The forum is locked.
The Ocean Color Forum has transitioned over to the Earthdata Forum (https://forum.earthdata.nasa.gov/). The information existing below will be retained for historical reference. Please sign into the Earthdata Forum for active user support.
I want to retrieve lake chl_a and other products, but failed, i tried to shut down processing option\landmask in seadas6.0 VA MODIS\L2gen,4(L1B to L2 processing), but the results still involve ocean without lake. So is there some options in dialog box to choose if i want to retrieve lake products?Thank you.
You need to enable land processing (yes I know, this is not terribly intuitive):
proc_land=1
Sean
proc_land=1
Sean
Sean,
I am using seadas 6.1 (with update 01) and want to process lake (near the sea) for chlorophyll using high resolution modis channels.
With 1 km resolution and OC3 algorithm I got 3 pixels for that area, but when I go to the higher resolution (250 or 500) and OC2/OC3 algorithm I don't get any data.
I enabled proc_land, changed landmask to landmask_null, disabled maskland. Do you have any other advice?
It seems that the problem is related to the OC2 algorithm and atmospheric correction since I also don't get any data when using OC2 algorithm with 1 km.
Also, when using high resolution channels I expected to get more pixels closer to the coast, but is seems that I am still at the similar distance from the coast as with 1km resolution.
And last question, OC2 algorithm seems to give much lower values compared to OC3 especially for the "coastal" pixels.
Do you have any comment?
thanks a lot,
igor
I am using seadas 6.1 (with update 01) and want to process lake (near the sea) for chlorophyll using high resolution modis channels.
With 1 km resolution and OC3 algorithm I got 3 pixels for that area, but when I go to the higher resolution (250 or 500) and OC2/OC3 algorithm I don't get any data.
I enabled proc_land, changed landmask to landmask_null, disabled maskland. Do you have any other advice?
It seems that the problem is related to the OC2 algorithm and atmospheric correction since I also don't get any data when using OC2 algorithm with 1 km.
Also, when using high resolution channels I expected to get more pixels closer to the coast, but is seems that I am still at the similar distance from the coast as with 1km resolution.
And last question, OC2 algorithm seems to give much lower values compared to OC3 especially for the "coastal" pixels.
Do you have any comment?
thanks a lot,
igor
Igor,
Setting proc_land=1 ensures that terrain height corrections are made -
which are often necessary for processing data over lakes at any
significant altitude. If your lake of interest is near sea level, this
will not have much of an impact.
Processing at 250 or 500m resolution does not necessarily increase
coverage near coastlines. The masks and flags are based on band
that are native 1km. Processing higher resolution data simply
replicates these 1km bands (a 1km pixel becomes 4 at 500m, but 4 of
the same value). An examination of the l2_flags may help you to
understand what is preventing valid retrievals.
Not getting any retrievals using OC2 suggests that an algorithm
failure condition exists (which can be confirmed with the l2_flags)
which may be that the 488nm band (or possibly even the 547 nm)
was negative. You could try using a fixed aerosol model.
See http://oceancolor.gsfc.nasa.gov/REPROCESSING/R2009/ocv6/
for a comparison of the algorithms. Every effort has been made to
ensure that the algorithms are as consistent as possible, however,
given the available radiometric information, the algorithms will differ
especially at higher chl concentrations. Two (and even three) bands
are generally not sufficient to provide enough information to
accurately estimate chlorophyll in coastal waters where non-chlorophyll
absorption can dominate the blue portion of the spectrum. Nature
of the beast I'm afraid.
Sean
Setting proc_land=1 ensures that terrain height corrections are made -
which are often necessary for processing data over lakes at any
significant altitude. If your lake of interest is near sea level, this
will not have much of an impact.
Processing at 250 or 500m resolution does not necessarily increase
coverage near coastlines. The masks and flags are based on band
that are native 1km. Processing higher resolution data simply
replicates these 1km bands (a 1km pixel becomes 4 at 500m, but 4 of
the same value). An examination of the l2_flags may help you to
understand what is preventing valid retrievals.
Not getting any retrievals using OC2 suggests that an algorithm
failure condition exists (which can be confirmed with the l2_flags)
which may be that the 488nm band (or possibly even the 547 nm)
was negative. You could try using a fixed aerosol model.
See http://oceancolor.gsfc.nasa.gov/REPROCESSING/R2009/ocv6/
for a comparison of the algorithms. Every effort has been made to
ensure that the algorithms are as consistent as possible, however,
given the available radiometric information, the algorithms will differ
especially at higher chl concentrations. Two (and even three) bands
are generally not sufficient to provide enough information to
accurately estimate chlorophyll in coastal waters where non-chlorophyll
absorption can dominate the blue portion of the spectrum. Nature
of the beast I'm afraid.
Sean