Effect of off-zenith observations on reducing the impact of precipitation on ground-based microwave radiometer measurement accuracy

2014 ◽  
Vol 140-141 ◽  
pp. 85-94 ◽  
Author(s):  
Guirong Xu ◽  
Randolph (Stick) Ware ◽  
Wengang Zhang ◽  
Guangliu Feng ◽  
Kewen Liao ◽  
...  
Keyword(s):  
Measurement Accuracy ◽  
Microwave Radiometer ◽  
The Impact ◽  
Radiometer Measurement

Methods for Restricting Maximum Exposure Rate in Computerized Adaptative Testing

Methodology ◽  
2007 ◽  
Vol 3 (1) ◽  
pp. 14-23 ◽  
Author(s):  
Juan Ramon Barrada ◽  
Julio Olea ◽  
Vicente Ponsoda
Keyword(s):  
Measurement Accuracy ◽  
Computerized Adaptive Testing ◽  
Computation Time ◽  
Adaptive Testing ◽  
Exposure Rate ◽  
Control Parameters ◽  
The Impact ◽  
Two Alternatives ◽  
Selection Of ◽  
Maximum Exposure

Abstract. The Sympson-Hetter (1985) method provides a means of controlling maximum exposure rate of items in Computerized Adaptive Testing. Through a series of simulations, control parameters are set that mark the probability of administration of an item on being selected. This method presents two main problems: it requires a long computation time for calculating the parameters and the maximum exposure rate is slightly above the fixed limit. Van der Linden (2003) presented two alternatives which appear to solve both of the problems. The impact of these methods in the measurement accuracy has not been tested yet. We show how these methods over-restrict the exposure of some highly discriminating items and, thus, the accuracy is decreased. It also shown that, when the desired maximum exposure rate is near the minimum possible value, these methods offer an empirical maximum exposure rate clearly above the goal. A new method, based on the initial estimation of the probability of administration and the probability of selection of the items with the restricted method ( Revuelta & Ponsoda, 1998 ), is presented in this paper. It can be used with the Sympson-Hetter method and with the two van der Linden's methods. This option, when used with Sympson-Hetter, speeds the convergence of the control parameters without decreasing the accuracy.

The impact of duration observations on precision of results GNSS measurements

2017 ◽  
Vol 921 (3) ◽  
pp. 7-13 ◽  
Author(s):  
S.V. Grishko
Keyword(s):  
Measurement Accuracy ◽  
Functional Dependence ◽  
Observation Time ◽  
Satellite Networks ◽  
Satellite Measurements ◽  
Proposed Model ◽  
Actual Error ◽  
Gnss Measurements ◽  
The Impact ◽  
Qualitative Characteristics

This paper shows that the accuracy of relative satellite measurements depend not only on the length of the baseline, as it is regulated by the rating formula of accuracy of GNSS equipment, but also on the duration of observations. As a result of the strict adjustment much redundant satellite networks with different duration of observations obtained covariance matrix of baselines, the most realistic reflecting the actual error of satellite observations. Research of forms of communication of these errors from length of the baseline and duration of its measurement is executed. A significant influence of solar activity on accuracy of satellite measurements, in general, leads to unequal similar series of measurements made at different periods, for example, in the production of monitoring activities. The model of approximation of the functional dependence of accuracy of the baseline from its length and duration of observations having good qualitative characteristics is offered. Based on the proposed model, we analyzed the dynamics of changes in measurement accuracy with an increase in observation time.

scholarly journals Winter 2018 major sudden stratospheric warming impact on midlatitude mesosphere from microwave radiometer measurements

2019 ◽  
Author(s):  
Yuke Wang ◽  
Valery Shulga ◽  
Gennadi Milinevsky ◽  
Aleksey Patoka ◽  
Oleksandr Evtushevsky ◽  
...  
Keyword(s):  
Zonal Wind ◽  
Geopotential Height ◽  
Microwave Radiometer ◽  
Recovery Phase ◽  
The Arctic ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Easterly Wind ◽  
The Impact ◽  
Midlatitude Mesosphere

Abstract. The impact of a major sudden stratospheric warming (SSW) in the Arctic in February 2018 on the mid-latitude mesosphere was investigated by performing microwave radiometer measurements of carbon monoxide (CO) and zonal wind above Kharkiv, Ukraine (50.0° N, 36.3° E). The mesospheric peculiarities of this SSW event were observed using recently designed and installed microwave radiometer in East Europe for the first time. The data from the ERA-Interim and NCEP–NCAR reanalyses, as well as the Aura Microwave Limb Sounder measurements, have been also used. Microwave observations of the daily CO profiles in January–March 2018 allowed retrieving mesospheric zonal wind at 70–85 km (below the winter mesopause) over the Kharkiv site. The reverse of the mesospheric westerly from about 10 m s−1 to the easterly wind of about −10 m s−1 around 10 February has been registered. Local microwave observations in the NH midlatitudes combined with reanalysis data show wide ranges of daily variability in CO, zonal wind, temperature and geopotential height in the mesosphere and stratosphere during the SSW 2018. Oscillations in the vertical CO profile, zonal wind, and geopotential height during the SSW, stratopause disappearance after the SSW onset and strong CO and westerly wind peaks at the start of the SSW recovery phase have been observed. The observed CO variability can be explained by vertical and horizontal air mass redistribution due to planetary wave activity with the replacement of the CO-rich air by CO-poor air and vice versa, in agreement with other studies. The results of microwave measurements of CO and zonal wind in the midlatitude mesosphere at 70–85 km altitudes, which still is not adequately covered by ground-based observations, are useful for improving our understanding of the SSW impacts in this region.

scholarly journals Uncertainties of ground-based microwave radiometer retrievals in zenith and off-zenith observations under snow conditions

2017 ◽  
Vol 10 (1) ◽  
pp. 155-165 ◽  
Author(s):  
Wengang Zhang ◽  
Guirong Xu ◽  
Yuanyuan Liu ◽  
Guopao Yan ◽  
Dejun Li ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Microwave Radiometer ◽  
Retrieval Algorithm ◽  
Mean Square ◽  
Atmospheric Conditions ◽  
Vapor Density ◽  
Heavy Snowfall ◽  
Snow Conditions ◽  
The Impact ◽  
Mean Square Errors

Abstract. This paper is to investigate the uncertainties of microwave radiometer (MWR) retrievals in snow conditions and also explore the discrepancies of MWR retrievals in zenith and off-zenith observations. The MWR retrievals were averaged in a ±15 min period centered at sounding times of 00:00 and 12:00 UTC and compared with radiosonde observations (RAOBs). In general, the MWR retrievals have a better correlation with RAOB profiles in off-zenith observations than in zenith observations, and the biases (MWR observations minus RAOBs) and root mean square errors (RMSEs) between MWR and RAOB are also clearly reduced in off-zenith observations. The biases of temperature, relative humidity, and vapor density decrease from 4.6 K, 9 %, and 1.43 g m−3 in zenith observations to −0.6 K, −2 %, and 0.10 g m−3 in off-zenith observations, respectively. The discrepancies between MWR retrievals and RAOB profiles by altitude present the same situation. Cases studies show that the impact of snow on accuracies of MWR retrievals is more serious in heavy snowfall than in light snowfall, but off-zenith observation can mitigate the impact of snowfall. The MWR measurements become less accurate in snowfall mainly due to the retrieval algorithm, which does not consider the effect of snow, and the accumulated snow on the top of the radome increases the signal noise of MWR measurements. As the snowfall drops away by gravity on the sides of the radome, the off-zenith observations are more representative of the atmospheric conditions for RAOBs.

scholarly journals Winter 2018 major sudden stratospheric warming impact on midlatitude mesosphere from microwave radiometer measurements

2019 ◽  
Vol 19 (15) ◽  
pp. 10303-10317 ◽  
Author(s):  
Yuke Wang ◽  
Valerii Shulga ◽  
Gennadi Milinevsky ◽  
Aleksey Patoka ◽  
Oleksandr Evtushevsky ◽  
...  
Keyword(s):  
Zonal Wind ◽  
Microwave Radiometer ◽  
Polar Vortex ◽  
The Arctic ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Time Data ◽  
Easterly Wind ◽  
The Impact ◽  
Midlatitude Mesosphere

Abstract. The impact of a major sudden stratospheric warming (SSW) in the Arctic in February 2018 on the midlatitude mesosphere is investigated by performing the microwave radiometer measurements of carbon monoxide (CO) and zonal wind above Kharkiv, Ukraine (50.0∘ N, 36.3∘ E). The mesospheric peculiarities of this SSW event were observed using a recently designed and installed microwave radiometer in eastern Europe for the first time. Data from the ERA-Interim and MERRA-2 reanalyses, as well as the Aura microwave limb sounder measurements, are also used. Microwave observations of the daily CO profiles in January–March 2018 allowed for the retrieval of mesospheric zonal wind at 70–85 km (below the winter mesopause) over the Kharkiv site. Reversal of the mesospheric westerly from about 10 m s−1 to an easterly wind of about −10 m s−1 around 10 February was observed. The local microwave observations at our Northern Hemisphere (NH) midlatitude site combined with reanalysis data show wide-ranging daily variability in CO, zonal wind, and temperature in the mesosphere and stratosphere during the SSW of 2018. The observed local CO variability can be explained mainly by horizontal air mass redistribution due to planetary wave activity. Replacement of the CO-rich polar vortex air by CO-poor air of the surrounding area led to a significant mesospheric CO decrease over the station during the SSW and fragmentation of the vortex over the station at the SSW start caused enhanced stratospheric CO at about 30 km. The results of microwave measurements of CO and zonal wind in the midlatitude mesosphere at 70–85 km altitudes, which still are not adequately covered by ground-based observations, are useful for improving our understanding of the SSW impacts in this region.

Monodispersion Soot Particle Interference on NO2 Concentration Measurement Accuracy Using NDIR

2013 ◽  
Vol 345 ◽  
pp. 251-254
Author(s):  
Yan Jun Zhao ◽  
Shou Guang Cheng ◽  
Bin Qu
Keyword(s):  
Light Intensity ◽  
Measurement Accuracy ◽  
Solution Method ◽  
Soot Particle ◽  
Measurement Methods ◽  
Concentration Measurement ◽  
Infrared Light ◽  
Soot Particles ◽  
Characteristic Wavelength ◽  
The Impact

NDIR is one of the NO2 concentration measurement methods. The NO2 concentration can be figured out by measuring the attenuation of the infrared light intensity on the characteristic wavelength. But the infrared light intensity is also attenuated by the monodispersion soot particles because of the particles absorption and scattering. So the monodispersion soot particles can impact the NO2 concentration accuracy. The interference of the monodispersion particles is discussed in the paper. Simulation results show that the impact parameters on the NO2 concentration accuracy include the received scattering angle range, particle size and concentration. The solution method is brought out and NO2 concentration measurement accuracy can be improved.

scholarly journals Assessment of Multi-Scale SMOS and SMAP Soil Moisture Products across the Iberian Peninsula

2020 ◽  
Vol 12 (3) ◽  
pp. 570 ◽  
Author(s):  
Gerard Portal ◽  
Thomas Jagdhuber ◽  
Mercè Vall-llossera ◽  
Adriano Camps ◽  
Miriam Pablos ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Iberian Peninsula ◽  
Spatial Scale ◽  
Temporal Dynamics ◽  
Microwave Radiometer ◽  
Added Value ◽  
Optical Data ◽  
Enhanced Resolution ◽  
The Impact

In the last decade, technological advances led to the launch of two satellite missions dedicated to measure the Earth’s surface soil moisture (SSM): the ESA’s Soil Moisture and Ocean Salinity (SMOS) launched in 2009, and the NASA’s Soil Moisture Active Passive (SMAP) launched in 2015. The two satellites have an L-band microwave radiometer on-board to measure the Earth’s surface emission. These measurements (brightness temperatures TB) are then used to generate global maps of SSM every three days with a spatial resolution of about 30–40 km and a target accuracy of 0.04 m3/m3. To meet local applications needs, different approaches have been proposed to spatially disaggregate SMOS and SMAP TB or their SSM products. They rely on synergies between multi-sensor observations and are built upon different physical assumptions. In this study, temporal and spatial characteristics of six operational SSM products derived from SMOS and SMAP are assessed in order to diagnose their distinct features, and the rationale behind them. The study is focused on the Iberian Peninsula and covers the period from April 2015 to December 2017. A temporal inter-comparison analysis is carried out using in situ SSM data from the Soil Moisture Measurements Station Network of the University of Salamanca (REMEDHUS) to evaluate the impact of the spatial scale of the different products (1, 3, 9, 25, and 36 km), and their correspondence in terms of temporal dynamics. A spatial analysis is conducted for the whole Iberian Peninsula with emphasis on the added-value that the enhanced resolution products provide based on the microwave-optical (SMOS/ERA5/MODIS) or the active–passive microwave (SMAP/Sentinel-1) sensor fusion. Our results show overall agreement among time series of the products regardless their spatial scale when compared to in situ measurements. Still, higher spatial resolutions would be needed to capture local features such as small irrigated areas that are not dominant at the 1-km pixel scale. The degree to which spatial features are resolved by the enhanced resolution products depend on the multi-sensor synergies employed (at TB or soil moisture level), and on the nature of the fine-scale information used. The largest disparities between these products occur in forested areas, which may be related to the reduced sensitivity of high-resolution active microwave and optical data to soil properties under dense vegetation.

A Novel Kind of Turbidity Sensor and its Measurement Method

2012 ◽  
Vol 424-425 ◽  
pp. 1253-1257
Author(s):  
Xing Qiao Liu ◽  
Peng Zhang
Keyword(s):  
Measurement Accuracy ◽  
Test Results ◽  
Measurement Circuit ◽  
The Core ◽  
On Line ◽  
New Type ◽  
The Impact ◽  
Sensor Probe ◽  
Easy Operation ◽  
Higher Sensitivity

In this paper, the scattering measuring principle of turbidity is introduced firstly. The new type of turbidity sensor probe designed in this paper overcomes the deficiencies of existing technologies, which has higher sensitivity, strong anti-interference and can detect the turbidity accurately and continuously. The system designed with the core of MCU C8051F020 is presented. Then the design of turbidity sensor probe, data acquisition, processing and non-linear compensation are introduced in detail. Besides, in order to eliminate the impact of temperature on the turbidity measurement and improve the measurement accuracy, temperature measurement circuit has been designed. Test results have shown that the designed on-line turbidity-meter has some advantages: low price, high precision, easy operation etc. It can be widely applied in the fields of waterworks, industrial production, aquaculture, environmental protection and so on

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