Not logged inOcean Color Forum
Forum Ocean Color Home Help Search Login
Up Topic Products and Algorithms / Satellite Data Products & Algorithms / ask about SeaWiFs Chl (locked)
- By hn.huynh Date 2012-03-19 09:35
Hi,

I have just downloaded daily mapped Chl_a files from SeaWiFS. I would like to ask that Chl_a is converted into log10 before or not yet.
I intend to extract the data for the region from 0-24 N, 99-121 E, so it is OK if I use the mapped product or I have to use L3bin product?
And, because this is the first time I use Chlorophyll, could you please introduce me some documents about this kind of data?

Thank you in advance for your reply.

HN
- By norman Date 2012-03-19 10:38
The chlorophyll data in our mapped files have not been log transformed;
they are stored as 32-bit floating-point geophysical values with units
of milligrams per cubic meter.

The mapped products are made from the corresponding binned products.
They are somewhat easier to work with than the binned products, but
they contain less information than the binned products.

Please spend some time looking over our on-line documentation.
http://oceancolor.gsfc.nasa.gov/DOCS/

Regards,
Norman
- By hn.huynh Date 2012-03-19 11:04
Hi,

Thank you for your answer.
I have another question. I have just downloaded a binned file of chlor_a. I used matlab to import data and the size of chlor_a is 1x444025. How can I extract the data for the region 99-121E, 0-24N, and reshape its size to m x n?

Best regards,

HN
 
- By norman Date 2012-03-19 11:12
Our group has very little MatLab experience.
You might be able to get help from the community
by posting to the bulletin board that we have set
up for the purpose.
http://oceancolor.gsfc.nasa.gov/forum/oceancolor/board_show.pl?bid=18

Another alternative would be to use a program I wrote
some years ago to extract bin file data as ASCII text.
See the following post.
http://oceancolor.gsfc.nasa.gov/forum/oceancolor/topic_show.pl?pid=3604#pid3604

Norman
- By hn.huynh Date 2012-03-19 11:48
I'm sorry I don't understand one thing. You said that "the binned product contains more information than the mapped product". It means that when the binned product is transformed to the mapped product, some data disappear??? If I extract the data from the binned product and reshape it to m x n, I have the same problem??? Could you please explain clearly me this problem?

Thank you

HN
- By norman Date 2012-03-19 12:13 Edited 2012-03-19 12:15
HN,

What you lose in the transition from level-3 bin
to level-3 mapped is some statistical information
about the spatial and temporal variability of the
original level-2 data that went into the level-3
product.  Some people are not interested in that
additional information or just do not want to deal
with the more difficult binned format.  Which
product you use depends on what you are trying
to show with the data.

Have you read the following?
http://oceancolor.gsfc.nasa.gov/DOCS/Ocean_Level-3_Binned_Data_Products.pdf
http://oceancolor.gsfc.nasa.gov/DOCS/Ocean_Level-3_SMI_Products.pdf

You may also wish to peruse the following.

http://oceancolor.gsfc.nasa.gov/cgi/tech_memo.pl?32
(Note that the log-transformation of the data described
in Tech Memo 32 was abandoned before the SeaWiFS mission
began.)

http://www.ioccg.org/reports/report4.pdf

Norman

P.S.  Have you considered installing SeaDAS?
http://oceancolor.gsfc.nasa.gov/seadas/
That package will read both types of level-3 data.
Up Topic Products and Algorithms / Satellite Data Products & Algorithms / ask about SeaWiFs Chl (locked)



Responsible NASA Official: Gene C. Feldman
Curator: OceanColor Webmaster
Authorized by: Gene C. Feldman
Updated: 03 July 2013
Privacy Policy and Important Notices NASA logo