Inquiry Regarding Time Scale on quaternion data and Geometrical Correction Calculation on Jason-2 Mission

[abd_ruby87]

Dear NASA Distributed Active Archive Centers,
I trust this letter finds you well. I am writing to seek clarification and guidance regarding the use of laser data from the Time Transfer by Laser Link (T2L2) on the Jason-2 mission. Specifically, my inquiries are related to the computation of geometrical corrections necessary for accurate data analysis.
In my analysis, I have encountered a discrepancy in the reflection and detection points due to the Laser Retroreflector Arrays (LRA) and detection unit not being co-located during the laser time transfer on the Jason-2 mission. To address this issue, I understand that it is crucial to compute geometrical corrections for each echo obtained.
Upon reviewing the provided information, I noticed that the geometrical correction is determined using the local rectangular coordinates of the reflection and detection points in the satellite reference frame, along with the attitude of the Jason-2 mission represented in the form of quaternions (attachment photo). The quaternion data is available at the following link: https://cddis.nasa.gov/archive/doris/ancillary/quaternions/ja2/.

To facilitate my analysis further, I have two specific questions:

Time Scale in Attitude Data:
I would like to verify the type of time scale present in the attitude data of Jason-2 satellite files accessible through the provided link. Could you confirm whether the time scale used is Coordinated Universal Time (UTC) or International Atomic Time (TAI)?
Geometrical Correction Equations:
In order to accurately calculate the geometrical correction, I am seeking information on the considerations and equations essential for utilizing the attitude data of the Jason-2 satellites. If there are specific formulas or guidelines that govern this process, I would appreciate your guidance in this regard.

I believe that your expertise and resources are crucial for addressing these inquiries, and I am confident that your assistance will greatly contribute to the success of my research. Thank you for your time and attention to this matter.

I look forward to your prompt response and appreciate your ongoing commitment to advancing scientific understanding through the dissemination of valuable data.

Sincerely,
Abdelrahim Ruby
Department of Surveying Engineering
Faculty of Engineering Shoubra - Benha University
108 Shoubra St. - Cairo - Egypt
E-mail: abdelrahim.ruby@feng.bu.edu.eg

[CDDIS – RB]

Abdelrahim,

We consulted with the Jason-2 science team, and we were provided with the following answers for your questions:

1. I would like to verify the type of time scale present in the attitude data of Jason-2 satellite files accessible through the provided link. Could you confirm whether the time scale used is Coordinated Universal Time (UTC) or International Atomic Time (TAI)?

The dates provided in the quaternion files are UTC times.

2. In order to accurately calculate the geometrical correction, I am seeking information on the considerations and equations essential for utilizing the attitude data of the Jason-2 satellites. If there are specific formulas or guidelines that govern this process, I would appreciate your guidance in this regard.

Information about the location of the LRA and the associated geometrical corrections can be found at:
https://ilrs.gsfc.nasa.gov/missions/satellite_missions/past_missions/jas2_com.html
See also the following, since the Jason-1/2/3 LRAs are very similar:
https://ilrs.gsfc.nasa.gov/docs/2020/Jason3correctionSLR.pdf

If you have any further questions, please let us know.

Ross Bagwell
Deputy DAAC Manager
CDDIS

[abd_ruby87]

Dear Mr. Bagwell,
I trust this letter finds you well.
I am writing to express my sincere gratitude for your invaluable assistance in helping me find the answer to my recent question, and I wanted to take a moment to extend my heartfelt thanks.
Best regards,