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MISR Level 3 Products Quality Statement |
Georecitified Radiance: Mike Smyth, Amy Braverman
Aerosol: Mike Smyth, Amy Braverman
Land Surface: Mike Smyth, Amy Braverman
Albedo: Mike Smyth, Amy Braverman
Cloud: Mike Smyth, Amy Braverman
This statement applies to the MISR Level 3 Georectified Radiance product, MISR Level 3 Aerosol product, the MISR Level 3 Land Surface product, the MISR Level 3 Albedo product, and the MISR Level 3 Cloud product with a production date of December 1, 2005, or later until such a time as further improvements to MISR software or ancillary inputs are made. See the Versioning Page for an in-depth explanation of the differences between various MISR product versions. Quality statements covering earlier time periods may be accessed through links at the bottom of this page.
An extensive review of product quality has not yet been performed. Please read the summary words of caution if you have not done so already.
Although there are warnings relating to Beta and Provisional quality parameters, the MISR Level 3 software which generated this product is believed to be functioning quite well except where noted below. This statement highlights major known problems with the products, as well as functionalities which are currently not implemented.
All component global georectified radiance parameters now have a "Stage 3 Validated" status.
The Level 3 Georectified Radiance product is a summary of the L1B2 Terrain and L1B2 Ellipsoid Radiance products and therefore, all of the Level 1 quality statements apply.
All component global aerosol parameters now have a "Stage 2 Validated" status.
The Level 3 Aerosol product is a summary of the Level 2 Aerosol product, therefore all of the Level 2 aerosol quality statements apply.
Notes on using MISR Level 3 Aerosol Data:
Key issues currently being addressed by the MISR team and associates that bear upon the use of the Level 3 aerosol products for regional and global scale studies:
A paper looking deeply into a possible resolution of this calibration difference is in preparation:
Lyapustin, A., Y. Wang, R. Kahn, R. Wolfe, J. Xiong, K. Thome, A. Smirnov, C. Bruegge, A. Ignatov, O. Dubovik, 2006. Analysis of MODIS-MISR Calibration Difference: Implications for Data Fusion, Remt. Sens. Environ., in preparation. Note that the absolute calibration stability, as well as the band-to-band and camera-to-camera relative calibration for MISR itself, are within a few percent or better.
Cloud masking is under study by the MISR team, as well as several other groups. For aerosol retrievals, the MISR cloud mask has eight separate tests to draw upon, and the logic that defines their use is being optimized with the help of numerous cloud validation cases, distributed globally. Some work has already appeared regarding MISR cloud detection (e.g., DiGirolamo and Wilson, TGARS 2003; Zhao and DiGirolamo, JAM 2004), but current tasks need to be completed before that aspect of the product will be validated.
The MISR Level 2 aerosol microphysical property values are currently being validated. Level 3 aggregates will be released once these quantities are at least Provisionally Validated. Improvements in the Aerosol Retrieval Algorithm based on the validation studies may also result in incremental improvements in the optical depth values for the more challenging cases.
All component global land surface parameters now have a "Stage 1" status with the exception of
DHR Shortwave which has a "Provisional" status.
LAI and FPAR for needleleaf biome type which has a "Provisional" status (other biome types are "Stage 1").
The Level 3 Land Surface product is a summary of the Level 2 Land Surface product, and therefore all of the Level 2 land surface quality statements apply. In particular, it is noted that optical depth blunders in the Level 2 product can frequently occur over snow/ice fields due to low spatial contrast and also as a consequence of inadequate cloud screening. Many such blunders have been observed over Greenland and Antarctica. Therefore, these two geographic areas are currently being excluded in the Level 3 Global Land Product but with the expectation that they will be included at a later date.
All (narrowband) component global albedo parameters now have a "Stage 1" (except at high latitudes) status. The broadband albedos are still Provisional.
The Level 3 Albedo product is a summary of the Level 2 Albedo product, and therefore all of the Level 2 albedo quality statements apply. Note in particular that at high latitudes, notably poleward of 60 degrees, the angular models used in the Albedo retrievals currently fail due to extreme anistropy. Albedos in these regions are frequently over-estimated.
The cloud parameter Height Histograms and the Wind Vectors both have a "Stage 2" status.
The Level 3 Cloud product is a summary of the Level 2 Cloud product, and therefore all of the Level 2 cloud quality statements apply.
Note in particular the following properties of the retrieved heights:
The pattern-matchers used in the stereo height retrievals identify the location of greatest contrast, which is not necessarily the highest point in the cloud. MISR, along with many other instruments, has difficulty in retrieving the height of optically thin clouds. The optical depth threshold at which the algorithm identifies the thin cloud rather than the underlying object depends on the contrast of the underlying feature. The reader should take this inherent limitation of the retrievals into account when comparing MISR heights to other instruments or to model results.
For the extreme case of very dark features (such as open water) near bright features such as snow, clouds with optical depth of at least 2 and perhaps as much as 5 can be missed. When boundary layer clouds such as stratocumulus or trade cumulus are present, cirrus clouds with optical depths of 2 to 5 are sometimes not retrieved. However, for cases without lower clouds or underlying bright surfaces, thin cirrus clouds with optical depths near 0.5 (over heterogeneous land) and perhaps even smaller (over dark water) are usually detected.
