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Institute for Space−Earth Environmental Research, Nagoya U.

Lessons learned from cal/val activity for
GPM/DPR

Nobuhiro Takahashi
Institute for Space-Earth Environmental Research (ISEE),Nagoya University, Japan
Pre-launch EarthCARE science and validation WS,
13-17, November 2023

Japanese spaceborne precipitation radars and cloud profiling radar
Institute for Space−Earth Environmental Research, Nagoya U.

overlapping
period

2
1995

2000

2005

2010

1997 - 2015

2015

2020
GPM/DPRKu-band (13.6GHz)
Ka-band (35.5GHz)

TRMM/PRKu-band (13.8GHz)

2025

2030

EarthCARE/CPR
w-band (94 GHz)
with Doppler

2014-orbit boostoverlapping
periodTropics to mid-latitude
single frequency to dual frequency
TRMM precip.

GPM precip.

PMM/KuDPR
Ku-band (13.6GHz)
Doppler

Better sensitivity & Doppler

Development of multi-satellite precipitation map
GSMaP (0.1 x 0.1 deg., hourly)

1.Understanding cloud-precipitation processes
2.Collaboration with numerical models
3.Monitoring extreme phenomena

Technological heritage and Challenges
1.Phased array technology from TRMM/PR,
GPM/DPR
2.Doppler velocity measurement technology
from EarthCARE/CPR
3.Challenges to DPCA technology

GPM/DPR

KuPR

Institute for Space−Earth Environmental Research, Nagoya U.

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 GPM core observatory launched Feb. 28, 2014
 It will be in operation beyond 2030 because of orbit
boost (400 to 443 km) in November 2023

 KuPR 13.6 GHz footprint 5 km swath 245 km
 sensitivity: 17 dBZ

 KaPR 35.5 GHz footprint 5 km swath 120 km (245 km after May 2018) sensitivity: 12 dBZ (high sensitivity mode) First introduction of variable PRF
 EarthCARE/CPR introduces same approach Matched beam between Ku- and Ka-bandradars128-elementantenna

KaPR
128-element
antenna

Institute for Space−Earth Environmental Research, Nagoya U.

Calibration and validation of DPR
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 Calibration
 Internal calibration for Receiver system
 External calibration using ARC for overall performance of the radar
 target: 1 dB accuracy

 Long term monitoring σ0 (normalized surface backscattering cross section)
 target: 0.1 dB accuracy

 Validation
 Rainfall
 gauge (simultaneous data for statistical comparison) operational radar (simultaneous data for statistical comparison) phased array radars (simultaneous 3D comparison) Snowfall
 radar (simultaneous data for statistical comparison) in-situ (particle measurements at ground/balloon)Calibration of GPM/DPR
Institute for Space−Earth Environmental Research, Nagoya U.

5Active Radar Calibrator (ARC)

Scan pattern during external calibration
DPR operates 3-times dense sampling

Masaki et al. (2020)
Add description

ARC• External calibration using Active Radar Calibrator (ARC) to calibrate overall performance of theradar (echo power, not for Doppler)• 10 times a year (Masaki et al. 2020)• Antenna pattern is also estimated• Internal calibration to see the relationship between received power and output digital count.
• These ideas are common both GPM/DPR and EarthCARE/CPR

External calibration result (Ku-band)
Institute for Space−Earth Environmental Research, Nagoya U.

6• both radar show the accuracy within 0.5 dB• No increasing/decreasing trend cannot be seen with this accuracy

KuPR 受信系
KuPR Receiver

KuPR Transmitter
Courtesy of T. Masaki (RESTEC)• More precise trend of radar performance is evaluated by using normalized
surface backscattering cross section (𝜎 0 ) statistically𝜎 0 trendInstitute for Space−Earth Environmental Research, Nagoya U.

7• using the 9-degree incident angle data
• almost independent from sea surface wind.

• Statistical analysis shows a slight trend (-0.03dB/yr).
• This change affects the global precipitation trend.

• Statistics of 𝜎 0 will be available for EarthCARE/CPR . Careful treatment is needed
to remove the effect of sea surface wind, because CPR is nadir looking radar.
• From this viewpoint, roll maneuver is important for CPR calibration.
Monthly averaged 𝜎 0Courtesy of T. Masaki (RESTEC)

Validation in the GPM/DPR (rainfall)Institute for Space−Earth Environmental Research, Nagoya U.

8 statistical approach using ground instrument
network by Japan Meteorological
Agency (JMA)
JMA rain gauge stations

About 1,300 stations (average intervals of 17
km throughout Japan)( figures provided by JMA )Accumulated snowfall amount(Nov. 2014-May 2015)

JMA radar network

JMA operates a network of 20
C-band Doppler weather radars
across Japan

Validations with JMA rain gauge data
Institute for Space−Earth Environmental Research, Nagoya U.

9Error = (DPR – Gauge)/Gauge (%)

6 areas
A.
B.
C.
D.
E.
F.

Averaged errors over Japan:-11.9% (DPR)

Pacific Ocean side
Inland Sea area
Sea of Japan side
KantoTohoku
Hokkaido•••••

Two years of data from April 2014 to March 2016
AMeDAS data at overpasses only
Gauge data are 10 min data immediately after the overpasses
Rain total is estimated at each 0.5×0.5 deg. box, and means andstandard deviations of 6 colored areas are calculated.
To exclude snow fall data, if the surface temperature is below 6degrees, data in that box are not used.
Oki et al. (2020, https://doi.org/10.1007/978-3-030-35798-6_3)

Validations with the US MRMS
 US Multi-Radar Multi-Sensor (MRMS) Dataset (provided by NASA GV team) June 2014 – May 2015 without winter season (Dec. Jan. Feb)
 DPR overpass time only
Error = (DPR – MRMS)/MRMS (%)
Averaged errors over the US:-4.8% (DPR)

DPR - MRMS
MRMS

Institute for Space−Earth Environmental Research, Nagoya U.

10Oki et al. (2020, https://doi.org/10.1007/978-3-030-35798-6_3)

GPM GV field campaigns in Japan

Institute for Space−Earth Environmental Research, Nagoya U.

11Focusing mainly on solid precipitation and melting snow to validate because DPR
is expected for better estimation of snow.

Ship-based campaign
in 2015 with JAMSTEC

Dual Ka radarsystem facing eachother for precise
attenuation
measurement(Nakamura et al. 2011, 2018,2021)

Site

Targets

PeriodPI

Parameters

Instruments

Okinawa

Rain(Subtropics)-- July 2011

Nagoya Univ.
/NICT/JAXA

Rain Rate,
Attenuation characteristics (Ka),DSD (profile, ground),Melting layer depth,

Ka-band GV radar x2,
COBRA
400MHz WPR,2DVD,
Disdrometer,
Micro Rain Radar (MRR), ORG

TsukubaRain(theTemperateZone )/Melting layer

Summer
2011

NIED,
Nagoya Univ.
/NICT/JAXA

Rain Rate,
DSD (profile, ground),Attenuation profile through melting
layer

Ka-band GV radar x2,
KaW-band radar,
400MHz WPR,
2DVD, Disdrometer,
Micro Rain Radar (MRR), ORG

Mt. Fuji

Melting
layer

Autumn2011

Nagoya Univ.
/NICT/JAXA

Attenuation profile through melting
layer,DSD (profile, ground)Ka-band GV radar x2,2DVD,
Disdrometer,
Micro Rain Radar (MRR), ORG

Nagaoka

Wet snow

Winter2012

NIED,Nagoya Univ.
/NICT/JAXA

DSD (profile),
Rain rate (snow),
Attenuation characteristics, (Ka)
Snow particle parameters (density,particle size, falling speed etc., )Ka-band GV radar x2,
X-band Radar, Lidar,
2DVD,
Snow Particle Obs. system

SapporoSnow(dry/wet)
RainSprinter2012 –winter 2013

Hokkaido
Univ.,
Nagoya Univ.
/NICT/JAXA

Rain profile,Rain rate (rain, snow),
Attenuation characteristics,
Snow particle parameters (density,particle size, falling speed etc., )Ka-band GV radar x2,
X-band radar,
2DVD, Lidar,Micro Rain Radar (MRR),
Snow Particle Obs. system

Mt. Zao

MeltinglayerAutumn
2013-May 2015

Nagoya Univ.
/NICT/JAXA

Attenuation profile through melting
layer,DSD (profile, ground)Ka-band GV radar x2,2DVD, ORG, Disdrometer,
Micro Rain Radar (MRR)Institute for Space−Earth Environmental Research, Nagoya U.

12Particle fall velocity measurement
By K. Suzuki(Yamaguchi Univ.)
by a newly-developed particle imaging radiosonde "Rainscope"
Rainscope is a balloon-borne particle imaging radiosonde. It can capture clear images ofprecipitation particles, and is equipped with two infrared sensors, so it is possible to measure thefall velocity of particles in clouds by measuring the passing time.
Convective caseon June 25, 2022

Fig. Particle images obtained
from Rainscope launched into
convective thunderstorm cloud.
Values indicate temperature,diameter, and terminal velocity,respectively.

Phased Array Weather Radar (PAWR) and MP-PAWR
Institute for Space−Earth Environmental Research, Nagoya U.

13❑ Full 3D scan in 30 sec❑ It is possible to compare simultaneouscomparison of 3D structure❑ Detail of this radar is shown in poster

PAWR (Okinawa/NICT)

MP-PAWR
MP-PAWR （Kobe/NICT)PAWR （Tsukuba/MRI）PAWR （Chiba/JRC)

MP-PAWR （Osaka/Osaka U. & NICT)By User:Monaneko - File:Japan template large.svg, CC 表示-継承 3.0,
https://commons.wikimedia.org/w/index.php?curid=24076518

validation using GPM-CloudSat matchup data
Institute for Space−Earth Environmental Research, Nagoya U.

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A-Train – GPM collocated dataset (Turk et al. 2021)

 GPM-CloudSat matchup
data set (Turk et al.,2021) is used tocompare DPR profile
with CloudSat/CPR.
 It helps for better
understand ofprecipitation system.
 JAXA is preparing tocreate synergetic
dataset collocated
GPM-EarthCARE data.

Institute for Space−Earth Environmental Research, Nagoya U.

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Summary: comparison of cal/val between
GPM/DPR and EarthCARE/CPR[CAL]Echo power

GPM/DPR• scanning radar• power only
ARC + σ0

EarthCARE/CPR• nadir looking• power and Doppler
ARC + σ0 ＋ roll maneuver[CAL/VAL]Doppler velocity

N/A

ARC (for pointing of CPR)sea surface Doppler velocity[VAL]Geophysical value(method)rain (rain gauge, radar)snow (in-situ, polarimetricradar)cloud (radar, in-situ)
ice (cloud radar, polarimetricradar and in-situ)
velocity (WINDAS, verticalpointing radar)• For GPM/DPR, statistical approach is needed for precise calibrationand validation that is reflected to cal/val plan for EarthCARE/CPR.
• Validation of solid precipitation needs comprehensive observation
including in-situ ground-based observation, remote sensing, balloon
observation and so on.

Thank you for your attention
Institute for Space−Earth Environmental Research, Nagoya U.

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By K. Suzuki(Yamaguchi Unv.)

Particle fall velocity measurement
by a newly-developed particle imaging radiosonde "Rainscope"
Institute for Space−Earth Environmental Research, Nagoya U.

(a)Water droplet(Atlas et al. 1973)(b)

Water droplet(Atlas et al. 1973)● Frozen drop
△ Graupel

Lump graupel(Locatelli and Hobbs 1974)

Hexagonal graupel(Locatelli and Hobbs 1974)

Lump graupel(Locatelli and Hobbs 1974)

Densely rimed aggregates(Ishizaka 1995)

Rimed aggregates(Ishizaka 1995)

Hexagonal graupel(Locatelli and Hobbs 1974)

Fig. Relationship between particle diameter and fall velocity in rain (circle) and snow (cross)during Rainscope ground tests in December 2021.

Fig. Relationship between diameter and fall velocity of precipitation particle obtained from Rainscope launchings. (a)stratiform cloud on February 20, 2021 (b) only graupel and frozen particle observed below the -10ºC level convective
cloud on June 25, 2022. *Note that the axis scales and symbols are different in the two figures..
Particle fall velocity measurements in clouds:- Raindrop’s related to diameter (well known, e.g. Altas et al. 1973) → Potential for possible validation of updraft in clouds- Solid particle’s depend on density → better understanding of cloud microphysics, especially solid hydrometeor formation

Calibration of EarthCARE/CPR
Institute for Space−Earth Environmental Research, Nagoya U.

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 The external calibration study for EarthCARE/CPR was described in
Horie et al. (2010, https://doi.org/10.1109/IGARSS.2010.5650733)
There are three calibrations
 Okada et al. (2009) showed CPR Operation Image.
considered for the CPR.
1. The internal calibration for
signal processing unit which
will be processed electricallyand this calibration need tostop the observation.
2. The sea surface calibration
which will be performed tocalibrate RF performance andto get normalized radar crosssection.
3. The external calibration which
will be performed using groundbased radar calibrator (ARC).

JAXA/EarthCARE validation activities
Institute for Space−Earth Environmental Research, Nagoya U.

•••

Long-term observation network
Lidar network (AD-Net) by NIES
SKYNET observation stations
Wind Profilers by JMAetc.

Location ofgroundbasedinstruments→which can provide
detailed validations of theJAXA EarthCARE productsCampaign• Ground-based doppler CPR observation
developed by NICT•Multiple-field-of-view multiplescattering polarization lidar(MFMSPL), High spectral resolution
lidar, Direct Detection Doppler lidar(355nm) by Prof. Okamoto’s kakenhi
kiban S 17H06139
They are located in NICTTokyo with other ground
instruments.

Comparison with othersatellite data
(CloudSat, CALIPSO,
GCOM-C/SGLI, MODIS,VIIRS, CERES, etc.)→which can provide
global evaluations ofthe JAXA EarthCARE
products
JAXA’ GCOM-C satellite(carrying SGLI sensor)

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Validation of the CPR in the NICT Tokyo
Institute for Space−Earth Environmental Research, Nagoya U.

HG-SPIDER ( NICT's Ground-based validation CPR )NICT will
operate several
groundinstruments
including theground cloudradar (HGSPIDER).

MFMSPL, HSRL,
Direct Detection
Doppler lidar(355nm) weredeveloped by Prof.
Okamoto (KyusyuUniv.)’s Kakenhi.

HG-SPIDER: High sensitivity Ground-based SPIDER (CPR)

Item

Specification

Frequency

94.090GHz

Tx Power

1500W at EIK(peak)

Antenna Gain55.9 dBi

Beam Width

0.3 degrees

Polarization

Linear Polarization

Pulse Width

0.5/1.0/2.0μs

PRF

3,000 - 10,000 Hz

Sensitivity-40dBZ@15km(Integ. 1sec.)

Antenna
Scanning

Fixed (zenithpointing)Range

150m - 20km

Doppler
Function

Pulse-PairProcessing

Z factor

Doppler Velocity

Better sensitivity thanEarthCARE/CPR

・The HG-SPIDER is located in NICT Koganei (Validation Site)with other Instruments;
lidars by Prof. Okamoto’s kakenhi, wind profiler,
microwave radiometer, all-sky camera, etc...

20JAXA/EarthCARE validation activities

Institute for Space−Earth Environmental Research, Nagoya U.

 The JMA operates 33 wind profile network (WINDAS：WInd profiler
21
Network and Data Acquisition System).
 The NICT is studying a validation of the CPR Doppler velocity using theWINDAS.

Slides provided by Yuichi Ohno (NICT)