scholarly journals On the Optimal Design of Doppler Scatterometers

2018 ◽  
Author(s):  
Ernesto Rodriguez
Keyword(s):  
Radial Velocity ◽  
Incidence Angle ◽  
Pulse Length ◽  
Sampling Strategy ◽  
Doppler Spectrum ◽  
Pencil Beam ◽  
Pulse Separation ◽  
Sensitivity Equations ◽  
Antenna Length ◽  
Selection Of

Pencil-beam Doppler scatterometers are a promising remote sensing tool for measuring ocean vector winds and currents from space. While several point designs exist in the literature, these designs have been constrained by the hardware they inherited, and the design is sub-optimal. Here, I present guidelines to optimize the design of these instruments starting from the basic sensitivity equations. Unlike conventional scatterometers or pencil-beam imagers, appropriate sampling of the Doppler spectrum and optimizing the radial velocity error lead naturally to a design that incorporates a pulse-to-pulse separation and pulse length that vary with scan angle. Including this variation can improve radial velocity performance significantly and the optimal selection of system timing and bandwidth is derived. Following this, optimization of the performance based on frequency, incidence angle, antenna length, and spatial sampling strategy are considered. It is shown that antenna length influences the performance most strongly, while the errors depend only on the square root of the transmit transmit power. Finally, a set of example designs and associated performance are presented.

scholarly journals On the Optimal Design of Doppler Scatterometers

2018 ◽  
Vol 10 (11) ◽  
pp. 1765 ◽  
Author(s):  
Ernesto Rodriguez
Keyword(s):  
Radial Velocity ◽  
Incidence Angle ◽  
Pulse Length ◽  
Sampling Strategy ◽  
Doppler Spectrum ◽  
Pencil Beam ◽  
Pulse Separation ◽  
Sensitivity Equations ◽  
Antenna Length ◽  
Selection Of

Pencil-beam Doppler scatterometers are a promising remote sensing tool for measuring ocean vector winds and currents from space. While several point designs exist in the literature, these designs have been constrained by the hardware they inherited, and the design is sub-optimal. Here, guidelines to optimize the design of these instruments starting from the basic sensitivity equations are presented. Unlike conventional scatterometers or pencil-beam imagers, appropriate sampling of the Doppler spectrum and optimizing the radial velocity error lead naturally to a design that incorporates a pulse-to-pulse separation and pulse length that vary with scan angle. Including this variation can improve radial velocity performance significantly and the optimal selection of system timing and bandwidth is derived. Following this, optimization of the performance based on frequency, incidence angle, antenna length, and spatial sampling strategy are considered. It is shown that antenna length influences the performance most strongly, while the errors depend only on the square root of the transmit power. Finally, a set of example designs and associated performance are presented.

scholarly journals Long-Term Coudé Radial-Velocity Studies With a 1.2-m Telescope

2001 ◽  
Vol 183 ◽  
pp. 283-288
Author(s):  
C.D. Scarfe
Keyword(s):  
Radial Velocity ◽  
Binary Stars ◽  
Star System ◽  
Standard Star ◽  
Stellar Spectra ◽  
Multiple Stars ◽  
Binary And Multiple Stars ◽  
Selection Of

AbstractI have used the 1.2-m telescope and coudé spectrograph of the Dominion Astrophysical Observatory for more than 30 years in a program of radial-velocity observations of binary stars. The program was begun with photographic plates as detectors, but for 20 years the primary detector has been the radial-velocity scanner, which cross-correlates stellar spectra with an artificial mask.Since some of the binaries under observation have periods of several years, the instrument’s stability is an important consideration. I have therefore been obliged to observe standard stars and asteroids to check its performance. These observations are of relevance to efforts to improve the IAU standard star system.I will describe the telescope, spectrograph and scanner, and will briefly discuss some of the results obtained for a selection of binary and multiple stars.

scholarly journals Malaria intermittent preventive treatment in Nigeria: a qualitative study to explore barriers

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Fatima Mahmud Muhammad ◽  
Saharnaz Nedjat ◽  
Haniye Sadat Sajadi ◽  
Mahboubeh Parsaeian ◽  
Abraham Assan ◽  
...  
Keyword(s):  
Qualitative Study ◽  
Pregnant Women ◽  
Intermittent Preventive Treatment ◽  
Sampling Strategy ◽  
Preventive Treatment ◽  
Group Discussions ◽  
Content Analysis Method ◽  
Conventional Content Analysis ◽  
Sulphadoxine Pyrimethamine ◽  
Selection Of

Abstract Background While the use of sulphadoxine pyrimethamine (SP) is effective in preventing malaria infection during pregnancy, there are challenges limiting its uptake in Nigeria. This study aimed at exploring the barriers to IPTp usage among pregnant women in Kano state - Nigeria. Methods This is a qualitative study. The purposive sampling strategy was used for identification and selection of 14 key informants for interviews. In addition, six focus group discussions (FGDs) were conducted with pregnant women (3 FGDs) and married men (3 FGDs). The conventional content analysis method was used to interpret meaning from the content of the data. MAXQDA 10 software was used for data management and analysis. Results Poor policy implementation, poor antenatal care attendance, inadequate access to intermittent preventive treatment at the community levels, lack of sustainable funding, and poor community engagement emerged as major barriers to IPTp use in Nigeria. Conclusion While the political will to allocate sufficient financial resources could help improve service delivery and IPTp usage among pregnant women, community participation is critical to sustain the gains.

scholarly journals Selection of visual information for lightness judgements by eye movements

2013 ◽  
Vol 368 (1628) ◽  
pp. 20130056 ◽  
Author(s):  
Matteo Toscani ◽  
Matteo Valsecchi ◽  
Karl R. Gegenfurtner
Keyword(s):  
Eye Movements ◽  
Visual System ◽  
Visual Information ◽  
Selection Process ◽  
Sampling Strategy ◽  
Selection Strategy ◽  
Eye Fixations ◽  
Target Layer ◽  
Highly Correlated ◽  
Selection Of

When judging the lightness of objects, the visual system has to take into account many factors such as shading, scene geometry, occlusions or transparency. The problem then is to estimate global lightness based on a number of local samples that differ in luminance. Here, we show that eye fixations play a prominent role in this selection process. We explored a special case of transparency for which the visual system separates surface reflectance from interfering conditions to generate a layered image representation. Eye movements were recorded while the observers matched the lightness of the layered stimulus. We found that observers did focus their fixations on the target layer, and this sampling strategy affected their lightness perception. The effect of image segmentation on perceived lightness was highly correlated with the fixation strategy and was strongly affected when we manipulated it using a gaze-contingent display. Finally, we disrupted the segmentation process showing that it causally drives the selection strategy. Selection through eye fixations can so serve as a simple heuristic to estimate the target reflectance.

Interviews with Whom?

2020 ◽  
pp. 45-65
Author(s):  
Kathleen Gerson
Keyword(s):  
Sampling Strategy ◽  
Snowball Sampling ◽  
The Core ◽  
Theoretical Sampling ◽  
Good Sample ◽  
Selection Of

Chapter 3 considers the principles underlying the selection of an appropriate sample for depth interviewing and the range of strategies available to identify and recruit participants in that sample. Rather than claiming representativeness, as a quantitative researcher might, a depth interviewer aims to select a sample capable of yielding theoretically generalizable insights—an approach called theoretical sampling. Theoretical sampling focuses on finding a variety of participants who are well positioned to reveal the practices, mechanisms, and relationships the research seeks to explain. The chapter then looks at the range of strategies for finding a good sample and deciding whom to include and whom to exclude. Whether the sampling strategy involves recruiting randomly selected participants, snowball sampling, seeking volunteers, or some combination, a good sample contains both the core controls and the built-in comparisons needed to answer the study questions and develop an explanation for the outcomes.

scholarly journals Masses of the components of SB2 binaries observed with Gaia – V. Accurate SB2 orbits for 10 binaries and masses of the components of 5 binaries

2020 ◽  
Vol 496 (2) ◽  
pp. 1355-1368
Author(s):  
J-L Halbwachs ◽  
F Kiefer ◽  
Y Lebreton ◽  
H M J Boffin ◽  
F Arenou ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Binary Stars ◽  
Main Sequence ◽  
Spectroscopic Binaries ◽  
Orbital Elements ◽  
Evolved Stars ◽  
The Individual ◽  
The Masses ◽  
Stellar Masses ◽  
Selection Of

ABSTRACT Double-lined spectroscopic binaries (SB2s) are one of the main sources of stellar masses, as additional observations are only needed to give the inclinations of the orbital planes in order to obtain the individual masses of the components. For this reason, we are observing a selection of SB2s using the SOPHIE spectrograph at the Haute-Provence observatory in order to precisely determine their orbital elements. Our objective is to finally obtain masses with an accuracy of the order of one per cent by combining our radial velocity (RV) measurements and the astrometric measurements that will come from the Gaia satellite. We present here the RVs and the re-determined orbits of 10 SB2s. In order to verify the masses, we will derive from Gaia, we obtained interferometric measurements of the ESO VLTI for one of these SB2s. Adding the interferometric or speckle measurements already published by us or by others for four other stars, we finally obtain the masses of the components of five binary stars, with masses ranging from 0.51 to 2.2 solar masses, including main-sequence dwarfs and some more evolved stars whose location in the HR diagram has been estimated.

scholarly journals The Atmospheric Radiation Measurement Program Cloud Profiling Radars: An Evaluation of Signal Processing and Sampling Strategies

2005 ◽  
Vol 22 (7) ◽  
pp. 930-948 ◽  
Author(s):  
Pavlos Kollias ◽  
Bruce A. Albrecht ◽  
Eugene E. Clothiaux ◽  
Mark A. Miller ◽  
Karen L. Johnson ◽  
...  
Keyword(s):  
Sampling Strategy ◽  
Department Of Energy ◽  
Radiative Properties ◽  
Doppler Spectrum ◽  
Doppler Velocity ◽  
Atmospheric Radiation ◽  
Operational Mode ◽  
Temporal Sampling ◽  
Noise Characteristics ◽  
Moment Estimates

Abstract The U.S. Department of Energy (DOE) Atmospheric Radiation Measurements (ARM) program operates millimeter-wavelength cloud radars (MMCRs) in several specific locations within different climatological regimes. These vertically pointing cloud profiling radars supply the three most important Doppler spectrum moment estimates, which are the radar reflectivity (or zero moment), the mean Doppler velocity (or first moment), and the Doppler spectrum width (or second moment), as a function of time and height. The ARM MMCR Doppler moment estimates form the basis of a number of algorithms for retrieving cloud microphysical and radiative properties. The retrieval algorithms are highly sensitive to the quality and accuracy of the MMCR Doppler moment estimates. The significance of these sensitivities should not be underestimated, because the inherent physical variability of clouds, instrument-induced noise, and sampling strategy limitations all potentially introduce errors into the Doppler moment estimates. In this article, the accuracies of the first three Doppler moment estimates from the ARM MMCRs are evaluated for a set of typical cloud conditions from the three DOE ARM program sites. Results of the analysis suggest that significant errors in the Doppler moment estimates are possible in the current configurations of the ARM MMCRs. In particular, weakly reflecting clouds with low signal-to-noise ratios (SNRs), as well as turbulent clouds with nonzero updraft and downdraft velocities that are coupled with high SNR, are shown to produce degraded Doppler moment estimates in the current ARM MMCR operational mode processing strategies. Analysis of the Doppler moment estimates and MMCR receiver noise characteristics suggests that the introduction of a set of quality control criteria is necessary for identifying periods of degraded receiver performance that leads to larger uncertainties in the Doppler moment estimates. Moreover, the temporal sampling of the ARM MMCRs was found to be insufficient for representing the actual dynamical states in many types of clouds, especially boundary layer clouds. New digital signal processors (DSPs) are currently being developed for the ARM MMCRs. The findings presented in this study will be used in the design of a new set of operational strategies for the ARM MMCRs once they have been upgraded with the new DSPs.

scholarly journals A Generalized Simulation Capability for Rotating Beam Scatterometers

2018 ◽  
Author(s):  
Zhen Li ◽  
Ad Stoffelen ◽  
Anton Verhoef
Keyword(s):  
Incidence Angle ◽  
Retrieval Algorithm ◽  
Pencil Beam ◽  
Wind Vector ◽  
Response Functions ◽  
Rotating Beam ◽  
Retrieval Performance ◽  
Wind Retrieval ◽  
Spatial Response

Abstract. Rotating-beam wind scatterometers exist in two types: rotating fan-beam and rotating pencil-beam. In our study, a generic simulation frame is established and verified to assess the wind retrieval skill of the three different scatterometers: SCAT on CFOSAT, WindRad on FY-3E and SeaWinds on QuikScat. Besides the comparison of the so-called 1st rank-solution retrieval skill of the input wind field, other Figure of Merits (FoMs) are applied to statistically characterize the associated wind retrieval performance from three aspects: wind vector root mean square error, ambiguity susceptibility, and wind biases. The evaluation shows that, overall, the wind retrieval quality of the three instruments can be ranked from high to low as WindRad, SCAT, and SeaWinds, where the wind retrieval quality strongly depends on the Wind Vector Cell (WVC) location across the swath. Usually, the higher the number of views, the better the wind retrieval, but the effect of increasing the number of views reaches saturation, considering the fact that the wind retrieval quality at the nadir and sweet swath parts stays relatively similar for SCAT and WindRad. On the other hand, the wind retrieval performance in the outer swath of WindRad is improved substantially as compared to SCAT due to the increased number of views. The results may be generally explained by the different incidence angle ranges of SCAT and WindRad, mainly affecting azimuth diversity around nadir and number of views in the outer swath. This simulation frame can be used for optimizing the Bayesian wind retrieval algorithm, in particular to avoid biases around nadir, but also to investigate resolution and accuracy through incorporating and analysing the spatial response functions of the simulated Level-1B data for each WVC.

Coastal Shoreline Extraction from Very High Resolution (VHR2) Satellite SAR Imagery

2020 ◽  
Author(s):  
Daithí Maguire ◽  
Eugene Farrell
Keyword(s):  
High Resolution ◽  
Incidence Angle ◽  
Speckle Noise ◽  
High Definition ◽  
Alos Palsar ◽  
Sar Imagery ◽  
Using Data ◽  
Study Sites ◽  
Very High ◽  
Selection Of

<p>Shoreline vectors are extracted from TerraSAR-X imagery based on the identification of peak backscatter intensity levels. The vectors are being catalogued and analysed to assess the accuracy/suitability of SAR imagery for identifying coastal erosion hotspots and for monitoring coastal change as input to forecasting models. The technique is being developed, tested and refined using data collected from three study sites on the west coast of Ireland (Brandon Bay; Clew Bay; Galway Bay).</p><p>The shoreline vectors are extracted from both archived and tasked TerraSAR-X imagery. The extracted shorelines are being validated using a combination of: 1) panchromatic and multispectral satellite imagery (VHR1 & VHR2), 2) panchromatic and RGB aerial imagery (VHR1), 3) LiDAR data and 4) repeat DGPS field survey data. In addition, these shoreline vectors are also being compared with equivalent extractions from other very high-resolution X-band SAR imagery (Cosmo-SkyMed) and high-resolution C-band and L-band SAR imagery (RADARSAT-2, ALOS PALSAR). The spatial accuracy of the extracted shorelines from tasked acquisitions will be further assessed using temporarily installed corner reflectors at a selection of the study sites.</p><p>SAR acquisition parameters (orbit pass direction, incidence angle, polarisation) and a selection of speckle noise reduction filters (e.g. Boxcar, Frost, Lee) were evaluated to determine the optimum combination for coastal sites with different physical characteristics.</p><p>Results are presented in high-definition video format using a combination of GIS, Earth browser and 3D visualisation platforms.</p>

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