The NASA and the JAXA performed orbit boost maneuvers in November 2023 that raised the altitude of the Global Precipitation Measurement (GPM) Core Observatory from 407 km to 442 km to extend its lifetime. Effects of the orbit boost on the spaceborne precipitation radar have been investigated in the Tropical Rainfall Measuring Mission (TRMM). This study evaluates effects on Dual-frequency Precipitation Radar (DPR) observations due to the orbit boost. Spatial resolution at the nadir and swath width is changed at 5.04km×5.04km and 255.8 km at the satellite altitude of 407 km to 5.48km×5.48km and 277.9 km at the satellite altitude of 442 km, respectively. Observation data confirmed that changes in the sampling were larger in the cross-track direction (about 5 km to 5.5 km at the nadir). It was found that the DPR coverage tendency was changed by the GPM orbit boost. By analyzing measured radar reflectivity factor at storm top height over the ocean, the sensitivity degradation was found for about 0.8-0.9dB for KuPR, and about 0.7-0.9dB for KaPR.

This study investigated the effects of the difference of beam-pointing directions on the Doppler measurements from a spaceborne Ku-band precipitation radar. The Doppler measurement system was a displaced phase center antenna (DPCA) using two antennas that are displaced in the along-track direction. When the beam-pointing directions of the two antennas deviate, Doppler measurements can degrade. The well-known formula for the uncertainty in Doppler velocity measurement is extended to include the effect of the difference of the beam-pointing directions, and a simulation confirmed the formula. The results show that the uncertainty increases from 0.21 to 0.38 m/s for a case of$S/N = 20$dB when one antenna footprint center is displaced from the other by half of the half-power beamwidth.

Recently, calibration methods of the ground-based weather radars with reference to spaceborne precipitation radars, such as the Global Precipitation Measurement (GPM) Dual-Frequency Precipitation Radar (DPR), have attracted lot of attention, because of their cost effectiveness and near real-time inputs. This paper describes evaluations for radar reflectivity factors (Z-factors) of S-band and C-band ground-based radars over the Indian region with reference to the GPM/DPR observations. By statistical analyses, using a matching program between the ground-based radar and the GPM/DPR, the S-band ground-based radar measurements at Cherrapunji, Meghalaya, India tended to be significantly underestimated. In this case, a mean bias in the Z-factors was 13.203dBZ was computed. On the other hand, the C-band ground-based radar at Shar, Sriharikota, India was well-corresponded with the GPM/DPR and the mean bias tended to be small (0.688 dBZ).

To enhance precipitation monitoring, this study attempts integration among Global Precipitation Measurement (GPM) products such as the Dual-Frequency Precipitation Radar (DPR) and the merged satellite precipitation product, and ground-based radars. Here, radar reflectivity and rainfall composites are produced using three ground-based radars in Fiji. Calibration correction factors of the ground-based radars are calculated with reference to the GPM/DPR in the radar reflectivity composite. In the rainfall composite, two types of correction factors are calculated. One is a factor of the ground radars with the GPM/DPR, and the other is a factor of the merged satellite precipitation product with the ground-based radars. For making the composite, a weighting function is implemented with consideration of a beam height in the ground-based radar. These techniques can be helpful for the precipitation monitoring, because it allows seamless monitoring from the ground-based radar's observation range to satellite observation areas.

Beam matching accuracy between KuPR and KaPR was evaluated by external calibration using ARC. The averaged distance between the beam centers of KuPR and KaPR is 318 m for Rx and 269 m for Tx before the beam matching parameters were changed. After the change, the distance is 92 m for Rx and 85 m for Tx. The distance between the beam matched footprints of KuPR and KaPR during normal observation were confirmed using the geolocation. In the inner swath, the averaged distance before and after the scan pattern change is 140 m and 32 m, respectively. In the outer swath of KuPR angle-bin number 38 to 49 after the scan pattern change, the averaged distance is 48 m. However, the KuPR beams at angle-bin number 1 to 12 are slightly shifted from the corresponding KaHS beams in the along-track direction. The magnitude of misalignment is 301 m.

This article describes four-year calibration results of the dual-frequency precipitation radar (DPR) onboard the Global Precipitation Measurement (GPM) Core Observatory. The calibration method basically follows the method that was used to calibrate the precipitation radar (PR) onboard the Tropical Rainfall Measuring Mission (TRMM) satellite. However, both the hardware and data processing method for calibration are improved by taking advantage of the lessons learned from the PR’s calibration. Since the response of the radar receivers was found to depend on the waveform, the active calibrator was improved in such a way that the external calibration can be performed with both continuous and pulse waves. The methods for evaluating the calibration data were also improved. Instead of assuming a Gaussian antenna pattern, the effective beamwidths were determined by assuming an antenna pattern created by the Taylor distribution that was used to design the antennas. The results of the calibration including these improvements provide the new precise parameters of DPR’s calibration. The new parameters increased the Ku-band precipitation radar’s (KuPR’s) radar reflectivity factor ($Z$) by about 1.3 dB and that of the Ka-band precipitation radar (KaPR) by about 1.2 dB from the precalibrated$Z$values, and the minimum detectable radar reflectivities were 15.46, 19.18, and 13.71 dBZ for KuPR, matched beam of KaPR, and high-sensitivity beam of KaPR, respectively. After applying the new calibration methods to both DPR and PR, normalized radar cross sections ($\sigma ^{0}$) from the DPR and PR agree with each other.

The scan pattern of Dual-frequency Precipitation Radar (DPR) onboard the Global Precipitation Measurement (GPM) core satellite was experimentally changed for about 1 day from 13UTC on September 26th, 2017 to observe from nadir to about +34° scan angle assuming future spaceborne precipitation radar with wider swath width. The height and strength of the surface echo clutter with larger incident angle were assessed statistically to examine the possibility of the rainfall retrieval with wide swath observation by DPR. The results indicate that even in the larger incident angle, relatively intense rainfall can be retrieved while shallow and weak rainfall may not be acceptable for retrieval because it should be masked by surface clutter.

The Dual-frequency Precipitation Radar (DPR) installed on the Global Precipitation Measurement (GPM) core satellite was developed by the Japan Aerospace Exploration Agency (JAXA) and the National Institute of Information and Communications Technology (NICT). GPM core observatory was successfully launched by H-IIA launch vehicle on Feb 28, 2014. JAXA is continuing DPR trend monitoring, calibration and validation operations to confirm that DPR keeps its function and performance on orbit. The results of DPR trend monitoring, calibration and validation showed that DPR kept its function and performance on orbit during the 3 years and 2 months prime mission period. JAXA confirmed the prime mission results of GPM/DPR total system achieved the success criteria and the performance indicators. GPM/DPR moved to extended mission phase. JAXA conducted two types of scan pattern change test operations. These useful data will help feasibility studies of the proposed KaPR scan pattern for the next DPR product version up and the future spaceborne radar development.

The scan directions of the high sensitivity beams of the Ka-band channel (KaHS) of the Dual-frequency Precipitation Radar (DPR) onboard the Global Precipitation Measurement (GPM) mission Core Satellite were experimentally changed from the original near-nadir swath to match with the Ku-band beams in the outer swaths for a day in September 2017. With this mode of operation, the dual-frequency ratio (DFR) between the Ka and Ku band reflectivity factors can be obtained over the entire swath. Furthermore, the DFR in the outer swaths has a better signal-to-noise ratio because KaHS's sensitivity is better than the KaMS that scans over the inner swath. This paper outlines results of this special experiment and some of the benefits expected in this mode of operation that will be implemented as the standard mode of operation in the spring of 2018.

The Dual-frequency Precipitation Radar (DPR) installed on the Global Precipitation Measurement (GPM) core satellite was developed by the Japan Aerospace Exploration Agency (JAXA) and the National Institute of Information and Communications Technology (NICT). This paper describes mission objectives, technical performance, resource allocation, ground test results, orbital check out results and orbital operation status of the DPR. The DPR system PFT has completed in February 2012. GPM core spacecraft satellite system test has completed at NASA Goddard Space Flight Center 2013. GPM core observatory was shipped to JAXA Tanegashima Space Center, JAPAN and GPM core observatory was successfully launched by H-IIA launch vehicle on Feb 28, 2014. DPR orbital check out was completed in May 2014. DPR products were released to the public on Sep. 2, 2014 and Normal Observation Operation period was started. The DPR Prime mission period was completed in May 2017. The prime mission results of the DPR are reported.

The Dual-frequency Precipitation Radar (DPR) installed on the Global Precipitation Measurement (GPM) core satellite was developed by JAXA and NICT. This paper describes mission objectives, technical performance, resource allocation, ground test results, orbital check out results and orbital operation status of the DPR. The DPR system PFT has completed in February 2012. GPM core spacecraft satellite system test has completed at NASA Goddard Space Flight Center 2013. GPM core observatory was shipped to JAXA Tanegashima Space Center, JAPAN and GPM core observatory was successfully launched by H-IIA launch vehicle on Feb 28, 2014. DPR orbital check out was completed in May 2014. DPR products released to the public on Sep. 2, 2014 and Normal Observation Operation period was started. The orbital operations status of DPR is reported in this paper.

The Tropical Rainfall Measuring Mission (TRMM) satellite was boosted from 350 km to 402.5 km to conserve its fuel keeping the altitude. As a result, the quality of the Precipitation Radar (PR) data slightly changed and, a mismatch of PR's beam between the transmission and reception antennas happened. Although latest version (V7) of PR's level-1 algorithm is corrected by a method, some systematic error of the beam-mismatch correction is found as the left-right asymmetric bias for PR's rain estimates sorted by its scan angle. The current study is conducted to advance the accuracy of the beam-mismatch correction and evaluate its improvement. The current method of the beam-mismatch correction works over the oceans and land, and its improvement is evaluated as about 96 (73) % mitigating the asymmetric bias for PR's rain estimates over the oceans (land) comparing to the V7 product.

The Dual-frequency Precipitation Radar (DPR) installed on the Global Precipitation Measurement (GPM) core satellite was developed by JAXA and NICT. This paper describes mission objectives, technical performance, resource allocation, ground test results, orbital check out results and orbital operation status of the DPR. The DPR system PFT has completed in February 2012. GPM core spacecraft satellite system test has completed at NASA Goddard Space Flight Center 2013. GPM core observatory was shipped to JAXA Tanegashima Space Center, JAPAN and GPM core observatory was successfully launched by H-IIA launch vehicle on Feb 28, 2014. DPR orbital check out was completed in May 2014. DPR products released to the public on Sep. 2, 2014 and Normal Observation Operation period was started. The orbital operations status of DPR is reported in this paper.

This paper describes current status of the level 1 algorithm development and calibration for the Dual-frequency Precipitation Radar (DPR) onboard the Global Precipitation Measurement (GPM). JAXA has carried out the calibration for the DPR since the GPM core observatory was launched on February 28, 2014 (JST). As a result of the external calibration, it is detected that some biases seemed to exist. However, JAXA has not adjusted the calibration coefficient of the DPR level 1 algorithm because of two reasons. One is the errors of the external calibration. In the external calibration, the measurement error and estimation error for the power may occur. The other reason is the continuity of the surface backscattering cross section (denoted as σ0) from Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR). Requirement of the continuity has been satisfied by using the current calibration coefficient.

The Dual-frequency Precipitation Radar (DPR) installed on the Global Precipitation Measurement (GPM) core satellite was developed by JAXA and NICT. This paper describes mission objectives, technical performance, resource allocation, design, proto-flight test (PFT) of the DPR instrument, satellite system test including launch operations and orbital check out results of the DPR. The DPR system PFT has completed in February 2012. DPR has handed over to NASA and integration of the DPR to the GPM core spacecraft have completed in May 2012. GPM core spacecraft satellite system test has completed at NASA Goddard Space Flight Center. GPM core observatory was shipped to JAXA Tanegashima Space Center, JAPAN and Launch Site Operations has completed. GPM core observatory was successfully launched by H-IIA launch vehicle on Feb 28, 2014. DPR orbital check out had started in March 2014 and it was completed in May 2014. The orbital check out results of DPR is reported in this paper.

The Global Precipitation Measurement (GPM) mission consists of the GPM core Observatory (satellite) and the constellation satellites. The GPM core Observatory launched at 3:37 on February 28, 2014 (JST) from Tanegashima Space Center in Japan. It carries the Dual-frequency Precipitation Radar (DPR) and the GPM Microwave Imager (GMI). The DPR consists of Ku-band precipitation radar (KuPR) and Ka-band precipitation radar (KaPR). These radars have developed by Japan Aerospace Exploration Agency (JAXA) and National Institute of Information and Communications Technology (NICT) [1] and GMI has developed by National Aeronautics and Space Administration (NASA). The DPR level 1 algorithm has been developed by the JAXA. The main roles of level 1 algorithm are limit check for fatal and caution incidents, orbital cut and calculation of geometric information and transformation for engineering value. JAXA also has the responsibility of calibration of the DPR. The calibration methods have two types. One is the internal calibration with onboard calibration system, and the other is the external calibration with Active Radar Calibrator (ARC). These calibrations will carry out densely by the public data release. This paper describes the concepts of the level 1 algorithm and the calibration methods.

The Dual-frequency Precipitation Radar (DPR) installed on the Global Precipitation Measurement (GPM) core satellite is being developed by JAXA and NICT. This paper describes mission objectives, technical performance, resource allocation, critical design, proto-flight test (PFT) of the DPR instrument and satellite system test status. The DPR system PFT has completed in February 2012. DPR has handed over to NASA and integration of the DPR to the GPM core spacecraft have completed in May 2012. GPM core spacecraft satellite system test has started at NASA Goddard Space Flight Center. After completion of all satellite system tests, the GPM core spacecraft will be sent to JAXA Tanegashima Space Center and launched by H-IIA launch vehicle.

The Dual-frequency Precipitation Radar (DPR) installed on the Global Precipitation Measurement (GPM) core satellite is being developed by JAXA and NICT. This paper describes objectives, technical performance, resource allocation, preliminary design, development model test, critical design and proto-flight test (PFT) of the DPR instrument. The DPR system PFT will be completed in 2011. After completion of all PFT, the DPR instrument will be verified as a space borne radar.

The Dual-frequency Precipitation Radar (DPR) installed on the Global Precipitation Measurement (GPM) core satellite is being developed by JAXA and NICT. This paper describes the results of preliminary design of the DPR instrument. GPM

The Dual-frequency Precipitation Radar (DPR) installed on the Global Precipitation Measurement (GPM) core satellite is being developed by JAXA and NICT. This work describes the mission objectives, the precipitation measurement method and techniques, and the construction of the DPR.