APPENDIX 3
OVERVIEW OF THE
EARTH CLOUD, AEROSOL AND RADIATIONEXPLORER (EarthCARE) MISSION

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1. Introduction
1.1

Cloud and Climate Change

Since the last report of IPCC (Third Report), the level of scientific understandings regarding the effect ofaerosols and clouds, show a good progress. From the most recent report (Fourth Assessment Report; FAR),
carbon dioxide is said to be the largest factor to the influence of the global warming. However, the effect ofcarbon dioxide to the global warming is considered to have been evaluated with a good accuracy. On the other
hand, the radiative forcing of clouds and aerosols still remains as the dominant uncertainty in the prediction of
the climate change in the future. It is reported that -0.5 W/m2 for aerosol direct effect and -0.7 W/m2 for cloud
albedo effect, -1.2 W/m2 as total aerosol, are counted for radiative forcing relating with aerosol/cloud. The figure
is large enough comparing with the total anthropogenic radiative forcing; +1.6 W/m2. We have to make a special
attention to the fact that the uncertainty of the cloud albedo effect, i.e. interactions between aerosol and cloud, isvery large; 2 W/m2. This leads, without the correct understanding of the interaction between aerosol and cloud,climate change to remain uncertainties to predict future status with sufficient accuracy.
Furthermore, FAR suggests that the cloud life cycle process should be examined not just for cloud forming
but also for the precipitation process or cloud termination process, which will affect global radiation budget
through latent heat release and changing the radiative characteristics of the ground surface by such as snowing(IPCC, 2007).

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EarthCARE mission and instruments

EarthCARE is an earth observation satellite that Japan and Europe have been jointly developing (Illingworthet al. 2015, Wehr et al. 2023). Using its four sensors (Cloud Profiling Radar, Lidar (ATLID), Multi-Spectral
Imager (MSI) and Broadband Radiometer (BBR)), clouds and aerosols (small particles like dust and dirt thatexist in the earth's atmosphere) will be observed on a global scale to improve the accuracy of climate change
predictions (see Table 1 and Figure 1).
Table 1 General characteristic of instruments

InstrumentCPRDescription
94 GHz Doppler Radar(see Table 2.)355 nm Hyper Spectral Resolution Lidar with three channels

ATLID

MSIBBR(Mie co-polar, Rayleigh, Mie cross-polar)
Push broom imager
Resolution 500m, swath 150 km
Seven channels (0.67, 0.865, 1.65, 2.21, 8.8, 10.8, 12.0 micron)Three views radiometer
Angle: Nadir, +- 55 deg
Two channels; 0.2–4, 4–50 micron

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Figure 1 Relationship between target geophysical parameters and instruments

Figure 2. Outlook of CPR and EarthCARE satellite
3-3The outlook of EarthCARE satellite and CPR are shown in figure 2. A sun synchronous orbit was chosen as
the observational orbit to cover all region of the Earth. Local time at equator of the orbit is 13:45 to 14:00 withconsideration of cloud processes being active in the afternoon.
To get the accurate aerosol/cloud observation data, several unique points are implemented for instrumentation.
The LIDAR is an Ultra Violet range single wavelength High Spectral Resolution LIDAR. The wavelength, 355
nm, has well sensitivity for the small aerosol particles that are missed by Radar, and make high transmit power
possible for its eye safe character. It is possible for the LIDAR signals to be strongly attenuated when theymeet dense regions composed by large particles such as clouds. High spectral resolution enables to receive
Mie and Rayleigh scattering signals independently. In this way, the optical properties of aerosols can be retrieved
directly, without an assumption of liar ratio. Through its polarization measurement, the depolarization ratio
can be calculated to estimate the nonsphericity of the observed particle. Doppler W-band Radar penetrates
thick cloud layers. Doppler measurement function distinguishes cumulus / convective cloud types and its particle
status inside of cloud layer. Using Doppler value, we precisely know kinds of cloud particles. The detailed
description of the Doppler Radar is noted in Section 2.1. The MSI has 7 channels with their central wavelengths
to be 0.67, 0.865, 1.65, 2.21, 8.8, 10.8 and 12.0 µm, respectively. These channels will be used with split
window method to get optical depth and effective radius of cloud and aerosols. Thermal infrared channel canbe used to retrieve the cloud top height. The ground resolution of MSI is 500 m2 and the swath width is 150km. BBR design is a heritage of past Earth Radiation Mission, such as ERBE or CERES. BBR has twochannels; one for the observing shortwave (0.25 ~ 4µm) and the other for longwave (4 ~ 50µm). Three angle
radiometer will be used for flux determination considering its angular distribution. The effect of cloud forcing
by the reflection of sunlight as well as by its emittence of longwave radiation are expected to be evaluated fromthe BBR observation. General characteristics for all four instruments are shown in Table 1.

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2. Doppler Cloud profiling RADAR
The new space borne radar; Cloud Profiling Radar (CPR) has been developed in the cooperation between
JAXA and NICT. From CPR observational requirements, we identified following design requirements. First
point is the high sensitivity. This requirement is divided into large antenna size requirement, low noise figure ofreceiver requirement and high power of transmitter requirement. Second point is the Doppler capability. To
materialize this function with satisfactory accuracy, large diameter of antenna with precise surface figure andhigh pulse repetition frequency (PRF) are required. To keep accuracy especially at boundary layer region, several
other fine characteristics, such as side lobe characteristics of antenna, cross polarization characteristics and soon, are also required for CPR design.
As the result of design, we chose pulse pair scheme for Doppler measurement. In addition, the diameter ofantenna was set as 2.5 m considering the limited diameter of launcher fairing. For transmitter, we employed
improved Extended Interaction Klystron (EIK), of which original model is already employed for CloudSAT
mission by NASA (Stephens et.al., 2002). The transmit power is 1.5 kW at end of three year mission. For PRF
design, CPR has variable control capability of PRF with satellite altitude information. This is for maximizing
frequency to keep good coherency between radar pulses, also good sensitivity by having much integration.
Outlook of CPR is shown in Figure 2 and major specification of CPR is shown in Table 2.
However, the PRF is a factor of trade off between observational heights. Considering the natural cloud height
distribution, the planned operation of CPR is to change observational height with latitude. As natural cloud height
distribution, for low latitude region, the cloud height is rather high; in contrast, the polar region cloud height israther low. The image of CPR operation is shown in Figure 3.

Table 2. General Specifications of CPR

ItemSpecification

Radar Type94 GHz Doppler Radar

Center frequency

94.05 GHz

Pulse width

3.3 micro second (equivalent to 500m vertical resolution)

Beam width

0.095 deg

Polarization

Circular

Transmit power> 1.5 KW (Klystron spec.)

Height rangeSensitivity*-0.5 ~ 20 km
500 m (100 m sample); Vertical
500 m integration; Horizontal-35 ~ +21 dBZ

Radiometric accuracy*< 2.7 dB

Doppler range*- 10 ~ +10 m/s

Resolution

Doppler accuracy*< 1 m/s
Pulse
repetition
Variable; 6100 ~ 7500 Hz
frequency
Pointing accuracy< 0.015 degree; at 10 km integration and 387 km orbit height

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Figure 3. CPR Operation Image

3. Operation Planning
EarthCARE was launched in May 2024. The calibrated engineering parameters (Level 1 data) and theretrieved physical parameters (Level 2 data) by all four sensors on EarthCARE will be stored and distributed
from both JAXA and ESA. Data are planned to be used by research institutes and agencies in order to improve
the accuracies of numerical weather/climate models. The data are also opened to researchers (after appropriateprocedures), and are used in the analysis of radiation/aerosol/cloud/precipitation process.

REFERENCES
Illingworth, A. J., H. W. Barker, A. Beljaars, M. Ceccaldi, H. Chepfer, N. Clerbaux, J. Cole, J. Delanoe, C.
Domenech, D. P. Donovan, S. Fukuda, M. Hirakata, R. J. Hogan, A. Huenerbein, P. Kollias, T. Kubota, T.
Nakajima, T. Y. Nakajima, T. Nishizawa, Y. Ohno, H. Okamoto, R. Oki, K. Sato, M. Satoh, M. W. Shephard, A.
Velazquez-Blazquez, U. Wandinger, T. Wehr, and G.-J. van Zadelhoff, 2015: The EarthCARE Satellite: The Next
Step Forward in Global Measurements of Clouds, Aerosols, Precipitation, and Radiation. Bull. Amer. Meteor.
Soc., 96, 1311-1332. https://doi.org/10.1175/BAMS-D-12-00227.1

Wehr, T., Kubota, T., Tzeremes, G., Wallace, K., Nakatsuka, H., Ohno, Y., Koopman, R., Rusli, S.,
Kikuchi, M., Eisinger, M., Tanaka, T., Taga, M., Deghaye, P., Tomita, E., and Bernaerts, D.: TheEarthCARE mission – science and system overview, Atmos. Meas. Tech., 16, 3581–3608,
https://doi.org/10.5194/amt-16-3581-2023, 2023.

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