scholarly journals High-Frequency Single-Board Doppler Minisodar for Precipitation Measurements. Part I: Rainfall and Hail

2005 ◽  
Vol 22 (4) ◽  
pp. 421-432
Author(s):  
Shixuan Pang ◽  
Hartmut Graßl
Keyword(s):  
High Frequency ◽  
Digital Signal ◽  
Rain Gauge ◽  
Refractive Indices ◽  
Subsequent Paper ◽  
Doppler Sodar ◽  
The Mean ◽  
Rain Events ◽  
Rain Rates ◽  
Good Agreement

Abstract A high-frequency Doppler sodar for precipitation measurements has been developed. Such a Doppler sodar (6–20 kHz) can almost always measure precipitation and turbulence spectra simultaneously. Therefore, the mean vertical wind and spectral broadening effects can be directly removed. As the acoustic refractive indices for ice and liquid water are almost the same, the acoustic retrieval of precipitation can also be applied to rain with small hail (e.g., diameter D < 10 mm) or large hail, but for the latter, neglecting the effects of different orientations and shapes of hailstones. The authors’ single-board minisodar is based on the digital signal processing (DSP) technique. The first prototype has been continuously operated at a coastal weather station since 25 October 2002. For stratiform rain events, the minisodar showed good agreement with a Joss–Waldvogel disdrometer and an optical rain gauge. However, for convective heavy showers, the minisodar always observed higher rain rates. The continuous, nonattended automatic operation of the minisodar has shown its capability for all kinds of precipitation measurements. The retrieval of precipitation rates for snow and graupel will be provided in a subsequent paper.

scholarly journals A comparison of rainfall measurements from multiple instruments

2013 ◽  
Vol 6 (7) ◽  
pp. 1585-1595 ◽  
Author(s):  
X. C. Liu ◽  
T. C. Gao ◽  
L. Liu
Keyword(s):  
Rain Rate ◽  
Rain Gauge ◽  
Measurement Range ◽  
Light Rain ◽  
Large Size ◽  
Drop Size Distributions ◽  
Rain Rates ◽  
Effect Of Light ◽  
Good Agreement

Abstract. Simultaneous observations of rainfall collected by a tipping bucket rain gauge (TBRG), a weighing rain gauge (WRG), an optical rain gauge (ORG), a present weather detector (PWD), a Joss–Waldvogel disdrometer (JWD), and a 2-D video disdrometer (2DVD) during January to October 2012 were analyzed to evaluate how accurately they measure rainfall and drop size distributions (DSDs). For the long-term observations, there were different discrepancies in rain amounts from six instruments on the order of 0% to 27.7%. The TBRG, WRG, and ORG have a good agreement, while the PWD and 2DVD record higher and the JWD lower rain rates when R > 20 mm h−1, the ORG agrees well with JWD and 2DVD, while the TBRG records higher and the WRG lower rain rates when R > 20 mm h−1. Compared with the TBRG and WRG, optical and impact instruments can measure the rain rate accurately in the light rain. The overall DSDs of JWD and 2DVD agree well with each other, except for the small raindrops (D < 1 mm). JWD can measure more moderate-size raindrops (0.3 mm < D < 1.5 mm) than 2DVD, but 2DVD can measure more small-size raindrops (D < 0.3 mm). 2DVD has a larger measurement range; more overall raindrops can be measured by 2DVD than by JWD in different rain rate regimes. But small raindrops might be underestimated by 2DVD when R > 15 mm h−1. The small raindrops tend to be omitted in the more large-size raindrops due to the shadow effect of light. Therefore, the measurement accuracy of small raindrops in the heavy rainfall from 2DVD should be handled carefully.

scholarly journals Ground Validation for the Tropical Rainfall Measuring Mission (TRMM)

2005 ◽  
Vol 22 (4) ◽  
pp. 365-380 ◽  
Author(s):  
David B. Wolff ◽  
D. A. Marks ◽  
E. Amitai ◽  
D. S. Silberstein ◽  
B. L. Fisher ◽  
...  
Keyword(s):  
Tropical Rainfall Measuring Mission ◽  
Rain Gauge ◽  
Marshall Islands ◽  
Error Statistics ◽  
Tropical Rainfall ◽  
Nasa Goddard Space ◽  
Ground Validation ◽  
Microwave Imager ◽  
Rain Rates ◽  
Good Agreement

Abstract An overview of the Tropical Rainfall Measuring Mission (TRMM) Ground Validation (GV) Program is presented. This ground validation (GV) program is based at NASA Goddard Space Flight Center in Greenbelt, Maryland, and is responsible for processing several TRMM science products for validating space-based rain estimates from the TRMM satellite. These products include gauge rain rates, and radar-estimated rain intensities, type, and accumulations, from four primary validation sites (Kwajalein Atoll, Republic of the Marshall Islands; Melbourne, Florida; Houston, Texas; and Darwin, Australia). Site descriptions of rain gauge networks and operational weather radar configurations are presented together with the unique processing methodologies employed within the Ground Validation System (GVS) software packages. Rainfall intensity estimates are derived using the Window Probability Matching Method (WPMM) and then integrated over specified time scales. Error statistics from both dependent and independent validation techniques show good agreement between gauge-measured and radar-estimated rainfall. A comparison of the NASA GV products and those developed independently by the University of Washington for a subset of data from the Kwajalein Atoll site also shows good agreement. A comparison of NASA GV rain intensities to satellite retrievals from the TRMM Microwave Imager (TMI), precipitation radar (PR), and Combined (COM) algorithms is presented, and it is shown that the GV and satellite estimates agree quite well over the open ocean.

scholarly journals Correction of Radar Reflectivity and Differential Reflectivity for Rain Attenuation at X Band. Part II: Evaluation and Application

2005 ◽  
Vol 22 (11) ◽  
pp. 1633-1655 ◽  
Author(s):  
S-G. Park ◽  
M. Maki ◽  
K. Iwanami ◽  
V. N. Bringi ◽  
V. Chandrasekar
Keyword(s):  
Drop Size ◽  
Earth Science ◽  
Radar Data ◽  
Rain Gauge ◽  
Radar Rainfall ◽  
X Band ◽  
Rain Events ◽  
Differential Reflectivity ◽  
Rainfall Estimates ◽  
Good Agreement

Abstract In this paper, the attenuation-correction methodology presented in Part I is applied to radar measurements observed by the multiparameter radar at the X-band wavelength (MP-X) of the National Research Institute for Earth Science and Disaster Prevention (NIED), and is evaluated by comparison with scattering simulations using ground-based disdrometer data. Further, effects of attenuation on the estimation of rainfall amounts and drop size distribution parameters are also investigated. The joint variability of the corrected reflectivity and differential reflectivity show good agreement with scattering simulations. In addition, specific attenuation and differential attenuation, which are derived in the correction procedure, show good agreement with scattering simulations. In addition, a composite rainfall-rate algorithm is proposed and evaluated by comparison with eight gauges. The radar-rainfall estimates from the uncorrected (or observed) ZH produce severe underestimation, even at short ranges from the radar and for stratiform rain events. On the contrary, the reflectivity-based rainfall estimates from the attenuation-corrected ZH does not show such severe underestimation and does show better agreement with rain gauge measurements. More accurate rainfall amounts can be obtained from a simple composite algorithm based on specific differential phase KDP, with the R(ZH_cor) estimates being used for low rainfall rates (KDP ≤ 0.3° km−1 or ZH_cor ≤ 35 dBZ). This improvement in accuracy of rainfall estimation based on KDP is a result of the insensitivity of the rainfall algorithm to natural variations of drop size distributions (DSDs). The ZH, ZDR, and KDP data are also used to infer the parameters (median volume diameter D0 and normalized intercept parameter Nw) of a normalized gamma DSD. The retrieval of D0 and Nw from the corrected radar data show good agreement with those from disdrometer data in terms of the respective relative frequency histograms. The results of this study demonstrate that high-quality hydrometeorological information on rain events such as rainfall amounts and DSDs can be derived from X-band polarimetric radars.

scholarly journals A TRMM-Calibrated infrared technique for rainfall estimation: application on rain events over eastern Mediterranean

2006 ◽  
Vol 7 ◽  
pp. 181-188 ◽  
Author(s):  
H. Feidas ◽  
G. Kokolatos ◽  
A. Negri ◽  
M. Manyin ◽  
N. Chrysoulakis
Keyword(s):  
Eastern Mediterranean ◽  
Regional Scale ◽  
Tropical Rainfall Measuring Mission ◽  
Rain Gauge ◽  
Tropical Areas ◽  
Trmm Precipitation ◽  
Remote Sensing Techniques ◽  
Rain Events ◽  
Rain Rates ◽  
Rain Gauge Network

Abstract. The aim is to evaluate the use of a satellite infrared (IR) technique for estimating rainfall over the eastern Mediterranean. The Convective-Stratiform Technique (CST), calibrated by coincident, physically retrieved rain rates from the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR), is applied over the Eastern Mediterranean for four rain events during the six month period of October 2004 to March 2005. Estimates from this technique are verified over a rain gauge network for different time scales. Results show that PR observations can be applied to improve IR-based techniques significantly in the conditions of a regional scale area by selecting adequate calibration areas and periods. They reveal, however, the limitations of infrared remote sensing techniques, originally developed for tropical areas, when applied to precipitation retrievals in mid-latitudes.

scholarly journals Dual-polarization radar rainfall estimation in Korea according to raindrop shapes obtained by using a 2-D video disdrometer

2016 ◽  
Vol 9 (8) ◽  
pp. 3863-3878 ◽  
Author(s):  
Hae-Lim Kim ◽  
Mi-Kyung Suk ◽  
Hye-Sook Park ◽  
Gyu-Won Lee ◽  
Jeong-Seok Ko
Keyword(s):  
Korean Peninsula ◽  
Ground Truth ◽  
Rain Gauge ◽  
Dual Polarization ◽  
Radar Rainfall ◽  
Axis Ratio ◽  
Raindrop Size Distribution ◽  
The Mean ◽  
Rain Rates ◽  
Differential Reflectivity

Abstract. Polarimetric measurements are sensitive to the sizes, concentrations, orientations, and shapes of raindrops. Thus, rainfall rates calculated from polarimetric radar are influenced by the raindrop shapes and canting. The mean raindrop shape can be obtained from long-term raindrop size distribution (DSD) observations, and the shapes of raindrops can play an important role in polarimetric rainfall algorithms based on differential reflectivity (ZDR) and specific differential phase (KDP). However, the mean raindrop shape is associated with the variation of the DSD, which can change depending on precipitation types and climatic regimes. Furthermore, these relationships have not been studied extensively on the Korean Peninsula. In this study, we present a method to find optimal polarimetric rainfall algorithms for the Korean Peninsula by using data provided by both a two-dimensional video disdrometer (2DVD) and the Bislsan S-band dual-polarization radar. First, a new axis-ratio relation was developed to improve radar rainfall estimations. Second, polarimetric rainfall algorithms were derived by using different axis-ratio relations. The rain gauge data were used to represent the ground truth situation, and the estimated radar-point hourly mean rain rates obtained from the different polarimetric rainfall algorithms were compared with the hourly rain rates measured by a rain gauge. The daily calibration biases of horizontal reflectivity (ZH) and differential reflectivity (ZDR) were calculated by comparing ZH and ZDR radar measurements with the same parameters simulated by the 2DVD. Overall, the derived new axis ratio was similar to the existing axis ratio except for both small particles (≤ 2 mm) and large particles (≥ 5.5 mm). The shapes of raindrops obtained by the new axis-ratio relation carried out with the 2DVD were more oblate than the shapes obtained by the existing relations. The combined polarimetric rainfall relations using ZDR and KDP were more efficient than the single-parameter rainfall relation for estimated 2DVD rainfall; however, the R(ZH, ZDR) algorithm showed the best performance for radar rainfall estimations, because the rainfall events used in the analysis consisted mainly of weak precipitation and KDP is relatively noisy at lower rain rates (≤ 10 mm h−1). Some of the polarimetric rainfall algorithms can be further improved by new axis-ratio relations.

scholarly journals A Robust Error-Based Rain Estimation Method for Polarimetric Radar. Part II: Case Study

2012 ◽  
Vol 51 (9) ◽  
pp. 1702-1713 ◽  
Author(s):  
Acacia S. Pepler ◽  
Peter T. May
Keyword(s):  
Estimation Method ◽  
Heavy Rain ◽  
Rain Gauge ◽  
Polarimetric Radar ◽  
Composite Methods ◽  
A New Technique ◽  
Rain Events ◽  
Radar Part ◽  
Rain Rates

AbstractRainfall estimation using polarimetric radar involves the combination of a number of estimators with differing error characteristics to optimize rainfall estimates at all rain rates. In Part I of this paper, a new technique for such combinations was proposed that weights algorithms by the inverse of their theoretical errors. In this paper, the derived algorithms are validated using the “CP2” polarimetric radar in Queensland, Australia, and a collocated rain gauge network for two heavy-rain events during November 2008 and a larger statistical analysis that is based on data from between 2007 and 2009. Use of a weighted combination of polarimetric algorithms offers some improvement over composite methods that are based on decision-tree logic, particularly at moderate to high rain rates and during severe-thunderstorm events.

scholarly journals The high-frequency resistance of superconducting tin

1940 ◽  
Vol 176 (967) ◽  
pp. 522-533 ◽  
Keyword(s):  
High Frequency ◽  
Skin Effect ◽  
Wave Length ◽  
Low Frequency ◽  
Mean Free Path ◽  
Low Frequencies ◽  
The Mean ◽  
Absolute Measurements ◽  
Eddy Current Heating ◽  
Good Agreement

The high-frequency resistance of tin in the superconducting state was measured at a wave-length of 20.5 cm. by a calorimetric method based on the principle of eddy-current heating. It was found that the resistance decreases gradually when the temperature falls below the transition point in contrast to the sudden drop in resistance peculiar to direct currents. An explanation of such a behaviour is given based on the assumption of the simultaneous presence of normal and superconducting electrons. Good agreement between theory and experiment was found. Absolute measurements of the conductivity in the normal state at low temperatures with both high and low frequencies were carried out, and it was found that at the temperature of liquid helium the conductivity for high frequency is considerably lower than for low frequency. This behaviour is possibly due to the fact that the mean free path of the electrons becomes larger than the penetration depth due to skin effect under the conditions of high conductivity and high frequency.

scholarly journals Thermotropic, refracting and thermo-optical properties in three homologs of 4-n-alkyl-4’-cyanobiphenyls

2015 ◽  
Vol 55 (1) ◽  
Author(s):  
Arif Nesrullajev
Keyword(s):  
Field Model ◽  
Internal Field ◽  
Refractive Indices ◽  
Temperature Behaviour ◽  
Isotropic Liquid ◽  
Smectic A ◽  
The Mean ◽  
Geometry Parameter ◽  
Average Polarizability ◽  
Good Agreement

Investigations of temperature behaviour of the mean refractive index n, ordinary no and extraordinary ne refractive indices, and birefringence Δn have been carried out for three homologues of 4-n-alkyl-4’-cyanobiphenyls (n = 8, 10, 12). The principal polarizabilities α0 and αe, effective geometry parameter αeg and average polarizability αave have been calculated using the isotropic internal field model (Vuks approach). Temperature behaviour of the order parameter in regions of the smectic A–nematic, nematic–isotropic liquid and smectic A–isotropic liquid is discussed. All of the optical and orientational parameters, which have been obtained in this work, are in good agreement with the theoretical approach.

scholarly journals The Varying Response of Microwave Signatures to Different Types of Overland Rainfall Found over the Korean Peninsula

2010 ◽  
Vol 27 (4) ◽  
pp. 785-792 ◽  
Author(s):  
Eun-Kyoung Seo ◽  
Guosheng Liu ◽  
Myoung-Seok Suh ◽  
Byung-Ju Sohn
Keyword(s):  
Korean Peninsula ◽  
Tropical Rainfall Measuring Mission ◽  
Rain Gauge ◽  
Additional Information ◽  
Ice Particles ◽  
Systematic Biases ◽  
Microwave Imager ◽  
Rain Events ◽  
Microwave Signatures ◽  
Rain Rates

Abstract The Tropical Rainfall Measuring Mission (TRMM) precipitation radar and ground rain measurements were used to investigate the performance of the TRMM Microwave Imager (TMI) land algorithm. In particular, data from a dense network of rain gauges being operated over the Korean Peninsula were utilized. To retrieve information related to the rainfall rate over land, the TRMM land algorithm relies mainly on brightness temperature TB depression at vertically polarized 85(V) GHz because of scattering by ice particles. It refers to the relationships between 85(V)-GHz TBs and rain rates in its predefined database. By comparing the TMI rain rates with the surface rain gauge and TRMM radar measurements, it was found that there are a variety of relationships between 85(V)-GHz TBs and rainfall rates resulting from the various types of precipitating clouds. The TMI land algorithm, therefore, could not resolve some raining clouds such as warm clouds as well as cold clouds having small amounts of ice particles above the rain layer. The rainfall amounts for those missed rain events are significant. As a result, rain rates produced by the land algorithm show systematic biases, which are a function of raining cloud types. Meanwhile, it is found that the 37-GHz TMI channels contain additional information on surface rain; the uncertainties in retrieving rain rates from TBs at TMI frequencies can be reduced up to 11% if all polarized 37- and 85-GHz TBs are used as predictors.

scholarly journals Sea surface freshening inferred from SMOS and ARGO salinity: impact of rain

Ocean Science ◽  
2013 ◽  
Vol 9 (1) ◽  
pp. 183-192 ◽  
Author(s):  
J. Boutin ◽  
N. Martin ◽  
G. Reverdin ◽  
X. Yin ◽  
F. Gaillard
Keyword(s):  
European Space Agency ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Surface Salinity ◽  
Salinity Stratification ◽  
Space Agency ◽  
The Mean ◽  
Microwave Imager ◽  
Rain Events ◽  
Rain Rates

Abstract. The sea surface salinity (SSS) measured from space by the Soil Moisture and Ocean Salinity (SMOS) mission has recently been revisited by the European Space Agency first campaign reprocessing. We show that, with respect to the previous version, biases close to land and ice greatly decrease. The accuracy of SMOS SSS averaged over 10 days, 100 × 100 km2 in the open ocean and estimated by comparison to ARGO (Array for Real-Time Geostrophic Oceanography) SSS is on the order of 0.3–0.4 in tropical and subtropical regions and 0.5 in a cold region. The averaged negative SSS bias (−0.1) observed in the tropical Pacific Ocean between 5° N and 15° N, relatively to other regions, is suppressed when SMOS observations concomitant with rain events, as detected from SSM/Is (Special Sensor Microwave Imager) rain rates, are removed from the SMOS–ARGO comparisons. The SMOS freshening is linearly correlated to SSM/Is rain rate with a slope estimated to −0.14 mm−1 h, after correction for rain atmospheric contribution. This tendency is the signature of the temporal SSS variability between the time of SMOS and ARGO measurements linked to rain variability and of the vertical salinity stratification between the first centimeter of the sea surface layer sampled by SMOS and the 5 m depth sampled by ARGO. However, given that the whole set of collocations includes situations with ARGO measurements concomitant with rain events collocated with SMOS measurements under no rain, the mean −0.1 bias and the negative skewness of the statistical distribution of SMOS minus ARGO SSS difference are very likely the mean signature of the vertical salinity stratification. In the future, the analysis of ongoing in situ salinity measurements in the top 50 cm of the sea surface and of Aquarius satellite SSS are expected to provide complementary information about the sea surface salinity stratification.

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