scholarly journals Attenuation-Based Estimates of Rainfall Rates Aloft with Vertically Pointing Ka-Band Radars

2005 ◽  
Vol 22 (1) ◽  
pp. 43-54 ◽  
Author(s):  
Sergey Y. Matrosov
Keyword(s):  
Mie Scattering ◽  
Rainfall Rate ◽  
Suggested Approach ◽  
Ka Band ◽  
Retrieval Error ◽  
Range Resolution ◽  
Retrieval Errors ◽  
The Difference ◽  
Radar Calibration ◽  
In The Beginning

Abstract An approach is suggested to retrieve low-resolution rainfall rate profiles and layer-averaged rainfall rates, Ra, from radar reflectivity measurements made by vertically pointing Ka-band radars. This approach is based on the effects of attenuation of radar signals in rain and takes advantage of the nearly linear relation between specific attenuation and rainfall rate at Ka-band frequencies. The variability of this relation due to temperature, details of raindrop size distributions, and the nature of rain (convective versus stratiform) is rather small (∼10%) and contributes little to errors in rainfall rate retrievals. The main contribution to the retrieval errors comes from the uncertainty of the difference in the nonattenuated radar reflectivities in the beginning and the end of the range resolution interval. For 2- and 1-dB uncertainties in this difference, the retrieval errors due to this main contribution are less than 34% and 17%, correspondingly, for rains with Ra ≈ 10 mm h−1 at a 1-km resolution interval. The heavier rain rates are retrieved with a better accuracy since this retrieval error contribution is proportional to 1/Ra. The retrieval accuracy can also be improved but at the expense of more coarse vertical resolutions of retrievals since the main retrieval error contribution is also proportional to the reciprocal of the resolution interval. The Mie scattering effects at Ka band results in less variability in nonattenuated reflectivities (cf. lower radar frequencies), which aids the suggested approach. Given that radar receivers are not saturated, the rainfall rates can be retrieved using cloud radars that were originally designed for measuring only nonprecipitating and weakly precipitating clouds. An important advantage of the attenuation-based retrievals of rainfall is that absolute radar calibration is not required. The inclusion of rainfall information will improve the characterization of the atmospheric column obtained with such radars used for climate research. The applications of the suggested approach are illustrated using the vertically pointing Ka-band radar measurements made during a field experiment in southern Florida. The retrieval results are in good agreement with surface estimates of rainfall rates.

scholarly journals Characteristic Raindrop Size Retrievals from Measurements of Differences in Vertical Doppler Velocities at Ka- and W-Band Radar Frequencies

2017 ◽  
Vol 34 (1) ◽  
pp. 65-71 ◽  
Author(s):  
Sergey Y. Matrosov
Keyword(s):  
Great Plains ◽  
Doppler Velocity ◽  
Rain Event ◽  
Ka Band ◽  
W Band ◽  
The Difference ◽  
Raindrop Size ◽  
Radar Calibration ◽  
Drop Size Distributions ◽  
Mean Differences

AbstractA Ka-band (~35 GHz) and W-band (~94 GHz) radar approach to retrieve profiles of characteristic raindrop sizes, such as mean mass-weighted drop diameters Dm, from measurements of the difference in the mean vertical Doppler velocities (DDV) is analyzed. This retrieval approach is insensitive to radar calibration errors, vertical air motions, and attenuation effects. The Dm–DDV relations are derived using long-term measurements of drop size distributions (DSDs) from different observational sites and do not assume a functional DSD shape. Unambiguous retrievals using this approach are shown to be available in the Dm range of approximately 0.5–2 mm, with average uncertainties of around 21%. Potential retrieval ambiguities occurring when larger drop populations exist can be avoided by using a Ka-band vertical Doppler velocity threshold. The performance of the retrievals is illustrated using a long predominantly stratiform rain event observed at the Atmospheric Radiation Measurement (ARM) Southern Great Plains site. An intercomparison of DDV-based estimates of characteristic raindrop sizes with independent estimates available from ground-based disdrometer measurements reveal good agreement, with a correlation coefficient of 0.88, and mean differences between radar and disdrometer-based Dm of approximately 14% for the entire range of unambiguous retrievals. The Ka–W-band DDV method to retrieve mean mass-weighted drop sizes is applicable to measurements from new dual-wavelength ARM cloud radars that are being deployed at a variety of observational facilities. An illustration for the retrievals at the Oliktok Point ARM facility is also given.

scholarly journals Characterization of affine ruled surfaces

1997 ◽  
Vol 39 (1) ◽  
pp. 17-20 ◽  
Author(s):  
Włodzimierz Jelonek
Keyword(s):  
Shape Operator ◽  
Ruled Surfaces ◽  
Affine Sphere ◽  
Affine Surface ◽  
Codazzi Tensor ◽  
Difference Tensor ◽  
The Difference ◽  
In The Beginning ◽  
Affine Metric

The aim of this paper is to give certain conditions characterizing ruled affine surfaces in terms of the Blaschke structure (∇, h, S) induced on a surface (M, f) in ℝ3. The investigation of affine ruled surfaces was started by W. Blaschke in the beginning of our century (see [1]). The description of affine ruled surfaces can be also found in the book [11], [3] and [7]. Ruled extremal surfaces are described in [9]. We show in the present paper that a shape operator S is a Codazzi tensor with respect to the Levi-Civita connection ∇ of affine metric h if and only if (M, f) is an affine sphere or a ruled surface. Affine surfaces with ∇S = 0 are described in [2] (see also [4]). We also show that a surface which is not an affine sphere is ruled iff im(S - HI) =ker(S - HI) and ket(S - HI) ⊂ ker dH. Finally we prove that an affine surface with indefinite affine metric is a ruled affine sphere if and only if the difference tensor K is a Codazzi tensor with respect to ∇.

The Influence of a Gonadotrophin on the Seasonal Changes in the Testis and Deferent Duct of the Chaffinch (Fringilla coelebs)

1949 ◽  
Vol s3-90 (9) ◽  
pp. 1-11
Author(s):  
J. W. SLUITER ◽  
G. J. van OORDT
Keyword(s):  
Interstitial Cells ◽  
Seminiferous Tubules ◽  
Control Bird ◽  
Interstitial Tissue ◽  
Fringilla Coelebs ◽  
Large Numbers ◽  
Different Seasons ◽  
The Difference ◽  
In The Beginning ◽  
Progressive Stage

1. Male chaffinches (Fringilla coelebs) were treated with gestyl, a gonadotrophin prepared from pregnant mare serum, in different seasons; using different techniques their testes and deferent ducts were histologically studied after autopsy on 11 August, 30 November, 28 January, and 5 May. 2. After Champy-fixation and Altmann-staining two types of interstitial cells can be distinguished in the intertubular tissue of sexually active chaffinches: lipoid cells. (= Leydig cells) and secretion cells. 3. Results of gestyl-administration: In summer- and winter-birds (PI. I) whose testes are in the resting stage, the testis-tubule diameter shows a strong enlargement, which is partly due to the plasma of the cells being distinctly inflated; spermatogenesis does not take place. In the intertubular tissue lipoid and secretion cells appear in abnormally large numbers. In 10 days the deferent ducts pass over from the quiescent into the fully-activated stage. In spring-birds (Pl. III), being in the reproductive stage, the administration of gestyl has practically no effect. In this stage the intertubular tissue also contains both lipoid and secretion cells. 4. From the results mentioned under 3, and the fact that in the control bird of 28 January, being in the beginning of the progressive stage (Pl. II), many lipoid cells were found, whereas its deferent ducts were still quiescent, it is concluded that only the secretion cells produce the male sex-hormone. The lipoid cells, which amongst others contain cholesterol, possess only a trophic function. 5. The difference in reaction of the seminiferous tubules of birds to chorionic and hypophyseal gonadotrophins as well as the function of the interstitial cells are discussed. Most opinions on the last-mentioned subject are not sufficiently well founded, as the investigators used routine techniques only for the cytological investigation of the interstitial tissue.

scholarly journals Characterisation of the artificial neural network CiPS for cirrus cloud remote sensing with MSG/SEVIRI

2017 ◽  
Vol 10 (11) ◽  
pp. 4317-4339 ◽  
Author(s):  
Johan Strandgren ◽  
Jennifer Fricker ◽  
Luca Bugliaro
Keyword(s):  
Remote Sensing ◽  
Optical Thickness ◽  
Cirrus Clouds ◽  
Cirrus Cloud ◽  
Retrieval Error ◽  
Water Path ◽  
Retrieval Accuracy ◽  
Ice Water Path ◽  
Retrieval Errors ◽  
Ice Water

Abstract. Cirrus clouds remain one of the key uncertainties in atmospheric research. To better understand the properties and physical processes of cirrus clouds, accurate large-scale observations from satellites are required. Artificial neural networks (ANNs) have proved to be a useful tool for cirrus cloud remote sensing. Since physics is not modelled explicitly in ANNs, a thorough characterisation of the networks is necessary. In this paper the CiPS (Cirrus Properties from SEVIRI) algorithm is characterised using the space-borne lidar CALIOP. CiPS is composed of a set of ANNs for the cirrus cloud detection, opacity identification and the corresponding cloud top height, ice optical thickness and ice water path retrieval from the imager SEVIRI aboard the geostationary Meteosat Second Generation satellites. First, the retrieval accuracy is characterised with respect to different land surface types. The retrieval works best over water and vegetated surfaces, whereas a surface covered by permanent snow and ice or barren reduces the cirrus detection ability and increases the retrieval errors for the ice optical thickness and ice water path if the cirrus cloud is thin (optical thickness less than approx. 0.3). Second, the retrieval accuracy is characterised with respect to the vertical arrangement of liquid, ice clouds and aerosol layers as derived from CALIOP lidar data. The CiPS retrievals show little interference from liquid water clouds and aerosol layers below an observed cirrus cloud. A liquid water cloud vertically close or adjacent to the cirrus clearly increases the average retrieval errors for the optical thickness and ice water path, respectively, only for thin cirrus clouds with an optical thickness below 0.3 or ice water path below 5.0 g m−2. For the cloud top height retrieval, only aerosol layers affect the retrieval error, with an increased positive bias when the cirrus is at low altitudes. Third, the CiPS retrieval error is characterised with respect to the properties of the investigated cirrus cloud (ice optical thickness and cloud top height). On average CiPS can retrieve the cirrus cloud top height with a relative error around 8 % and no bias and the ice optical thickness with a relative error around 50 % and bias around ±10 % for the most common combinations of cloud top height and ice optical thickness. Similarities with physically based retrieval methods are evident, which implies that even though the retrieval methods differ in the implementation of physics in the model, the retrievals behave similarly due to physical constraints. Finally, we also show that the ANN retrievals have a low sensitivity to radiometric noise in the SEVIRI observations. For optical thickness and ice water path the relative uncertainty due to noise is less than 10 % down to sub-visual cirrus. For the cloud top height retrieval the uncertainty due to noise is around 100 m for all cloud top heights.

Urethane Energy Absorbers for Automobile Bumpers

1973 ◽  
Vol 46 (4) ◽  
pp. 843-861 ◽  
Author(s):  
P. A. Weller
Keyword(s):  
High Efficiency ◽  
Current Model ◽  
Test Device ◽  
Microcellular Foam ◽  
Real Thing ◽  
Suggested Approach ◽  
Current Specification ◽  
The Government ◽  
Energy Absorbers ◽  
In The Beginning

Abstract It is believed that the concepts and data presented here are not only useful for the design and application of urethane foam for bumpers, but demonstrate the inherent fitness of the material for this purpose. To review quickly the factors listed in the beginning of the paper: 1. Urethane-faced bumpers will not only prevent damage to the bumper or vehicle, but will eliminate or minimize damage to the object impacted. 2. Repeated tests at severe overloads have demonstrated the recoverability of the foam after repeated impacts. 3. High hysteresis of urethane results in minimum rebound. 4. The material is velocity responsive within the specification range. 5. A wide variety of usable arrangements plus ready moldability provide considerable styling freedom. 6. Temperature compensation features assure designable performance consistency. 7. High efficiency or form factor is achievable, resulting in minimum force and stroke. 8. No maintenance is required. 9. Urethane microcellular foam is among the lower cost plastic materials on a per pound basis. Low densities and discreet placement can result in very competitive systems. Steel stroking bumpers are designed to ward off blows with emphasis on protection of the vehicle on which they are mounted. As a result, they present a far more hostile motoring environment than ever before for anything or anyone except another similar bumper. Urethane bumpers have a great potential for creating a far less hostile environment for everyone and everything, including fronts and rears of current vehicles, sides of all vehicles, other objects, pedestrians, and occupants. The current specification severely inhibits the realization of that potential. Doing anything about it is no easy matter since it could easily lead into a specification of horrendous complexity. However, following is one suggested approach. In testing for occupant protection, a manikin or dummy is selected as a representative test device. It is by no means truly interchangeable with the real thing or all situations, but does provide a firm and representative means for reasonable evaluation and standardization. In like manner, it would be possible to select a reasonably typical front or rear current-model configuration to serve as a representative test device on the face of the pendulum, and simply specify “no damage to the test device” rather than “no contact to specified planes”. A manufacturer could be contracted with by the government to produce identical test devices for all who wished to run such tests. Such a specification could be amended to the current specification as an alternate, rather than attempting to revise what is already an excellent document for the steel stroking bumper.

scholarly journals Low-Cost Ka-Band Cloud Radar System for Distributed Measurements within the Atmospheric Boundary Layer

2020 ◽  
Vol 12 (23) ◽  
pp. 3965
Author(s):  
Roberto Aguirre ◽  
Felipe Toledo ◽  
Rafael Rodríguez ◽  
Roberto Rondanelli ◽  
Nicolas Reyes ◽  
...  
Keyword(s):  
Continuous Wave ◽  
Low Cost ◽  
Medium Size ◽  
Physical Parameters ◽  
Mountain Range ◽  
Ka Band ◽  
Range Resolution ◽  
Cloud Radar ◽  
Marine Stratus ◽  
Application Fields

Radars are used to retrieve physical parameters related to clouds and fog. With these measurements, models can be developed for several application fields such as climate, agriculture, aviation, energy, and astronomy. In Chile, coastal fog and low marine stratus intersect the coastal topography, forming a thick fog essential to sustain coastal ecosystems. This phenomenon motivates the development of cloud radars to boost scientific research. In this article, we present the design of a Ka-band cloud radar and the experiments that prove its operation. The radar uses a frequency-modulated continuous-wave with a carrier frequency of 38 GHz. By using a drone and a commercial Lidar, we were able to verify that the radar can measure reflectivities in the order of −60 dBZ at 500 m of distance, with a range resolution of 20 m. The lower needed range coverage imposed by our case of study enabled a significant reduction of the instrument cost compared to existent alternatives. The portability and low-cost of the designed instrument enable its implementation in a distributed manner along the coastal mountain range, as well as its use in medium-size aerial vehicles or balloons to study higher layers. The main features, limitations, and possible improvements to the current instrument are discussed.

scholarly journals Historians, are Archeologists Your Siblings?

1995 ◽  
Vol 22 ◽  
pp. 369-408 ◽  
Author(s):  
Jan Vansina
Keyword(s):  
Good Reason ◽  
African History ◽  
Historical Reconstruction ◽  
Distinctive Features ◽  
Archaeological Material ◽  
The Past ◽  
History Of ◽  
The Difference ◽  
In The Beginning ◽  
Relative Scarcity

The historian of pre-nineteenth century Africa…cannot get far without the aid of archaeology.Nevertheless, historians have good reason to be cautious about historical generalisations by archaeologists and about their own use of archaeological material…: it would be a rash historian who totally accepted the conclusions of Garlake and Huffman with the same simple-minded trust as I myself accepted the conclusions of Summers and Robinson.In the beginning, historians of Africa put great store by archeology. Was its great time depth not one of the distinctive features of the history of Africa, a condition that cannot be put aside without seriously distorting the flavor of all its history? Did not the relative scarcity and the foreign authorship of most precolonial written records render archeological sources all the more precious? Did not history and archeology both deal with the reconstruction of human societies in the past? Was the difference between them not merely the result of a division of labor based on sources, so that historical reconstruction follows in time and flows from archeological reconstruction? Such considerations explain why the Journal of African History has regularly published regional archeological surveys in order to keep historians up to date.

The efficacy of reading using the physical response technique in second language learning

2016 ◽  
Vol 6 (11) ◽  
pp. 134 ◽  
Author(s):  
Maria Helena Lott Lage ◽  
Victor Hackett ◽  
William Leslie
Keyword(s):  
Second Language ◽  
Language Learning ◽  
Second Language Learning ◽  
Physical Response ◽  
The Difference ◽  
In The Beginning

Resumo: O objetivo desta experiência foi testar a eficácia da leitura no estágio inicial do aprendizado de uma segunda língua. A lição usada foi baseada na técnica Total Physical Response, de James J. Asher, e consistiu de 10 emissões diferentes de 1 palavra cada.Chegou-se à conclusão de que aqueles que possuíam um roteiro e puderam lê-lo durante a aula, obtiveram um resultado 33.58 melhor do que os que não leram.Uma segunda hipótese testada lidou com a ação versus a não-ação. A diferença nos resultados obtidos pelos grupos de ação versus os grupos de não-ação não chegou a ser significativa. Abstract: The purpose of this experiment was to test the efficiency of readng in the beginning stage of second language learning. The lesson we used was based on the Total Physical Response technique, and consisted of ten different one-word utterances.It was found that those who possessed a script and were able to read it during the lesson outperformed those who did not read by 33.58.A second hypothesis we tested dealt with acting versus non-acting. The difference in the results obtained by the acting groups versus those who did not act was found to be insignificant.

scholarly journals Synergetic use of millimeter- and centimeter-wavelength radars for retrievals of cloud and rainfall parameters

2010 ◽  
Vol 10 (7) ◽  
pp. 3321-3331 ◽  
Author(s):  
S. Y. Matrosov
Keyword(s):  
Liquid Water ◽  
Rain Rate ◽  
Wet Season ◽  
Liquid Water Path ◽  
Vertical Column ◽  
Suggested Approach ◽  
Ka Band ◽  
Water Path ◽  
Climate Research ◽  
W Band

Abstract. A remote sensing approach for simultaneous retrievals of cloud and rainfall parameters in the vertical column above the US Department of Energy's (DOE) Climate Research Facility at the Tropical Western Pacific (TWP) Darwin site in Australia is described. This approach uses vertically pointing measurements from a DOE Ka-band radar and scanning measurements from a nearby C-band radar pointing toward the TWP Darwin site. Rainfall retrieval constraints are provided by data from a surface impact disdrometer. The approach is applicable to stratiform precipitating cloud systems when a separation between the liquid hydrometeor layer, which contains rainfall and liquid water clouds, and the ice hydrometeor layer is provided by the radar bright band. Absolute C-band reflectivities and Ka-band vertical reflectivity gradients in the liquid layer are used for retrievals of the mean layer rain rate and cloud liquid water path (CLWP). C-band radar reflectivities are also used to estimate ice water path (IWP) in regions above the melting layer. The retrieval uncertainties of CLWP and IWP for typical stratiform precipitation systems are about 500–800 g m−2 (for CLWP) and a factor of 2 (for IWP). The CLWP retrieval uncertainties increase with rain rate, so retrievals for higher rain rates may be impractical. The expected uncertainties of layer mean rain rate retrievals are around 20%, which, in part, is due to constraints available from the disdrometer data. The applicability of the suggested approach is illustrated for two characteristic events observed at the TWP Darwin site during the wet season of 2007. A future deployment of W-band radars at the DOE tropical Climate Research Facilities can improve CLWP estimation accuracies and provide retrievals for a wider range of stratiform precipitating cloud events.

Sign in / Sign up

Export Citation Format

Share Document