[ecco-support] [EXTERNAL] Where does OBP data before 2002 come from?

[Fenty, Ian G (US 329C)]

Hi Yaohua,

Ou is correct that the ECCO Version 4 Release 4 solution is not constrained to global ocean bottom pressure data prior to 2002.  However, ECCO does provide an estimate of global ocean bottom pressure starting from 1992.  The ECCO ocean bottom pressure is a prognostic term from the data-constrained model simulation.  The ECCO model is constrained by many other data besides GRACE, including satellite altimetry.  So while ECCO does not use remotely-sensed OBP observations prior to the GRACE mission, we still can and do provide estimates of ocean bottom pressure over the entire 1992-2017 period.  

>> Also, what is the difference between the grided OBP data  from ECCO website (1992~2017) and those from NASA JPL website (starting in 2002 only)? If we are interested in the OBP data in the South

The difference between the gridded OBP data from ECCO Version 4 Release 4 (1992-2017) and that from the NASA JPL GRACE website (starting from 2002) is that the JPL GRACE dataset is the OBP data calculated from only the satellite while the ECCO provides an estimate of OBP that combines data from GRACE, satellite altimeters, and many other datasets (https://ecco-group.org/data.htm). Even over the common period of GRACE, there will be some disagreement between ECCO OBP and JPL GRACE OBP.  One reason for these differences is that OBP from GRACE has a much coarser spatial resolution due to limitations of the observing system. 

Does that help?

-Ian




-----Original Message-----
From: <ecco-support-bounces at mit.edu> on behalf of Ou Wang <ou.wang at jpl.nasa.gov>
Reply-To: "ECCO support list, wider membership" <ecco-support at mit.edu>
Date: Thursday, February 25, 2021 at 11:58 AM
To: "ECCO support list, wider membership" <ecco-support at mit.edu>
Subject: Re: [ecco-support] [EXTERNAL] Where does OBP data before 2002 come from?

    Yaohua,

    There are *no* ocean bottom pressure (OBP) data before 2002 used in ECCO V4. The GRACE data since 2002 is the only OBP data used. If you referred the OBP files for 1922-2001, e.g. GRACE_jpl_rl05m_20180122_1992…, GRACE_jpl_rl05m_20180122_2001,
     in 
    https://ecco.jpl.nasa.gov/drive/files/Version4/Release4/input_ecco/input_bp <https://ecco.jpl.nasa.gov/drive/files/Version4/Release4/input_ecco/input_bp>, they only contain fill values (-999) and there are no valid data in those files.


    Regards,
    Ou

    From: <ecco-support-bounces at mit.edu> on behalf of "yhzhu at fio.org.cn" <yhzhu at fio.org.cn>
    Reply-To: "ECCO support list, wider membership" <ecco-support at mit.edu>
    Date: Thursday, February 25, 2021 at 11:43 AM
    To: ecco-support <ecco-support at mit.edu>
    Subject: [EXTERNAL] [ecco-support] Where does OBP data before 2002 come from?



    Dear Sir/madam,

    We have noticed that the ECCO4 product uses the Ocean Bottom Pressure (OBP) data from 1992.1.1 to 2017.12.31. However, the GRACE satellite was launched in 2002. We are wondering how the grided OBP data before 2002 were obtained? Could you
     please list some references which validate or examine these data? Also, what is the difference between the grided OBP data  from ECCO website (1992~2017) and those from NASA JPL website (starting in 2002 only)? If we are interested in the OBP data in the South
     China Sea region, can we use  the one downloaded from ECCO4  between 1992.1.1 and 2017.12.31, or,  better use the segment after 2002?

    Your help is much appreciated.

    Best regards,

    Yaohua Zhu



    ________________________________________

    yhzhu at fio.org.cn