Measurement of the brightness temperature distribution of plasma bunches

1982 ◽  
Vol 22 (5) ◽  
pp. 615-617
Author(s):  
V. I. Kirko ◽  
I. A. Stadnichenko
Keyword(s):  
Temperature Distribution ◽  
Brightness Temperature

The VSOP 5 GHz Active Galactic Nucleus Survey. IV. The Angular Size/Brightness Temperature Distribution

2004 ◽  
Vol 616 (1) ◽  
pp. 110-122 ◽  
Author(s):  
S. Horiuchi ◽  
E. B. Fomalont ◽  
W. K. Scott, A. R. Taylor ◽  
J. E. J. Lovell ◽  
G. A. Moellenbrock ◽  
...  
Keyword(s):  
Temperature Distribution ◽  
Brightness Temperature ◽  
Active Galactic Nucleus ◽  
Angular Size ◽  
5 Ghz

scholarly journals A full treatment of peculiar velocities on the reionization light cone

2019 ◽  
Vol 490 (1) ◽  
pp. 1255-1269 ◽  
Author(s):  
Emma Chapman ◽  
Mario G Santos
Keyword(s):  
Temperature Distribution ◽  
Brightness Temperature ◽  
Light Cone ◽  
Cosmological Parameters ◽  
Line Of Sight ◽  
Physical Parameters ◽  
Hydrogen Atoms ◽  
Peculiar Velocities ◽  
Full Treatment ◽  
Full Calculation

ABSTRACT Accurate simulations of the 21-cm signal from the Epoch of Reionization require the generation of maps at specific frequencies given the values of astrophysical and cosmological parameters. The peculiar velocities of the hydrogen atoms producing the 21-cm radiation result in a shift in the observed frequency of the 21-cm radiation and changes the amplitude of the signal itself. This is not an effect we can remove but instead needs to be accurately modelled to ensure we infer the correct physical parameters from an observation. We describe the full calculation of the distortion of the 21-cm signal, and propose a new code that integrates the 21-cm intensity along the line of sight for each individual light cone pixel to fully capture the intensity contributions from multiple redshifts. This algorithm naturally deals with the typical divergences found in standard approaches, allowing for large optical depths and 21-cm absorption events at high redshifts. We find the new method results in up to a 60 per cent decrease in power on the largest scales on the sky, and an increase of over 80 per cent on the smallest scales on the sky. We find that the new implementation of the light cone results in a longer tail of bright temperatures in the brightness temperature distribution, as a result of the successful circumventing of a previous cap that had to be implemented to avoid a divergence in the brightness temperature. We conclude that this full treatment of the evolution of the light cone pixel can be an important effect.

scholarly journals Measuring the Brightness Temperature Distribution of Extragalactic Radio Sources with Space VLBI

2001 ◽  
Vol 549 (1) ◽  
pp. L55-L58 ◽  
Author(s):  
S. J. Tingay ◽  
R. A. Preston ◽  
M. L. Lister ◽  
B. G. Piner ◽  
D. W. Murphy ◽  
...  
Keyword(s):  
Temperature Distribution ◽  
Brightness Temperature ◽  
Radio Sources ◽  
Extragalactic Radio Sources

Research on 3mm Band Radiometric Brightness Temperature Inversion

2012 ◽  
Vol 239-240 ◽  
pp. 320-323
Author(s):  
Guang Feng Zhang ◽  
Qi Wang ◽  
Guo Wei Lou
Keyword(s):  
Remote Sensing ◽  
Integral Equation ◽  
Temperature Distribution ◽  
Brightness Temperature ◽  
Fredholm Integral Equation ◽  
Error Compensation ◽  
Water Surface ◽  
Temperature Inversion ◽  
Calculation Model ◽  
Inversion Method

A MMW radiometer is widely used in remote sensing and guidance. In order to obtain the real brightness temperature distribution of the target, we need to solve the first kind of ill Fredholm integral equation of radiometric antenna temperature. The paper presents a kind of inversion method for modifying antenna pattern and the approach of error compensation. Compared with the theoretical calculation model of 3mm smooth water surface, the results show this algorithm has a higher accuracy for the measurement application.

scholarly journals Multi-Parameter Regularization Method for Synthetic Aperture Imaging Radiometers

2021 ◽  
Vol 13 (3) ◽  
pp. 382
Author(s):  
Xiaocheng Yang ◽  
Zhenyi Yang ◽  
Jingye Yan ◽  
Lin Wu ◽  
Mingfeng Jiang
Keyword(s):  
Temperature Distribution ◽  
Brightness Temperature ◽  
Regularization Method ◽  
Noise Suppression ◽  
Synthetic Aperture ◽  
Regularization Methods ◽  
Synthetic Aperture Imaging ◽  
Original Distribution ◽  
Band Limited ◽  
Parameter Regularization

Synthetic aperture imaging radiometers (SAIRs) are powerful passive microwave systems for high-resolution imaging by use of synthetic aperture technique. However, the ill-posed inverse problem for SAIRs makes it difficult to reconstruct the high-precision brightness temperature map. The traditional regularization methods add a unique penalty to all the frequency bands of the solution, which may cause the reconstructed result to be too smooth to retain certain features of the original brightness temperature map such as the edge information. In this paper, a multi-parameter regularization method is proposed to reconstruct SAIR brightness temperature distribution. Different from classical single-parameter regularization, the multi-parameter regularization adds multiple different penalties which can exhibit multi-scale characteristics of the original distribution. Multiple regularization parameters are selected by use of the simplified multi-dimensional generalized cross-validation method. The experimental results show that, compared with the conventional total variation, Tikhonov, and band-limited regularization methods, the multi-parameter regularization method can retain more detailed information and better improve the accuracy of the reconstructed brightness temperature distribution, and exhibit superior noise suppression, demonstrating the effectiveness and the robustness of the proposed method.

scholarly journals Homogeneous vs Biased IGM: Impact on Reionization

2021 ◽  
Vol 8 ◽  
Author(s):  
Dinesh Raut
Keyword(s):  
Temperature Distribution ◽  
Brightness Temperature ◽  
Large Scale ◽  
Extreme Values ◽  
Neutral Hydrogen ◽  
Matter Density ◽  
Constant Density ◽  
Bias Parameter ◽  
Temperature Maps ◽  
The Impact

This paper considers the impact of large scale biasing of the IGM on reionization. The two simplest but extreme scenarios for IGM biasing are: an unbiased IGM which has a constant density and an IGM with density equal to the collapsed matter density. In this work, the relationship between the IGM density and the collapsed matter density is defined through an IGM bias parameter. The two extreme scenarios of homogeneous and perfectly biased IGM are produced for two extreme values of this bias parameter. It is found that, for the same level of reionization (i.e., for same global neutral hydrogen fraction). one could get very different 21 cm brightness temperature distributions for different values of this bias parameter. These distributions could give an order of magnitude more or less power as compared to the uniform case. It is also found that there exists a critical value for the IGM bias parameter for which there could be a near washout of the structure in the 21 cm brightness temperature distribution (i.e., zero power or a nearly uniform 21 cm brightness temperature distribution). To address the problem, a new method of generating 21 cm brightness temperature maps is used. The method uses the results of n-body simulations and then employs ray tracing to obtain the 21 cm brightness temperature maps. Towards the end, a prescription for the IGM bias parameter is given. This is derived within the framework of the Press-Schechter theory.

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