Hiroshi Kuroiwa

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.

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.

Observation of the Kyucho in the Bungo Channel by HF Radar

Observations of sea surface currents by HF radar were carried out in the Bungo Channel in summer 1992. The current ellipses of M2 constituent obtained by the observational results agree quite well with those obtained by the ADCP observations, showing that the accuracy of the HF radar measurements is of the same level as ADCP. The results revealed the current structures and their change with the Kyucho in detail. The Kyucho is influenced by the complicated coastal geometry and does not propagate straightly into the Bungo Channel. It propagates further inward after charging the coastal bays with warm water. The current directions change largely, since the currents turn around the stagnant region in the bay filled with the warm water. The northward intrusion begins to be weakened in the southern part of the channel, while it still persists in the northern part. The northward current speeds of the observed Kyucho are about 50 cm/s and sometimes attain 60 to 70 cm/s.

A Proposal of Pulse-Pair Doppler Operation on a Spaceborne Cloud-Profiling Radar in the W Band

Pulse-pair Doppler operation is considered for the spaceborne mission. In a formalism, the condition that a measured Doppler velocity on pulse-pair operation corresponds to that on the FFT operation is derived. The coherent coupling effect of the spectral broadenings between Doppler fading and vertical wind shears is shown to strongly depend on the flight direction of a platform. This coupling effect, which has been ignored for groundbased and airborne radars, is characteristic for the space mission. Two kinds of pulse-pair operations, polarization diversity method and conventional contiguous pulse-pair method, are studied to determine the accuracy of Doppler velocity as a function of cloud reflectivity and pulse-pair interval. Advantages and disadvantages of these operations, including adverse effects of beam-pointing error, ground clutters, and sidelobes, are discussed along with a variety of parameters to design the optimum operation. In the assessment of the Doppler feasibility, new features suitable to the space mission are also proposed.

Four-year result of external calibration for Precipitation Radar (PR) of the Tropical Rainfall Measuring Mission (TRMM) satellite

External calibration experiments using active radar calibrator (ARC) were conducted for the calibration of the Precipitation Radar (PR) of the Tropical Rainfall Measuring Mission (TRMM) satellite from 1998 to 2001. Three modes of ARC operation are used for the experiment: the ARC transmitter mode for the receiver system of PR, the ARC receiver mode for the transmitter of PR, and the transponder mode for the overall system of PR. The experiments were conducted several times a year. The results of the experiments show that the performance of the PR is close to the prelaunch performance and that PR has been working stably for four years.

Cloud profiling radar for EarthCARE mission

Concept and expected performance of cloud profiling radar (CPR) for EarthCARE are described based on preliminary design study conducted to date. High sensitivity and Doppler capability are two significant new features in this CPR. Particularly, Doppler capability is the first attempt to spaceborne atmospheric radar, which requires great efforts in technical development and feasibility validation. We have developed a new numerical simulation method to assess Doppler velocity accuracy applicable to this application, and results are compared with conventional approximation method. Validity and limitation of the approximation method are indicated from comparison with numerical method. It is shown that requirements to radar sensitivity and Doppler measurements will be satisfied. However, because these requirements to CPR are very tough, further detailed study on both design optimization and assessment technique development are necessary. Under radar operation with very high pulse repetition frequency (PRF) required in this CPR, surface clutter interference caused through antenna sidelobes is an important issue. Analysis on this issue and preliminary requirements to the antenna sidelobes are also discussed.

Measurement of Ocean Surface Currents by the CRL HF Ocean Surface Radar of FMCW Type. Part 2. Current Vector

The Communications Research Laboratory (CRL) has been developing high-frequency ocean surface radars (HFOSRs). The CRL dual-site HFOSR system can clarify the distribution of surface currents with a nominal range of 50 km. This paper presents a theoretical and experimental analysis of the measurement error of the current vector obtained by the CRL HFOSR system, using a comparison of instantaneous current vectors acquired by the HFOSR system and current meters moored at a depth of 2 m, taking account of the vertical current shear. The theoretical analysis shows that the probability distribution of the measurement error of the current vector forms concentric ellipses at a spatial scale that depends on the RMS measurement error of radial current velocity and with an aspect ratio that depends only on the azimuthal difference of the radar beams. When the azimuthal difference is a right angle, the measurement error of the current vector is at a minimum. A comparison between instantaneous current vectors measured by the CRL HFOSR system and moored current meters shows that the distribution of the difference vector between the radar current and the meter current agrees well with the theoretical measurement error of the current vector and that the RMS of difference vector length is about 10 cm s−1 while the azimuthal difference between two radar beams is between 45 and 135 degrees. The accuracy of current measurement by the dual-site HFOSR system is therefore considered to be less than 10 cm s−1 in this range of azimuthal difference. The theoretical analysis will be applicable for a wider range of the azimuthal difference of the radar beams.

Development results of TRMM precipitation radar

A precipitation radar (PR) has been developed by the National Space Development Agency of Japan (NASDA) in cooperation with the Communication Research Laboratory (CRL). The PR was integrated into the Tropical Rainfall Measuring Mission (TRMM) satellite and TRMM satellite system testing is ongoing by NASA. Throughout the various tests of PR it was confirmed that the PR satisfies its requirements.

On-orbit test and calibration results of TRMM precipitation Radar

Precipitation radar (PR) on-board the Tropical Rainfall measuring Mission (TRMM) satellite is the first rain radar to measure precipitation from space. After the successful launch of the TRMM satellite in last November, initial on- orbit test and calibration of the PR were conducted for about two months. From these tests, it was confirmed that on-orbit performances of the PR are fundamentally coincident with those verified at ground test and satisfy the specifications.

95-GHz cloud radar and lidar systems: preliminary results of cloud microphysics

In this paper, we report the preliminary studies of cloud microphysics by using ground-based 95GHz cloud radar and lidar systems. Although the active sensors are expected to increase our knowledge about clouds, e.g., vertical profiles of clouds, the single use of radar or lidar gives limited information and it is difficult to retrieve the ice water content (IWC and effective radius of cloud particles. We develop the new method for the combinational use of radar and lidar signals. The algorithm includes the attenuation corrections on both signals which is a long standing problems especially in the analysis of lidar signals. The system enables to retrieve the vertical profiles of effective radius and IWC in each cloud layer. Since both active sensors have dual polarization capabilities, the system provides a unique opportunity to study cloud microphysics form many aspects, e.g., vertical profiles of the relationship between effective radius, IWC and/or depolarization ratio. This system also has a great potential to study aerosol-cloud interaction studies.