For the special issue of the fully successful TRMM mission which is the first US-Japan joint mission launched by a Japanese rocket, the first attempt to measure global precipitation precisely and three dimensionally by a satellite-borne radar, and the first space project in Japan proposed and brought into reality by researchers except for with Institute for Space and Astrophysical Science, this article attempts to introduce the very essential facts of the desperate efforts by many people in the pre-historic era of the project that started in the middle 1970s and tries to send a cordial message for the young generations.
The concept of Tropical Rain fall Measuring Mission (TRMM) originates back in mid 1980's. After longer than 10 years of development by NASA, Communication Research Laboratory (CRL) and NASDA (National Space Development Agency of Japan), it was successfully launched in 1997. TRMM is now operating. For better understanding of the whole TRMM program, we introduce TRMM program. Topics cover as follows ; historical background, observing and scientific objectives, measuring precipitation by space remote-sensing, mission profile of TRMM satellite, raison d'être in the wide range of Earth Observing satellites worldwide, validation of precipitation, scientific research plan and the future follow-on mission. TRMM is a new Earth observing satellite and very different from LANDSAT, SPOT, NOAA, NASDA's MOS-1, JERS-1 or ADEOS. Through this introduction, the author hopes the maximum exploitation of TRMM data.
The Precipitation Radar (PR) onboard the Tropical Rainfall Measuring Mission (TRMM) satellite, the first rain radar in space, has been developed jointly by National Space Development Agency of Japan (NASDA) and Communication Research Laboratory (CRL), based on a basic research conducted at CRL since 1980s. From a series of tests on the ground before launch, the PR was found to meet almost all the specifications. It has also been confirmed from the initial check-out conducted just after the TRMM launch that the PR functions normally and holds the same performance as those measured before launch.
The TRMM precipitation radar (PR) data processing and analysis algorithms are developed by the international TRMM PR team. This paper outlines the TRMM PR algorithms. The total algorithm system with the flow diagram, and the functions of each algorithm are introduced. The validation methods of the TRMM PR algorithms and some examples of PR products obtained by the PR algorithms are also presented.
TRMM Microwave Imager (TMI) aboard Tropical Rainfall Measuring Mission (TRMM) offers a chance of new researches in two ways ; one is using 10 GHz data which are newly available from TMI, and the other is a composite utilization of data from TMI, Precipitation Radar (PR), Visible Infrared Scanner (VIRS) which are all aboard TRMM. From 10 GHz data, sea surface temperature (SST) can be retrieved, and, furthermore, sea surface wind speed under rainy condition, soil moisture over land will be expected. On the other hand, a method of mechanical calibration deployed for Special Sensor Microwave Imager (SSM/I) and TMI appears to have some calibration errors, which are revealed by intercomparison of SST between TMI and truth data. Composite utilization of TMI, PR, and VIRS will improve accuracy of retrieved parameters such as precipitation, SST, sea surface wind speed, snow water equivalence, and soil moisture.
Visible-Infrared Scanner (VIRS) is a five-channel visible-infrared radiometer on board TRMM. The VIRS will serve as a background imager and will provide the cloud context. The VIRS is also to serve as a 'bridge' from TRMM rainfall estimates to estimates made with geostationary satellite using VIS/IR technique. Therefore, the TRMM rainfall estimates can be used as a calibration data for the geostationary infrared rainfall estimate which has been done for 20 years. In this report, we review the current usage of corresponding VIRS channels for rainfall estimation and extraction of other useful meteorological information such as water vapor, cloud properties etc. Some preliminary results using the actual VIRS/PR/TMI data are also presented. The ratio of ch 1/ch 2 shows good indicator for dense ice cloud which correspond well to rain identified by PR. The smaller values of brightness temperature difference between ch 3 and ch 4, and also ch 4 and ch 5 show reasonable correspondence to rain area identified by PR.
TRMM consists of a several kind of sensors, one of which is CERES (Clouds and the Earth's Radiant Energy System). The objective of CERES is to estimate the earth radiation budget at the top of the atmosphere and the surface, which is depending on the earth-atmosphere activities. The radiation budget of the earth is one of basic parameters for climate research. The CERES has been designed for this purpose and can give successive products over ERBE. The CERES is not only on the TRMM, but also will be on the other polar orbiters because of its importance of data-succession. In this report, after a brief history of earth radiation budget research using satellite data, a basic concept of CERES and a flow of retrieval algorithm of radiation budget are introduced, and then an example of preliminary results is shown.
Lightning Image Sensor (LIS) which is equipped on Tropical Rainfall Measuring Mission satellite (TRMM) is introduced in this report. It is noticed that LIS consists of an optical detection system with telescope lens and CCD matrix, and a data processing unit. The specification of LIS is given from the aspects of both hardware and software. The preliminary observation results are presented. Discussions from meteorological aspects are presented, and the comparison with ground base measurement for the evaluation of LIS function is shown.
A precipitation radar (PR) has been first flown on TRMM satellite which was launched in November, 1997. Although a radar can give detailed rain rate distribution information, there are several uncertainties in estimated rain rate profiles caused by a variation of rain drop size distribution and attenuation of a radar wave due to rain itself. On the satellite, a multi-frequency microwave radiometer (TRMM Microwave Imager, TMI) is also installed in addition to the PR. This configuration allows us to use both the PR and TMI data simultaneously for effective estimation of rain rate profiles. After brief description of rain measurements with a radar and a radiometer, a TRMM day-1 radar/radiometer combined rain-profiling algorithm, which was developed for an early days application, is explained plainly. Some topics are suggested for future research on the radar/radiometer combined algorithm. The combined use of the PR and TMI data should not be only a supplemental use of each of them, rather it should be an advanced data fusion as a second generation algorithm.
The TRMM data processing and distribution system is very unique and the first attempt for NASDA and NASA. Now TRMM is operated by NASA and NASA receives TRMM data at NASA/WSC through TDRS. Received raw data are distributed to NASA/GSFC, NASA/LaRC and NASA/MSFC separately depending on the sensors. NASDA/EOC receives PR Level 0, HK, PR Q/L and TMI Q/L data from NASA/SDPF in GSFC, TMI Level 1 product from TSDIS, processed and combined data of TMI and VIRS from GSFC's DAAC, processed data of CERES from LaRC's DAAC, processed data of CERES from LaRC's DAAC and processed data of LIS from MSFC. PR level 0 are processed to Level 1, Level 2 and Level 3 products at both NASDA/EOC and TSDIS. EOC distributes these standard products of PR, TMI, VIRS, CERES, LIS and Combined data according to the data request from users through EUS or FAX. Usually these data one distributed by media such as 8 mm tape, DAT, CD-ROM or MO. New information for researchers is available at EORC home page. The URL is http://www.eorc.nasda.go.jp./TRMM/.
The life time of TRMM is only three years. This is mainly because of the fuel consumption. The three year life time is not enough to observe interannual variation of the monsoon activity. Thus, TRMM follow-on mission has been discussed for several years. The main objectives of TRMM follow-on are : (1) to extend the TRMM rain observation, (2) to observe with wider coverage up to near 60 degree latitude, and (3) to observe vertical structure of rain. Since the diurnal variation of the precipitation exists even in the mid and high latitude, non-sun synchronous orbit is required to avoid the bias. Good sensitivity and capability to discriminate rain and snow are required for the observation in mid- and high latitude regions. The vertical structure is very important to study the precipitation process and the latent heat release. It is also important to bridge to microwave radiometer estimations. To meet the objectives, the candidates of the core sensors are a dual-wavelength precipitation radar and a TMI-like microwave radiometer. A VIRS-type visible infrared radiometer and LIS are also desirable.