Hiroaki Horie

Simulation of EarthCARE Spaceborne Doppler Radar Products Using Ground-Based and Airborne Data: Effects of Aliasing and Nonuniform Beam-Filling

This paper describes the expected performance of the Doppler cloud profiling radar being built for the Earth Cloud Aerosols Radiation Explorer (EarthCARE) mission of the Japanese Aerospace Exploration Agency and the European Space Agency. Spaceborne Doppler radar data are simulated starting from high-resolution Doppler measurements provided by ground-based and airborne Doppler radars, ranging from nonconvective to moderately convective scenarios. The method hinges upon spatial and spectral resampling to consider the specificities of the spaceborne configuration. An error analysis of the resulting Doppler product is conducted to address aliasing and nonuniform beam-filling (NUBF) problems. A perturbation analysis is applied to explore the latter problem and allow for a self-standing systematic correction of NUBF using merely the received reflectivity factor and mean Doppler velocities as measured by the instrument. The results of our simulations show that, at a horizontal integration of 1 km, after proper de-aliasing and NUBF correction, the radar will typically yield a velocity accuracy in the order of 1.3 m·s-1 over intertropical regions where the pulse-repetition frequency (PRF)=6.1 kHz, of 0.8 m·s-1 where the cloud-profiling radar (CPR) operates at PRF=7 kHz, and, of 0.7 m·s-1 over high latitudes where the CPR of EarthCARE will operate at PRF=7.5 kHz.

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.

The external calibration study for EarthCARE/CPR

The Cloud Profiling Radar (CPR) is one of key sensors on EarthCARE for joint project between Europe and Japan. The CPR is developed by National Institute of Information and Communications Technology (NICT) in Japan and Japanese Aerospace Exploration Agency (JAXA). The CPR uses W-band frequency and large antenna diameter in order to obtain enough sensitivity. In other words, beam footprint becomes small but antenna scanning cannot be performed. Two external calibration methods are considered. The first method is external calibration using active radar calibrator (ARC). It is foreseen the difficulty to place exact location on sub-satellite track. The second method is external calibration using naturally distributed target, such as sea surface. We describe about test experiment for first method and statistical analysis using satellite data for second method as the feasibility study.

A digital-analog hybrid technique for low range sidelobe pulse compression

Pulse compression using a digital-analog hybrid technique is studied to achieve very low range sidelobes for potential application to spaceborne rain radar. Range sidelobe suppression of 60 dB is attained in both calculation and test measurement by optimizing the transmission signal to cancel the defects in pulse compression process.

Design and development status of the EarthCARE Cloud Profiling Radar

The Cloud Profiling Radar (CPR) for the EarthCARE mission has been jointly developed by JAXA and NICT in Japan. The CPR is a millimeter-wave radar which has a large deployable antenna and its unique feature is vertical Doppler velocity measurement capability. The Engineering Model development and testing are now ongoing and the predicted performance will be verified after a series of tests. This paper will present the latest design and development status of the EarthCARE CPR.

Development status of cloud profiling radar for EarthCARE

Global three-dimensional cloud distributions and their properties are important information to estimate the earth radiation budget more precisely. The interactions between cloud particles and aerosols are also focused to improve accuracies of climate model. In order to meet expectations of scientists developing climate models for global warming problem, European and Japanese space agencies plan to launch a satellite called EarthCARE. The Cloud Profiling Radar (CPR), which will be the first millimeter-wave Doppler radar in space, is installed on this satellite as one of main sensors to observe clouds. This paper describes the latest design and development status of EarthCARE CPR.

Near nadir scattering properties at W-band frequency for the sea surface

The sea surface is considered a useful natural calibration target for satelliteborne cloud profiling radar with a narrow antenna beam. However, the normalized radar cross section (NRCS) of the sea surface at W-band frequency is not well known. It is known that the NRCS depends on the wind speed and direction over ocean. We made experiments to measure sea surface NRCS under various conditions using NICTs W-band airborne cloud profiling radar (SPIDER). The sea surface properties measured in this experiment are similar to these measured with microwave scatterometers at other frequencies

Retrieval of cloud microphysics using 95-GHz cloud radar and microwave radiometer

Vertical profile of liquid water cloud microphysics is retrieved by a newly proposed algorithm using radar and microwave radiometer. The data used in this algorithm is obtained form a 95-GHz cloud profiling radar (CPR) and a dual-wavelength microwave radiometer. This technique is applicable to liquid water clouds and its products are vertical profiles of attenuation-corrected radar reflectivity factor, liquid water content (LWC), and cloud dropsize distribution. The basic idea of this algorithm is to solve the radar equation with a constraint of integrated liquid water content (LWP: liquid water path) obtained from microwave radiometer. The main features of this algorithm are that it yields an attenuation-corrected radar reflectivity factor and the analytical solution is stable for the attenuation expected in typical stratocumulus clouds. Examples of its application to cloud data observed with a 95 GHz CPR and a microwave radiometer at Kashima, Japan on 4 February 2000 are described. The larger cloud drop size than the typical value retrieved and descending motion seen in the clouds examined is explained by the existence of drizzle particles in the lower part of cloud layer.

Test of the Specific Differential Propagation Phase Shift (KDP) Technique for Rain-Rate Estimation with a Ku-Band Rain Radar

Abstract The variation in drop size distribution (DSD) and the attenuation at higher frequencies are the two major impairments for quantitative rain-rate estimation. The sensitivity of rain-rate estimators (such as reflectivity factor Z, differential reflectivity ZDR, and the specific differential propagation phase shift KDP), to the variations in DSD, raindrop shape parameter, and also to the variation in temperature, is examined at 13.8 GHz using the T-matrix procedure. It has been found that KDP is not only less sensitive to the variations in these physical quantities but is also linearly related to rain rate. The degree of deviation in KDP due to raindrop shape variation is almost comparable to that due to the DSD variations. The computed phase shift upon backscattering, δ, is a very large quantity at 13.8 GHz (e.g., δ = 24° for a raindrop with 6.5 mm diameter). It has been noticed that δ is almost comparable to KDP and even higher than KDP, especially at lower rain rates. Nevertheless, through proper...

System Design of Cloud Profiling Radar for Earthcare

European and Japanese space agencies plan to launch a satellite called EarthCARE (Earth Clouds, Aerosols and Radiation Explorer). The Cloud Profiling Radar (CPR), which will be the first millimeter-wave Doppler radar in space, is installed on this satellite as a main sensor to observe clouds. This paper describes the outline of the system design of EarthCARE CPR.