Problem in Downloading Aerosol Optical Depth Data and Ångstrom Exponent

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samaneh94
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Problem in Downloading Aerosol Optical Depth Data and Ångstrom Exponent

by samaneh94 » Tue Jan 04, 2022 4:28 am America/New_York

Hello everyone;
I have a problem downloading AOD data in different wavelengths and Angstrom exponent to have an evaluation of the aerosol type in the Aral Sea and the southeast coast of the Caspian Sea.

at the first step, I tried MOD04_L2, MYD04_L2, MOD04_3k, and MYD04_3K for the mentioned region using https://ladsweb.modaps.eosdis.nasa.gov/search/ but the downloaded data which are in .hdf format are empty for the AOD and aerosol types!!!!

my second try was using the google earth engine and I succeeded to download the data for the region but the problem is that it only contains AOD in 0.55 and 0.47 and they are not good for calculating the Angstrom Exponent!!

and the final step was using Noaa and its JPSS_GRAN product. It has my favorite products but a single data for a single day has an 800-megabyte volume! I need data for several days and it is not possible to download and use this bunch of data!

I spend a lot of time on it and yet there is no result!! please help me if you have an idea that you think will help me.

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LAADS_UserServices_M
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Re: Problem in Downloading Aerosol Optical Depth Data and Ångstrom Exponent

by LAADS_UserServices_M » Tue Jan 04, 2022 9:43 am America/New_York

The MODIS Aerosol products (MxD04_L2 and MxD04_3k) monitor the ambient aerosol loading and some properties of the aerosol over cloud-free snow/ice-free land and ocean surfaces. If you don't see values in any file means that algorithms could not retrieve AOD
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at that location for that particular time. You can use images provided for each data file under "Image" column on ladsweb to see if AOD values are calculated for that particular granules (see attached screenshots).

If you prefer, you can convert files in hdf format to GeoTiff format by using LAADS post-processing utility available during search and order at the last (5 REVIEW & ORDER) step. Let us know if you need further help on this.

Aerosol Product (04_L2) Scientific Data Sets (SDS) incldue following Angstrom Exponent SDSs which you can order as individual file by using parameter sub-setting in LAADS post-processing utility under "Sds":

1. Angstrom_Exponent_Land
Description: Angstrom Exponent at 0.47 and 0.67 µm
Valid Range: -1.0 to 5.0

2. Angstrom_Exponent_1_Ocean
Description: Angstrom Exponent for 0.55 and 0.86 µm
Valid Range: -1.0 to 5.0

3. Angstrom_Exponent_2_Ocean
Description: Angstrom Exponent for 0.865 and 2.130 µm
Valid Range: -1.0 to 5.0

4. Deep_Blue_Angstrom_Exponent_Land
Description: Deep Blue Angstrom Exponent for Land (0.412-0.47 micron) with all quality data (QA Confidence Flag = 1, 2, 3)
Valid Range: -0.5 to 5.0

For more information visit product page at:

https://atmosphere-imager.gsfc.nasa.gov ... s/aerosol/
or
https://atmosphere-imager.gsfc.nasa.gov ... at-content
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Attachments
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Regards,
LAADS User Services

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samaneh94
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Re: Problem in Downloading Aerosol Optical Depth Data and Ångstrom Exponent

by samaneh94 » Wed Jan 05, 2022 7:49 am America/New_York

Hello,
thanks for your information.

I tried that and some of the images were empty again but some of them weren't. the second group images were empty on the Aral Sea again (see the screenshot)!!!!

each image has a different location in spite of that I defined the only Aral sea in the location section (step 3)
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GES DISC - jimacker
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Re: Problem in Downloading Aerosol Optical Depth Data and Ångstrom Exponent

by GES DISC - jimacker » Wed Jan 05, 2022 10:31 am America/New_York

Question for the user:

Have you considered aerosol data products from the Ozone Measuring Instrument (OMI)? OMI provides data in additional wavelengths.

samaneh94
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Re: Problem in Downloading Aerosol Optical Depth Data and Ångstrom Exponent

by samaneh94 » Thu Jan 06, 2022 7:04 am America/New_York

[quote="GES DISC - jimacker" post_id=10082 time=1641396692 user_id=96]
Question for the user:

Have you considered aerosol data products from the Ozone Measuring Instrument (OMI)? OMI provides data in additional wavelengths.
[/quote]

many thanks for sharing your idea!
Yes, I saw them on Giovanni's platform. But there is a problem. the OMI results were really different from MODIS's in my case study (Aral Sea). I thought that MODIS is more accurate because it is more used in different studies (I am not sure!).
Do you know any paper that can help me in this way??

thank tou again

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Re: Problem in Downloading Aerosol Optical Depth Data and Ångstrom Exponent

by LAADS_UserServices_M » Thu Jan 06, 2022 9:01 am America/New_York

Regarding:
" each image has a different location in spite of that I defined the only Aral sea in the location section (step 3)"

This is because search will pick all granules (complete 5-min swaths) which include your defined area of interest.
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samaneh94
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Re: Problem in Downloading Aerosol Optical Depth Data and Ångstrom Exponent

by samaneh94 » Fri Jan 07, 2022 10:40 am America/New_York

[quote=LAADS_UserServices_M post_id=10087 time=1641477699 user_id=88]
Regarding:
" each image has a different location in spite of that I defined the only Aral sea in the location section (step 3)"

This is because search will pick all granules (complete 5-min swaths) which include your defined area of interest.
[/quote]

Dear user;
Thanks for your comment.
Yes, it includes the granule, but my defined area of the interest is empty in that picture!! this is my main problem!!!!

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Re: Problem in Downloading Aerosol Optical Depth Data and Ångstrom Exponent

by LAADS_UserServices_M » Thu Feb 17, 2022 9:55 am America/New_York

Sorry we missed your reply. If the image is blank that means AOD was not observed for that location at that time because "MODIS Aerosol products monitor the ambient aerosol loading and some properties of the aerosol over cloud-free snow/ice-free land and ocean surfaces."
Regards,
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