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Hi,
I need some help about my orders. I am using Seawifs Level2 daily images, and I am interested in GAC resolution for Chla, nLw(λ) and Aot865, from the geographical range of 29 to 34N and -62 to -67W. In fact, I want to extract values from a small box inside this range (31.1 to 32.2N and -63.6 to -64.7W). However, for all the days that I have ordered, around 360 images, only 187 images contain the full box range that I need. When I open some of those incomplete images, I can see that the longitude range is just a very small part of my order, and looking to the MLAC file for the same day, and the same geographical range, the MLAC image is complete.
I have tried changing the search radius from 72 km for 800km or 1200km, but the results are the same.
Since I need as much image as I can, how is the best way to order those data to get the region that I am interested, for all my time series? What happen between MLAC and GAC that makes the image no longer include my area of interest?
Thank you in advance!
By @sean
Date 2011-03-22 02:07
The SeaWiFS GAC data are limited to a sensor scan angle of 45 degrees,
(which translates to 56 degree view angle - due to the sensor tilt and earth curvature)
This is NOT the full scan angle range of the sensor (58.3 degrees scan angle)
So, the MLAC swath covers about 2,800 km, while the GAC swath covers abot 1,502 km GAC.
This means that the MLAC coverage is about 650km more on each side of the swath
than the GAC.
Regards,
Sean
Hi Sean, thank you, I understand, but I still have some doubts.
For example, I have insitu data for 12/02/98, and I am trying to get images for 11, 12 and 13/02. However, I could get only image for 12/02 with the all range that I need. In attach, fig 1 and 2 is the 12/02 images MLAC and GAC, from where I can get my region in GAC, and fig 3 and 4 is an example of 11/02 where I see that GAC is just a small part of MLAC. So, why does it happen only for some of them? I still do not understand how should I make my searching in order to have my region of interest for all those days, in this case for 11 and 13 as well.
Thank you,
Fernanda
I am sorry for sequential questions, but I am testing something to figure out the problem.
Well, looking to the level-3 image for the same days that I get problems, it seems that my region is in between two swaths, at least could see that in two examples that I've tried. I am attaching those images. Is that possible?? Does it mean that I really don't have data for many days in my region??
Thank you again!!
By @norman
Date 2011-03-22 19:12
Hi Fernanda,
Because a picture (or two) is worth a thousand words,
please consider the following two images.
Regards,
Norman
Oh yes, I got it. If I want as much data as I can, I should use MLAC images then, alright?
Thank you so much.
Regards,
Fernanda
By @norman
Date 2011-03-22 20:13
Fernanda,
It depends on your needs. MLAC coverage is only available
where the satellite transmissions were collected by a ground
station or where the spacecraft was commanded to record
LAC on board. GAC data were stored on board the spacecraft
to give us global coverage (albeit at reduced resolution and a
narrower swath width).
I would say, given your relatively small area of interest, that you
probably want to use the higher resolution MLAC data where they
are available and fill in with the subsampled GAC when MLAC scenes
are not available.
Norman
Alright, that is very clear.
Thank you so much,
Cheers!
Topic Products and Algorithms / Satellite Data Access / Problems to get all daily images for certain region (locked) (3881 hits)
