# Seafloor Geodesy Data Standardization Task Force within the Inter-Commission Committee on Marine Geodesy (ICCM) report for the International Association of Geodesy (IAG)

Pierre Sakic, David Schmidt, Valérie Ballu, Jesse Hutchinson, Martin Heesemann, Kaifei He, Motoyuki Kido, Yuto Nakamura, John Desanto, Keiichi Tadokoro, et al.

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Pierre Sakic, David Schmidt, Valérie Ballu, Jesse Hutchinson, Martin Heesemann, et al. Seafloor Geodesy Data Standardization Task Force within the Inter-Commission Committee on Marine Geodesy (ICCM) report for the International Association of Geodesy (IAG). Inter-Commission Committee on Marine Geodesy (ICCM) of the International Association of Geodesy (IAG). 2023. hal-04319233

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Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
**Seafloor Geodesy Data Standardization Task Force**
within the Inter-Commission Committee on
**Marine Geodesy (ICCM)**

*report for the International Association of Geodesy (IAG)*

July 2023, updated in November 2023

Pierre Sakic & David Schmidt on behalf of the Task Force

With the contribution of Valérie Ballu, Jesse Hutchinson, Martin Heesemann, Kaifei He, Motoyuki Kido, Yuto Nakamura, John DeSanto, Keiichi Tadokoro, Surui Xie, Yusuke Yokota, Shun-ichi Watanabe

Since the 19th of October 2022, representatives of the seafloor geodesy community meet on a regular basis within an ad hoc working group called the *Seafloor Geodesy Data Standardization Task Force* (SFGDSTF). This task force has been placed under the umbrella of the IAG's Inter-Commission Committee on Marine Geodesy (ICCM).

**Goals**

During the kickoff meeting, the goals of the task force were defined as follows:

* Enable the shareability of the seafloor geodesy data collected by the different working groups around the world

* Give better visibility to these data

* Respect the FAIR data principles (Findable, Accessible, Interoperable, Reusable)

* A special emphasis has to be given to the interoperability of seafloor geodetic data, i.e., the possibility to easily use data of one working group with the software of another one for instance.

* Identify how data can be easily stored in existing repositories or establish expectations for new repositories.

* Establish community-supported data standards that can be adopted by the repositories/data centers

More generally, this exercise has provided a venue for international colleagues to share technical details on differing approaches and find common issues of concern.
**Considered techniques**

The task force initially discussed a range of seafloor geodetic techniques. Given the considerable interest in GNSS-Acoustic by those who participated in the initial discussion, it was agreed to start discussions with this technique. Nevertheless, the task force is interested in a wide range of techniques, and will likely revisit other techniques in the future. Techniques of future interest may include:

* Acoustic ranging

* Ocean bottom pressure sensors (OBP)

* Tiltmeters

* Optical Fiber Strainmeter

* Seafloor gravimetry

* Mast Seafloor <> Surface combining GNSS+attitude measurement

* Multi-beam Bathymetry

It would be highly valuable if other working groups similar to the current one could emerge within the task force to consider the other techniques mentioned above, like the OBP for instance. An initial discussion towards this goal was carried out during the Seafloor Pressure Geodesy workshop held in Rhode Island, April 2023 (conveners: Matt Wei, Randy Watts and William Wilcock, funded by NSF).

**Involved research teams/personals**

The task force tries to meet virtually on a monthly basis. Usually, it gathers the following representatives from a broad panel of research groups across the globe:

* Valérie Ballu (CNRS/La Rochelle University, France)

* Jesse Hutchinson (Ocean Networks Canada, Canada)

* Martin Heesemann (Ocean Networks Canada, Canada)

* Kaifei He (China University of Petroleum, China)

* Motoyuki Kido (Tohoku University, Japan)

* Yuto Nakamura (Japan Coast Guard, Japan)

* Pierre Sakic (Institut de Physique du Globe de Paris, France), animator

* David Schmidt (University of Washington, USA)

* John DeSanto (University of Washington, USA)

* Keiichi Tadokoro (Nagoya University, Japan)

* Surui Xie (University of Houston, USA)

* Yusuke Yokota (University of Tokyo, Japan)

* Shun-ichi Watanabe (Japan Coast Guard, Japan)

The list above includes those who have regularly attended the discussion. Nevertheless, others have participated for one or two sessions, and participation remains open to anyone.

An original invitation to join the task for was sent through the [seafloor-geodesy-community@earthscope.org](mailto:seafloor-geodesy-community@earthscope.org) listserv (facilitated by Earthscope/ex-UNAVCO). Since then, The seafloor geodesy community is informed
about the task force's progress through a dedicated mailing list:
[seafloor-geodesy-data-standardization@groupes.renater.fr](mailto:seafloor-geodesy-data-standardization@groupes.renater.fr)

it is possible to register for the mailing list via the following link:
[https://groupes.renater.fr/sympa/subscribe/seafloor-geodesy-data-standardization](https://groupes.renater.fr/sympa/subscribe/seafloor-geodesy-data-standardization)

As of July 2023, the mailing list has 32 subscribers.

A public workspace has been set up for collaborative work; the link is available upon request.

## Summary of work and exchanges

As mentioned above, it was decided to focus first on the GNSS/A acoustics data. Since it regroups different observables of different natures, the reflections can be a basis for the other technique's data standardization.

The members of the working group initially completed standardized description sheets of their own data formats. The description sheets are available in the shared workspace.

The task force members also introduced and detailed their data format during a dedicated session. There are many similarities between the 5 formats presented. And all user group utilize ASCII data tables as their primary file type.

## The main technical points which have been discussed

*Should we continue with such an ASCII/CSV style for GNSS-A data?*

⇒ **Yes**

This decision has been justified by the fact that it is a data representation style that is more or less "universal" since all the members of the Task Force are use to it. To quote David Schmidt "such representation format must remain community-driven".

*The necessity to explicitly include both the send and receive ping epochs?*
*If not, which one is the best?*

⇒ **We include both**

*What data level (raw versus initially processed) is appropriate for broad dissemination of GNSS-A data, and ingestion by processing codes?*

⇒ **Level 1:** raw observation i.e. RINEXs, lever arms, waveforms...

⇒ **Level 2:** a "master/main" file with preprocessed data
*Question of the time scale/representation of the recorded epochs?*

⇒ **UTC scale**, a reference epoch in the header, and the seconds w.r.t. the reference for each event

*Question of the Surface platform position representation? Which coordinates representation?*

⇒ **ECEF representation**. A sufficient level of detail must be provided regarding the reference frame in the metadataheader

**Definition of a level 2 file prototype**

The task force has used several meetings to identify standardized column headings and flags for a universal GNSS-A Level-2 data file. This file would contain all the preprocessed GNSS/A data (two-way travel time, the position of the surface ship/platform, INS attitude if any...). It is expected that this file format would allow groups to easily share data, and that these data could be ingested into any GNSS-A data processing package.

The Japan Coast Guard format developed for the software GARPOS, has been retained as the basis for the definition of a common exchange file. It takes the form of a CSV file. The preliminary version of this prototype definition is given as an appendix.

**Future points of discussions**

(prospective and non-exhaustive)

For the next work sessions of the task force, the emphasis should be given to:

* Data to be included as Level 1 data (GNSS record as RINEX, raw waveforms...)

* The definition of the best relevant Data Quality indicators for a GNSS/A acquisition

* The improvement of metadata records.

* In the medium term, the possibility of archiving data in a binary format such as NetCDF.

# Appendix

*Draft of GNSS-A data format standardization*

Pages hereafter
Definitions of column in GNSS-A standard CSV format

<table><caption>Table 1. Definitions of column in GNSS-A standard CSV format</caption><thead><tr><td>Index</td><td>Necessity</td><td>Description</td></tr></thead><tbody><tr><td>MT_ID</td><td>Essential</td><td>ID of mirror transponder</td></tr><tr><td>TravelTime</td><td>Essential</td><td>Observed travel time (net value) [sec.]</td></tr><tr><td>T_transmit</td><td>Essential</td><td>Transmission time of acoustic signal [sec. from origin]</td></tr><tr><td>X_transmit</td><td>Essential</td><td>Transducer position at T_transmit in ECEF [m]</td></tr><tr><td>Y_transmit</td><td>Essential</td><td>Transducer position at T_transmit in ECEF [m]</td></tr><tr><td>Z_transmit</td><td>Essential</td><td>Transducer position at T_transmit in ECEF [m]</td></tr><tr><td>T_received</td><td>Essential</td><td>Reception time of acoustic signal [sec. from origin]</td></tr><tr><td>X_received</td><td>Essential</td><td>Transducer position at T_received in ECEF [m]</td></tr><tr><td>Y_received</td><td>Essential</td><td>Transducer position at T_received in ECEF [m]</td></tr><tr><td>Z_received</td><td>Essential</td><td>Transducer position at T_received in ECEF [m]</td></tr><tr><td>ant_X0</td><td>Optional</td><td>GNSS position at T_transmit in ECEF [m]</td></tr><tr><td>ant_Y0</td><td>Optional</td><td>GNSS position at T_transmit in ECEF [m]</td></tr><tr><td>ant_Z0</td><td>Optional</td><td>GNSS position at T_transmit in ECEF [m]</td></tr><tr><td>roll0</td><td>Optional</td><td>Roll at T_transmit (in degree)<br/>*rotation around "forward" axis in ATD offset</td></tr><tr><td>pitch0</td><td>Optional</td><td>Pitch at T_transmit (in degree)<br/>*rotation around "rightward" axis in ATD offset</td></tr><tr><td>heading0</td><td>Optional</td><td>Heading at T_transmit (in degree from north)<br/>*rotation around "downward" axis in ATD offset</td></tr><tr><td>ant_X1</td><td>Optional</td><td>GNSS position at T_received in ECEF [m]</td></tr><tr><td>ant_Y1</td><td>Optional</td><td>GNSS position at T_received in ECEF [m]</td></tr><tr><td>ant_Z1</td><td>Optional</td><td>GNSS position at T_received in ECEF [m]</td></tr><tr><td>roll1</td><td>Optional</td><td>Roll at T_received (in degree)</td></tr><tr><td>pitch1</td><td>Optional</td><td>Pitch at T_received (in degree)</td></tr><tr><td>heading1</td><td>Optional</td><td>Heading at T_received (in degree from north)</td></tr><tr><td>[other]</td><td>Optional</td><td>Any other optional indices<br/>* should be defined in the header or other documents</td></tr></tbody></table>
# Definitions of site information file in GNSS-A standard format

Separate the field with "=" such as: `[variable name] = [value]"`

* List of value should be separated with space.

* Other format such as YAML would also be acceptable but should clearly be determined in the WG.

Contains the following essential information:

<table><thead><tr><td>Variable</td><td>Format</td><td>Description</td></tr></thead><tbody><tr><td>Site_name</td><td>character</td><td>GNSS-A site name or code</td></tr><tr><td>Campaign</td><td>character</td><td>Observation campaign name</td></tr><tr><td>TimeOrigin</td><td>YYYY-MM-DD hh:mm:ss.s</td><td>Origin of time used in the file [UTC]</td></tr><tr><td>RefFrame</td><td>character</td><td>Reference frame used in the file</td></tr><tr><td>MTlist</td><td>list of character</td><td>List of ID of mirror transponders</td></tr><tr><td>[*]_appPos</td><td>list of float</td><td>Approximate positions of transponder in ECEF [m]<br/>[*] should be replaced with MT's ID.</td></tr><tr><td>ATDoffset (optional)</td><td>list of float</td><td>ATD offset (or local-tie/ lever-arm) defined as the vector of GNSS to transducer with [forward, rightward, downward] in [m]</td></tr><tr><td>[other] (optional)</td><td>N/A</td><td>Any other optional values<br/>* should be clearly defined in comments or other documents</td></tr><tr><td>Comments (optional)</td><td>character</td><td>Any other optional comments</td></tr></tbody></table>

<Example of Site Information file (*in ini file format but it should be discussed)>

Site_name = CHOS

Campaign = 1204.meiyo_m4

TimeOrigin = 2012-04-19 00:00:00.000

RefFrame = ITRF2008

MTlist = M01 M02 M03 M04

M01_appPos = xxxxxxx.xxx yyyyyyyy.yyy zzzzzzz.zzz

M02_appPos = xxxxxxx.xxx yyyyyyyy.yyy zzzzzzz.zzz

M03_appPos = xxxxxxx.xxx yyyyyyyy.yyy zzzzzzz.zzz

M04_appPos = xxxxxxx.xxx yyyyyyyy.yyy zzzzzzz.zzz
Draft of GNSS-A data format standardization

Version 0.230629 after discussion of the standardization
Taskforce meeting of the 27th June 2023

Definitions of column in GNSS-A standard CSV format

<table><caption>Table 1. Definitions of column in GNSS-A standard CSV format</caption><thead><tr><td>Index</td><td>Necessity</td><td>Description</td></tr></thead><tbody><tr><td>MT_ID</td><td>Essential</td><td>ID of mirror transponder</td></tr><tr><td>TDC_ID</td><td>Optional</td><td>ID of the reception transducer</td></tr><tr><td>TravelTime</td><td>Essential</td><td>Observed travel time (net value) [sec.]</td></tr><tr><td>aSNR</td><td>Optional</td><td>Signal/Noise Ratio of the acoustic ping</td></tr><tr><td>acc</td><td>Optional</td><td>acoustic_Cross_Correlation of the acoustic ping</td></tr><tr><td>dbV</td><td>Optional</td><td>acoustic Decibel Volt voltage of the acoustic ping</td></tr><tr><td>quality flag</td><td>Optional</td><td>String defining the quality of the record</td></tr><tr><td>T_transmit</td><td>Essential</td><td>Transmission time of acoustic signal [sec. from origin]</td></tr><tr><td>X_transmit</td><td>Essential</td><td>Transducer position at T_transmit in ECEF [m]</td></tr><tr><td>Y_transmit</td><td>Essential</td><td>Transducer position at T_transmit in ECEF [m]</td></tr><tr><td>Z_transmit</td><td>Essential</td><td>Transducer position at T_transmit in ECEF [m]</td></tr><tr><td>trans_sigX0</td><td>Optional</td><td>Transducer position std at transmit</td></tr><tr><td>trans_sigY0</td><td>Optional</td><td>Transducer position std at transmit</td></tr><tr><td>trans_sigZ0</td><td>Optional</td><td>Transducer position std at transmit</td></tr><tr><td>T_received</td><td>Essential</td><td>Reception time of acoustic signal [sec. from origin]</td></tr><tr><td>X_received</td><td>Essential</td><td>Transducer position at T_received in ECEF [m]</td></tr><tr><td>Y_received</td><td>Essential</td><td>Transducer position at T_received in ECEF [m]</td></tr><tr><td>Z_received</td><td>Essential</td><td>Transducer position at T_received in ECEF [m]</td></tr><tr><td>trans_sigX1</td><td>Optional</td><td>Transducer position std at receive</td></tr><tr><td>trans_sigY1</td><td>Optional</td><td>Transducer position std at receive</td></tr><tr><td>trans_sigZ1</td><td>Optional</td><td>Transducer position std at receive</td></tr><tr><td>ant_X0</td><td>Optional</td><td>GNSS position at T_transmit in ECEF [m]</td></tr><tr><td>ant_Y0</td><td>Optional</td><td>GNSS position at T_transmit in ECEF [m]</td></tr><tr><td>ant_Z0</td><td>Optional</td><td>GNSS position at T_transmit in ECEF [m]</td></tr><tr><td>ant_sigX0</td><td>Optional</td><td>GNSS antenna std at transmit</td></tr><tr><td>ant_sigY0</td><td>Optional</td><td>GNSS antenna std at transmit</td></tr><tr><td>ant_sigZ0</td><td>Optional</td><td>GNSS antenna std at transmit</td></tr><tr><td>ant_cov_XY0</td><td>......</td><td>Covariance matrix</td></tr><tr><td>heading0</td><td>Optional</td><td>Heading at T_transmit (in degree from north)</td></tr><tr><td>pitch0</td><td>Optional</td><td>Pitch at T_transmit (in degree)</td></tr><tr><td>roll0</td><td>Optional</td><td>Roll at T_transmit (in degree)</td></tr><tr><td>ant_X1</td><td>Optional</td><td>GNSS position at T_received in ECEF [m]</td></tr><tr><td>ant_Y1</td><td>Optional</td><td>GNSS position at T_received in ECEF [m]</td></tr><tr><td>ant_Z1</td><td>Optional</td><td>GNSS position at T_received in ECEF [m]</td></tr><tr><td>ant_sigX1</td><td>Optional</td><td>GNSS antenna std at transmit</td></tr><tr><td>ant_sigY1</td><td>Optional</td><td>GNSS antenna std at transmit</td></tr><tr><td>ant_sigZ1</td><td>Optional</td><td>GNSS antenna std at transmit</td></tr><tr><td>roll1</td><td>Optional</td><td>Roll at T_received (in degree)</td></tr><tr><td>[other]</td><td>Optional</td><td>Any other optional indices<br/>* should be defined in the header or other documents</td></tr><tr><td>doa_R</td><td>Optional</td><td>direction of arrival vector wrt Roll vector direction</td></tr><tr><td>doa_P</td><td>Optional</td><td>direction of arrival vector wrt Pitch vector direction</td></tr><tr><td>doa_H</td><td>Optional</td><td>direction of arrival vector wrt Heading vector direction</td></tr></tbody></table>
*ECEF or local ENU or Lat-Lon-Height should be discussed in the WG.

## Definitions of header in GNSS-A standard CSV format

* Line should start with "#"

* Separate the field with "=" such as: "[variable name] = [value]"

* List of value should be separated with space.

* Contains the following essential information:

<table><thead><tr><td>Variable</td><td>Format</td><td>Description</td></tr></thead><tbody><tr><td>Site_name</td><td>character</td><td>GNSS-A site name or code</td></tr><tr><td>Campaign</td><td>character</td><td>Observation campaign name</td></tr><tr><td>UTCdate</td><td>YYYY-MM-DD</td><td>Origin of time used in the file</td></tr><tr><td>RefFrame</td><td>character</td><td>Reference frame used in the file and reference epoch of the reference frame. e.g. ITRF20XX@YYYY.YY</td></tr><tr><td>MTlist</td><td>list of character</td><td>List of ID of mirror transponders</td></tr><tr><td>[*]_appPos</td><td>list of float</td><td>Approximate positions of transponder in ECEF [m] [*] should be replaced with MT's ID.</td></tr><tr><td>ATDOffset (optional)</td><td>list of float</td><td>ATD offset (or local-tie/ lever-arm) defined as the vector of GNSS to transducer with [forward, rightward, downward] in [m]</td></tr><tr><td>[other] (optional)</td><td>N/A</td><td>Any other optional values * should be clearly defined in comments or other documents</td></tr><tr><td>Comments (optional)</td><td>character</td><td>Any other optional comments</td></tr><tr><td>&lt;MT|TDC&gt;_ [*]_Delay</td><td>float</td><td>Turn-Around-Time implemented in transponder or transducer [*] should be replaced with MT's ID or TDC's ID.</td></tr></tbody></table>

## Example of header

# Site_name = CHOS
# Campaign = 1204.meiyo_m4
# UTCdate = 2012-04-19
# RefFrame = ITRF2008
# MTlist = M01 M02 M03 M04
# M01_appPos = -36.5030 698.5700 -1509.5790
# M02_appPos = 750.0060 -9.6570 -1548.1650
# M03_appPos = 9.6750 -781.3210 -1556.1690
# M04_appPos = -768.0610 -32.3080 -1519.3960
<figure><img src="image_2.png" /></figure>