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.
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.
A rain-rate range-profiling algorithm has been developed for 'standard' data processing of TRMM Precipitation Radar (PR). Major challenges in the algorithm include the corrections for the effects of rain attenuation and non-uniform beam filling (NUBF) and in the rejection of surface clutter. A combination of the Hitschfield-Bordan and surface reference methods is used to correct radar returns for the rain attenuation. The NUBF effects are estimated from the spatial variations of the estimated total path integral of attenuation from the top of rain to the surface in the vicinity of the radar beam concerned. In this paper, we first outline the range profiling algorithm. Next we show two examples of PR observation; a typhoon over Pacific and a squall line over Florida. In the Florida case, we compare the PR and ground-based radar measurements. The results indicate that this algorithm is basically working well. Further studies are needed to statistically evaluate the performance.
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.
An eight-element of bread board model for TRMM (Tropical Rainfall Measuring Mission) precipitation radar has been developed in Communications Research Laboratory (CRL), Japan. The active array system, which consists of all solid components, such as SSPA, LNA, and PIN-diode phase shifter, is integrated to check the basic performance as the spaceborn rain radar. After describing the characteristics of major components, overall performance of antenna scanning is described.
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