The EarthCARE Mission - Science and System Overview

Tobias Wehr1,†, Takuji Kubota2, Georgios Tzeremes1, Kotska Wallace1, Hirotaka Nakatsuka2,

Yuichi Ohno4, Rob Koopman1, Stephanie Rusli1, Maki Kikuchi2, Michael Eisinger3, Toshiyuki Tanaka2, Masatoshi Taga2, Patrick Deghaye1, Eichi Tomita2, and Dirk Bernaerts1

1European Space Agency, ESA-ESTEC, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands, 2Japan Aerospace Exploration Agency (JAXA) Japan, 305-8505 2 Chome-1-1, Sengen, Tsukuba, Ibaraki, Japan 3European Space Agency, ESA-ECSAT, Fermi Avenue, Didcot OX11 0FD, United Kingdom 4National Institute of Information and Communications Technology (NICT) Japan, 184-8795 4-2-1 Nukui-Kitamachi, Koganei, Tokyo, Japan †deceased, 1 February 2023

The paper provides a comprehensive description of the EarthCARE Mission covering the science rationale and objectives, instrument suite, ground system and data products.  The mission is expected to be launched in 2024, and the paper provides valuable background information for the science community at launch and for posterity. 

Overall Assessment:  Publish with very minor grammatical changes

Strengths:

The EarthCARE mission promises to advance our understanding of the Earth’s climate system with coincident measurements of aerosols, clouds, precipitation, and thermal/visible radiation.  The mission heralds’ first-time spacebased measurements on the vertical motion within clouds with a doppler radar and the profile typing of aerosols with a UV high spectral resolution lidar.  Both measurement capabilities are significant steps forward for helping to answer questions on aerosol/cloud radiative forcing, and the mission’s long development is recognition of the extreme technical challenges faced. The payload includes a multispectral imager and a broadband radiometer that enables a 3-dimensional construction of clouds and their radiative influence that goes far beyond the capabilities offered by the international A-Train constellation.  

The paper is a roadmap to the scientific, technical, and programmatic aspects of the mission.  It excels in providing in-depth descriptions in each of these subject areas, which, in turn, yields context for understanding how each was integral to the design and development of the mission.  It is not, however, a traditional scientific investigation; rather the paper provides a necessary foundation of details to enable future investigations based on the new data products. In this reviewer’s opinion, the manuscript is appropriate for Atmospheric Measurement Techniques.

The paper begins with a concise explanation on the mission’s scientific objectives and requirements.  The mission bases its rationale on IPCC reports as a collective body of evidence pointing out that large uncertainties in the prediction of climate sensitivity to CO2 increase are related to cloud feedbacks and the large diversity in cloud processes and morphology.   It further acknowledges the importance of extending records such as acquired by CALIPSO and CloudSat to detect changes in cloud feedback as the climate warms.

The description of the measurement detection and accuracy requirements is valuable as well as the description on the mission concept design.  An appreciation is given for how these evolved and relates to the care and thought into the engineering and science trades that took place behind the scenes.  The content is very mature and will provide a useful reference to future users of these data.

The spacecraft and instrument descriptions are detailed and provide significant background information on their design that will serve the community as a go-to-reference on EarthCARE.  The information further gives a sense of the instrument personalities and features to be expected on-orbit.

The explanation of the ground-system showcases the flow of communications and data across the supporting institutions and facilities. The overview description of the data products complements the description of the instruments and their calibration. An explanation of the data processing system, general data catalogue and data accessibility is provided.  Two diagrams are also included that map geophysical variables to data products from the ESA and JAXA production streams.  

The paper is lucid and contains many details with appropriate references to additional algorithm references or instrument performance papers; yet, the pace of the story is light and engaging.  The graphics are well-constructed and aid the text.  The structure of the paper is logical.  The necessity for the use of acronyms for a complex mission is understandable, but weighs heavy on a first-time reader.

The paper includes a significant library of reference material that provides a foundation for the paper and aids readers seeking additional information.

The paper further acknowledges the many efforts of the lead author whom shepherd through a wide range of issues to a successful launch for EarthCARE and its on-orbit operation; sadly with his passing this year, he will be greatly missed.

Weaknesses (or quibbles)

Many acronyms are introduced multiple times.  The usual convention is to introduce them once.

Acronyms are introduced with both capitalized and uncapitalized wording. Use the same convention throughout the manuscript.

Some references appear out of sequence.  For example, lines 73-78 highlight the value of extending the CloudSat cloud top height record with W-band observations with CPR (Takahashi et al., 2019) and also doing the same for the CALIPSO record with ATLID (Vaillant de Guelis 2018 and Chepfer et al 2014).  It would be more appropriate to recognize the Chepfer first as the idea was noted in 2014.  

Could the authors provide information on the mass, power utilization, data volume and geometrical dimensions for each instrument? This information is available for the MSI but does not appear for ATLID or CPR.  Perhaps it is available, not easy to find.

This paper represents a relevant contribution describing the joint ESA and JAXA (Japan Aerospace Exploration Agency) EarthCARE (Cloud, Aerosol and Radiation Explorer) mission. What is interesting is that all the relevant aspects of the mission are presented in one single paper, while re-directing the interested reader to other publications to dive into more details, e.g. about the various products that will be available. 

The main objective of the EarthCARE mission (assessing the Earth radiation budget considering the impact of clouds and aerosols) is well explained and the mission logic and scientific requirements are clearly presented.

This paper represents also a tribute to the work and scientific contribution of Dr. Tobias Wehr, who dedicated himself to the EarthCARE and many other missions.

The paper readability can be improves by performing a minor revision of the document. Please find below some suggestions:

1) Abstract: it would be good to provide information on the orbit type (sun-synchronous) and local time of descending node (LTDN).

2) There are many acronyms introduced without spelling them (e.g. IPCC, CMIP6, GCM in section 2; DFA in Figure 7; MREF in Figure 10; Table 2, PBL; etc.). An appendix including the definition of the acronyms would help.

3) Section 5.2, Line 293: The CPR instrument modes are introduced without explaining them. It is assumed that the modes refer to the maximum altitude sampled in the atmosphere, but it should be clearly explained. Please clarify.

4) Line 404: The solar calibration is performed over the South or North Polar Region? Unclear from the text.

5) Please consider swapping figure 16 and 17, since 17 is referred first in the text (line 414), followed by figure 16 (line 450). This is applicable also in other parts of the paper.

6) Figure 17 caption mentions solid horizontal grey lines, but they are not visible. Alternatively, should be solid black lines? Please check consistency between figure and caption.

7) Lines 488-493: This text is potentially confusing. First, it must be noted that the section related to the products is introduced later in the paper (section 8.2), and this could already generate some confusion in a general reader. Moreover, the text refers to “not unfiltered” BBR Level 1 products. The use of a double negative in English can lead to a further confusing interpretation. It is suggested to use “artefacts-corrected” or simply “corrected” instead of “unfiltered”.

8) Line 522: what is a PGM-HT cage?

Figure 22: The figure shows the point spread functions for the BBR TW and SW channels, but it does not clearly indicate which is which, namely red vs. violet. Please clarify the caption.

Typos/text

Table 2: ATLID is not mentioned in this table, it is only mentioned as “the instrument”

Line 144: performaces - performances 

Line 219, format of reference – remove A. G. 

Line 235: suggestion - The output from this laser consists of linearly…

Line 265: th perfomace - performance

Line 393: dedudancy  - redundancy

Line 394: channelss - channels

Line 604: Fligh - Flight

Line 701: Please add “the” before “Joint Simulator”

Line 703: Please add “the” before before “Joint Simulator” and “Satellite Data Simulator”