scholarly journals Spatial Averaging of HF Radar Data for Wave Measurement Applications

2013 ◽  
Vol 30 (9) ◽  
pp. 2216-2224 ◽  
Author(s):  
Lucy R. Wyatt ◽  
Jasmine B. D. Jaffrés ◽  
Mal L. Heron
Keyword(s):  
Radar Data ◽  
Hf Radar ◽  
High Temporal Resolution ◽  
Spatial Averaging ◽  
Spectral Estimates ◽  
Wave Measurements ◽  
Temporal Averaging ◽  
Time Periods ◽  
The Impact ◽  
Very High

Abstract HF radar data are often collected for time periods that are optimized for current measurement applications where, in many cases, very high temporal resolution is needed. Previous work has demonstrated that this does not provide sufficient averaging for robust wave measurements to be made. It was shown that improvements could be made by averaging the radar data for longer time periods. HF radar provides measurements over space as well as in time, so there is also the possibility to average in space. However, the radar data are correlated in space because of the range and azimuth processing. The implications of this are discussed and estimates of the impact on the reduction in variance in the radar Doppler spectral estimates are obtained. Spatial inhomogeneities and temporal nonstationarity in the ocean wave field itself also need to be taken into account. It is suggested that temporal averaging over periods of up to one hour and spatial averaging over 9–25 nearest neighbors may be suitable, and these will be explored in later work.

scholarly journals Spatial and Temporal Averaging Windows and Their Impact on Forecasting: Exactly Solvable Examples

2018 ◽  
Vol 4 (1) ◽  
pp. 23-49 ◽  
Author(s):  
Ying Li ◽  
Samuel N. Stechmann
Keyword(s):  
Forecast Skill ◽  
Time Averaging ◽  
Spatial Averaging ◽  
Spatiotemporal Model ◽  
Weather And Climate ◽  
Exactly Solvable ◽  
Temporal Averaging ◽  
The Impact ◽  
Basic Intuition ◽  
Local Value

Abstract In making weather and climate predictions, the goal is often not to predict the instantaneous, local value of temperature, wind speed, or rainfall; instead, the goal is often to predict these quantities after averaging in time and/or space-for example, over one day or one week. What is the impact of spatial and/or temporal averaging on forecasting skill?Here this question is investigated using simple stochastic models that can be solved exactly analytically. While the models are idealized, their exact solutions allow clear results that are not affected by errors from numerical simulations or from random sampling. As a model of time series of oscillatory weather fluctuations, the complex Ornstein-Uhlenbeck process is used. To furthermore investigate spatial averaging, the stochastic heat equation is used as an idealized spatiotemporal model for moisture and rainfall. Space averaging and time averaging are shown to have distinctly different impacts on prediction skill. Spatial averaging leads to improved forecast skill, in line with some forms of basic intuition. Time averaging, on the other hand, is more subtle: it may either increase or decrease forecast skill. The subtle effects of time averaging are seen to arise from the relative definitions of the time averaging window and the lead time. These results should help in understanding and comparing forecasts with different temporal and spatial averaging windows.

scholarly journals A simplified method for the detection of convection using high resolution imagery from GOES-16

2020 ◽  
Author(s):  
Yoonjin Lee ◽  
Christian D. Kummerow ◽  
Milija Zupanski
Keyword(s):  
High Spatial Resolution ◽  
Radar Data ◽  
High Temporal Resolution ◽  
Infrared Sensors ◽  
Convective Clouds ◽  
Brightness Temperatures ◽  
High Resolution Imagery ◽  
Developed Nations ◽  
Very High ◽  
Reflectance Data

Abstract. The ability to detect convective regions and assimilating the proper heating in these regions is the most important skill in forecasting severe weather systems. Since radars are most directly related to precipitation and are available in high temporal resolution, their data are often used for both detecting convection and estimating latent heating. However, radar data are limited to land areas, largely in developed nations, and early convection is not detectable from radars until drops become large enough to produce significant echoes. Visible and Infrared sensors on a geostationary satellite can provide data that are less sensitive to drop size, but they also have shortcomings: their information is almost exclusively from the cloud top. Relatively new geostationary satellites, GOES-16 and GOES-17, along with Himawari-8, can make up for some of this lack of vertical information through the use of very high spatial and temporal resolutions. This study develops two algorithms to detect convection at different life stages using 1-minute GOES-16 ABI data. Two case studies are used to explain the two methods, followed by results applied to one month of data over the contiguous United States. Vertically growing clouds in early stages were detected using decreases in brightness temperatures over ten minutes. Of the detected clouds, the method correctly identifies 71.0 % to be convective. For mature convective clouds which no longer show decreases in brightness temperature, the lumpy texture, and rapid temporal evolution can be observed using 1-minute high spatial resolution reflectance data. The algorithm that uses texture and evolution for mature convection detects with an accuracy of 85.8 %. 54.7 % of clouds that are identified as convective by the ground-based radars are missed by the satellite. These convective clouds are largely under optically thick cloud shields.

scholarly journals SuperDARN radar HF propagation and absorption response to the substorm expansion phase

2002 ◽  
Vol 20 (10) ◽  
pp. 1631-1645 ◽  
Author(s):  
J. K. Gauld ◽  
T. K. Yeoman ◽  
J. A. Davies ◽  
S. E. Milan ◽  
F. Honary
Keyword(s):  
Radar Data ◽  
Hf Radar ◽  
Data Loss ◽  
Expansion Phase ◽  
Operational Strategies ◽  
Radio Science ◽  
Radar Systems ◽  
Hf Propagation ◽  
Propagation Paths ◽  
The Impact

Abstract. Coherent scatter HF ionospheric radar systems such as SuperDARN offer a powerful experimental technique for the investigation of the magnetospheric substorm. However, a common signature in the early expansion phase is a loss of HF backscatter, which has limited the utility of the radar systems in substorm research. Such data loss has generally been attributed to either HF absorption in the D-region ionosphere, or the consequence of regions of very low ionospheric electric field. Here observations from a well-instrumented isolated substorm which resulted in such a characteristic HF radar data loss are examined to explore the impact of the substorm expansion phase on the HF radar system. The radar response from the SuperDARN Hankasalmi system is interpreted in the context of data from the EIS-CAT incoherent scatter radar systems and the IRIS Riometer at Kilpisjarvi, along with calculations of HF absorption for both IRIS and Hankasalmi and ray-tracing simulations. Such a study offers an explanation of the physical mechanisms behind the HF radar data loss phenomenon. It is found that, at least for the case study presented, the major cause of data loss is not HF absorption, but changes in HF propagation conditions. These result in the loss of many propagation paths for radar backscatter, but also the creation of some new, viable propagation paths. The implications for the use of the characteristics of the data loss as a diagnostic of the substorm process, HF communications channels, and possible radar operational strategies which might mitigate the level of HF radar data loss, are discussed.Key words. Ionosphere (ionosphere-magnetosphere interactions). Magnetospheric physics (storms and substorms). Radio science (radio wave propagation)

scholarly journals Signal Sampling Impacts on HF Radar Wave Measurement

2009 ◽  
Vol 26 (4) ◽  
pp. 793-805 ◽  
Author(s):  
Lucy R. Wyatt ◽  
J. Jim Green ◽  
Andrew Middleditch
Keyword(s):  
Power Spectra ◽  
Hf Radar ◽  
Wave Measurements ◽  
Radar Systems ◽  
Ocean Surface Wave ◽  
Radar Wave ◽  
The Impact ◽  
Geographical Locations ◽  
Buoy Measurements ◽  
Impact Predictions

Abstract Averaging is required for the measurement of ocean surface wave spectra and parameters with any measurement system in order to reduce the variance in the estimates. Sampling theory for buoy measurements is well known. The same theory can be applied to the impact of sampling on the estimation of high-frequency (HF) radar power spectra from which wave measurements are derived. Some work on the impacts on the HF radar wave measurements themselves is reviewed and applied to datasets obtained with three different radar systems, operating at different radio frequencies in different geographical locations. Comparisons with collocated buoy measurements are presented showing qualitative agreement with the sampling impact predictions but indicating that there are more sources of differences than can be explained by sampling. Increased averaging is applied to two of these datasets to demonstrate the improvement in data quality and quantity that can be obtained.

Experimental Investigation of the Impact of Dual Time Periods on Crash Hazardous Location Identification

ICCTP 2011 ◽  
2011 ◽  
Author(s):  
Gilbert Leano ◽  
Wen Cheng ◽  
Xudong Jia ◽  
Lingqi Kong ◽  
Robert Brennan
Keyword(s):  
Experimental Investigation ◽  
Time Periods ◽  
Location Identification ◽  
The Impact

scholarly journals Do Prospective Teachers Care About PISA Studies? A Pilot Study among University Students in Germany

2017 ◽  
Vol 10 (5) ◽  
pp. 26 ◽  
Author(s):  
Olga Ioannidou ◽  
Despoina Georgiou ◽  
Andreas Obersteiner ◽  
Nilufer Deniz Bas ◽  
Christine Mieslinger
Keyword(s):  
Teacher Education ◽  
University Students ◽  
Prospective Teachers ◽  
International Student ◽  
Teacher Education Program ◽  
Student Assessment ◽  
International Student Assessment ◽  
The Impact ◽  
Very High ◽  
Expected Outcomes

The results of international comparison studies such as the Program for International Student Assessment (PISA) have initiated intense discussions about educational reforms in Germany. Although in-service and pre-service teachers are an essential part of such reforms, little is known about their attitudes towards PISA studies. The present study aims to fill this gap through the investigation of pre-service teachers’ awareness, interest, perception, and attitudes towards PISA. A questionnaire was used to survey a sample of 107 university students who were participating in a teacher education program. The results reveal that 100% of the participants are aware of PISA. Nearly 69% of the participants think that the impact of PISA is rather high or very high, while 41% of them believe that PISA results are reliable. Accordingly, half of the participants seem to be interested in PISA results for their country. The present study discusses these findings in the light of the expected outcomes as proposed in standards for teacher education.

scholarly journals Representation of climate change consequences in British newspapers

2021 ◽  
pp. 026732312097872
Author(s):  
Maria Laura Ruiu
Keyword(s):  
Climate Change ◽  
Public Understanding ◽  
Left Group ◽  
Impact Of Climate Change ◽  
Human Control ◽  
Time Periods ◽  
The Impact

This article explores British newspaper descriptions of the impact of climate change across three time periods. It shows a reduction in representing the consequences of climate change as ‘out of human control’. It also shows a decrease in adopting alarming and uncertain descriptions within the centre-left group, whereas mocking the effects of climate change is a peculiarity of right-leaning narratives. The complexity of climate narratives produces a variety of representations of the consequences of climate change, which in turn might increase ‘uncertainty’ in public understanding of climate change.

scholarly journals Vertical to Horizontal UHS Ratios for Low to Medium Seismicity Regions with Deep Soil atop Deep Geological Sediments—An Example of the City of Osijek, Croatia

2021 ◽  
Vol 11 (15) ◽  
pp. 6782
Author(s):  
Borko Đ. Bulajić ◽  
Marijana Hadzima-Nyarko ◽  
Gordana Pavić
Keyword(s):  
Ground Motions ◽  
Spectral Amplitude ◽  
Eurocode 8 ◽  
Uniform Hazard Spectra ◽  
Study Region ◽  
Spectral Estimates ◽  
Local Soil ◽  
The Impact ◽  
Deep Soils ◽  
The City

The severity of vertical seismic ground motions is often factored into design regulations as a component of their horizontal counterparts. Furthermore, most design codes, including Eurocode 8, ignore the impact of local soil on vertical spectra. This paper investigates vertical pseudo-absolute acceleration spectral estimates, as well as the ratios of spectral estimates for strong motion in vertical and horizontal directions, for low to medium seismicity regions with deep local soil and deep geological sediments beneath the local soil. The case study region encompasses the city of Osijek in Croatia. New regional frequency-dependent empirical scaling equations are derived for the vertical spectra. According to these equations, for a 0.3 s spectral amplitude at deep soils atop deep geological sediments compared to the rock sites, the maximum amplification is 1.48 times. The spectra of vertical components of various real strong motions recorded in the surrounding region are compared to the empirical vertical response spectra. The new empirical equations are used to construct a Uniform Hazard Spectra for Osijek. The ratios of vertical to horizontal Uniform Hazard Spectra are generated, examined, and compared to Eurocode 8 recommendations. All the results show that local soil and deep geology conditions have a significant impact on vertical ground motions. The results also show that for deep soils atop deep geological strata, Eurocode 8 can underestimate the vertical to horizontal spectral ratios by a factor of three for Type 2 spectra while overestimating them by a factor of two for Type 1 spectra.

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