Subject: Marine Geospatial Ecology Tools (MGET) help
Text archives
| From: | "Jason Roberts" <> |
|---|---|
| To: | <> |
| Cc: | <> |
| Subject: | RE: [mget-help] problem with AVISO SSHA data |
| Date: | Mon, 24 Oct 2011 18:23:07 -0400 |
Hi Larissa,
We're glad you're finding MGET useful for your research.
Although the data for the MGET AVISO tools and the and OceanWatch AVISO data
originate with the same organization (AVISO), they are not directly
comparable. MGET's tools download data directly from the AVISO OPeNDAP
servers. They are intended to provide a geoprocessing-style interface to the
live AVISO data and give identical values to what AVISO is providing at that
moment through their OPeNDAP interface and netCDF files available on their
FTP server.
OceanWatch works a bit differently. The OceanWatch servers periodically
download data from the AVISO servers and store a copy of it. Then they
present a website that allows it to be downloaded in various formats and
sometimes in different spatiotemporal griddings than what was originally
provided by AVISO. For example, the AVISO Delayed Time (DT) datasets are
distributed with a 7-day time increment at 1/3 degree resolution, while the
OceanWatch site allows you to obtain them on monthly increments at 1/4
degree resolution. Presumably, OceanWatch interpolated a this new
spatiotemporal grid from the original 7-day, 1/3 degree data.
Another possible reason for differences between MGET and OceanWatch is that
because OceanWatch caches its own copy of the AVISO data, it must be
diligent about redownloading the entire AVISO dataset when AVISO reprocesses
it. The reprocessing happen periodically--once per year or so--and if
OceanWatch has not done that yet, it may be operating on an older version of
the data than is visible through MGET (which always operates against the
latest reprocessing, because it's just querying the AVISO servers directly).
If you are finding that values are radically different between the two and
there is no reasonable explanation (e.g. you are looking at a bend in the
Loop Current or where an eddy is coming through) then we should follow up in
more detail. I know the developer of OceanWatch and we can investigate
further, if necessary.
Best regards,
Jason
-----Original Message-----
From:
[mailto:]
Sent: Monday, October 24, 2011 5:33 PM
To:
Subject: [mget-help] problem with AVISO SSHA data
I am very happy to have recently come across your toolbox; it has proved
quite
useful in my research! I had previously obtained AVISO SSHA data through
the
Ocean Watch website (http://las.pfeg.noaa.gov/oceanWatch/oceanwatch.php) but
I
am now switching to your toolbox for this. However, I noticed some
discrepancies between these two datasets even though they are (if I
understand
correctly) from the same satellites. I am using the monthly Global DT-Upd
Merged MSLA SSH and comparing it to monthly SSHA data from the Ocean Watch
site
for the same time periods in the Gulf of Mexico. In some cases, one dataset
will show negative SSHA while the other will show positive SSHA for the same
time and location. Do you have any ideas as to why these two datasets are so
different? Any help with this problem is very much appreciated!
-Larissa Kitchens
We're glad you're finding MGET useful for your research.
Although the data for the MGET AVISO tools and the and OceanWatch AVISO data
originate with the same organization (AVISO), they are not directly
comparable. MGET's tools download data directly from the AVISO OPeNDAP
servers. They are intended to provide a geoprocessing-style interface to the
live AVISO data and give identical values to what AVISO is providing at that
moment through their OPeNDAP interface and netCDF files available on their
FTP server.
OceanWatch works a bit differently. The OceanWatch servers periodically
download data from the AVISO servers and store a copy of it. Then they
present a website that allows it to be downloaded in various formats and
sometimes in different spatiotemporal griddings than what was originally
provided by AVISO. For example, the AVISO Delayed Time (DT) datasets are
distributed with a 7-day time increment at 1/3 degree resolution, while the
OceanWatch site allows you to obtain them on monthly increments at 1/4
degree resolution. Presumably, OceanWatch interpolated a this new
spatiotemporal grid from the original 7-day, 1/3 degree data.
Another possible reason for differences between MGET and OceanWatch is that
because OceanWatch caches its own copy of the AVISO data, it must be
diligent about redownloading the entire AVISO dataset when AVISO reprocesses
it. The reprocessing happen periodically--once per year or so--and if
OceanWatch has not done that yet, it may be operating on an older version of
the data than is visible through MGET (which always operates against the
latest reprocessing, because it's just querying the AVISO servers directly).
If you are finding that values are radically different between the two and
there is no reasonable explanation (e.g. you are looking at a bend in the
Loop Current or where an eddy is coming through) then we should follow up in
more detail. I know the developer of OceanWatch and we can investigate
further, if necessary.
Best regards,
Jason
-----Original Message-----
From:
[mailto:]
Sent: Monday, October 24, 2011 5:33 PM
To:
Subject: [mget-help] problem with AVISO SSHA data
I am very happy to have recently come across your toolbox; it has proved
quite
useful in my research! I had previously obtained AVISO SSHA data through
the
Ocean Watch website (http://las.pfeg.noaa.gov/oceanWatch/oceanwatch.php) but
I
am now switching to your toolbox for this. However, I noticed some
discrepancies between these two datasets even though they are (if I
understand
correctly) from the same satellites. I am using the monthly Global DT-Upd
Merged MSLA SSH and comparing it to monthly SSHA data from the Ocean Watch
site
for the same time periods in the Gulf of Mexico. In some cases, one dataset
will show negative SSHA while the other will show positive SSHA for the same
time and location. Do you have any ideas as to why these two datasets are so
different? Any help with this problem is very much appreciated!
-Larissa Kitchens
Archives powered by MHonArc.