Rainfall Rate Measurements Research Articles

A sound budget for the southeastern Bering Sea: Measuring wind, rainfall, shipping, and other sources of underwater sound

Ambient sound in the ocean contains quantifiable information about the marine environment. A passive aquatic listener (PAL) was deployed at a long-term mooring site in the southeastern Bering Sea from 27 April through 28 September 2004. This was a chain mooring with lots of clanking. However, the sampling strategy of the PAL filtered through this noise and allowed the background sound field to be quantified for natural signals. Distinctive signals include the sound from wind, drizzle and rain. These sources dominate the sound budget and their intensity can be used to quantify wind speed and rainfall rate. The wind speed measurement has an accuracy of +/-0.4 m s(-1) when compared to a buoy-mounted anemometer. The rainfall rate measurement is consistent with a land-based measurement in the Aleutian chain at Cold Bay, AK (170 km south of the mooring location). Other identifiable sounds include ships and short transient tones. The PAL was designed to reject transients in the range important for quantification of wind speed and rainfall, but serendipitously recorded peaks in the sound spectrum between 200 Hz and 3 kHz. Some of these tones are consistent with whale calls, but most are apparently associated with mooring self-noise.

Time-dependent <i>Z-R</i> relationships for estimating rainfall fields from radar measurements

Abstract. The operational use of weather radars has become a widespread and useful tool for estimating rainfall fields. The radar-gauge adjustment is a commonly adopted technique which allows one to reduce bias and dispersion between radar rainfall estimates and the corresponding ground measurements provided by rain gauges. This paper investigates a new methodology for estimating radar-based rainfall fields by recalibrating at each time step the reflectivity-rainfall rate (Z-R) relationship on the basis of ground measurements provided by a rain gauge network. The power-law equation for converting reflectivity measurements into rainfall rates is readjusted at each time step, by calibrating its parameters using hourly Z-R pairs collected in the proximity of the considered time step. Calibration windows with duration between 1 and 24 h are used for estimating the parameters of the Z-R relationship. A case study pertaining to 19 rainfall events occurred in the north-western Italy is considered, in an area located within 25 km from the radar site, with available measurements of rainfall rate at the ground and radar reflectivity aloft. Results obtained with the proposed method are compared to those of three other literature methods. Applications are described for a posteriori evaluation of rainfall fields and for real-time estimation. Results suggest that the use of a calibration window of 2–5 h yields the best performances, with improvements that reach the 28% of the standard error obtained by using the most accurate fixed (climatological) Z-R relationship.

Spatial variability of steady-state infiltration into a two-layer soil system on burned hillslopes

Rainfall–runoff simulations were conducted to estimate the characteristics of the steady-state infiltration rate into 1-m 2 north- and south-facing hillslope plots burned by a wildfire in October 2003. Soil profiles in the plots consisted of a two-layer system composed of an ash on top of sandy mineral soil. Multiple rainfall rates (18.4–51.2 mm h −1 ) were used during 14 short-duration (30 min) and 2 long-duration simulations (2–4 h). Steady state was reached in 7–26 min. Observed spatially-averaged steady-state infiltration rates ranged from 18.2 to 23.8 mm h −1 for north-facing and from 17.9 to 36.0 mm h −1 for south-facing plots. Three different theoretical spatial distribution models of steady-state infiltration rate were fit to the measurements of rainfall rate and steady-state discharge to provided estimates of the spatial average (19.2–22.2 mm h −1 ) and the coefficient of variation (0.11–0.40) of infiltration rates, overland flow contributing area (74–90% of the plot area), and infiltration threshold (19.0–26 mm h −1 ). Tensiometer measurements indicated a downward moving pressure wave and suggest that infiltration-excess overland flow is the runoff process on these burned hillslope with a two-layer system. Moreover, the results indicate that the ash layer is wettable, may restrict water flow into the underlying layer, and increase the infiltration threshold; whereas, the underlying mineral soil, though coarser, limits the infiltration rate. These results of the spatial variability of steady-state infiltration can be used to develop physically-based rainfall–runoff models for burned areas with a two-layer soil system.

Slant path rain attenuation comparison of prediction models for satellite applications in Malaysia

A 2‐year campaign of slant path rain attenuation measurements has been carried out in Malaysia using the Superbird‐C satellite beacon at 12.255 GHz. The rain intensity time series have been recorded with a conventional tipping‐bucket rain gauge located at the station, during a continuous observation period spanning the same 2 years of the beacon measurements. The experimental cumulative distributions of rainfall rate and rain attenuation are presented. Two years of rain attenuation measurements at 12.255 GHz shows high values that have been detected for small percentage of time; for example, the attenuation exceeded 25 dB for 0.01% of time. The rainfall rate is compared with International Telecommunications Union–Radiocommunication (ITU‐R) maps, and the measured rain rate distribution is close to that derived from the ITU‐R maps. Measured rain attenuation values are compared with several prediction models. A good agreement has been found in the comparison of the experimental distribution with some prediction models (Ramachandran, Bryant, Matricciani, and Exponential Cell (EXCELL) with percentage errors below 11%) calculated using the measured rainfall rate distribution. The lack of rain measurement data from equatorial and tropical regions for verification causes predictions obtained from existing models to deviate from direct measurements.

Spatial rain correlation analysis for application in site diversity design

Analysis of spatial correlation of rainfall rate and of slant path rain attenuation in order to optimize site separation and baseline orientation in site diversity design is presented. For this study, 4 years of rainfall rate measurements were obtained from the Hydrological Radar Experiment dense rain gauge network and associated radar facility in South England. The slant path rain attenuation correlations are analyzed for a hypothetical Earth‐space propagation path at 20 GHz. Results show that the correlation of slant path rain attenuations at two diversity sites reaches a minimum at a separation of about 20 km between the two sites and a baseline orientation of acute angle above 30°.

Inferences from catchment-scale tracer circulation experiments

In this paper the mechanisms determining the mobilization and transport of solutes driven by rainfall through runoff pathways at catchment scales are investigated through the analysis of tracer experiments. The hydro-chemical response of a small catchment in Northern Italy has been monitored in continuous during 4 weeks by properly measuring rainfall rates, streamflows and stream flux concentrations. The chemical response has been analyzed by employing two different tracers: nitrates from diffuse agricultural sources (NO3-) and lithium from a point injection (Li+). A modelling exercise simulating the observed hydro-chemical response of the test catchment has also been carried out. Inferences from the comparative analyses prove instructive, in particular concerning the scaling of mobilization processes and the age of runoff water. Indeed, the interactions between old and new water were found to be central to understand the mechanisms driving the transfer of solutes and pollutants from soil to stream water. The modeling exercises also evidenced the noteworthy potential of the formulation of transport by residence time distributions to describe large scale solute transport processes. (C) 2009 Elsevier B.V. All rights reserved.

Continental Passive Microwave-Based Rainfall Estimation Algorithm: Application to the Amazon Basin

Abstract This paper presents a new statistical algorithm to estimate rainfall over the Amazon Basin region using the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI). The algorithm relies on empirical relationships derived for different raining-type systems between coincident measurements of surface rainfall rate and 85-GHz polarization-corrected brightness temperature as observed by the precipitation radar (PR) and TMI on board the TRMM satellite. The scheme includes rain/no-rain area delineation (screening) and system-type classification routines for rain retrieval. The algorithm is validated against independent measurements of the TRMM–PR and S-band dual-polarization Doppler radar (S-Pol) surface rainfall data for two different periods. Moreover, the performance of this rainfall estimation technique is evaluated against well-known methods, namely, the TRMM-2A12 [the Goddard profiling algorithm (GPROF)], the Goddard scattering algorithm (GSCAT), and the National Environmental Satellite, Data, and Information Service (NESDIS) algorithms. The proposed algorithm shows a normalized bias of approximately 23% for both PR and S-Pol ground truth datasets and a mean error of 0.244 mm h−1 (PR) and −0.157 mm h−1 (S-Pol). For rain volume estimates using PR as reference, a correlation coefficient of 0.939 and a normalized bias of 0.039 were found. With respect to rainfall distributions and rain area comparisons, the results showed that the formulation proposed is efficient and compatible with the physics and dynamics of the observed systems over the area of interest. The performance of the other algorithms showed that GSCAT presented low normalized bias for rain areas and rain volume [0.346 (PR) and 0.361 (S-Pol)], and GPROF showed rainfall distribution similar to that of the PR and S-Pol but with a bimodal distribution. Last, the five algorithms were evaluated during the TRMM–Large-Scale Biosphere–Atmosphere Experiment in Amazonia (LBA) 1999 field campaign to verify the precipitation characteristics observed during the easterly and westerly Amazon wind flow regimes. The proposed algorithm presented a cumulative rainfall distribution similar to the observations during the easterly regime, but it underestimated for the westerly period for rainfall rates above 5 mm h−1. NESDIS1 overestimated for both wind regimes but presented the best westerly representation. NESDIS2, GSCAT, and GPROF underestimated in both regimes, but GPROF was closer to the observations during the easterly flow.

Hybrid Distributed Instrumentation Network for Integrating Meteorological Sensors Applied to Modeling RF Propagation Impairments

Rainfall rate is the main cause of fades in the frequency bands above 10 GHz. To optimize the planning of satellite and terrestrial radio communication systems operating on these frequency bands, it is essential to have a detailed knowledge of the temporal and spatial distributions of the rainfall rate. For this reason, it is necessary to develop experimental networks, which provide adequate data to study, prevent, and compensate the rain fade. In this paper, an experimental instrumentation network is presented. This network comprises weather stations that are capable of measuring rainfall rate, temperature, and humidity; a weather radar; and three radio links. This paper first introduces the rationale and the state of the art in meteorological sensors and describes the experimental network for automatic data acquisition as a distributed process system. The design of the experimental network is explained in detail. Finally, the interest in millimeter wavelength for broadband applications is outlined, and some research lines from the collected data are presented.

60- to 1-Min Rainfall-Rate Conversion: Comparison of Existing Prediction Methods with Data Obtained in the Southeast Asia Region

AbstractRainfall-rate statistics are frequently derived on the basis of rain gauge recordings with effective integration times of 10 min or longer. The conversion of such data to equivalent statistics for an effective integration time of 1 min is very important to predict rainfall attenuation at a location accurately. Because of the limited availability of 1-min rainfall-rate data, conversion of available rainfall-rate distributions with longer integration times to the desired 1-min distributions is needed. Several methods for converting 60-min rainfall rates to 1-min rainfall rates are tested against measured rainfall rates from tropical, high-rainfall-rate regions. Segal’s method was found to perform the best overall when compared with other conversion methods.

A Study of Precipitation Effect on Tropospheric Electromagnetic Wave Propagation at Frequency 19.5 GHz

In this article, we take advantage of a terrestrial propagation link at Ka-band 19.5 GHz located on the campus of the National Central University in Chung-Li City to carry out a tropospheric radio propagation experiment. Data collected in 2004 were used in data analysis to provide a deeper understanding of the precipitation effect on tropospheric electromagnetic wave propagation at Ka-band. The results indicate that the relation between specific attenuation ĸe of 19.5 GHz radio wave amplitude and the measured rain fall rate R (in unit of mm hr -1 ) is of the form: ĸe = aR b (in unit dB km -1 ) with a = 0.0699 and b = 1.0984, which is fairly close to that obtained by assuming Laws-Parsons drop size distribution. In order to study the overall attenuation characteristics of Ka-band radio wave influenced by precipitation particles, we used a ground-based 2D disdrometer to measure the terminal velocities of raindrops and their size distributions. The result shows that the relation between raindrop diameter and terminal velocity in terms of the Power-Law relation, i.e., V(D) = AD B , and the drop size distribution can be expressed in the form of a Gamma distribution function, i.e., N(D) = N0D μ exp(-δD). With these results, the corresponding rain attenuation of the electromagnetic wave at Ka-band is estimated and discussed in this article.

Worst Month Rain Statistics Measurement in Malaysia

Excess attenuation due to rainfall is one of the most important constraints to the performance of microwave radio links. In temperate climates at frequencies above 10 GHz, rainfall rates have significant effects on the performance of microwave radio links. Therefore the behavior of radio communication links varies seasonally over a year. This paper presents on the results obtained from the analysis of 3 years rainfall rate and attenuation measurements that were carried out in Universiti Sains Malaysia (USM). The collected data were used to derive the average worst month statistics and its relationship with the average annual distribution. This relationship was found to be suitable with the one proposed by ITU. Therefore the average 3 years of the worst month data provides further support to usefulness of the ITU worst month model.

Rainfall Attenuation and Rainfall Rate Measurements in Malaysia Comparison with Prediction Models

Attenuation due to rain is a primary cause of communication impairment on satellite-earth paths, especially above 10GHz. Rainfall is a serious source of attenuation at such a frequency. This paper presents the characteristics of rain distribution in USM based on measured one minute rain rate. For attenuation of rain, predictions models like ITU and VIHT (Variable Isotherm Height Technique) model were used to estimate the effect of rain on Ku band signals. Data of rain attenuation and rainfall rates collected at USM are estimated and compared with the predicted models. The ITU model followed closely to the measured rainfall rate and attenuation data whereas the VIHT models overestimated the measured rainfall rate and attenuation data.

Annual and Diurnal Slant Path Rain Attenuation Statistics in Athens Obtained With the Synthetic Storm Technique

We present annual/seasonal rainfall rate statistics derived from a 29-month data bank of 1 sample/min, measured by a disdrometer located inside the National Technical University of Athens Campus. We discuss both the inaccuracy and the unavailability of the measuring equipment, as well as the statistical reliability of the rainfall rate sample. Additionally, after applying the Synthetic Storm Technique on the measured rainfall rate time series, we present the first long term simulated annual/seasonal and diurnal rain attenuation statistics, at 12 GHz for a hypothetical downlink from Hellas Sat 2 to Athens. According to the results, we predict that communication downlinks working in the afternoon and early evening hours must be given an extra power margin, to compensate for high rain attenuation

Long‐term statistics of tropospheric attenuation from the Ka/U band ITALSAT satellite experiment in the United Kingdom

Long‐term statistics of tropospheric attenuation were derived from almost 4 years of measurements made in the south of England using the ITALSAT F1 beacon signals at 49.5, 39.6, and 18.7 GHz; coincident rainfall rate measurements were made at the site of the receiving ground station. A method to remove the nonatmospheric changes of the beacon signals and to establish the reference levels from which to measure the excess and total attenuation has been presented in detail. The accuracy of fade level retrieval is estimated to be ∼±0.5 dB. A new method for predicting the annual total attenuation statistics has been proposed and validated against our data and data collected in Italy at 18.7, 39.6, and 49.5 GHz. For both locations, the new proposed method gives much better predictions compared with the established International Telecommunication Union recommendation method. A significant monthly and seasonal variation was observed in the attenuation and rainfall statistics and should be taken into consideration when planning the design and use of future slant path systems. We have seen that the attenuation statistics are subject to diurnal variations; however, for the period analyzed, this variation does not seem to follow a particular pattern.

Measurement of Rain-Induced Zenith-Path Attenuation Using 19.9 GHz Radiometer at Amritsar (India)

The paper presents the results of 19.9 GHz radiometric propagation studies conducted over a period of one year at Amritsar, for determining rain-induced zenith path attenuation. The zenith path attenuation has been determined by the measurements of sky noise temperature received by the radiometer. The results obtained from the experiment are presented in the form of annual cumulative distributions of rain rate, sky noise temperature, and zenith path attenuation together with worst-month statistics. The rainfall rate cumulative distribution as predicted by ITU-R for our geographical location is lower than the actually measured rainfall rate cumulative distribution. The cumulative distribution of zenith path attenuation predicted by using ITU-R model overestimates the measured cumulative distribution of zenith path attenuation.

Correcting Land Surface Model Predictions for the Impact of Temporally Sparse Rainfall Rate Measurements Using an Ensemble Kalman Filter and Surface Brightness Temperature Observations

Current attempts to measure short-term (<1 month) rainfall accumulations using spaceborne radiometers are characterized by large sampling errors associated with low observation frequencies for any single point on the globe (from two to eight measurements per day). This degrades the value of spaceborne rainfall retrievals for the monitoring of surface water and energy balance processes. Here a data assimilation system, based on the assimilation of surface L-band brightness temperature (TB) observations via the ensemble Kalman filter (EnKF), is introduced to correct for the impact of poorly sampled rainfall on land surface model predictions of root-zone soil moisture and surface energy fluxes. The system is evaluated during the period from 1 April 1997 to 31 March 1998 over two sites within the U.S. Southern Great Plains. This evaluation includes both a data assimilation experiment, based on synthetically generated TB measurements, and the assimilation of real TB observations acquired during the 1997 Southern Great Plains Hydrology Experiment (SGP97). Results suggest that the EnKF-based assimilation system is capable of correcting a substantial fraction (>50%) of model error in root-zone (40 cm) soil moisture and latent heat flux predictions associated with the use of temporally sparse rainfall measurements as forcing data. Comparable gains in accuracy are demonstrated when actual TB measurements made during the SGP97 experiment are assimilated.

Rainfall-induced satellite beacon attenuation in tropical and equatorial regions

A four-year campaign of rainfall rate and rain-induced slant-path attenuation measurements was conducted on four satellite beacon links located in the equatorial, tropical and subtropical regions of Brazil. The cumulative distributions of attenuation derived from the measured data are presented and compared with those obtained with existing prediction methods.

Rain attenuation measurements at 15 and 18 GHz

A two-year campaign of point rainfall rate and rain attenuation measurements was performed in six terrestrial line-of-sight links operating at 15 and 18 GHz in southeastern Brazil. Results indicate that the attenuation due to rain in terrestrial links in tropical regions is underestimated by existing prediction methods based on experimental data from temperate climates.

Rainfall rate measurement with a polarimetric radar at an attenuated wavelength

Among the many ways investigated for radar estimation of rainfall, polarimetric methods are the most promising. However most polarimetric algorithms are degraded by attenuation by precipitation and clouds and by calibration error. A new method was recently proposed in which the differential polarimetric attenuation is used to perform an accurate rain rate measurement. The method is independent of the radar calibration and of the attenuation by undetected clouds. This algorithm is also usable as a qualitative hail detector, as well as a detector of anomalous propagation. The goal of the paper is to describe the results of the first experimental implementation of this method using the 35 GHz RABELAIS radar, as attenuated radar, and the 3 GHz CAMRa radar as a reference. We show that the proposed algorithm is stable and enables us to retrieve the actual rain rate even from an observed signal attenuated by more than 30 dB. The results are insensitive to the value used for the power coefficient of the Z(R) relation.

Comparing model and measured rainfall rates obtained from a combination of remotely sensed and in situ observations

The Olympus program was designed to develop new telecommunications technology in space and develop new market applications. This study analyzes attenuation data from two of the Olympus satellite beacons, those operating at 19.77 and 12.502 GHz. It is shown that the difference in the two attenuations provides estimates of rainfall rate that are in close agreement with rain gauge and distrometer measurements at the ground receiver site and along the propagation path. Modeling demonstrates that the attenuation difference using 19.77 and 12.502 GHz is a useful estimator of rainfall because it is largely independent of drop shape and size distribution, making it linearly related to rainfall rate. Attenuation along the propagation path due to the melting layer or ice introduces inaccuracies into estimates of rainfall. However, this difficulty would be eliminated if the method were to be used on terrestrial line‐of‐site links. Thus attenuation difference provides a means of improving the quality of rainfall estimates when used together with gauges and radar observations.