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Where to find Deep Blue data, and how to use it

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What geophysical data quantities does Deep Blue provide?

For all of our data sets from the assorted satellite instruments, the main scientific geophysical data product is the aerosol optical depth (AOD), also called aerosol optical thickness (AOT), at a wavelength of 550 nm. This quantity has been validated against AERONET and other data sources and has generally understood error characteristics.

Each of our retrievals also has a quality assurance (QA) flag associated with it, which can be used to filter out retrievals which may potentially be of a lower quality (due to, e.g. sub-pixel cloud contamination). For most scientific applications, it is strongly recommended that users apply these QA flags before scientific use of the data. For ease of use, each of our files also includes a data set including only those retrievals passing these QA tests. This is referred to as the 'best estimate' data set within the file metadata, and it is expected that most users will do their analyses based on this. Note that level 3 data (see below) are only comprised of such 'best estimate' retrieval pixels.

Depending on the sensor and underlying surface/atmospheric conditions, certain other data products, such as the Ångström exponent, are also provided.

More information on specific geophysical data quantities, their uncertainties, and usage caveats can be found in our product user guides and peer-reviewed journal papers. If in doubt, please feel free to get in contact with us and ask questions.

 

Data levels

NASA Earth Science data sets are classified into different 'levels':

  • Level 0 data consist of raw instrument and payload data from the spacecraft.
  • Level 1 data consist of uncalibrated (level 1a, L1a) and calibrated and georeferenced (level 1b, L1b) measurements made by sensors.
  • Level 2 (L2) data consist of geophysical information (e.g. AOD) obtained by processing L1b data with algorithms such as Deep Blue. L2 data are provided as orbit-level (SeaWiFS) or granule-level (AVHRR, MODIS, VIIRS) data.
  • Level 3 (L3) data consist of spatially (e.g. 1 degree) and temporally (e.g. daily, 8-day, monthly) aggregated L2 products on a regular grid.

Deep Blue provides L2 and L3 data products. These are freely available from the locations below. Some simple visualizations of aerosol data, including Deep Blue, can be created at NASA's Giovanni portal. Note that Giovanni does not always have the latest data version ingested, however, so users are encouraged to turn to the official source data products after an exploratory analysis in Giovanni.

 

AVHRR (multiple sensors from 1981 onwards)

Note: this AVHRR data set should be considered a demonstration research-level data product, still under validation, and comments/suggestions are welcome.

AVHRR Deep Blue L2 and L3 products are available at the NCCS Data Portal. The current data version is Version 1 (V001). These data products are stored in NetCDF4 format, compliant with CF version 1.6 metadata conventions. A user guide is also available to download.

Direct ftp access to AVHRR L2 and L3 data is available at ftp://dataportal.nccs.nasa.gov or ftp://nccs.nasa.gov with username AVHRRDeepBlue and no password.

At present, we have processed data from the AVHRR sensors on the following platforms (periods with Equatorial local solar crossing times from approximately 1:30-3 pm):

  • NOAA11 from 1989-1990
  • NOAA14 from 1995-1999
  • NOAA18 from 2006-2011

Level 2 data are available as 5-minute granules, with a horizontal pixel size of approximately 8.8x8.8 km2 at the sub-satellite point. Level 3 data are gridded aggregates at 1 degree resolution, on daily and monthly time scales. Monthly data are aggregated from daily data.

While users are encouraged strongly to read the data set documentation and related publications to determine the most appropriate use of the data for their specific application, some key science data sets (SDS) stored in the NetCDF files for the AVHRR data product are listed below. Note that, in most software languages, SDS names are case-sensitive.

SDS name Description
L2 files  
latitude Central latitude of the retrieval pixel, degrees North.
longitude Central longitude of the retrieval pixel, degrees East.
aerosol_optical_thickness_550_land_ocean The AOD at 550 nm, from the Deep Blue algorithm over land, and the SOAR algorithm over water.
aerosol_optical_thickness_550_land_ocean_best_estimate

As above, except only populated for those retrieval pixels passing quality assurance tests.

This is the SDS that is it anticipated the majority of data users will use.

aerosol_optical_thickness_confidence_flag_land_ocean Confidence flag (also known as 'quality flag') for AOD retrievals. Ranges from 0 (no retrieval) to 3 (highest confidence).
angstrom_exponent_ocean

Ångström exponent over water; defined between 550 nm and band 2 (approximately 850 nm).

L3 files  
latitude Central latitude of the grid cell, degrees North.
longitude Central longitude of the grid cell, degrees East.
aerosol_optical_thickness_550_land_ocean_mean

Average AOD at 550 nm, from the Deep Blue algorithm over land, and the SOAR algorithm over water, constructed from those retrieval pixels passing quality assurance tests.

angstrom_exponent_ocean

Average Ångström exponent over water; defined between 550 nm and band 2 (approximately 850 nm).

 

SeaWiFS (1997-2010)

SeaWiFS Deep Blue L2 and L3 products and documentation are available at the NASA GES DISC (project referred to there as 'Consistent Long-Term Aerosol Data Records over Land and Ocean from SeaWIFS' button on the radio menu). The current data version is Version 4 (v004). The older v003 is similar in many respects, but should be considered obsolete, and data users are strongly encouraged to use the most recent data version for scientific analyses.

While users are encouraged strongly to read the data set documentation and related publications to determine the most appropriate use of the data for their specific application, some key science data sets (SDS) stored in the hdf files for the SeaWiFS data product are listed below. Note that, in most software languages, SDS names are case-sensitive.

SDS name Description
L2 files  
latitude Central latitude of the retrieval pixel, degrees North.
longitude Central longitude of the retrieval pixel, degrees East.
aerosol_optical_thickness_550_land_ocean The AOD at 550 nm, from the Deep Blue algorithm over land, and the SOAR algorithm over water.
aerosol_optical_thickness_550_land_ocean_best_estimate

As above, except only populated for those retrieval pixels passing quality assurance tests.

This is the SDS that is it anticipated the majority of data users will use.

aerosol_optical_thickness_confidence_flag_land_ocean Confidence flag (also known as 'quality flag') for AOD retrievals. Ranges from 0 (no retrieval) to 3 (highest confidence).
angstrom_exponent_land Ångström exponent over land; defined between 412-470 nm for 'bright' surfaces, and 470-670 nm for 'dark' surfaces.
angstrom_exponent_ocean

Ångström exponent over water; defined between 440-870 nm.

L3 files  
latitude Central latitude of the grid cell, degrees North.
longitude Central longitude of the grid cell, degrees East.
aerosol_optical_thickness_550_land_ocean

Average AOD at 550 nm, from the Deep Blue algorithm over land, and the SOAR algorithm over water.

aerosol_optical_thickness_550_land_ocean_best_estimate As above, except only populated for those retrieval pixels passing quality assurance tests.
angstrom_exponent_land

Average Ångström exponent over land; defined between 412-470 nm for 'bright' surfaces, and 470-670 nm for 'dark' surfaces.

angstrom_exponent_ocean

Average Ångström exponent over water; defined between 440-870 nm.

 

MODIS (2000-present for Terra, 2002-present for Aqua)

MODIS Deep Blue L2 and L3 data products are available at the NASA LAADS 'search' page.The current data version is Collection 6.1 (C6.1). Older versions should at this point be considered obsolete. Data users are strongly encouraged to use the most recent data version for scientific analyses.

MODIS data files are stored in hdf4 format. File specifications and other information can be found on the MODIS Atmospheres portal. Slides and recorded webinars designed for new and experienced MODIS data users covering the C6 MODIS Atmospheres data products, including Deep Blue, can be found here.

Products for MODIS Terra have filenames beginning MOD, while those for Aqua begin MYD.  Search and download for MODIS L2 and L3 data is available via NASA LAADS.

While users are encouraged strongly to read the data set documentation and related publications to determine the most appropriate use of the data for their specific application, some key science data sets (SDS) stored in the hdf files for the MODIS data product are listed below. Note that, in most software languages, SDS names are case-sensitive.

SDS name Description
L2 files (MOD04_L2, MYD04_L2)  
Latitude Central latitude of the retrieval pixel, degrees North.
Longitude Central longitude of the retrieval pixel, degrees East.
Deep_Blue_Aerosol_Optical_Depth_550_Land The AOD at 550 nm.
Deep_Blue_Aerosol_Optical_Depth_550_Land_Best_Estimate

As above, except only populated for those retrieval pixels passing quality assurance tests.

This is the SDS that is it anticipated the majority of data users will use.

Deep_Blue_Aerosol_Optical_Depth_550_Land_QA_Flag

Quality flag for AOD retrievals. Ranges from 0 (no retrieval) to 3 (highest confidence).

Deep_Blue_Angstrom_Exponent_Land

Ångström exponent over land; defined between 412-470 nm for 'bright' surfaces, and 470-670 nm for 'dark' surfaces.

Deep_Blue_Aerosol_Optical_Depth_550_Land_Estimated_Uncertainty
 
Uncertainty estimate (to be understood one standard deviation confidence interval around the retrieved value) for 550 nm AOD. See this paper for more details.
AOD_550_Dark_Target_Deep_Blue_Combined

Union of Deep Blue and Dark Target land and ocean data.

See this paper for more details and relative merits of Deep Blue, Dark Target, and this merged data set.

L3 daily files (MOD08_D3, MYD08_D3)  
Latitude

Central latitude of the grid cell, degrees North.

Longitude

Central longitude of the grid cell, degrees East.

Deep_Blue_Aerosol_Optical_Depth_550_Land_Mean

Average AOD at 550 nm, for retrievals passing QA checks.

Deep_Blue_Angstrom_Exponent_Land_Mean

Average Ångström exponent over land; defined between 412-470 nm for 'bright' surfaces, and 470-670 nm for 'dark' surfaces.

AOD_550_Dark_Target_Deep_Blue_Combined_Mean Average AOD at 550 nm from the union of Deep Blue with Dark Target land and ocean data.

L3 8-day (MOD08_E3, MYD08_E3) and monthly (MOD08_M3, MYD08_M3) files

 

Latitude

Central latitude of the grid cell, degrees North.

Longitude Central longitude of the grid cell, degrees East.
Deep_Blue_Aerosol_Optical_Depth_550_Land_Mean_Mean

Average (mean of daily means) AOD at 550 nm, for retrievals passing QA checks.​

Deep_Blue_Angstrom_Exponent_Land_Mean_Mean

Average (mean of daily means) Ångström exponent over land; defined between 412-470 nm for 'bright' surfaces, and 470-670 nm for 'dark' surfaces.

AOD_550_Dark_Target_Deep_Blue_Combined_Mean_Mean

Average (mean of daily means) AOD at 550 nm from the union of Deep Blue with Dark Target land and ocean data.

 

VIIRS (2012-present)

The VIIRS Deep Blue Version 1 L2 and L3 data products are available through the LAADS DAAC and EarthData.
- LAADS DAAC
- EarthData
Level 2 data are provided in 6-minute granules, at approximately 6 km x 6 km pixel size at the sub-satellite point. Level 3 daily (D3) and monthly (M3) composites at 1 degree horizontal resolution are also available. All VIIRS data files are in NetCDF4 format. More details of file specifications and other information can be found on the LAADS.
While users are encouraged strongly to read the data set documentation and related publications to determine the most appropriate use of the data for their specific application, some key science data sets (SDS) stored in the NetCDF4 files for the VIIRS data product are listed below. Note that, in most software languages, SDS names are case-sensitive.

SDS name Description
L2 files (AERDB_L2)  
Latitude Central latitude of the retrieval pixel, degrees North.
Longitude Central longitude of the retrieval pixel, degrees East.
Aerosol_Optical_Thickness_550_Land The AOD at 550 nm over land.
Aerosol_Optical_Thickness_550_Land_Best_Estimate

As above, except only populated for those retrieval pixels passing quality assurance tests.

This is the SDS that is it anticipated the majority of data users will use.

Aerosol_Optical_Thickness_550_Ocean

The AOD at 550 nm over ocean

Aerosol_Optical_Thickness_550_Ocean_Best_Estimate

As above, except only populated for those retrieval pixels passing quality assurance tests.

This is the SDS that is it anticipated the majority of data users will use.

Aerosol_Optical_Thickness_550_Land_Ocean
 
The combined AOD at 550 nm, from the Deep Blue algorithm over land, and the SOAR algorithm over water.
Aerosol_Optical_Thickness_550_Land_Ocean_Best_Estimate

As above, except only populated for those retrieval pixels passing quality assurance tests.

This is the SDS that is it anticipated the majority of data users will use.

Aerosol_Optical_Thickness_QA_Flag_Land Quality flag for AOD retrievals over land. Ranges from 0 (no retrieval) to 3 (highest confidence).
Aerosol_Optical_Thickness_QA_Flag_Ocean Quality flag for AOD retrievals over ocean. Ranges from 0 (no retrieval) to 3 (highest confidence).
Angstrom_Exponent_Land Ångström exponent over land; defined between 412-488 nm for 'bright' surfaces, and 488-670 nm for 'dark' surfaces.
Angstrom_Exponent_Ocean Ångström exponent over ocean; defined between 550-865 nm over water.
Angstrom_Exponent_Land_Ocean The combined Ångström exponent over land and ocean; defined as above.
Angstrom_Exponent_Land_Ocean_Best_Estimate The combined Ångström exponent over land and ocean for those retrieval pixels passing quality assurance tests.
Aerosol_Optical_Thickness_550_STDV_Land Deep Blue standard deviation of aerosol optical thickness at 550 nm within cell over land.
Aerosol_Optical_Thickness_550_STDV_Ocean SOAR standard deviation of aerosol optical thickness at 550 nm within cell over water.
Aerosol_Type_Land Aerosol optical model over land.
-999=no retrieval, 0=dust, 1=smoke, 2=high altitude smoke, 3=pyrocumulonimbus clouds, 4=non-smoke fine mode, 5=mixed, 6=background
Aerosol_Type_Ocean SOAR retrieved aerosol optical model over water. -999=no retrieval, 1=dust, 2=fine dominated, 3=maritime, 4=mixed
Aerosol_Type_Land_Ocean Aerosol optical model over land and water. -999=no retrieval, 0=dust(land+ocean), 1=smoke, 2=high altitude smoke, 3=pyrocumulonimbus clouds, 4=non-smoke fine mode, 5=mixed(land+ocean), 6=background(land+ocean maritime), 7=fine dominated
L3 daily files (AERDB_D3, AERDB_M3)  
Latitude

Central latitude of the grid cell, degrees North.

Longitude

Central longitude of the grid cell, degrees East.

Aerosol_Optical_Thickness_550_Land_Mean

Average AOD at 550 nm over land, for retrievals passing QA checks. ​

Aerosol_Optical_Thickness_550_Ocean_Mean

Average AOD at 550 nm over ocean, for retrievals passing QA checks.

Aerosol_Optical_Thickness_550_Land_Ocean_Mean Average combined AOD at 550 nm over land and ocean, for retrievals passing QA checks.
Angstrom_Exponent_Land_Mean Average Ångström exponent over land; defined between 412-488 nm for 'bright' surfaces, and 488-670 nm for 'dark' surfaces.
Angstrom_Exponent_Ocean_Mean Average Ångström exponent over ocean; defined between 550-870 nm.
Angstrom_Exponent_Land_Ocean_Mean Average Ångström exponent over land and ocean.

 

Reading MODIS data with Panoply - a brief example

Procedures for reading in data files vary dependent on the programming language in question. See the links tab for some links to hdf software. Panoply is a free tool which can be used to load and map data products in various file formats, including those used by Deep Blue data. This section provides an example using Panoply to read MODIS Level 2 aerosol data. You can download the example granule used directly here. A true-color image of this granule is shown below.

MODIS Terra true color image for the granule MOD04_L2.A2012221.1020 used as an example.

Run Panoply and select the file using 'File->Open' in the upper menu. Next, navigate to the data set Deep_Blue_Aerosol_Optical_Depth_550_Land_Best_Estimate, as shown below.

Panoply menu showing the various data sets stored in the MODIS L2 aerosol products.

Now, click on 'Create Plot'. A further menu will appear, asking how to plot the data--the option of using the latitude/longitude within the file should be used (and is the default in the present version of Panoply). Click again. Then, although the precise appearance will vary depending on your plotting preferences, you should see something like the below.

Your AOD map should look something like this.

Congratulations! You have read in Deep Blue data.