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Up Topic Products and Algorithms / Satellite Data Products & Algorithms / Make atmospheric correction for MODIS by SWIR in Seadas (locked)
- By zhigang Date 2014-12-26 16:18
Hi everyone,
Recently, I try to make AC by SWIR for processing very high turbid inland lakes,such as TaiHu Lake in China.
However, a result with mostly NaN values(subseting as inland lakes zones) was showed when I using seads l2gen to make AC for MODIS Aqua, selecting -9 Multi-scattering of 2 band model selecting using Want (2009) algorithm of aer_opt options in Processing Tabs.
I don't know why. Is that the saturation of the NIR and SWIR bands? Did someone suffer this problem?
- By seanbailey Date 2014-12-29 15:28
The l2_flags should give an indication as to why there are no valid retrievals. 
One possibility is a failure of the NIR/SWIR switching.  The switching is based
on a threshold derived from the a method that requires a valid 748nm  retrieval.
If that fails, which can happen if 748nm is saturated, switching will fail.

If 748nm is saturated over Lake Taihu, you're probably looking at floating algae,
in which case even if there is a successful retrieval from the SWIR, it will be
extremely suspect.

- By zhigang Date 2015-01-10 07:48
Thank you ,Sean. I have attempted to process lots of images, yet lots of results are not satisfying (Most are NaN in turbid waterbody). Otherwise, my master told me it is hard to identify the land and too turbid water (generally, those are inland water) by threshold when make atmospheric correction in seadas.  Maybe, I should wait for more effective AC algorithm using to process inland water.
- By seanbailey Date 2015-01-10 16:42
When the issues are relate to the pixel-by-pixel aerosol determination - particularly in small regional studies - you may have success with a fixed aerosol implementation.
If you have a priori knowledge of the aerosol type, you can simply choose a single aerosol model.  You could also take an iterative approach, using valid aerosol retrievals in a first run to select the aerosol model to use in as second, fixed aerosol run (an approach described by Hu et al., 2000

- By zhigang Date 2015-01-13 05:36
That means I can modify the parameters of aerosol models in l2gen  to make atmospheric corrections based on my priori knowledge of aerosol properties for studying areas.
Thank you again, sean. I will read more publications about AC over turbid waters like Hu et al.(2000).
Up Topic Products and Algorithms / Satellite Data Products & Algorithms / Make atmospheric correction for MODIS by SWIR in Seadas (locked)

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