ◽  
Spectral Signatures ◽  
Cloud Regimes

AbstractThe spectrum of reflected solar radiation emerging at the top of the atmosphere is rich with Earth system information. To identify spectral signatures in the reflected solar radiation and directly relate them to the underlying physical properties controlling their structure, over 90 000 solar reflectance spectra are computed over West Africa in 2010 using a fast radiation code employing the spectral characteristics of the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY). Cluster analysis applied to the computed spectra reveals spectral signatures related to distinct surface properties, and cloud regimes distinguished by their spectral shortwave cloud radiative effect (SWCRE). The cloud regimes exhibit a diverse variety of mean broadband SWCREs, and offer an alternative approach to define cloud type for SWCRE applications that does not require any prior assumptions. The direct link between spectral signatures and distinct physical properties extracted from clustering remains robust between spatial scales of 1, 20, and 240 km, and presents an excellent opportunity to understand the underlying properties controlling real spectral reflectance observations. Observed SCIAMACHY spectra are assigned to the calculated spectral clusters, showing that cloud regimes are most frequent during the active West African monsoon season of June–October in 2010, and all cloud regimes have a higher frequency of occurrence during the active monsoon season of 2003 compared with the inactive monsoon season of 2004. Overall, the distinct underlying physical properties controlling spectral signatures show great promise for monitoring evolution of the Earth system directly from solar spectral reflectance observations.

scholarly journals Estimation of Leaf Nitrogen Content from Spectral Characteristics of Rice Canopy

2001 ◽  
Vol 1 ◽  
pp. 81-89 ◽  
Author(s):  
Chwen-Ming Yang
Keyword(s):  
Nitrogen Content ◽  
Linear Relationship ◽  
Spectral Reflectance ◽  
Spectral Characteristics ◽  
Leaf Nitrogen ◽  
Leaf Nitrogen Content ◽  
Nitrogen Application ◽  
Spectral Signatures ◽  
Growing Period ◽  
Application Rates

Ground-based remotely sensed reflectance spectra of hyperspectral resolution were monitored during the growing period of rice under various nitrogen application rates. It was found that reflectance spectrum of rice canopy changed in both wavelength and reflectance as the plants developed. Fifteen characteristic wavebands were identified from the apparent peaks and valleys of spectral reflectance curves, in accordance with the results of the first-order differentiation, measured over the growing season of rice. The bandwidths and center wavelengths of these characteristic wavebands were different among nitrogen treatments. The simplified features by connecting these 15 characteristic wavelengths may be considered as spectral signatures of rice canopy, but spectral signatures varied with developmental age and nitrogen application rates. Among these characteristic wavebands, the changes of the wavelength in band 11 showed a positive linear relationship with application rates of nitrogen fertilizer, while it was a negative linear relationship in band 5. Mean reflectance of wavelengths in bands 1, 2, 3, 5, 11, and 15 was significantly correlated with application rates. Reflectance of these six wavelengths changed nonlinearly after transplanting and could be used in combination to distinguish rice plants subjected to different nitrogen application rates. From the correlation analyses, there are a variety of correlation coefficients for spectral reflectance to leaf nitrogen content in the range of 350-2400 nm. Reflectance of most wavelengths exhibited an inverse correlation with leaf nitrogen content, with the largest negative value (r = �0.581) located at about 1376 nm. Changes in reflectance at 1376 nm to leaf nitrogen content during the growing period were closely related and were best fitted to a nonlinear function. This relationship may be used to estimate and to monitor nitrogen content of rice leaves during rice growth. Reflectance of red light minimum and near-infrared peak and leaf nitrogen content were correlated nonlinearly.

scholarly journals A parameterization of sub-grid topographical effects on solar radiation in the E3SM Land Model (version 1.0): implementation and evaluation over the Tibetan Plateau

2021 ◽  
Vol 14 (10) ◽  
pp. 6273-6289
Author(s):  
Dalei Hao ◽  
Gautam Bisht ◽  
Yu Gu ◽  
Wei-Liang Lee ◽  
Kuo-Nan Liou ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Surface Energy ◽  
Surface Temperature ◽  
Snow Cover ◽  
Land Surface ◽  
Spatial Scales ◽  
The Tibetan Plateau ◽  
Topographic Effects ◽  
Earth System

Abstract. Topography exerts significant influences on the incoming solar radiation at the land surface. A few stand-alone regional and global atmospheric models have included parameterizations for sub-grid topographic effects on solar radiation. However, nearly all Earth system models (ESMs) that participated in the Coupled Model Intercomparison Project (CMIP6) use a plane-parallel (PP) radiative transfer scheme that assumes that the terrain is flat. In this study, we incorporated a well-validated sub-grid topographic (TOP) parameterization in the Energy Exascale Earth System Model (E3SM) Land Model (ELM) version 1.0 to quantify the effects of sub-grid topography on solar radiation flux, including the shadow effects and multi-scattering between adjacent terrain. We studied the role of sub-grid topography by performing ELM simulations with the PP and TOP schemes over the Tibetan Plateau (TP). Additional ELM simulations were performed at multiple spatial resolutions to investigate the role of spatial scale on sub-grid topographic effects on solar radiation. The Moderate Resolution Imaging Spectroradiometer (MODIS) data was used to compare with the ELM simulations. The results show that topography has non-negligible effects on surface energy budget, snow cover, snow depth, and surface temperature over the TP. The absolute differences in surface energy fluxes for net solar radiation, latent heat flux, and sensible heat flux between TOP and PP exceed 20, 10, and 5 W m−2, respectively. The differences in land surface albedo, snow cover fraction, snow depth, and surface temperature between TOP and PP exceed 0.1, 0.1, 10 cm, and 1 K, respectively. The magnitude of the sub-grid topographic effects is dependent on seasons and elevations and is also sensitive to the spatial scales. Although the sub-grid topographic effects on solar radiation are larger with more spatial details at finer spatial scales, they cannot be simply neglected at coarse spatial scales. When compared to MODIS data, incorporating the sub-grid topographic effects overall reduces the biases of ELM in simulating surface energy balance, snow cover, and surface temperature, especially in the high-elevation and snow-covered regions over the TP. The inclusion of sub-grid topographic effects on solar radiation parameterization in ELM will contribute to advancing our understanding of the role of the surface topography on terrestrial processes over complex terrain.

scholarly journals A Parameterization of Sub-grid Topographical Effects on Solar Radiation in the E3SM Land Model (Version 1.0): Implementation and Evaluation Over the Tibetan Plateau

2021 ◽  
Author(s):  
Dalei Hao ◽  
Gautam Bisht ◽  
Yu Gu ◽  
Wei‐Liang Lee ◽  
Kuo-Nan Liou ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Surface Energy ◽  
Surface Temperature ◽  
Snow Cover ◽  
Land Surface ◽  
Spatial Scales ◽  
The Tibetan Plateau ◽  
Topographic Effects ◽  
Earth System

Abstract. Topography exerts significant influences on the incoming solar radiation at the land surface. A few stand-alone regional and global atmospheric models have included parameterizations for sub-grid topographic effects on solar radiation. However, nearly all Earth System Models (ESMs) that participated in the Coupled Model Intercomparison Project (CMIP6) use a plane-parallel (PP) radiative transfer scheme that assumes the terrain is flat. In this study, we incorporated a well-validated sub-grid topographic (TOP) parameterization in the Energy Exascale Earth System Model (E3SM) Land Model (ELM) version 1.0 to quantify the effects of sub-grid topography on solar radiation flux, including the shadow effects and multi-scattering between adjacent terrain. The Moderate Resolution Imaging Spectroradiometer (MODIS) data was used to evaluate the performance of ELM. We studied the role of sub-grid topography by performing ELM simulations with the PP and TOP schemes over the Tibetan Plateau (TP). Additional ELM simulations were performed at multiple spatial resolutions to investigate the role of spatial scale on sub-grid topographic effects on solar radiation. When compared to MODIS data, incorporating the sub-grid topographic effects overall reduces the biases of ELM in simulating surface energy balance, snow cover and surface temperature especially in the high-elevation and snow-cover regions over the TP. Topography has non-negligible effects on surface energy budget, snow cover, and surface temperature over the TP. The absolute differences in surface energy fluxes for net solar radiation, latent heat flux, and sensible heat flux between TOP and PP exceed 20 W/m2, 10 W/m2, and 5 W/m2, respectively. The differences in land surface albedo, snow cover fraction, and surface temperature between TOP and PP exceed 0.1, 20%, and 1K, respectively. The magnitude of the sub-grid topographic effects is dependent on seasons and elevations, and is also sensitive to the spatial scales. Although the sub-grid topographic effects on solar radiation are more significant with more spatial details at finer spatial scales, they cannot be simply neglected at coarse spatial scales. The inclusion of sub-grid topographic effects on solar radiation parameterization in ELM will contribute to advancing our understanding of the role of the surface topography on terrestrial processes over complex terrain.

Assessing the capacity of Earth System Models to simulate spatiotemporal variability in fire weather indicators

2021 ◽  
Author(s):  
Carolina Gallo Granizo ◽  
Jonathan Eden ◽  
Bastien Dieppois ◽  
Matthew Blackett
Keyword(s):  
Climate Change ◽  
Spatial Scales ◽  
Fire Danger ◽  
Spatiotemporal Variability ◽  
Global Evaluation ◽  
Fire Weather ◽  
Earth System ◽  
Fire Weather Index ◽  
System Models ◽  
Earth System Models

<p>Weather and climate play an important role in shaping global fire regimes and geographical distributions of burnable areas. At the global scale, fire danger is likely to increase in the near future due to warmer temperatures and changes in precipitation patterns, as projected by the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC). There is a need to develop the most reliable projections of future climate-driven fire danger to enable decision makers and forest managers to take both targeted proactive actions and to respond to future fire events.</p><p>Climate change projections generated by Earth System Models (ESMs) provide the most important basis for understanding past, present and future changes in the climate system and its impacts. ESMs are, however, subject to systematic errors and biases, which are not fully taken into account when developing risk scenarios for wild fire activity. Projections of climate-driven fire danger have often been limited to the use of single models or the mean of multi-model ensembles, and compared to a single set of observational data (e.g. one index derived from one reanalysis).</p><p>Here, a comprehensive global evaluation of the representation of a series of fire weather indicators in the latest generation of ESMs is presented. Seven fire weather indices from the Canadian Forest Fire Weather Index System were generated using daily fields realisations simulated by 25 ESMs from the 6<sup>th</sup> Coupled Model Intercomparison Project (CMIP6). With reference to observational and reanalysis datasets, we quantify the capacity of each model to realistically simulate the variability, magnitude and spatial extent of fire danger. The highest-performing models are identified and, subsequently, the limitations of combining models based on independency and equal performance when generating fire danger projections are discussed. To conclude, recommendations are given for the development of user- and policy-driven model evaluation at spatial scales relevant for decision-making and forest management.</p>

Design, Modeling, and Experimental Drag Characterization of a Bio-Inspired, Shape-Adapting Underwater Vehicle

2018 ◽  
Author(s):  
Levi D. DeVries ◽  
Michael D. M. Kutzer ◽  
Rebecca E. Richmond ◽  
Archie C. Bass
Keyword(s):  
Spatial Scales ◽  
Autonomous Underwater Vehicles ◽  
Major Axis ◽  
Underwater Vehicle ◽  
Great Promise ◽  
Hydrodynamic Drag ◽  
Control Input ◽  
Semi Major Axis ◽  
Generative Modeling

Autonomous underwater vehicles (AUVs) have shown great promise in fulfilling surveillance, scavenging, and monitoring tasks, but can be hindered in expansive, cluttered or obstacle ridden environments. Traditional gliders and streamlined AUVs are designed for long term operational efficiency in expansive environments, but are hindered in cluttered spaces due to their shape and control authority; agile AUVs can penetrate cluttered or sensitive environments but are limited in operational endurance at large spatial scales. This paper presents the prototype testbed design, modeling, and experimental hydrodynamic drag characterization of a novel self-propelled underwater vehicle capable of actuating its shape morphology. The vehicle prototype incorporates flexible, buckled fiberglass ribs to ensure a rigid shape that can be actuated by modulating the length of the semi-major axis. Tools from generative modeling are used to represent the vehicle shape by using a single control input actuating the vehicles length-to-diameter ratio. By actuating the length and width characteristics of the vehicle’s shape to produce a desired drag profile, we derive the feasible speeds achievable by shape actuation control. Tow-tank experiments with an experimental proto-type suggest shape actuation can be used to manipulate the drag by a factor between 2.15 and 5.8 depending on the vehicle’s operating speed.

scholarly journals PHYSICAL PROPERTIES OF THREE SONGKHLA LAGOON FISH SPECIES IN THE LOWER GULF OF THAILAND DURING AND AFTER THE MONSOON SEASON

2018 ◽  
Vol 16 (5) ◽  
pp. 6113-6127
Author(s):  
H. T. T. HUE ◽  
S. PRADIT ◽  
C. JARUNEE ◽  
A. LIM ◽  
T. NITIRATSUWAN ◽  
...  
Keyword(s):  
Physical Properties ◽  
Fish Species ◽  
Monsoon Season ◽  
Gulf Of Thailand

scholarly journals Spatiotemporal patterns of synchronous heavy rainfall events in East Asia during the Baiu season

2021 ◽  
Author(s):  
Frederik Wolf ◽  
Ugur Ozturk ◽  
Kevin Cheung ◽  
Reik V. Donner
Keyword(s):  
System Dynamics ◽  
East Asia ◽  
Heavy Rainfall ◽  
Spatial Organization ◽  
Monsoon Season ◽  
Spatiotemporal Patterns ◽  
Extreme Weather Events ◽  
Earth System ◽  
Rainfall Events ◽  
Heavy Rainfall Events

<p>Investigating the synchrony and interdependency of heavy rainfall occurrences is crucial to understand the underlying physical mechanisms and reduce physical and economic damages by improved forecasting strategies. In this context, studies utilizing functional network representations have recently contributed to significant advances in the understanding and prediction of extreme weather events.</p><p>To thoroughly expand on previous works employing the latter framework to the East Asian Summer Monsoon (EASM) system, we focus here on changes in the spatial organization of synchronous heavy precipitation events across the monsoon season (April to August) by studying the temporal evolution of corresponding network characteristics in terms of a sliding window approach. Specifically, we utilize functional climate networks together with event coincidence analysis for identifying and characterizing synchronous activity from daily rainfall estimates with <span>a spatial resolution of 0.25° </span>between 1998 and 2018. Our results demonstrate that the formation of the Baiu front as a main feature of the EASM is reflected by a double-band structure of synchronous heavy rainfall with two centers north and south of the front. Although the two separated bands are strongly related to either low- or high-level winds which are commonly assumed to be independent, we provide evidence that it is rather their mutual interconnectivity that changes during the different phases of the EASM season in a characteristic way.</p><p>Our findings shed some new light on the interplay between tropical and extratropical factors controlling the EASM intraseasonal evolution, which could potentially help improving future forecasts of the Baiu onset in different regions of East Asia.</p><p> </p><p>Further details: F. Wolf, U. Ozturk, K. Cheung, R.V. Donner: Spatiotemporal patterns of synchronous heavy rainfall events in East Asia during the Baiu season. Earth System Dynamics (in review). Discussion Paper: Earth System Dynamics Discussions, (2020)</p>

scholarly journals Towards a more objective evaluation of modelled land-carbon trends using atmospheric CO<sub>2</sub> and satellite-based vegetation activity observations

2013 ◽  
Vol 10 (6) ◽  
pp. 4189-4210 ◽  
Author(s):  
D. Dalmonech ◽  
S. Zaehle
Keyword(s):  
Land Surface ◽  
Climate Model ◽  
Spatial Scales ◽  
Evaluation Framework ◽  
Atmospheric Co2 ◽  
Evaluation Methodology ◽  
Surface Model ◽  
System Modelling ◽  
Earth System ◽  
Vegetation Activity

Abstract. Terrestrial ecosystem models used for Earth system modelling show a significant divergence in future patterns of ecosystem processes, in particular the net land–atmosphere carbon exchanges, despite a seemingly common behaviour for the contemporary period. An in-depth evaluation of these models is hence of high importance to better understand the reasons for this disagreement. Here, we develop an extension for existing benchmarking systems by making use of the complementary information contained in the observational records of atmospheric CO2 and remotely sensed vegetation activity to provide a novel set of diagnostics of ecosystem responses to climate variability in the last 30 yr at different temporal and spatial scales. The selection of observational characteristics (traits) specifically considers the robustness of information given that the uncertainty of both data and evaluation methodology is largely unknown or difficult to quantify. Based on these considerations, we introduce a baseline benchmark – a minimum test that any model has to pass – to provide a more objective, quantitative evaluation framework. The benchmarking strategy can be used for any land surface model, either driven by observed meteorology or coupled to a climate model. We apply this framework to evaluate the offline version of the MPI Earth System Model's land surface scheme JSBACH. We demonstrate that the complementary use of atmospheric CO2 and satellite-based vegetation activity data allows pinpointing of specific model deficiencies that would not be possible by the sole use of atmospheric CO2 observations.

Physical properties, spectral reflectance and thickness development of first year fast ice in Kongsfjorden, Svalbard

1999 ◽  
Vol 18 (2) ◽  
pp. 275-282 ◽  
Author(s):  
Sebastian Gerland ◽  
Jan-Gunnar Winther ◽  
Jon Børre Ørbæk ◽  
Boris V. Ivanov
Keyword(s):  
Physical Properties ◽  
Spectral Reflectance ◽  
First Year ◽  
Fast Ice

Statistical Analysis of Spatial Structure in Natural Images

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 176-176
Author(s):  
R Watt ◽  
P Carlin
Keyword(s):  
Spatial Scales ◽  
Spectral Characteristics ◽  
Natural Images ◽  
Large Sets ◽  
Image Characteristics ◽  
Power Spectral ◽  
Distribution Of Values ◽  
Noise Image ◽  
Energy Maps ◽  
Do So

When a sample of natural images is taken and compared with a set of noise images, the two are obviously distinguishable. Even when the noise images are set to have the same power spectral characteristics as the natural images, there is no doubt which is a normal image and which is a noise image. In the study to be reported, we have examined the nature of the spatial characteristics of natural images that allow them to be so discriminated from noise images. The approach is to process large sets of images belonging to various categories through mechanisms that have some similarities to known operations in biological visual systems. Thus, the images are filtered at various spatial scales and at various orientations; the filter outputs are combined into local energy maps; and features are detected in such processed images. The result of these calculations is the distribution of values of some parameter which describes a particular image characteristics for each set of images. Parameters that could support adequate discrimination between two sets of images, for example natural images and noise images, will have largely non-overlapping distributions. In practice it is found that no simple parameters can distinguish obviously different sets of images, but parameters that encapsulate spatial patterns, especially those related to non-accidental image properties, can do so. It is concluded that filter outputs must be followed by nontrivial spatial operations. Suggestions are made as to what are the most plausible.

Sign in / Sign up

Export Citation Format

Share Document