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.
The Global Precipitation Measurement (GPM) is a successor to the Tropical Rainfall Measuring Mission (TRMM)
which has opened a new era for precipitation system measurement from space. The scope of GPM is much wider than
that of TRMM. GPM will provide three hourly precipitation observation over the globe, that is, much higher temporal
resolution with wider coverage than TRMM. Current precipitation measurement is far from enough for the water
resources management which requires very high spatial and temporal resolution. The three hourly global precipitation
observation with GPM which will be attained by international collaboration with microwave radiometers will greatly
contribute not only to the precipitation sciences but also to real-world applications. GPM consists of a core satellite and
constellation satellites (Fig. 1). The GPM core satellite will be equipped with a dual-wavelength radar (DPR) and a
microwave radiometer, and will work to provide reference standard for the GPM constellation radiometers. Development
of DPR, the key instrument, has already been completed and delivered to NASA by JAXA. Ground measurements of
precipitation using newly developed Ka-radar system for DPR algorithm development are undergoing. The rain retrieval
algorithms are being developed with close collaboration with NASA.
Bangladesh region is interesting regions in a core region of the Asian monsoon. The Bangladesh region is a very flat
region facing to the Bay of Bengal. The precipitaion characteristics are studied using the long-term Tropical Rainfall
Measuring Mission (TRMM) data. Over the Bangladesh, the stability of the atmosphere seems to affect the precipitation
system in the vertical profiles. In the pre-monsoon season, rain rate increases with height in the lower part of the profile,
while in the mature monsoon season, rain rate is nearly constant in the lower part of the profile. The structure of
precipitation system is more persistent and homogenous in the mature monsoon season. The rain top is higher in premonsoon season than in mature monsoon season. The rain total is generally determined by rain frequency. The
horizontal size of the precipitation systems is larger for pre-monsoon season than for mature monsoon season. In other
words, the precipitation system is small but many in the mature monsoon season. This fact may be explained that the
atmosphere is sufficently humid to be easily triggered by small liftings. These characteristics are reflected in the rain
retrieval biases in precipitation radar and microwave radiometers in space.
We have been developing a data-set of global land surface microwave emissivity calculated from 9-channel Bright ness Temperatures (TBs) from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and atmospheric profile data from Japanese 25-year Reanalysis Project (JRA-25). The surface emissivity is derived using the non-scattering radiative transfer equation for regions identified as no-rain by TRMM Precipitation Radar (PR). An Empirical Orthogonal Function (EOF) analysis has been applied to this emissivity data-set. Emissivities at high frequencies, difficult to estimate due to high sensitivity to clouds and water vapor, are estimated from lower frequencies by using the principal components. Contributions from EOF1 to EOF4 are
dominant and with the others being less than 1 %. Therefore, 5 high-frequency emissivities can be estimated
from the other 4 emissivities at lower frequencies with 4 principal components. For example, when 37 GHz Horizontal emissivity on June 1998 is estimated from 4 channels of 10 and 19 GHz, correlation coefficient with the original estimate is 0.93 and the result of linear fitting shows an inclination of 0.97 and a cutoff of 0.02 for global data. This estimation method is applied for each area, each land surface condition (surface type and soil wetness) and so on, in search of optimal performance of the algorithm. The advantage of using the EOF analysis as described above is to minimize the cloud contamination at high frequency TB. A cloud-clearing method is also explored to improve the reliability of the EOFs.
The Global Precipitation Measurement (GPM) is a successor of the Tropical Rainfall Measuring Mission (TRMM)
which has opened a new era for precipitation system measurement from space including much better global rain maps.
The scope of GPM is much wider than that of TRMM. GPM will provide three hourly precipitation measurement over
the globe, that is, much higher temporal resolution with wider coverage than TRMM. Current precipitation measurement
is far from enough for the water resources management which requires very high spatial and temporal resolution. The
three hourly global precipitation measurement with GPM will greatly contribute not only to the precipitation sciences but
to real-world applications. The GPM core satellite will be equipped with a dual-wavelength radar (DPR) and a
microwave radiometer, and will work as a reference standard for the GPM constellation radiometers. The development
of the space segment is going well, and the core satellite launch is scheduled in the middle of 2013. DPR is a 14/35 GHz
radar system. The 14 GHz radar is similar to the TRMM precipitation radar but the 35 GHz radar is a new one with
scanning ability. The rain retrieval algorithms using DPR is underway. The basic idea is to use the difference of rain
attenuation at two frequencies in the liquid layer, and the deviation from the Rayleigh scattering in the solid precipitation
layer. Field experiments for the DPR algorithm development are also designed. A dual Ka-band radar system which is
now being developed will be a powerful tool for the field experiments. The dual Ka-radar system can measure both the
specific attenuation and the equivalent radar reflectivity at Ka-band.
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.
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
The Huaihe River basin has dry winter and wet summer seasons, and the structure of the atmospheric boundary layer
shows the seasonal march. The change was continuously observed using a flux tower, a Doppler sodar, and a boundary
layer profiler for more than two years. The mixed layer development was strongly affected by the surface conditions, that
is, the wheat field, bare soil, and paddy field. When the surface is wet, the development of the mixed layer is weak and
vice versa. Generally, the development was controlled by the surface sensible heat flux. But the development of the
mixed was also affected by large scale up/downdraft. When a large scale subsidence exists, the development of the
mixed layer is suppressed. A so-called LES simulation was performed in order to study the vertical profiles of the
sensible heat and latent heat fluxes. It was found that the profile over paddy field is in between those over dry land and
over ocean. The importance of the buoyancy due to the water vapor was also confirmed.
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.
Global precipitation measurement is essential not only for the research of the global change but also for the water resources management. Currently, satellite precipitation measurement is not sufficient for the detailed study of the precipitation and is far from enough for the water resources management which requires very high spatial and temporal resolution. To fill the gap at least partly, the Global Precipitation Measurement (GPM) 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 which uses radiowaves of 13 and 35 GHz is now being developed in Japan. The DPR will observe 3D 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 retreaval of solid precipitation rate is another challenge. The solid precipitation has another parameter of density which varies significantly. The hydrometeor shape also deviates significantly from a sphere. Several algorithms including a combination with the microwave radiometer would be applied to the DPR.
A strong candidate for the next generation spaceborne rain radar is a dual-wavelength one. The performance of the radar was studied. First, the sensitivity of the shorter wavelength radar was investigated. Based on the data taken by a single-wavelength precipitation radar aboard the Tropical Rainfall Measuring Mission satellite, the frequency distribution of the received power of the shorter wavelength radar was calculated assuming typical rain attenuation. If the receiver noise level is equivalently about 10 dBZ, the missing rain fraction is about 15.41% over land and 3.22% over ocean. Second, the accuracy of the rainrate estimate was studied based on disdrometer measured data. The intrinsic radar signal fluctuation, the Mie scattering effect and receiver noise effect were incorporated. The result shows good potential for accurate rainrate estimate. Third, rainrate estimate of dry snow was investigated. Based on the disdrometer data, snow particle distribution was generated using non-coalescence, non-breakup assumption. After using an empirical relationship between snow density and particle size, a rainrate retrieval formula for snow was proposed. It was also shown that dual-wavelength radar has a good capability for discrimination of snow from rain.
Mirror image is a virtual image of precipitation below the ocean surface when we use an airborne or a spaceborne radar to view the rainfall over ocean. It is due to a double reflection, that is energy reflected form the sea surface goes to the precipitation and back to the radar via a second reflection at sea surface. We investigated the mirror image characteristics using TRMM Precipitation Radar data and found: 1) The radar can detect the mirror image clearly over the ocean, 2) the mirror image echo corresponds well to the direct rain echo at nadir and near nadir incidence angle, 3) in a weak rain region, mirror echo intensity is nearly proportional to the direct echo power except near noise level, 4) in the strong rain region, rain attenuation effect clearly appears, and 5) the ratio of mirror echo power to direct echo power is affected by the rain attenuation which varies with the bright band height and the range of the target rain from surface. Further, we performed a simple simulation in order to confirm the above characteristics. The signal fluctuation, noise contamination, rain attention and surface cross section are taken into account in the simulation, and the results of simulation confirmed the observation results.
We have been working on rainfall observation project at tropical site in India, in order to study tropical storm structure and raindrop size distribution (DSD) characteristics for improving the current PR rainfall retrieval algorithm, and for making the ground validation of TRMM PR observation. At Gadanki (53-MHz VHF MST radar, an L-band lower atmospheric wind profiler (LAWP), a disdrometer and an optical rain gauge (ORG) are set up to obtain more knowledge on vertical properties of DSD and rain structure during monsoon season. Measurements of drop size distribution (DSD) with disdrometer have been providing the information to study basic DSD characteristics in tropical India. We have found a clear seasonal dependence in Reflectivity (Z) - Rainfall (R) relations (i.e. DSD characteristics) in India. Our results indicate that there are about 3-times differences peak-to-peak in estimates of rain rate using a single Z-R relation. It seems that this type of seasonal dependence should be taken into account to improve the accuracy of the PR algorithm. Drop size distribution characteristics were retrieved in moderate/heavy precipitation using VHF wind profiler. The retrieved drop size parameters were compared to corresponding disdrometer data and found that there is reasonably good agreement between the measurements, lending credence to the profiler retrievals of DSD parameters. Preliminary study on the ground validation of TRMM PR shows fairly good agreement between the disdrometer and TRMM precipitation radar measurements.