scholarly journals Assessment of the “Zero-Bias Line” Homogenization Method for Microwave Radiometers Using Sentinel-3A and Sentinel-3B Tandem Phase

2020 ◽  
Vol 12 (19) ◽  
pp. 3154
Author(s):  
Bruno Picard ◽  
Ralf Bennartz ◽  
Frank Fell ◽  
Marie-Laure Frery ◽  
Mathilde Siméon ◽  
...  
Keyword(s):  
Homogenization Method ◽  
Zero Bias ◽  
Common Reference ◽  
Brightness Temperatures ◽  
Homogenization Approach ◽  
Linear Correction ◽  
Bias Line ◽  
The Difference ◽  
Global Mean Sea Level ◽  
Microwave Radiometers

The long-term stability of microwave radiometers (MWR) on-board altimetry missions is critical to reduce the uncertainty on the global mean sea level estimate. Harmonization and homogenization steps are applied to MWR observations in that perspective. The Sentinel-3 tandem phase provides a unique opportunity to quantify the uncertainties on the “zero-bias line” homogenization approach defined by Bennartz et al. (2020). Initially developed to improve the performance of the wet tropospheric correction retrieval, it is used here to provide a common reference for the inter-calibration between Sentinel-3A and Sentinel-3B MWR. A simplified version of the “zero-bias line” approach, a linear correction depending on brightness temperatures, allows to strongly reduce the bias between the two radiometers for both channels (about 0.5 K) and the standard deviation of the difference (0.3 K). The full version of the approach adding a dependency on wind speed has improved the quality of the WTC retrieval (Bennartz et al. 2020) but degrades the performance of the homogenization. It is thus recommended to apply the simplified version of this approach in the processing of fundamental data record. The quantification of the uncertainties on the homogenization approach is only possible due to the ideal configuration of the Sentinel-3 tandem phase. The same dataset and the same metrics could be used to assess other approaches.

scholarly journals Inter-calibrating SMMR brightness temperatures over continental surfaces

2020 ◽  
Author(s):  
Samuel Favrichon ◽  
Carlos Jimenez ◽  
Catherine Prigent
Keyword(s):  
Land Surface ◽  
Microwave Remote Sensing ◽  
Calibration Method ◽  
Diurnal Cycles ◽  
Brightness Temperatures ◽  
Linear Correction ◽  
Long Time ◽  
Microwave Imager ◽  
Microwave Radiometers ◽  
Global Precipitation

Abstract. Microwave remote sensing can be used to monitor the time evolution of some key parameters over land, such as land surface temperature or surface water extent. Observations are made with instrument such as the Scanning Microwave Multichannel Radiometer (SMMR) before 1987, the Special Sensor Microwave/Imager (SSM/I) and the following Special Sensor Microwave Imager/Sounder (SSMIS) from 1987 and still operating, to the more recent Global Precipitation Mission Microwave Imager (GMI). As these instruments differ on some of their characteristics and use different calibration schemes, they need to be inter-calibrated before long time series products can be derived from the observations. Here an inter-calibration method is designed to remove major inconsistencies between the SMMR and other microwave radiometers for the 18 GHz and 37 GHz channels over continental surfaces. Because of a small overlap in observations and a ~6 h difference in overpassing times between SMMR and SSM/I, GMI was chosen as a reference despite the lack of a common observing period. The diurnal cycles from three years of GMI brightness temperatures are first calculated, and then used to evaluate SMMR differences. Based on a statistical analysis of the differences, a simple linear correction is implemented to calibrate SMMR on GMI. This correction is shown to also reduce the biases between SMMR and SSM/I, and can then be applied to SMMR observations to make them more coherent with existing data record of microwave brightness temperatures over continental surfaces.

scholarly journals Inter-calibrating SMMR brightness temperatures over continental surfaces

2020 ◽  
Vol 13 (10) ◽  
pp. 5481-5490
Author(s):  
Samuel Favrichon ◽  
Carlos Jimenez ◽  
Catherine Prigent
Keyword(s):  
Land Surface ◽  
Microwave Remote Sensing ◽  
Calibration Method ◽  
Diurnal Cycles ◽  
Brightness Temperatures ◽  
Linear Correction ◽  
Long Time ◽  
Microwave Imager ◽  
Microwave Radiometers ◽  
Global Precipitation

Abstract. Microwave remote sensing can be used to monitor the time evolution of some key parameters over land, such as land surface temperature or surface water extent. Observations are made with instruments, such as the Scanning Microwave Multichannel Radiometer (SMMR) before 1987, the Special Sensor Microwave/Imager (SSM/I) and the subsequent Special Sensor Microwave Imager/Sounder (SSMIS) from 1987 and still operating, and the more recent Global Precipitation Measurement Microwave Imager (GMI). As these instruments differ on some of their characteristics and use different calibration schemes, they need to be inter-calibrated before long-time-series products can be derived from the observations. Here an inter-calibration method is designed to remove major inconsistencies between the SMMR and other microwave radiometers for the 18 and 37 GHz channels over continental surfaces. Because of a small overlap in observations and a ∼6 h difference in overpassing times between SMMR and SSM/I, GMI was chosen as a reference despite the lack of a common observing period. The diurnal cycles from 3 years of GMI brightness temperatures are first calculated and then used to evaluate SMMR differences. Based on a statistical analysis of the differences, a simple linear correction is implemented to calibrate SMMR on GMI. This correction is shown to also reduce the biases between SMMR and SSM/I, and can then be applied to SMMR observations to make them more coherent with existing data records of microwave brightness temperatures over continental surfaces.

Convergence–confinement analysis of a bolt-supported tunnel using the homogenization method

2006 ◽  
Vol 43 (5) ◽  
pp. 462-483 ◽  
Author(s):  
Henry Wong ◽  
Didier Subrin ◽  
Daniel Dias
Keyword(s):  
Input Parameter ◽  
Uniaxial Stress ◽  
Homogenization Method ◽  
External Input ◽  
Proposed Model ◽  
Homogenization Approach ◽  
Parametric Studies ◽  
Perfect Bonding ◽  
The Moment ◽  
Grouted Bolts

The behaviour of tunnels reinforced with radially disposed fully grouted bolts is investigated in this paper. Perfect bonding and ideal diffusion of bolt tension are assumed, so that the bolt tension can be assimilated to an equivalent uniaxial stress tensor. An analytical model of the convergence–confinement type is proposed that accounts for the delayed action of bolts due to ground decompression prior to bolt installation. This factor leads to nonsimultaneous yielding, and more generally, a different stress history for each constituent, requiring special treatments in the incremental elastoplasticity calculations. Nonetheless, the resulting model remains sufficiently simple, and an analytical solution is still accessible. Charts are provided to allow for parametric studies and quick preliminary designs. Comparisons with 3D numerical calculations show that the model gives precise results if the correct convergence at the moment of bolt installation is used as an "external" input parameter, validating the homogenization approach. An approximate methodology based on previous works is proposed to determine this parameter to render the proposed model "self-sufficient." Its predictions are again compared to 3D numerical computations, and the results are found to be sufficiently accurate for practical applications.Key words: reinforcement, anisotropy, analytical, lining, yield, elastoplasticity.

scholarly journals Impact of cirrus clouds heterogeneities on top-of-atmosphere thermal infrared radiation

2014 ◽  
Vol 14 (11) ◽  
pp. 5599-5615 ◽  
Author(s):  
T. Fauchez ◽  
C. Cornet ◽  
F Szczap ◽  
P. Dubuisson ◽  
T. Rosambert
Keyword(s):  
Radiative Transfer ◽  
Monte Carlo Model ◽  
Thermal Infrared ◽  
Brightness Temperatures ◽  
Spectral Bands ◽  
Thickness Standard ◽  
The Difference ◽  
Scale Properties ◽  
Parallel Approximation ◽  
The Impact

Abstract. This paper presents a study of the impact of cirrus cloud heterogeneities on the thermal infrared brightness temperatures at the top of the atmosphere (TOA). Realistic 3-D cirri are generated by a cloud generator based on simplified thermodynamic and dynamic equations and on the control of invariant scale properties. The 3-D thermal infrared radiative transfer is simulated with a Monte Carlo model for three typical spectral bands in the infrared atmospheric window. Comparisons of TOA brightness temperatures resulting from 1-D and 3-D radiative transfer show significant differences for optically thick cirrus (τ > 0.3 at 532 nm) and are mainly due to the plane-parallel approximation (PPA). At the spatial resolution of 1 km × 1 km, two principal parameters control the heterogeneity effects on brightness temperatures: i) the optical thickness standard deviation inside the observation pixel, ii) the brightness temperature contrast between the top of the cirrus~and the clear-sky atmosphere. Furthermore, we show that the difference between 1-D and 3-D brightness temperatures increases with the zenith view angle from two to ten times between 0° and 60° due to the tilted independent pixel approximation (TIPA).

Effects of lyophilization of serum on the measurement of apolipoproteins A-I and B

1990 ◽  
Vol 36 (2) ◽  
pp. 366-369 ◽  
Author(s):  
S M Marcovina ◽  
J L Adolphson ◽  
M Parlavecchia ◽  
J J Albers
Keyword(s):  
Reference Materials ◽  
Apolipoprotein B ◽  
Matrix Effects ◽  
Reference Intervals ◽  
Assay Method ◽  
Common Reference ◽  
Apolipoprotein A ◽  
Quality Control Materials ◽  
Standardization Process ◽  
The Difference

Abstract A common accuracy-based standardization program is indispensable for establishing reference intervals for the clinical use of apolipoproteins. The development and distribution of reference materials and quality-control materials that do not exhibit matrix effects between methods is essential to the standardization process. We examined the suitability of lyophilized material as a common reference material for the measurement of apolipoproteins A-I and B. We determined values for apolipoproteins A-I and B in frozen and lyophilized serum pools, using different immunochemical approaches. We found little or no differences in apolipoprotein A-I values between frozen and lyophilized pools as determined by the different methods. In contrast, values for apolipoprotein B in lyophilized samples were consistently lower than those obtained for frozen samples. After adjusting for the effect of dilution due to reconstitution, the difference in the apolipoprotein B values for lyophilized as compared with frozen samples ranged from -26% to 4%, depending upon the assay method. Evidently, serum pools in lyophilized from are not a suitable matrix for reference materials for apolipoprotein B measurements but can be used for apolipoprotein A-I measurements.

PATMOS-x v6.0: Improvements to AVHRR Cloud Climate Record and Analysis of the Updated Data

2020 ◽  
Author(s):  
Coda Phillips ◽  
Michael Foster ◽  
Andrew Heidinger
Keyword(s):  
High Resolution ◽  
Detection Accuracy ◽  
Cloud Detection ◽  
Edge Preserving ◽  
Brightness Temperatures ◽  
Cloud Properties ◽  
Satellite Sensors ◽  
The Difference ◽  
Climate Analysis ◽  
Spectral Channels

<p>Since 1978, an Advanced Very-High-Resolution Radiometer (AVHRR) has flown onboard 17 polar-orbiting satellites. Together, they are the longest global record from a homogeneous set of satellite sensors. The Pathfinder Atmosphere’s Extended (PATMOS-x) dataset is a long-term cloud record derived from the AVHRR radiances, and suitable for climate analysis. It has demonstrated intersensor stability and has been rigorously compared with other cloud datasets.</p><p>However, the AVHRR alone has only limited spectral information, so cloud detection during nighttime or over ice is challenging. Therefore, performance degrades over regions with extreme diurnal patterns or low temperatures such as the poles, despite our interest.</p><p>The next production version of PATMOS-x will include numerous algorithmic changes as well as the use of High-resolution Infrared Radiation Sounder (HIRS) spectral channels to improve detection accuracy in previously difficult conditions. The low-resolution HIRS soundings are upsampled to match the AVHRR pixels through an edge-preserving process called “fusion”. The higher-resolution AVHRR imagery guides the upsampling and the resulting combination is spectrally consistent with the AVHRR and has a high spatial resolution.</p><p>For cloud detection, the difference between the AVHRR and HIRS 11μm and HIRS 6.7μm brightness temperatures has been added as a feature in the naive Bayesian cloud detector. The effect on cloud precision is seen especially in the Antarctic where false-positive cloud detections have decreased dramatically.</p><p>Other cloud properties can be improved with the new spectral channels. For example, the new cloud phase algorithm uses the HIRS 6.7μm to determine cloud phase and the AVHRR and HIRS 11μm-13.3μm beta ratio identifies overlapping clouds. Also, the 11μm, 12μm, and HIRS 13.3μm are used in the new cloud height algorithm.</p><p>We report on the development of this new version of the PATMOS-x cloud climate dataset, and the methods used to calibrate and homogenize the participating sensors. Finally, observed trends in the improved dataset will be examined and related to the old dataset. In particular, attention will be given to whether high-latitude analysis of climatic trends is finally possible on the new dataset.</p>

Detection of Fog Involving Heavy Pollutants by Using the New Geostationary satellite Himawari-8

2020 ◽  
Author(s):  
Hongbin Wang ◽  
Zhiwei Zhang ◽  
Duanyang Liu
Keyword(s):  
Satellite Observation ◽  
Geostationary Satellite ◽  
Japan Meteorological Agency ◽  
Composite Image ◽  
Brightness Temperatures ◽  
The Difference ◽  
Grid Points ◽  
High Level ◽  
Different Levels ◽  
Better Than

<p>Himawari-8 is the new geostationary satellite of the Japan Meteorological Agency (JMA) and carries the Advanced Himawari Imager (AHI), which is greatly improved over past imagers in terms of its number of bands and its temporal/spatial resolution. In this work, two different methods for the detection of the different levels of fog involving heavy pollutants by using the Himawari-8 were developed in China. The two different methods are the method of the difference between the 11.2 mm and 3.9 mm brightness temperatures (BTD<sub>3.9-11.2</sub>) and the method of 3.9 mm Pseudo-Emissivity (ems<sub>3.9</sub>).  The 3.9 mm Pseudo-Emissivity is the ratio of the observed 3.9 mm radiance and the 3.9 mm blackbody radiance calculated using the 11.2 mm brightness temperature. We identified the parameters optimal threshold at the 2400 stations and the grid points using the BTD<sub>3.9-11.2</sub> and ems<sub>3.9</sub> for different levels of fog involving heavy pollutants. Results on land and sea from the two methods were compared with surface observations from 2400 weather stations in China and CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) VFM (Vertical Feature Mask) products. The results show that both the method of BTD<sub>3.9-11.2</sub> and the method of ems<sub>3.9</sub> can accurately identify the different levels of fog involving heavy pollutants and the accuracy of ems<sub>3.9 </sub>method is slightly better than the BTD<sub>3.9-11.2</sub>. The accuracy of two methods has increased significantly and the false alarm rate has significantly decreased with the decrease of the visibility. When the visibility is less than 50 m, the HR, FAR and KSS of the BTD<sub>3.9-11.2</sub> method (the ems<sub>3.9 </sub>method) were 0.89 (0.90), 0.15 (0.15) and 0.74 (0.75), respectively. When mid- or high-level clouds were removed using surface temperature of the ground observations, the HR and KSS of two methods for the different levels of fog has increased significantly, and the FAR has significantly decreased. When the visibility is less than 1000 m, the HR of the BTD<sub>3.9-11.2</sub> method (the ems<sub>3.9 </sub>method) is increased to 0.81(0.85) from 0.71 (0.74), the FAR is decreased to 0.12 (0.13) from 0.27 (0.28), and the KSS is increased to 0.69 (0.72) from 0.44 (0.46). The KSS of two method increase by 0.23 and 0.26, respectively. Three cases analysis show that the fog area can be clearly identified by using the BTD<sub>3.9-11.2</sub>, ems<sub>3.9</sub> and RGB composite image. The results of the detection of sea fog by using Himawari-8 data and using CALIPSO VFM products have consistency.</p>

Comparison of Ground-Based Radar and Geosynchronous Satellite Climatologies of Warm-Season Precipitation over the United States

2008 ◽  
Vol 47 (12) ◽  
pp. 3264-3270 ◽  
Author(s):  
John D. Tuttle ◽  
Richard E. Carbone ◽  
Phillip A. Arkin
Keyword(s):  
United States ◽  
Brightness Temperature ◽  
Satellite Data ◽  
Warm Season ◽  
Propagation Speed ◽  
Radar Data ◽  
The United States ◽  
Temperature Threshold ◽  
Brightness Temperatures ◽  
The Difference

Abstract Studies in the past several years have documented the climatology of warm-season precipitation-episode statistics (propagation speed, span, and duration) over the United States using a national composited radar dataset. These climatological studies have recently been extended to other continents, including Asia, Africa, and Australia. However, continental regions outside the United States have insufficient radar coverage, and the newer studies have had to rely on geostationary satellite data at infrared (IR) frequencies as a proxy for rainfall. It is well known that the use of IR brightness temperatures to infer rainfall is subject to large errors. In this study, the statistics of warm-season precipitation episodes derived from radar and satellite IR measurements over the United States are compared and biases introduced by the satellite data are evaluated. It is found that the satellite span and duration statistics are highly dependent upon the brightness temperature threshold used but with the appropriate choices of thresholds can be brought into good agreement with those based upon radar data. The propagation-speed statistics of satellite events are on average ∼4 m s−1 faster than radar events and are relatively insensitive to the brightness temperature threshold. A simple correction procedure based upon the difference between the steering winds for the precipitation core and the winds at the level of maximum anvil outflow is developed.

scholarly journals Simultaneous measurement of NO and NO<sub>2</sub> by dual-channel cavity ring down spectroscopy technique

2019 ◽  
Author(s):  
Renzhi Hu ◽  
Zhiyan Li ◽  
Pinhua Xie ◽  
Hao chen ◽  
Xiaoyan Liu ◽  
...  
Keyword(s):  
Regression Line ◽  
High Sensitivity ◽  
Correlation Factor ◽  
Total Uncertainty ◽  
Suburban Areas ◽  
Enhanced Absorption ◽  
Dual Channel ◽  
Cavity Enhanced Absorption Spectroscopy ◽  
Linear Correction ◽  
The Difference

Abstract. Nitric oxide (NO) and nitrogen dioxide (NO2) are relevant to air quality due to their role in tropospheric ozone (O3) production. In China, NOx emission is high and exhausted from on-road vehicles makes up 20 % of total NOx emissions. Too much NOx are harmful to the human body and animals. In order to detect the NO and NO2 emissions on road, a dual-channel CRDS system for NO2 and NO detection is reported. In this system, NO is converted to NO2 by its reaction with excess O3 in NOx channel, such that NO can be determined through the difference between two channels. The detection limits of the developed CRDS system for NO2 and NOx measurements are estimated to be about 0.030 ppb (1σ, 1 s) and 0.040 ppb (1σ, 1 s), respectively. Considering the error sources of NO2 absorption cross section and RL determination, the total uncertainty of NO2 measurements is about 5 %. The CRDS method is capable of measuring species with high sensitivity and accuracy. The performance of the system was validated against a chemiluminescence (CL) analyzer (42i, Thermo Scientific, Inc.) when measuring the NO2 standard mixtures. The results of NO2 with standard mixtures sampled showed a linear correction factor (R2) of 0.99 in a slope of 1.031 ± 0.006, with an offset of (−0.940 ± 0.323) ppb. An intercomparison between the system and a cavity-enhanced absorption spectroscopy (CEAS) instrument for NO2 measurement was also conducted alone in ambient environment. Least-squares analysis showed that the slope and intercept of the regression line are 1.042 ± 0.002 and (−0.393 ± 0.040) ppb, respectively, with a linear correlation factor of R2 = 0.99. Another intercomparison conducted between the system and the CL analyzer for NO detection also showed a good agreement within their uncertainties, with an absolute shift of (0.352 ± 0.013) ppb, a slope of 0.957 ± 0.007 and a correlation coefficient of R2 = 0.99. The measurements of on-road vehicle emission plumes by this mobile CRDS instrument show the different emission characteristics in the urban and suburban areas of Hefei. The instrument provides a new method for retrieving fast variations of NO and NO2 plumes.

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