The Suomi National Polar-Orbiting Partnership (S-NPP) NASA Visible Infrared Imaging Radiometer Suite (VIIRS) Bidirectional Reflectance Distribution Function (BRDF) and Albedo Nadir BRDF-Adjusted Reflectance Daily Global 0.05 Degree Climate Modeling Grid (CMG) Version 1 product (VNP43C4) is derived from the 30 arc second CMG VNP43D Version 1 product suite. VNP43C3 is generated daily from all available high-quality reflectance data over a 16-day moving window emphasizing the ninth day of the retrieval period, which is reflected in the Julian date in the filename. The VNP43 algorithm uses the RossThick/Li-Sparse-Reciprocal (RTLSR) semi-empirical kernel-driven BRDF model, with the three kernel weights from VNP43C1 to compute NBAR values for the VIIRS Day/Night band (DNB), and moderate resolution bands M1 through M5, M7, M8, M10, and M11. The algorithm removes view angle effects from directional reflectances to model the values as if they were collected from a nadir view at local solar noon. The quality and inversion status of the majority of the underlying 30 arc second pixels is provided as well as the percentage of the underlying pixels that were present or were snow covered. Users are encouraged to assess the quality information before using the BRDF/Albedo data. This 0.05 degree (5,600 meters at the equator) CMG product covers the entire globe for use in climate simulation models.
The VNP43C4 product includes 10 layers containing NBAR values for VIIRS DNB and moderate resolution bands M1 through M5, M7, M8, M10, and M11. Along with the NBAR data for the 10 bands are five ancillary layers for uncertainty, quality, local solar noon, percent finer resolution inputs, and snow cover. A low-resolution browse image is also available showing NBAR bands M5, M4, and M3 as a red, green, blue (RGB) image in JPEG format.
|File Size||~90.342 MB|
|Temporal Extent||2012-01-19 to Present|
|Coordinate System||Geographic Latitude and Longitude|
|Number of Science Dataset (SDS) Layers||15|
|Columns/Rows||7200 x 3600|
|Pixel Size||5600 m|
|SDS Name||Description||Units||Data Type||Fill Value||No Data Value||Valid Range||Scale Factor|
|BRDF_Albedo_Uncertainty||BRDF inversion information||N/A||16-bit unsigned integer||32767||N/A||0 to 32766||0.001|
|BRDF_Quality||BRDF and albedo quality information||N/A||8-bit unsigned integer||255||N/A||0 to 5||N/A|
|Local_Solar_Noon||Local solar noon zenith angle||Degree||8-bit unsigned integer||255||N/A||0 to 90||N/A|
|Nadir_Reflectance_DNB||Nadir reflectance for Day/Night band (0.7 μm)||N/A||16-bit signed integer||32767||N/A||0 to 10000||0.0001|
|Nadir_Reflectance_M1||Nadir reflectance for band M1 (0.412 μm)||N/A||16-bit signed integer||32767||N/A||0 to 10000||0.0001|
|Nadir_Reflectance_M10||Nadir reflectance for band M10 (1.61 μm)||N/A||16-bit signed integer||32767||N/A||0 to 10000||0.0001|
|Nadir_Reflectance_M11||Nadir reflectance for band M11 (2.25 μm)||N/A||16-bit signed integer||32767||N/A||0 to 10000||0.0001|
|Nadir_Reflectance_M2||Nadir reflectance for band M2 (0.445 μm)||N/A||16-bit signed integer||32767||N/A||0 to 10000||0.0001|
|Nadir_Reflectance_M3||Nadir reflectance for band M3 (0.488 μm)||N/A||16-bit signed integer||32767||N/A||0 to 10000||0.0001|
|Nadir_Reflectance_M4||Nadir reflectance for band M4 (0.555 μm)||N/A||16-bit signed integer||32767||N/A||0 to 10000||0.0001|
|Nadir_Reflectance_M5||Nadir reflectance for band M5 (0.672 μm)||N/A||16-bit signed integer||32767||N/A||0 to 10000||0.0001|
|Nadir_Reflectance_M7||Nadir reflectance for band M7 (0.865 μm)||N/A||16-bit signed integer||32767||N/A||0 to 10000||0.0001|
|Nadir_Reflectance_M8||Nadir reflectance for band M8 (1.240 μm)||N/A||16-bit signed integer||32767||N/A||0 to 10000||0.0001|
|Percent_Inputs||Percent finer resolution data which contributed to the CMG||Percent||8-bit unsigned integer||255||N/A||0 to 100||N/A|
|Percent_Snow||Percent of underlying data flagged as snow||Percent||8-bit unsigned integer||255||N/A||0 to 100||N/A|
|0||Best quality, 100% with full inversions|
|1||Good quality, 75% or more with best full inversions and 90% or more with full inversions|
|2||Relative good quality, 75% or more with full inversions|
|3||Mixed, 75% or less full inversions and 25% or less fill values|
|4||All magnitude inversions or 50% or less fill values|
|5||50% or more fill values|
The quality and inversion status of the majority of the underlying 30 arc second pixels is provided as well as the percentage of the underlying pixels that were present or were snow covered. Therefore, quality should be considered when using this product for quantitative results. Product accuracy/uncertainty information can be found in section 4 of the Algorithm Theoretical Basis Document (ATBD).
The abnormally high activation of the high aerosol flag in the Collection 1 (C1) VNP09 product, has impacted downstream products. The VNP43 BRDF/Albedo/NBAR product is affected by reducing the number of otherwise acceptable observations used as input to characterize surface anisotropy. This effect (most obvious over arid bright surfaces), results in a reduced number of high quality full BRDF model inversions. Therefore, users should be aware that bright arid surfaces (normally associated with high quality BRDF/Albedo/NBAR retrievals) are likely to be somewhat represented by lower quality results in C1. VNP09 has been corrected for Collection 2 (C2). Therefore, users should avoid substantive use of C1 VNP43 over arid regions (and wait for C2 products). In any event, users are always strongly encouraged to download and use the extensive QA data provided in VNP43[I-M]A2, in addition to the briefer mandatory QA provided as part of the VNP43[I-M]A1, 3 and 4 products.
Additional known issues for VNP43 data products can be found on the VIIRS Land Quality Assessment website.