Dear all,
I went through to one day of data (for example 15.01.2018). It has data that starts from 00:00:00 to 23:55:00 so it is one day.
https://oceandata.sci.gsfc.nasa.gov/MODIS-Aqua/L2/2018/015/
Now I have some questions:
1. How data are stored? I think every data file is 5 minutes. Am I right?
2. If you look at the attachment, it shows cholorophyl_a data for one day. Is every square in picture one file data?
3. If you look at below data, four upper of them are at 00:20:00 and two below ones are at 00:25:00 but I do not know why we do not have for example chlorophyll every 5 minutes? I mean sometimes cholorophyll is missing. Why?
A2018015002000.L2_LAC_IOP.nc 2018-03-19 12:57:00 30817823
A2018015002000.L2_LAC_OC.nc 2018-03-19 12:04:00 26148251
A2018015002000.L2_LAC_SST.nc 2018-01-31 10:12:00 20611418
A2018015002000.L2_LAC_SST4.nc 2018-01-31 10:12:00 20175919
A2018015002500.L2_LAC_SST.nc 2018-01-31 10:11:00 22670140
A2018015002500.L2_LAC_SST4.nc 2018-01-31 10:08:00 22441236
Detailed questions about level2 data
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bluesky1987
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OB WebDev - norman
- Subject Matter Expert
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Detailed questions about level2 data
Hi,
1. Yes, each MODIS file we archive covers 5 minutes of data collection.
VIIRS data are split into 6-minute chunks. Other data sets such as
SeaWiFS have variable length files.
2. There was no attachment, but I'll assume you are referring to an
image such as the world map displayed on this page.
https://oceancolor.gsfc.nasa.gov/cgi/browse.pl?sub=level3&per=DAY&day=17721&sen=am&dnm=D
Yes, each region outlined in red represents one MODIS level-2 (and
level-1) scene. There are a few files for each scene: one for the
level-1 data, one for chlorophyll and Rrs products, one for IOP
products, and one or two for SST products. MODIS data additionally
have level-0 files.
3. While you will find a MODIS SST file for each 5-minute period during
the day (unless the sensor was off for some reason), chlorophyll
concentrations can only be computed for scenes that have enough
solar illumination (i.e. scenes collected during the daytime portion of
each orbit.) You will also find that MODIS SST4 files are only available
during the nighttime portion of each orbit.
Some additional information you may wish to consider:
When we bin level-2, data points into level-3 (i.e. mapped) products,
we choose the date of each datum not solely according to the UTC time
that that pixel was collected (as represented by the 5-minutes in each
scene), but also by the geographical location of the pixel with respect
to the antimeridian (180 degrees longitude). You can find out much more
about binning and data days in this publication.
http://ioccg.org/wp-content/uploads/2015/10/ioccg-report-04.pdf
See Chapter 4 for data day discussion.
I hope this helps.
Regards,
Norman
1. Yes, each MODIS file we archive covers 5 minutes of data collection.
VIIRS data are split into 6-minute chunks. Other data sets such as
SeaWiFS have variable length files.
2. There was no attachment, but I'll assume you are referring to an
image such as the world map displayed on this page.
https://oceancolor.gsfc.nasa.gov/cgi/browse.pl?sub=level3&per=DAY&day=17721&sen=am&dnm=D
Yes, each region outlined in red represents one MODIS level-2 (and
level-1) scene. There are a few files for each scene: one for the
level-1 data, one for chlorophyll and Rrs products, one for IOP
products, and one or two for SST products. MODIS data additionally
have level-0 files.
3. While you will find a MODIS SST file for each 5-minute period during
the day (unless the sensor was off for some reason), chlorophyll
concentrations can only be computed for scenes that have enough
solar illumination (i.e. scenes collected during the daytime portion of
each orbit.) You will also find that MODIS SST4 files are only available
during the nighttime portion of each orbit.
Some additional information you may wish to consider:
When we bin level-2, data points into level-3 (i.e. mapped) products,
we choose the date of each datum not solely according to the UTC time
that that pixel was collected (as represented by the 5-minutes in each
scene), but also by the geographical location of the pixel with respect
to the antimeridian (180 degrees longitude). You can find out much more
about binning and data days in this publication.
http://ioccg.org/wp-content/uploads/2015/10/ioccg-report-04.pdf
See Chapter 4 for data day discussion.
I hope this helps.
Regards,
Norman