Jun Awaka

Rain type classification algorithm for TRMM precipitation radar

A TRMM precipitation radar (PR) standard algorithm for classifying precipitation types is designated as the algorithm 2A-23. This algorithm classifies precipitation type into three categories: stratiform, convective, and other. In the case of convective precipitation, a further examination is made to determine whether it is warm rain or not. The algorithm 2A-23 also detects bright band and determines the height of a bright band when it is detected.

Rain profiling algorithm for TRMM Precipitation Radar data

Abstract This paper describes the TRMM standard algorithm 2A25 which estimates the instantaneous vertical profile of rain from Precipitation Radar (PR) data. Major challenges in rain profilling from the TRMM PR lie in the corrections for the effects of rain attenuation and non-uniform beam filling (NUBF) and in the rejection of surface clutter. A combination of the Hitschfeld-Bordan and surface reference methods is used to correct the attenuation effect in radar returns. The NUBF effects are estimated from the spatial variations of the estimated total path integral of attenuation from the top of the rain to the surface in the vicinity of the radar beam concerned. This paper outlines the critical part of the algorithm, and shows some results of comparisons of data taken nearly simultaneously by the TRMM PR and a ground-based radar.

Severe disturbances of VHF and GHz waves from geostationary satellites during a magnetic storm

Abstract Severe night-time scintillations of VHF and GHz waves (0.136, 1.7, 4 and 11.5 GHz) emitted from the three Japanese geostationary satellites were observed during a geomagnetic storm on February 15, 1978. The GHz scintillations were strongly enhanced when irregular fluctuation of total electron content (TEC) was superposed on the background TEC which was varying sharply with time. This indicates a close relationship between the scintillations and irregularities. Detailed analysis shows that the one-dimensional wavenumber power spectrum of irregularities obeys a form of k−2 and that the scintillation spectra vary as ƒ s −3 . The scintillation index, S4, seems to have a frequency dependence of ƒ −0.5 for 0.136 ⪅ ƒ ⪅ 1.7 GHz, f−1 for 1.7 ⪅ ƒ ⪅ 4 GHz and ƒ −2 for 4 ⪅ ƒ ⪅ 11.5 GHz. It is found that this scintillation event was accompanied with large decrease in the plasmaspheric electron content, which continued for one and a half days after the storm onset, and with appearance of localized electron density trough in the F-region ionosphere.

Airborne microwave rain-scatterometer /radiometer

Abstract An airborne microwave rain-scatterometer/radiometer system operated at 10 and 34-45 GHz was developed for the remote sensing of precipitation, especially rain, from an aeroplane. Airborne rain-scatterometers were developed as a first step for the development of the future spaceborne rain-scatterometer. Flight experiments of more than 30 hours were performed in co-operation with the ground-based C-band weather radar. The sensor system of the airborne microwave rain-scatterometer/radiometer, flight experiment in June 1981 cooperating with the ground-based weather radar, and results of data analyses are described.

Evaluation of Precipitation Estimates by at-Launch Codes of GPM/DPR Algorithms Using Synthetic Data from TRMM/PR Observations

The Global Precipitation Measurement (GPM) Core Observatory will carry a Dual-frequency Precipitation Radar (DPR) consisting of a Ku-band precipitation radar (KuPR) and a Ka-band precipitation radar (KaPR). In this study, “at-launch” codes of DPR precipitation algorithms, which will be used in GPM ground systems at launch, were evaluated using synthetic data based upon the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) data. Results from the codes (Version 4.20131010) of the KuPR-only, KaPR-only, and DPR algorithms were compared with “true values” calculated based upon drop size distributions assumed in the synthetic data and standard results from the TRMM algorithms at an altitude of 2 km over the ocean. The results indicate that the total precipitation amounts during April 2011 from the KuPR and DPR algorithms are similar to the true values, whereas the estimates from the KaPR data are underestimated. Moreover, the DPR estimates yielded smaller precipitation rates for rates less than about 10 mm/h and greater precipitation rates above 10 mm/h. Underestimation of the KaPR estimates was analyzed in terms of measured radar reflectivity (Zm) of the KaPR at an altitude of 2 km. The underestimation of the KaPR data was most pronounced during strong precipitation events of Zm <; 18 dBZ (high attenuation cases) over heavy precipitation areas in the Tropics, whereas the underestimation was less pronounced when the Zm > 26 (moderate attenuation cases). The results suggest that the underestimation is caused by a problem in the attenuation correction method, which was verified by the improved codes.

A theoretical formula for the prediction of cross-polarized signal phase

An approximate theoretical formula for the prediction of cross-polarized signal phase relative to co-polar signal is presented. In the formula, the phase of cross-polarized signal induced by rain is related to rainfall rate or rain-induced attenuation. The relation is derived by calculating the forward scattering amplitudes of the Pruppacher-Pitter type raindrops at 33 frequencies ranging from 3 to 40 GHz. The dependence of the relation on raindrop-size distribution is also discussed.

The relationship of raindrop-size distribution to attenuations experience at 50, 80, 140, and 240 GHz

Millimeter-wave rain attenuation measurements have been made at 50.4, 81.8, 140.7, and 245.5 GHz on a terrestrial path of 0.81 km. On the basis of these experimental results, a comparison between the model of specific attenuation currently adopted by the International Radio Consultative Committee (CCIR) and that based on the raindrop-size distribution derived from our previous propagation experiments at 11.5, 34.5, and 81.8 GHz is made. For the Japanese climate, it is found that the CCIR model underestimates the rain attenuation at frequencies above 80 GHz and that our specific attenuation model is effective for the prediction of rain attenuation in the whole millimeter-wave region.

Introduction of a melting layer model to a rain retrieval algorithm for microwave radiometers

Rain retrieval algorithm for spaceborne passive microwave radiometer with melting layer models is examined in this study. Two melting layer models proposed to explain the reflectivity profile of a bright band or radio wave attenuation observations are tested for the implementation into the rain retrieval algorithm by Aonashi and Liu(1). The attenuation property of a melting layer is examined by the path integrated attenuation obtained by measuring the surface echo of TRMM/PR data in low bright band height cases (e.g. < 2000m) and it is compared with model results because the PIA is closely related to the emission from the rain drops. Similarly, the relationship between the rain rates (R) derived from TRMM/PR and the brightness temperature (TB) derived from TRMM/TMI data for fixed brightband height is compared with the TB-R relationships from rain models with and without the melting layer model using the radiative transfer model by Liu(2). The results show that the effect of the melting layer is not negligible for passive microwave rain retrievals especially in weak rain rate cases and the retrieval error exceeds 20% for the rain rate less than 10 mm/h if the melting layer model is not introduced. The validity of the effect of the melting layer model in the retrieval algorithm is examined by using TRMM/PR data.

Propagation characteristics of millimetre and centimetre waves of ETS-II classified by rainfall types

A propagation experiment at the frequencies of 1.7, 11.5 and 34.5 GHz using Engineering Test Satellite Type IIEts-II was conducted at the Kashima earth station of the Radio Research Laboratories (Rrl).Several meteorological parameters were also measured simultaneously at the station using rain gauge networks, a C-band rain radar, a 35 GHz radiometer and meteorological instruments.The whole data for one year in this experiment were classified into three rain types such as stratus, cumulusand others by using radar data along the path mainly to determine the size of precipitation area and whether the radar bright band existed or not.Rainfall classified as stratus occurred for 45 % of the total rainfall time, whilst rainfall classified as cumulus occurred for 10 %, and others for 45 % of the total rainfall time. For the co-polar attenuation, a prediction method based upon an assumption of spatial homogeneity is found to be applicable to the Earth-space path for the stratus type, though the method is not applicable for the cumulus type. On the contrary, in the degradation ofXpd,a prediction method based upon an assumption of deformed raindrops is not applicable to the path for the stratustype, while the method is applicable for the cumulus type.AnalyseUne expérience de propagation à des fréquences de 1.7, 11.5 et 34.5 GHz utilisant le satelliteEts-II a été réalisée à la station de Kashima du Radio Research Laboratories. Quelques paramètres météorologiques ont simultanément été mesurés à la station, à l’aide de pluviomètres, d’un radar météorologique dans la bande C, d’un radiomètre à 35 GHz et de divers instruments météorologiques. Tous les résultats de l’expérience pour une année ont été classés suivant trois types de précipitations: stratus, cumuluset autres cas;ceci, grâce aux enregistrements du radar qui ont permis de déterminer l’aire couverte par la précipitation et l’existence ou non-existence de la bande brillante du radar. L’occurrence de précipitations du type stratus est observée durant 45% de la durée totale de précipitation, le type cumulusdurant 10% et le type autres cas45%. On trouve pour l’atténuation copolaire une méthode de prévision basée sur l’hypothèse d’homogénéité spatiale qui est utilisable sur un trajet Terre-espace pour une précipitation du type stratus mais ne l’est pas pour le cas cumulus.Par contre, pour la dégradation du découplage de polarisation croisée, une méthode de prévision supposant les gouttes déformées n’est pas applicable au type stratusmais l’est au type cumulus.

Analysis of the radio acoustic sounding system using a chirped acoustic wave

We investigated radio acoustic sounding system (RASS) echoes backscattered from refractive index fluctuations produced by an acoustic pulse linearly modulated in frequency (a chirped acoustic pulse). We have numerically simulated errors of the Doppler frequency shift which are caused by the fact that the widths of the acoustic and radar pulse are finite. We analytically showed that a RASS with a chirped acoustic pulse can correctly measure a wide range of Doppler shifts. The error of the Doppler shift measurement is found to be a function of the radar range resolution, the rate at which acoustic frequency is swept, and the width of the acoustic pulse. The error is also shown to be almost independent of the radar frequency and the lapse rates of the atmospheric temperatures. We have also numerically showed that when the chirped acoustic wave frequency is 50 Hz/s, errors are within 0.018°C when the radar frequency is 1357.5 MHz and the range resolution is 75 m. At the chirped wave frequency, errors are within 0.055°C for a 46.5-MHz radar with a 150-m range resolution. We also propose a method for designing a chirped acoustic pulse to measure atmospheric temperature.