Toshiaki Kozu

The Tropical Rainfall Measuring Mission (TRMM) Sensor Package

Abstract This note is intended to serve primarily as a reference guide to users wishing to make use of the Tropical Rainfall Measuring Mission data. It covers each of the three primary rainfall instruments: the passive microwave radiometer, the precipitation radar, and the Visible and Infrared Radiometer System on board the spacecraft. Radiometric characteristics, scanning geometry, calibration procedures, and data products are described for each of these three sensors.

Rain profiling algorithm for the TRMM precipitation radar

Describes an outline of the algorithm that estimates the instantaneous profiles of the true radar reflectivity factor and rainfall rate from the radar reflectivity profiles observed by the precipitation radar (PR) onboard the TRMM satellite. The major challenge of the algorithm lies in the correction of rain attenuation with the non-uniform beam filling effect. The algorithm was tested with synthetic data and the result is shown.

Development of precipitation radar onboard the Tropical Rainfall Measuring Mission (TRMM) satellite

The precipitation radar (PR) onboard the Tropical Rainfall Measuring Mission (TRMM) satellite is the first spaceborne radar to measure precipitation from space. The PR, operating at 13.8 GHz, is a 128-element active phased array that allows a fast and sophisticated cross-track scanning over a swath width of 215 km with a cross-range spatial resolution of about 4.3 km. The PR has a minimum detectable rain rate of 0.5 mm/h with range resolution of 250 m. In order to achieve a reliable and accurate rain echo data for three years mission life, functions for internal and external calibrations are implemented. Through a series of PR flight-model tests on the ground and an initial checkout just after the TRMM launch, it is confirmed that the PR functions properly and meets the performance requirements to quantitatively measure three-dimensional (3D) precipitation distribution from space.

Use of the Surface Reference Technique for Path Attenuation Estimates from the TRMM Precipitation Radar

Abstract Estimates of rain rate from the precipitation radar (PR) aboard the Tropical Rainfall Measuring Mission (TRMM) satellite require a means by which the radar signal attenuation can be corrected. One of the methods available is the surface reference technique in which the radar surface return in rain-free areas is used as a reference against which the path-integrated attenuation is obtained. Despite the simplicity of the basic concept, an assessment of the reliability of the technique is difficult because the statistical properties of the surface return depend not only on surface type (land/ocean) and incidence angle, but on the detailed nature of the surface scattering. In this paper, a formulation of the technique and a description of several surface reference datasets that are used in the operational algorithm are presented. Applications of the method to measurements from the PR suggest that it performs relatively well over the ocean in moderate to heavy rains. An indication of the reliability of...

Season-long daily measurements of multifrequency (Ka, Ku, X, C, and L) and full-polarization backscatter signatures over paddy rice field and their relationship with biological variables

The objective of this study was to investigate the interaction between microwave backscatter signatures and rice canopy growth variables, as well as to provide definitive insight into the interaction between backscatter and vegetation based on a comprehensive data set collected under the unique crop conditions of paddy rice (background is water surface). Our unique data consisted of daily microwave backscattering coefficients at all combinations of five frequencies (Ka, Ku, X, C, and L), all polarizations (HH, VH, HV, and VV), and four incident angles (25°, 35°, 45°, and 55°) for the entire rice crop period, from before transplantation until postharvest cultivation. A wide range of plant variables, such as leaf area index (LAI), and biomass of the whole plant and plant parts were measured periodically throughout the season. Analyses based on statistical correlation and a simple backscatter process model (the water cloud model) showed that LAI was best correlated with HH- and cross-polarization of the C-band, while fresh biomass was best correlated with HH- and cross-polarization of the L-band. Contrarily, the higher frequency bands (Ka, Ku, and X) were poorly correlated with LAI and biomass. Interestingly, the weight of heads (ultimately the grain yield) was highly correlated with the backscattering coefficient of the Ka- and Ku-bands, while the others were poorly correlated. The simple scattering process model may be applicable for C- and L-bands in rice canopies, while it may not be suitable for Ka- and Ku-bands. In the model, LAI was a better canopy descriptor for the C-band, while total fresh biomass was a better canopy descriptor for the L-band.

Rainfall Parameter Estimation from Dual-Radar Measurements Combining Reflectivity Profile and Path-integrated Attenuation

Abstract Rain rate estimation properties of multiparameter radar measurements combining radar reflectivity and microwave attenuations are studied through simulations using a two-year disdrometer dataset. In the first simulation, properties of “complete” multiparameter measurements, where error-free measurements are assumed for each radar resolution cell, are investigated. The result indicates that dual-parameter (DP) measurements provide an excellent accuracy in rain rate estimation. Most of the DP measurements possible from space are “semi-” dual-parameter (SDP) measurements, defined as DP measurements in which spatial resolution for the attenuation measurement is coarser than the resolution required for rain profiling. Considering this fact, an SDP measurement simulation is also made. The SDP measurement is an extension of the concept of the DP measurement in terms of the spatial resolution, and can provide information on raindrop size distribution (DSD) by employing a “two-scale” DSD model. It is shown...

The Shape–Slope Relation in Observed Gamma Raindrop Size Distributions: Statistical Error or Useful Information?

Abstract The three-parameter gamma distribution n(D) = N0Dµ exp(–ΛD) is often used to characterize a raindrop size distribution (DSD). The parameters µ and Λ correspond to the shape and slope of the DSD. If µ and Λ are related to one another, as recent disdrometer measurements suggest, the gamma DSD model is simplified, which facilitates retrieval of rain parameters from remote measurements. It is important to determine whether the µ–Λ relation arises from errors in estimated DSD moments, or from natural rain processes, or from a combination of both statistical error and rain physics. In this paper, the error propagation from moment estimators to rain DSD parameter estimators is studied. The standard errors and correlation coefficient are derived through systematic error analysis. Using numerical simulations, errors in estimated DSD parameters are quantified. The analysis shows that errors in moment estimators do cause correlations among the estimated DSD parameters and cause a linear relation between est...

A Study of Rain Estimation Methods from Space Using Dual-Wavelength Radar Measurements at Near-Nadir Incidence over Ocean

Abstract A question arising from the recent interest in spaceborne weather radar is what methods can be used to estimate precipitation parameters from space. In this paper, dual-wavelength airborne radar data obtained from flights conducted during 1988 and 1989 are used to compare rain rates derived from backscattering and attenuation methods. We begin with a survey of path-averaged rain rates estimated from six methods over four flights. The fairly large number of high rain-rate cases encountered during these experiments allows for the first tests of the surface-reference method applied to the low-frequency (10-GHz) data. To help interpret the results the surface reference methods are studied by means of scatterplots of the surface cross sections at the two frequencies under rain and no-rain conditions. Approximate criteria are given on combining attenuation and backscattering methods to increase the effective dynamic range of the radar. The dual-wavelength capability of the radar is also used to examine...

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.

TRMM Precipitation Radar

Abstract The Precipitation Radar (PR) onboard the Tropical Rainfall Measuring Mission (TRMM) satellite is the first spaceborne radar designed to measure the vertical structure of tropospheric precipitation. The PR, operating at 13.8 GHz, is a 128-element active phased array that allows fast and sophisticated cross-track scanning over a swath width of 215 km with a cross-range spatial resolution of about 4.3 km. The PR was designed to achieve a minimum detectable rain rate of 0.7 mm/h with a range resolution of 250 m. In order to achieve reliable and accurate rain echo data for a 3 year mission life, functions for internal and external calibrations have been implemented. After the launch of TRMM, a series of initial check-out was performed. In this presentation, we outline the PR system and the result of the initial check-out which confirms that the PR is functioning as expected.