A dual Ka-band radar system is developed by the Japan Aerospace Exploration Agency (JAXA) for the GPM DPR
algorithm development. The dual Ka-radar system which consists of two identical Ka-band radars can measure both the
specific attenuation and the equivalent radar reflectivity at Ka-band. Those parameters are important particularly for
snow measurement. Using the dual Ka-radar system along with other instruments, such as a polarimetric precipitation
radar, a windprofiler radar, ground-based rain measurement systems, the uncertainties of the parameters in the DPR
algorithm can be reduced. The verification of improvement of rain retrieval with the DPR algorithm is also included as
an objective. Observations using the dual Ka-radar system were performed in Okinawa Island, in Tsukuba, over the slope
of Mt. Fuji, and in Nagaoka, Japan. In Okinawa Island, the performance of the measurement has been confirmed by rain
observation. In Tsukuba, one radar was directed in vertical and the other was in slant direction. By this configuration,
total attenuation in the melting layer was estimated. The objective of the Mt. Fuji experiment was to observe the melting
layer. In Nagaoka, a lot of wet snow fell, and much data on the snow have been obtained. The main results are measured
k-Ze relationships. For the rain, reasonable k-Ze relationship has been obtained. The feasibility of total attenuation in
melting layer has been studied. Different k-Ze relationships have been obtained in snow observations.
KEYWORDS: Algorithm development, Radar, Satellites, Microwave radiation, Meteorology, Calibration, Ka band, Detection and tracking algorithms, Signal attenuation, Standards development
In July 2009, NASA and JAXA signed implementation phase Memorandum of Understanding to be the central body for
creating the Global Precipitation Measurement (GPM) partnership. The Global Precipitation Measurement (GPM)
started as an international project and a follow-on mission of the Tropical Rainfall Measuring Mission (TRMM) project
to achieve more accurate and frequent precipitation observations than it. A Dual-frequency Precipitation Radar (DPR) on
board the GPM core satellite is being developed steadily by JAXA and NICT, and consists of Ku-band (13.6GHz) and
Ka-band (35.5GHz) precipitation radars to measure light rainfall and snowfall as well as moderate-to-heavy rainfall. The
GPM core observatory scheduled to be launched by Japanese H-IIA rocket in summer of 2013.
In January 2010, JAXA has selected the principal investigators by the 6th Precipitation Measuring Mission (PMM)
Research Announcement, especially focusing on the GPM algorithm development and pre-launch validation. The GPM
standard algorithm will be developed by U.S.-Japan Joint GPM Algorithm Team, and Japanese members will play
central role in developing DPR and DPR/GMI combined algorithms. Pre-launch validation aims to contribute to the
development and improvement of algorithms, through validating parameter errors, which are involved in satellite-based
precipitation retrieval algorithms, such as attenuation by precipitation particles, raindrop size distribution, and drop
velocity and density of snowfall. JAXA will put two new field-portable Ka-band Ground Validation radars in 2009-2010
to achieve this target.
The new science team will be organized in April 2010, and team members expected to make effective interactions
between algorithm development and pre-launch validation activities.
The Global Precipitation Measurement (GPM) started as an international project and a follow-on and expansion of the
Tropical Rainfall Measuring Mission (TRMM). The GPM mission consists of two different categories of satellites. One
is a TRMM-like core satellite carrying both active and passive microwave instruments, jointly developed by Japan and
the US. The other is a constellation of satellites carrying passive microwave sensors and provided by partner agencies.
A Dual-frequency Precipitation Radar (DPR) for the GPM core satellite is being developed by JAXA and NICT, and
consists of Ku- and Ka-band precipitation radars to measure light rainfall and snowfall as well as moderate-to-heavy
rainfall. One major objectives of GPM is to contribute to operational utilization, and frequent and accurate precipitation
products, at less than 3-hour intervals, will be produced by combining multi-satellite microwave radiometers and
geostationary IR information. DPR will provide accurate rainfall database to microwave radiometers, and enhance their
algorithms, which will be used to make frequent rainfall map.
The DPR L1 algorithms are being developed by JAXA. Collaboration activities between Japan and the US have started
to develop L2/3 rainfall algorithms for DPR, and DPR/GMI combined products. Research activities to develop
algorithms for rainfall map products have been underway both in Japan and the US. Validation activities in JAXA will
be focused on contributions to algorithm development before and after the launch, as well as evaluation of the quality of
rainfall products. Pre-launch validation will include ground-based campaigns and utilization of synthetic data produced
by numerical models.
This paper introduces the present status of TRMM PR vesrion6 standard algorithms and proposes the possible
improvements of them in version 7. The present PR standard algorithm system is composed of 1B21, 1C21, 2A21, 2A23,
2A25, 3A25 and 3A26 algorithms. These algorithms are used to analyze more than ten-year TRMM PR data. The
algorithm 1B21 calculates PR received power, and 1C21 calculates Z value without rain attenuation correction. The
algorithm 2A21 calculates surface reference sigma-zero values and estimates the path-integrated attenuation(PIA) by
rain. The algorithm 2A23 detects bright band and classifies the rain type into the stratiform type, convective type and
others. The algorithm 2A25 estimates rain rate profiles and Z profiles with rain attenuation correction for each radar
beam. The algorithm 3A25 gives monthly statistical values of level 2 products. The algorithm 3A26 calculates monthly
averaged rain rates of 5 degree by 5 degree boxes by applying the multiple threshold statistical method.
Global Precipitation Measurement (GPM) started as an international mission and follow-on and expand mission of the
Tropical Rainfall Measuring Mission (TRMM) project to obtain more accurate and frequent observations of precipitation
than TRMM. The TRMM satellite achieved ten-year observation in November 2007, and is still operating to measure
tropical/subtropical precipitation. An important goal for the GPM mission is the frequent measurement of global
precipitation using a GPM core satellite and a constellation of multiple satellites. The accurate measurement of
precipitation will be achieved by the Dual-frequency Precipitation Radar (DPR) on the GPM core-satellite, which is
being developed by Japan Aerospace Exploration Agency (JAXA) and National Institute of Information and
Communications Technology (NICT) and consists of two radars, which are Ku-band precipitation radar (KuPR) and Kaband
radar (KaPR). KaPR will detect snow and light rain, and the KuPR will detect heavy rain. In an effective dynamic
range in both KaPR and KuPR, drop size distribution (DSD) information and more accurate rainfall estimates will be
provided by a dual-frequency algorithm. The frequent precipitation measurement every three hours at any place on the
globe will be achieved by several constellation satellites with microwave radiometers (MWRs). JAXA/EORC is
responsible for the GPM/DPR algorithm development for engineering values (Level 1) and physical products (e.g.
precipitation estimation) (Level 2 and 3) and the quality control of the products as the sensor provider. It is also
important for us to produce and deliver frequent global precipitation map in real time in order to make useful for various
research and application areas (i.e., the prediction of the floods).
The Global Precipitation Measurement (GPM) mission started as an expanded follow-on mission of the Tropical Rainfall
Measuring Mission (TRMM) project to obtain more accurate and frequent observations of precipitation than TRMM. An
important goal for the GPM mission is the frequent measurement of global precipitation using a GPM core satellite and a
constellation of multiple satellites. The GPM core satellite is developed by the US and Japan as like as TRMM, while the
constellation satellites are developed by various countries. The accurate measurement of precipitation will be achieved
by the Dual-frequency Precipitation Radar (DPR) installed on the GPM core satellite. DPR consists of two radars, which
are Ku-band (13.6 GHz) precipitation radar (KuPR) and Ka-band (35.5 GHz) radar (KaPR). KaPR will detect snow and
light rain, and the KuPR will detect heavy rain. In an effective dynamic range in both KaPR and KuPR, drop size
distribution (DSD) information and more accurate rainfall estimates will be provided by a dual-frequency algorithm. The
frequent precipitation measurement every three hours at any place on the globe will be achieved by several constellation
satellites with microwave radiometers (MWRs). JAXA/EORC is responsible for the GPM/DPR algorithm development
for engineering values (Level 1) and physical products (e.g. precipitation estimation) (Level 2 and 3) and the quality
control of the products as the sensor provider. It is also important for us to produce and deliver 3-hourly global
precipitation map in real time in order to make useful for various research and application areas (i.e., the prediction of
the floods). To secure the quality of estimates, the mission must place emphasis on validation of satellite data and
retrieval algorithms.
The Global Precipitation Measurement (GPM) mission is an expanded follow-on mission of the current Tropical Rainfall
Measuring Mission (TRMM). The concept of GPM is, 1) TRMM-like, non-sun-synchronous core satellite carrying the
Dual-frequency Precipitation Radar (DPR) to be developed by Japan and a microwave radiometer to be developed by
United States, and 2) constellation of satellites in polar orbit, each carrying a microwave radiometer provided by
international partner. The constellation system of GPM will make it possible every three-hour global precipitation
measurement. Because of its concept on focusing high-accurate and high-frequent global precipitation observation, GPM
has a unique position among future Earth observation missions. GPM international partnerships will embody concept of
GEOSS. Observation data acquired by the GPM mission are expected to be used for both Earth environmental research
and various societal benefit areas. One of most expected application fields is weather prediction. Use of high-frequent
observation in numerical weather prediction models will improve weather forecasting especially for extreme events such
as tropical cyclones and heavy rain. Another example is application to flood monitoring and forecasting. Recent
increasing needs of real-time flood information required from many countries especially in Asia will strongly support
operational application of GPM products in this field.
It is essential to measure global precipitation not only for the research of the climate change but also for the water resources management. In order to satisfy the requirements, the Global Precipitation Measurement (GPM) mission was proposed jointly by US and Japan. The basic concept of the GPM is to provide three hourly global precipitation maps using eight constellation satellites equipped with microwave radiometers and a core satellite equipped with the Dual-frequency Precipitation Radar (DPR) and a microwave radiometer. The DPR that uses radio waves of 14 and 35 GHz is now being developed in Japan. The DPR will observe three-dimensional precipitation structure and will provide essential data for microwave rain retrieval. GPM is partly a follow-on mission of the Tropical Rainfall Measuring Mission (TRMM), but the GPM will extend the observation to cold regions where solid precipitation frequently exists. Rain retrieval algorithms that use the DPR data are also being developed. Using two wavelength data, two parameters in the raindrop size distribution could be retrieved, which would result in precise rain retrieval. The retrieval of solid precipitation rate is another challenge. Several algorithms including a combination with the microwave radiometer would be applied to the DPR. It is important for the DPR algorithm validation to compare between precipitation rate through the calculation of DPR algorithm and that of the directly observed precipitation rate over the validation site. For this purpose, the most important and difficult issue is to construct the database of the physical parameters for the precipitation retrieval algorithms of DPR from the ground-based data using well-calibrated instruments.
The altitude of the Tropical Rainfall Measuring Mission (TRMM) satellite was raised from 350km to 402.5km in August 2001 in order to extend its lifetime. The minimum detectable value of Z-factor after the boost is 1.2dB higher. We compared the actual PR products before and after the altitude increase using statistical methods in order to verify the algorithms and the Precipitation Radar (PR) rain products after the orbit was raised, and to confirm the influence of raising the orbit on PR rain products. The reflectivity factor histograms do not exhibit any significant changes after the raising of the satellite, except for a 1.2dB increase of the minimum detectable value. The results are consistent with the estimation before the raising. The monthly global average of the conditional rain rate in 3A25 product increased 0.2 mm/h after the orbit raising. This result corresponded to the simulated rainfall average estimated from the 1C21 product before the raising. Changes in monthly global rainfall average of unconditional rain, height of rainfall and height of bright band due to the orbit raising were not significant. This result shows that the orbit change had little influence on the PR estimation.
The first Doppler radar observation on the Tibetan Plateau was conducted for the GEWEX/GAME-Tibet project in 1997 and 1998 in order to clarify the evolution and mesoscale structure of the rainfall system. The TRMM satellite also observed the rainfall in the Tibetan area in 1998. TRMM's precipitation radar (PR) detected a diurnal cycle of rainfall in Tibet. Much rainfall was brought both by convection in the daytime and by stratiform precipitation over a wide rain area in the evening. A case study was conducted to clarify the structure of stratiform rainfall. On 7 July, a synoptic convergence area developed in the southern part of the Plateau in the evening. Small convective echoes and stratiform echoes coexisted in the radar coverage at the beginning of the rainfall. Southwesterly wind dominated above the 6km ASL, but the wind direction below 6km ASL was variable during the rainfall. On 8 July, a cold front between southwesterly wind and northerly wind was detected over the radar site. A sudden wind direction change from westerly to northwesterly was observed below 8km ASL from the vertical profiles at the radar site with the passage of the cold frontal surface. The precipitation with the frontal passage was stratiform and has a low echo top.
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