# Presentation: 195471

## Understanding and Accessing MODIS Atmosphere Products

- Rich Kleidman   Science Systems and Applications
- Rob Levy            Science Systems and Applications
- Lorraine Remer  NASA Goddard Space Flight Center
- Shana Mattoo,, Alan Chu, Vanderlei Martins, Rong-Rong Li, and Yoram Kaufman

## MOD04   Aerosol MOD06   CloudMOD05   Water VaporMOD07   Atmosphere ProfileMOD35   Cloud Mask

- MODIS LEVEL II Product List

## Aerosol SDS and What They Really Mean

- The individual Land or Ocean SDS is generally preferred because
-          - it contains more wavelengths
-          - gives more information about quality
-          - at level 3 it gives a quality weighted product that screens
-             out anomalies
- Land_And_Ocean  Is useful if you need both together but may not give the same results as Land or Ocean

- The Ocean and Land algorithms each produce their own SDS’s.
- When both algorithms retrieve the same parameter they may be combined into a joint Land_and_Ocean SDS.

## MOD04           MODIS AEROSOL PRODUCTS         MYD04Important Points to Remember for MODIS Aerosol Products- Ocean and Land Products are produced using totally separateand distinct algorithms.  All current aerosol products are in       10 Km (10 x 10) resolution.- The most important products are Aerosol Optical Depth and Fine Fraction.  These exist for both Ocean and Land. - There have been major changes and improvements made with collection 5 most significantly to the land algorithm.- Fine Fraction over land should be seen as a qualitative     indicator not as a quantitative measurement.

## MOD04      Aerosol Products     MYD04

- Main Products - Ocean
- Effective_Optical_Depth_Average_Ocean
- Retrieved AOD at  .47, .55, .66, .86, 1.24, ***1.63***, 2.13
- Optical_Depth_Ratio_Small_Ocean_0.55*
- Fraction of Fine Mode AOD at 0.55
- Optical_Depth_Small_Average_Ocean
- AOD * Fine Mode Ratio

## MOD04               Aerosol Products            MYD04

- retrieval algorithm there may be many solutions within acceptable
- error limits.  These solutions are used to obtain the
- Average_Ocean SDS results.
- For all practical purposes our group at NASA Goddard uses
- Average_Ocean rather than Best_Ocean SDS’s

- Average_Ocean  vs  Best_Ocean

- MOD04               Aerosol Products            MYD04

## Quality Assurance is Extremely Important!!

- Quality_Assurance_Ocean
- Scale is 0 - 3
- We use Ocean QA above 0
- Factors:
- Number of pixels
- Error fitting
- How close to glint

- QA is our indication of how much confidence we have in
- quality of the retrieval.

- Quality_Assurance_Land
- Scale is 0 - 3
- We use Land QA of 3
- Factors:
- Number of pixels
- Error fitting
- Surface reflectance

## Additional Products - Ocean

**Optical_Depth_Large_Average_Ocean**
- (1 - Fine Fraction) * AOD   for the 7 ocean wavelenghts
**Mass_Concentration_Ocean***
- Total column mass per unit area in units of 1.0e-6g/cm2
**Angstrom_Exponent_1_Ocean***  0.55/0.86
**Angstrom_Exponent_2_Ocean***  0.86/2.1
**Optical_Depth_by_models_ocean**
- Retrieval AOT per model.  This information is carried into the level 3 products.
**Effective_Radius_Ocean**
- Effective Radius at 0.55 for both the fine and coarse modes.

## For Visualization purposes when you

- Image_Optical_Depth_Land_and_Ocean

- want an image of as much of the scene
- as possible.
- This SDS includes poor quality data

## MOD04 SDS and What They Really Mean

- Land_And_Ocean  vs Land or Ocean
- Land or Ocean separately is preferred because
-          - it contains more wavelengths
-          - gives more information about quality
-          - at level 3 it gives a quality weighted product that screens
-              out anomolies
- Land_And_Ocean  Useful if you need both together and may not
-                                 give the same results as Land or Ocean

- Average_Ocean  vs  Best_Ocean
- Average_Ocean  is the average of all solutions to the AOT retrieval algorithm having results within acceptable error limits.
- Best_Ocean is the single best solution to the AOT retrieval algorithm
- There are several SDS results that have two dimensions one corresponding to the average solution and one correponding to the best solution.

## MOD04   Aerosol Products

- Main Products - Land
- Corrected_Optical_Depth_Land
- Retrieved AOD at  .47, .55, and .66
- Optical_Depth_Ratio_Small_Land
- Fraction of Fine Mode Aerosol
- Not reported for AOD < 0.2
- Optical_Depth_Small_Land
- AOD * Fine Mode Ratio
- (may be a threshold)

- A Qualitative Product Only!

## Additional Products - Land

- Quality_Assurance_Land
- Scale is 0 - 3.  Highest number is best quality.
- Cloud_Fraction_Land
- Aerosol product algorithm cloud mask fraction not official MODIS cloud mask fraction.
- Mass_Concentration_Land
- Total column mass per unit area in units of 1.0e-6g/cm2
- Angstrom_Exponent_Land
- Ratio of .47/.66     This product does not compare well with Aeronet

- Additional Products - Land

## The standard MODIS aerosol LAND algorithm

-  relies on finding dark targets.
- For this reason it is unable to make retrievals over bright
- surfaces such as deserts.
- To correct this problem a new algorithm called
- “Deep Blue” was developed.
- Deep Blue relies on the blue wavelengths and libraries
- of surface reflectance to make retrievals in these areas.
- Deep Blue SDS Names:
- Deep_Blue_Aerosol_Optical_Depth_550_Land
- Deep_Blue_Aerosol_Optical_Depth_Land
- Deep_Blue_Angstrom_Exponent_Land
- Deep_Blue_Single_Scattering_Albedo_Land
- Deep_Blue_Surface_Reflectance_Land

## HDFLook,  Msphinx and Mgraphhttp://www-loa.univ-lille1.fr/Hdflook/http://www-loa.univ-lille1.fr/Msphinx/index.htmlhttp://www-loa.univ-lille1.fr/Mgraph/mgraphE.html

## ALWAYS CHECK YOUR DATA VISUALLY!

- AQUA Reprojected Granule

- Terra Reprojected Granule

- Flight
- Direction
- of the
- Overpass
- Gives a
- “Tilt” to the reprojected
- granule

- ~10:30 Local Time

- ~1:30 Local Time

- Unreprojected “raw” granules come as rectangles