+- ODL Forums (https://forum.oceandatalab.com)
+-- Forum: Syntool (https://forum.oceandatalab.com/forum-5.html)
+--- Forum: Questions (https://forum.oceandatalab.com/forum-10.html)
+--- Thread: Globcurrent resolution (/thread-56.html)
Globcurrent resolution - anise - 2023-04-23
Hi,
I am interested in total surface current in Oct/Nov 2015 around the Agulhas region (South Africa).
It seems like the globcurrent velocity fields/streamlines displayed on OVL are much higher resolution than the products I download from Copernicus and Globcurrent portal (0.25 deg). When I downloaded the products and plotted them my streamlines look coarser than yours. Do use some higher resolution (maybe regional) product for the display?
"Total surface current": https://resources.marine.copernicus.eu/?...EP_015_004, http://globcurrent.ifremer.fr/products-dat.
I am also interested in the finite-size Lyapunov Exponent, do you know where I can download the data product of this parameter?
Best regards,
Anis
RE: Globcurrent resolution - Lucile Gaultier - 2023-04-24
Hi Anis,
The resolution of the displayed GlobCurrent product is the same as the one from CMEMS unfortunately. Our streamline algorithm may create the impression that the resolution is higher but this is not the case.
For the FSLE (FInite-Size Lyapunov Exponents), there is a product available in Delayed Time on AVISO website: https://www.aviso.altimetry.fr/en/data/products/value-added-products/fsle-finite-size-lyapunov-exponents.html
It is however derived from the GlobCurrent geostrophic velocity (product CMEMS 008_047 for the reprocessed data and CMEMS 008_047 for the NRT) and not the total surface current that you were mentionning.
In the Agulhas area, the geostrophic velocity is mostly dominant so it should not be an issue.
There are also algorithms that exists to easily perform FSLE / FTLE computation in Matlab and Python.
Let me know if you need more info on that subject
All the best
Lucile
RE: Globcurrent resolution - anise - 2023-04-24
Hi,
Thank you for your reply.
Just to make sure I understand, so you mean that the FSLE displayed in OVL is calculated from the Globcurrent TOTAL surface current but the FSLE availble on AVISO is calculated from Globcurrent GEOSTRPHIC velocity?
I actually downloaded the FSLE product from AVISO and they indeed look a little different, in some areas, from the one displayed in OVL. Is that expected?
Yes, I am interested in FSLE/FTLE algorithms in python. Could you please give links.
Best regards,
Anis
RE: Globcurrent resolution - Lucile Gaultier - 2023-04-27
Hi Anis,
The FSLE displayed in OVL are also derive from the Geostrophic GlobCurrent Current if I am not mistaken. They were retrieved from AVISO when the algorithm were tested
They may look a bit different as we have processed the FSLE some time ago and the algorithm and gesotrophic current data have evolved since then. The FSLE is highly sensitive to the spatial initial and final length.
I can contact you privately to provide algorithms FSLE/ FTLE in python, I have not publish them but can share privately my git repository.
All the best
Lucile