Empirical models on urban surface emissivity retrieval based on different spectral response functions: A field study

2021 ◽  
Vol 197 ◽  
pp. 107882
Author(s):  
Xue Zhong ◽  
Lihua Zhao ◽  
Jie Wang ◽  
Haichao Zheng ◽  
Junru Yan ◽  
...  
Keyword(s):  
Field Study ◽  
Spectral Response ◽  
Empirical Models ◽  
Urban Surface ◽  
Response Functions ◽  
Surface Emissivity

scholarly journals Validation of ESA Sentinel-2 L2A Aerosol Optical Thickness and Columnar Water Vapour during 2017–2018

2019 ◽  
Vol 11 (14) ◽  
pp. 1649 ◽  
Author(s):  
María Ángeles Obregón ◽  
Gonçalo Rodrigues ◽  
Maria Joao Costa ◽  
Miguel Potes ◽  
Ana Maria Silva
Keyword(s):  
Water Vapour ◽  
Root Mean Square ◽  
Optical Thickness ◽  
Spectral Response ◽  
Aerosol Optical Thickness ◽  
Mean Bias Error ◽  
Mean Square ◽  
Response Functions ◽  
Mean Square Errors ◽  
Sentinel 2

This study presents a validation of aerosol optical thickness (AOT) and integrated water vapour (IWV) products provided by the European Space Agency (ESA) from multi-spectral imager (MSI) measurements on board the Sentinel-2 satellite (ESA-L2A). For that purpose, data from 94 Aerosol Robotic Network (AERONET) stations over Europe and adjacent regions, covering a wide geographical region with a variety of climate and environmental conditions and during the period between March 2017 and December 2018 have been used. The comparison between ESA-L2A and AERONET shows a better agreement for IWV than the AOT, with normalized root mean square errors (NRMSE) of 5.33% and 9.04%, respectively. This conclusion is also reflected in the values of R2, which are 0.99 and 0.65 for IWV and AOT, respectively. The study period was divided into two sub-periods, before and after 15 January 2018, when the Sentinel-2A spectral response functions of bands 1 and 2 (centered at 443 and 492 nm) were updated by ESA, in order to investigate if the lack of agreement in the AOT values was connected to the use of incorrect spectral response functions. The comparison of ESA-L2A AOT with AERONET measurements showed a better agreement for the second sub-period, with root mean square error (RMSE) values of 0.08 in comparison with 0.14 in the first sub-period. This same conclusion was attained considering mean bias error (MBE) values that decreased from 0.09 to 0.01. The ESA-L2A AOT values estimated with the new spectral response functions were closer to the correspondent reference AERONET values than the ones obtained using the previous spectral response functions. IWV was not affected by this change since the retrieval algorithm does not use bands 1 and 2 of Sentinel-2. Additionally, an analysis of potential uncertainty sources to several factors affecting the AOT comparison is presented and recommendations regarding the use of ESA-L2A AOT dataset are given.

Dielectric Response of β-HMX at THz Frequencies Calculated by Density Functional Theory

2011 ◽  
Author(s):  
Lulu Huang ◽  
Andrew Shabaev ◽  
Samuel G. Lambrakos ◽  
Noam Bernstein ◽  
Verne L. Jacobs ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Ground State ◽  
Dielectric Response ◽  
Electromagnetic Waves ◽  
Density Functional ◽  
Spectral Response ◽  
Resonance Structure ◽  
Response Functions ◽  
Functional Theory ◽  
State Resonance

We present calculations of ground state resonance structure associated with the high explosives β-HMX using density functional theory (DFT), which is for the construction of parameterized dielectric response functions for excitation by electromagnetic waves at compatible frequencies. These dielectric functions provide for different types of analyses concerning the dielectric response of explosives. In particular, these dielectric response functions provide quantitative initial estimates of spectral response features for subsequent adjustment with respect to additional information such as laboratory measurements and other types of theory based calculations. With respect to qualitative analysis, these spectra provide for the molecular level interpretation of response structure. The DFT software GAUSSIAN was used for the calculations of ground state resonance structure presented here.

scholarly journals Radiance Comparisons of MODIS and AIRS Using Spatial Response Information

2010 ◽  
Vol 27 (8) ◽  
pp. 1331-1342 ◽  
Author(s):  
M. M. Schreier ◽  
B. H. Kahn ◽  
A. Eldering ◽  
D. A. Elliott ◽  
E. Fishbein ◽  
...  
Keyword(s):  
Spectral Response ◽  
Lapse Rate ◽  
Response Functions ◽  
Temperature Lapse Rate ◽  
Earth Observing System ◽  
Spatial Response ◽  
Response Information ◽  
Moderate Resolution ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Water Vapor Mixing Ratio

Abstract The combination of multiple satellite instruments on a pixel-by-pixel basis is a difficult task, even for instruments collocated in space and time, such as the Moderate Resolution Imaging Spectroradiometer (MODIS) and Atmospheric Infrared Sounder (AIRS) on board the Earth Observing System (EOS) Aqua. Toward the goal of an improved collocation methodology, the channel- and scan angle–dependent spatial response functions of AIRS that were obtained from prelaunch measurements and calculated impacts from scan geometry are shown within the context of radiance comparisons. The AIRS spatial response functions are used to improve the averaging of MODIS radiances to the AIRS footprint, and the variability of brightness temperature differences (ΔTb) between MODIS and AIRS are quantified on a channel-by-channel basis. To test possible connections between ΔTb and the derived level 2 (L2) datasets, cloud characteristics derived from MODIS are used to highlight correlations between these quantities and ΔTb, especially for ice clouds in H2O and CO2 bands. Furthermore, correlations are quantified for temperature lapse rate (dT/dp) and the magnitude of water vapor mixing ratio (q) obtained from AIRS L2 retrievals. Larger values of dT/dp and q correlate well to larger values of ΔTb in the H2O and CO2 bands. These correlations were largely eliminated or reduced after the MODIS spectral response functions were shifted by recommended values. While this investigation shows that the AIRS spatial response functions are necessary to reduce the variability and skewness of ΔTb within heterogeneous scenes, improved knowledge about MODIS spectral response functions is necessary to reduce biases in ΔTb.

scholarly journals Preflight Spectral Calibration of Airborne Shortwave Infrared Hyperspectral Imager with Water Vapor Absorption Characteristics

Sensors ◽  
2019 ◽  
Vol 19 (10) ◽  
pp. 2259 ◽  
Author(s):  
Honglin Liu ◽  
Dong Zhang ◽  
Yueming Wang
Keyword(s):  
Water Vapor ◽  
Spectral Response ◽  
Spectral Characteristics ◽  
Calibration Method ◽  
Least Square ◽  
Response Functions ◽  
Water Vapor Absorption ◽  
Gaussian Shape ◽  
Spectral Calibration ◽  
Calibration Uncertainty

Due to the strong absorption of water vapor at wavelengths of 1350–1420 nm and 1820–1940 nm, under normal atmospheric conditions, the actual digital number (DN) response curve of a hyperspectral imager deviates from the Gaussian shape, which leads to a decrease in the calibration accuracy of an instrument’s spectral response functions (SRF). The higher the calibration uncertainty of SRF, the worse the retrieval accuracy of the spectral characteristics of the targets. In this paper, an improved spectral calibration method based on a monochromator and the spectral absorptive characteristics of water vapor in the laboratory is presented. The water vapor spectral calibration method (WVSCM) uses the difference function to calculate the intrinsic DN response functions of the spectral channels located in the absorptive wavelength range of water vapor and corrects the wavelength offset of the monochromator via the least-square procedure to achieve spectral calibration throughout the full spectral responsive range of the hyper-spectrometer. The absolute spectral calibration uncertainty is ±0.125 nm. We validated the effectiveness of the WVSCM with two tunable semiconductor lasers, and the spectral wavelength positions calibrated by lasers and the WVSCM showed a good degree of consistency.

scholarly journals Single-nanowire spectrometers

Science ◽  
2019 ◽  
Vol 365 (6457) ◽  
pp. 1017-1020 ◽  
Author(s):  
Zongyin Yang ◽  
Tom Albrow-Owen ◽  
Hanxiao Cui ◽  
Jack Alexander-Webber ◽  
Fuxing Gu ◽  
...  
Keyword(s):  
Single Cell ◽  
Spectral Response ◽  
Spectral Imaging ◽  
Visible Range ◽  
Response Functions ◽  
In Situ Characterization ◽  
Optical Components ◽  
Wide Range ◽  
Current Systems

Spectrometers with ever-smaller footprints are sought after for a wide range of applications in which minimized size and weight are paramount, including emerging in situ characterization techniques. We report on an ultracompact microspectrometer design based on a single compositionally engineered nanowire. This platform is independent of the complex optical components or cavities that tend to constrain further miniaturization of current systems. We show that incident spectra can be computationally reconstructed from the different spectral response functions and measured photocurrents along the length of the nanowire. Our devices are capable of accurate, visible-range monochromatic and broadband light reconstruction, as well as spectral imaging from centimeter-scale focal planes down to lensless, single-cell–scale in situ mapping.

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