Papers by Marios Anagnostou
This paper investigates a technique for estimating Drop Size Distribution (DSD) model parameters ... more This paper investigates a technique for estimating Drop Size Distribution (DSD) model parameters from attenuation-corrected X-band radar data. The DSD model is assumed to be a three parameter "normalized" gamma distribution. Closely matched X-band (XPOL) and S-band (S-POL) dualpolarization radar measurements collected during the International H2O Experiment (IHOP) are used to assess the X-band based DSD retrieval. The goal of this comparison is to understand the relative accuracy of X-band DSD retrievals relative to those based on S-(2.8 GHz) band radar observation. The study further provides limited evaluation of the X-band DSD estimates using in-situ 2D-video disdrometer measurements available from the Ionian Sea Rainfall Experiment (ISREX).
IEEE Transactions on Geoscience and Remote Sensing, 2008
Rainfall on the sea surface generates a loud and distinctive sound underwater. This sound propaga... more Rainfall on the sea surface generates a loud and distinctive sound underwater. This sound propagates downward and attenuates, producing an effective listening area or an equivalent "catchment basin" for a listening device that is a function of depth and frequency. Acoustical measurements of rainfall are reported from four passive aquatic listeners (PALs) at 60-, 200-, 1000-, and 2000-m depths from a mooring in the Ionian Sea off the southwestern coast of Greece (37N, 21.5E) from January to April 2004. These measurements are compared to colocated high-resolution X-band dual-polarization (XPOL) radar rainfall measurements. The XPOL radar reports the spatial distribution of rainfall variability over the listening areas of the PALs. Four quality-controlled rainfall events, including drizzle, squall line, and heavy rainfall, are presented in this study. The radar rainfall is spatially averaged over the mooring and compared with the four different acoustic measurements at different depths. To understand the issue of spatial averaging, quantitative comparisons are presented, showing a high correlation between the acoustic measurements and the area-averaged radar estimates at corresponding resolutions.
IEEE Transactions on Geoscience and Remote Sensing, 2008
Rainfall on the sea surface generates a loud and distinctive sound underwater. This sound propaga... more Rainfall on the sea surface generates a loud and distinctive sound underwater. This sound propagates downward and attenuates, producing an effective listening area or an equivalent "catchment basin" for a listening device that is a function of depth and frequency. Acoustical measurements of rainfall are reported from four passive aquatic listeners (PALs) at 60-, 200-, 1000-, and 2000-m depths from a mooring in the Ionian Sea off the southwestern coast of Greece (37N, 21.5E) from January to April 2004. These measurements are compared to colocated high-resolution X-band dual-polarization (XPOL) radar rainfall measurements. The XPOL radar reports the spatial distribution of rainfall variability over the listening areas of the PALs. Four quality-controlled rainfall events, including drizzle, squall line, and heavy rainfall, are presented in this study. The radar rainfall is spatially averaged over the mooring and compared with the four different acoustic measurements at different depths. To understand the issue of spatial averaging, quantitative comparisons are presented, showing a high correlation between the acoustic measurements and the area-averaged radar estimates at corresponding resolutions.
IEEE Transactions on Geoscience and Remote Sensing, 2008
Recent research has demonstrated the value of polarimetric measurements for the correction of rai... more Recent research has demonstrated the value of polarimetric measurements for the correction of rain-path attenuation at X-band radar frequency and the estimation of rain parameters including drop size distributions (DSD). The issue this study is concerned with is to what degree uncertainties in attenuation correction can affect the estimation of DSD. Since attenuation correction uncertainty enhances with rain path our
Journal of Hydrometeorology, 2004
An improved algorithm based on the self-consistent principle for rain attenuation correction of r... more An improved algorithm based on the self-consistent principle for rain attenuation correction of reflectivity Z H and differential reflectivity Z DR are presented for X-band radar. The proposed algorithm calculates the optimum coefficients for the relation between the specific attenuation coefficient and the specific differential phase, every 1 km along a slant range. The attenuation-corrected Z DR is calculated from reflectivity at horizontal polarization and from reflectivity at vertical polarization after attenuation correction. The improved rain attenuation correction algorithm is applied to the range-height indicator (RHI) scans as well as the plan position indicator (PPI) volume scan data observed by X-band wavelength (MP-X) radar, as operated by the National Research Institute for Earth Science and Disaster Prevention (NIED) in Japan. The corrected Z H and Z DR values are in good agreement with those calculated from the drop size distribution (DSD) measured by disdrometers.
IEEE Geoscience and Remote Sensing Letters, 2007
This letter evaluates the consistency of rainfall drop size distribution (DSD) parameters that we... more This letter evaluates the consistency of rainfall drop size distribution (DSD) parameters that were estimated from attenuation-corrected X-band dual-polarization (XPOL) radar measurements with estimates from a colocated S-band dual-polarization radar (S-Pol). The DSD retrieval technique uses reflectivity and differential reflectivity, and a constrained relationship to estimate the three parameters of a ldquonormalizedrdquo gamma distribution model. The more definitive S-Pol DSD parameter estimates are used as a reference to assess the performance of the corresponding XPOL estimates for different rain-path attenuation values. Results show that XPOL attenuation-corrected profiles can provide rainfall DSD estimations that are consistent to an S-band dual-polarization radar, even in cases of moderate to high rain-path attenuation.
Journal of Hydrology, 2010
Flash flood Mountainous basins Bright band Vertical profile of reflectivity (VPR)
IEEE Transactions on Geoscience and Remote Sensing, 2006
The accuracy of attenuation correction for X-band reflectivity (Z H ) and differential reflectivi... more The accuracy of attenuation correction for X-band reflectivity (Z H ) and differential reflectivity (Z DR ) measurements in rainfall is analyzed using coincident X-band and S-band polarimetric radar observations collected during the International H 2 O Project in the period of May-June 2002 at northwestern Oklahoma. Two distinct attenuation correction techniques that use the differential propagation phase shift (Φ DP ) information, which is not a power-dependent measurement, as a means to provide independent estimates of path-integrated attenuation are assessed. The study is facilitated by nonattenuated X-band Z H and Z DR profiles simulated based on raindrop size distribution parameters retrieved from matched multiparameter (Z H , Z DR , and K DP ) S-band observations. The major outcome of this assessment is that Φ DP -based attenuation correction for both techniques can reach almost unbiased measurements (within 5% mean relative error) and low random error (15-20% relative standard deviation). The study shows moderate differences in the error statistics of the evaluated techniques. The sensitivity of attenuation correction uncertainty with respect to the assumed variability in raindrops' oblateness-size relation and the noise in Φ DP measurement is also shown.
This study proposes investigation of new attenuation correction and microphysical retrieval metho... more This study proposes investigation of new attenuation correction and microphysical retrieval methods for X-band polarimetric radar (XPOL). It will concentrate on exploring the dependence of the retrieval on raindrop size distribution variability, and its sensitivity with respect to the selection of oblateness-size relation (or axial ratio) and maximum diameter limit. Variations in the assumed form of the raindrop axial ratio may result in significant biases in attenuation and microphysical retrievals. In addition, at this wavelength, resonance occurs for sizes larger than about 4 mm, and therefore several polarimetric variables exhibit non-monotone dependence on the drop diameter. An algorithm is developed and experimentally validated for retrieving DSD model parameters. The DSD model is assumed to be a three-parameter "normalized" gamma distribution. Coincidental and closely matched radar rays from non-attenuated (S-band) dual-polarization radar measurements and corresponding DSD retrievals are used to validate the proposed XPOL algorithm in terms of attenuation correction, as well as DSD parameter retrievals.
Recent research has demonstrated the value of polarimetric measurements for the correction of rai... more Recent research has demonstrated the value of polarimetric measurements for the correction of rain-path attenuation at X-band radar frequency and the estimation of rain parameters including drop size distributions (DSD). The issue this study is concerned with is to what degree uncertainties in attenuation correction can affect the estimation of DSD. Since attenuation correction uncertainty enhances with rain path our hypothesis is that DSD retrieval uncertainty at X-band may deteriorate with range. In this study we evaluate the relative accuracy of X-band DSD retrieval against DSD estimates from S- band radar observations and in-situ disdrometer spectra. We present comparisons of various techniques for estimating DSD model parameters from attenuation-corrected X-band dual- polarization radar data. Coincident X-band (XPOL) and S-band (S-Pol) dual-polarized radar measurements from the International H2O experiment (IHOP) as well as coincident X-band polarimetric radar (MP-X) measurements over disdrometer during a Typhoon storm case in Japan are used to assess the accuracy of the different DSD retrieval algorithms applied to X-band radar.
A large data set of rain drop size distribution (RSD) measurements collected with Joss-Waldvogel ... more A large data set of rain drop size distribution (RSD) measurements collected with Joss-Waldvogel (JWD) and 2D video disdrometers (2DVD) in UK, Athens, Japan and USA are analyzed. The objective of this work are manifold: i) show the differences of a wide climatological DSD-derived moments; ii) retrieve from this disdrometer data set the driving parameters of the normalized gamma RSD
It is well recognized that there exists a need for accurate prediction of precipitation, whether ... more It is well recognized that there exists a need for accurate prediction of precipitation, whether it is for improvement of flood warning systems, water system management, or groundwater recharge assessment . Weather radar has enabled us to improve our quantitative observations of precipitation in the field of radar hydrology. However, radar-based estimates of rainfall accumulation and/or rate are subject to numerous uncertainties. Some errors may arise due to the inherent complexity of the mechanical and electronic system of detection while others may be due to the complexity of the terrain. As a result, the relation between measured radar reflectivity and surface rainfall is highly complex and can be influenced by many factors . Even though it has been the subject of many studies, no satisfactory method has been developed to date for accurately estimating rainfall when high spatial and temporal resolution is required (Anagnostou and .
IEEE Transactions on Geoscience and Remote Sensing, 2006
The accuracy of attenuation correction for X-band reflectivity (Z H ) and differential reflectivi... more The accuracy of attenuation correction for X-band reflectivity (Z H ) and differential reflectivity (Z DR ) measurements in rainfall is analyzed using coincident X-band and S-band polarimetric radar observations collected during the International H 2 O Project in the period of May-June 2002 at northwestern Oklahoma. Two distinct attenuation correction techniques that use the differential propagation phase shift (Φ DP ) information, which is not a power-dependent measurement, as a means to provide independent estimates of path-integrated attenuation are assessed. The study is facilitated by nonattenuated X-band Z H and Z DR profiles simulated based on raindrop size distribution parameters retrieved from matched multiparameter (Z H , Z DR , and K DP ) S-band observations. The major outcome of this assessment is that Φ DP -based attenuation correction for both techniques can reach almost unbiased measurements (within 5% mean relative error) and low random error (15-20% relative standard deviation). The study shows moderate differences in the error statistics of the evaluated techniques. The sensitivity of attenuation correction uncertainty with respect to the assumed variability in raindrops' oblateness-size relation and the noise in Φ DP measurement is also shown.
IEEE Transactions on Geoscience and Remote Sensing, 2008
A large data set of raindrop size distribution (RSD) measurements collected with the Joss-Waldvog... more A large data set of raindrop size distribution (RSD) measurements collected with the Joss-Waldvogel disdrometer (JWD) and the 2-D video disdrometer (2DVD) in the U.K., Greece, Japan, and the U.S. are analyzed and modeled. This work extends a previous effort devoted to the exploitation of U.K. data and the design of a stochastic procedure to randomly generate synthetic RSD intermittent time series. This study seeks to: 1) explore the differences of RSD-derived moments for distinct hydroclimate regions, ranging from tropics to subtropics and mid and northern latitudes; 2) compare the governing parameters of the normalized gamma RSD for both stratiform and convective events and perform a sensitivity analysis by using different best fitting techniques; 3) exploit the time-correlation structure of the estimated RSD parameters as the input of a vector autoregressive stationary model used to simulate time series (or horizontal profiles) of RSDs and, consequently, its moments as the rain rate and concentration; and 4) characterize the distribution of the inter-rain duration and rain duration to design a semi-Markov chain to represent the intermittency feature of the rainfall process in a climatological framework. This climatological analysis and the related stochastic RSD generation model may find useful applications within both hydrometeorology and radio propagation.
Journal of The Atmospheric Sciences, 2006
The Keys Area Microphysics Project (KAMP), conducted as part of NASA's Fourth Convective and Mois... more The Keys Area Microphysics Project (KAMP), conducted as part of NASA's Fourth Convective and Moisture Experiment (CAMEX-4) in the lower Keys area, deployed a number of ground radars and four arrays of rain gauge and disdrometer clusters. Among the various instruments is an X-band dualpolarization Doppler radar on wheels (XPOL), contributed by the University of Connecticut. XPOL was used to retrieve rainfall rate and raindrop size distribution (DSD) parameters to be used in support of KAMP science objectives. This paper presents the XPOL measurements in KAMP and the algorithm developed for attenuation correction and estimation of DSD model parameters. XPOL observations include the horizontal polarization reflectivity Z H , differential reflectivity Z DR , and differential phase shift ⌽ DP . Here, Z H and Z DR were determined to be positively biased by 3 and 0.3 dB, respectively. A technique was also applied to filter noise and correct for potential phase folding in ⌽ DP profiles. The XPOL attenuation correction uses parameterizations that relate the path-integrated specific (differential) attenuation along a radar ray to the filtered-⌽ DP (specific attenuation) profile. Attenuation-corrected Z H and specific differential phase shift (derived from filtered ⌽ DP profiles) data are then used to derive two parameters of the normalized gamma DSD model, that is, intercept (N w ) and mean drop diameter (D 0 ). The third parameter (shape parameter ) is calculated using a constrained -⌳ relationship derived from the measured raindrop spectra. The XPOL attenuation correction is evaluated using coincidental nonattenuated reflectivity fields from the Key West Weather Surveillance Radar-1988 Doppler (WSR-88D), while the DSD parameter retrievals are statistically assessed using DSD parameters calculated from the measured raindrop spectra. Statistics show that XPOL DSD parameter estimation is consistent with independent observations. XPOL estimates of water content and N w are also shown to be consistent with corresponding retrievals from matched ER-2 Doppler radar (EDOP) profiling observations from the 19 September airborne campaign. Results shown in this paper strengthen the applicability of X-band dual-polarization high resolution observations in cloud modeling and precipitation remote sensing studies.
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2011
The ambient sound field in the ocean is a combination of natural and manmade sounds. Consequently... more The ambient sound field in the ocean is a combination of natural and manmade sounds. Consequently, the interpretation of the ambient sound field can be used to quantify these processes. In the frequency range from 1 to 50 kHz, the general character of ocean ambient sound is a slowly changing background that is closely associated with local wind speed, interspersed with shorter time scale events such as rain storms, ships and animal calls. At lower frequencies the underwater ambient sound budget includes geologically generated sound activities including underwater volcanic eruptions, seismic and seepage faults that generate bubbles, etc. that can also potentially be classified and quantified. Acoustic data are collected on hydrophones. Hydrophones are simple, robust sensors that can be deployed on most ocean instrumentation systems including surface or sub-surface moorings, bottom mounted systems, drifters, ARGO floats or autonomous underwater platforms. A dedicated oceanic underwater recorder called a passive acoustic listener (PAL) has been developed. A principal issue is to accurately distinguish different sound sources so that they can be quantified as part of a sound budget, and then quantified if appropriate. Based on ongoing data collected from the Poseidon II network the retrieval potential of multi-parameters from underwater sound, including meteorological (i.e., precipitation and winds) and in general geophysical, anthropogenetic (i.e., ships, submarines, etc.) and biological (whales, etc.) sources is presented.
IEEE Transactions on Geoscience and Remote Sensing, 2008
A large data set of raindrop size distribution (RSD) measurements collected with the Joss-Waldvog... more A large data set of raindrop size distribution (RSD) measurements collected with the Joss-Waldvogel disdrometer (JWD) and the 2-D video disdrometer (2DVD) in the U.K., Greece, Japan, and the U.S. are analyzed and modeled. This work extends a previous effort devoted to the exploitation of U.K. data and the design of a stochastic procedure to randomly generate synthetic RSD intermittent time series. This study seeks to: 1) explore the differences of RSD-derived moments for distinct hydroclimate regions, ranging from tropics to subtropics and mid and northern latitudes; 2) compare the governing parameters of the normalized gamma RSD for both stratiform and convective events and perform a sensitivity analysis by using different best fitting techniques; 3) exploit the time-correlation structure of the estimated RSD parameters as the input of a vector autoregressive stationary model used to simulate time series (or horizontal profiles) of RSDs and, consequently, its moments as the rain rate and concentration; and 4) characterize the distribution of the inter-rain duration and rain duration to design a semi-Markov chain to represent the intermittency feature of the rainfall process in a climatological framework. This climatological analysis and the related stochastic RSD generation model may find useful applications within both hydrometeorology and radio propagation.
Dual-polarized weather radars are capable to detect and identify different classes of hydrometeor... more Dual-polarized weather radars are capable to detect and identify different classes of hydrometeors, within stratiform and convective storms exploiting polarimetric diversity. A model- supervised Bayesian method for hydrometeor classification (BRAHC), tuned for S- and X- band, is described in this study. The critical issue of X-band radar data processing is the path attenuation correction, usually negligible at S-band. During the IHOP experiment (Oklahoma, 2002) two dual-polarized radars, at S- and X- bands, were deployed and jointly operated with closely matched scanning strategies, giving the opportunity to perform experimental comparisons between coincident measurements at different frequencies. Results of hydrometeor classification and water content estimates at S- and X- bands are discussed and the impact of path attenuation correction is quantitatively analyzed.
Atmospheric Research, 2009
In this work the capability of reliable rainfall measurements with small weather radars in comple... more In this work the capability of reliable rainfall measurements with small weather radars in complex terrain for flood forecasting purposes is examined. Rain measurements were carried out during winter-spring 2007 with a mobile X-band dual-polarization radar in the northwestern mountainous part of the island of Crete in Greece. In this area a 2D-video disdrometer and a network of raingauges was installed for radar calibration and evaluation of rainfall measurements, respectively. The complex terrain of the experimental site may significantly reduce the performance of rain measurements due to ground clutter and partial or total beam blockage. A beam blockage algorithm using high resolution terrain data was applied in order to find areas with significant terrain effects and estimate correction of the radar measurements. Rain attenuation correction was based on modern sophisticated algorithms using differential phase measurements. The accuracy of rainfall estimation from standard or polarimetric algorithms at plan position indicator (PPI) scans was examined for high-temporal resolution (1 min) rainfall rates and accumulated rainfall values for winter and spring time rain events. For high elevation measurements, which were required in order to avoid terrain effects in large areas of interest, a correction for the vertical-profile-of-reflectivity (VPR) was also applied to the radar data. An average VPR model used in the corresponding correction of reflectivity was constructed based on range-height indicator (RHI) scans. It was concluded that quantitative high resolution X-band radar observations of rainfall in complex terrain is possible after careful application of all the above processing steps.
Journal of The Acoustical Society of America, 2008
An experiment to evaluate the inherent spatial averaging of the underwater acoustic signal from r... more An experiment to evaluate the inherent spatial averaging of the underwater acoustic signal from rainfall was conducted in the winter of 2004 in the Ionian Sea southeast of the coast of Greece. A mooring with four passive aquatic listeners (PALs) at 60, 200, 100, and 2000 m was deployed at 36.85ºN, 21.52ºE, 17 km west of a dual-polarization X-band coastal radar (XPOL) at Methoni, Greece. A dense rain gauge network was set up in Finikounda, 10 km east from Methoni to calibrate the radar. Eight rain events were recorded during the deployment; six of these events were recorded by both the PALs and the XPOL radar.
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Papers by Marios Anagnostou