The MCD18A2 Version 6 is a Moderate Resolution Imaging Spectroradiometer (MODIS) Terra and Aqua combined Photosynthetically Active Radiation (PAR) gridded Level 3 product produced daily at 5 kilometer pixel resolution with estimates of PAR every 3 hours. PAR is incident solar radiation in the visible spectrum (400-700 nanometers) and is an important variable in land-surface models that address a variety of scientific and application issues. The MCD18 products are based on a prototyping algorithm that uses multi-temporal signatures of MODIS data to derive surface reflectance and then calculate incident PAR using the look-up table (LUT) approach. The LUTs consider different types of loadings of aerosols and clouds at a variety of illumination/viewing geometry. Global PAR products are generated from MODIS and geostationary satellite data. Additional details regarding the methodology used to create the data are available in the Algorithm Theoretical Basis Document (ATBD).
Provided in the MOD18A2 product are layers for instantaneous PAR array for each individual MODIS overpass and 3-hour PAR array along with a View Zenith Angle layer.
MODIS radiation products from 2001 through 2008 are early release data validated to Beta maturity level. Data from 2018 to present have undergone additional processing that fixed various programming errors that negatively affected product accuracy and are considered to be validated to Provisional maturity status.
|File Size||~5 MB|
|Temporal Extent||2001-01-01 to Present|
|Geographic Dimensions||1200 km x 1200 km|
|Number of Science Dataset (SDS) Layers||12|
|Columns/Rows||240 x 240|
|Pixel Size||5600 m|
|SDS Name||Description||Units||Data Type||Fill Value||No Data Value||Valid Range||Scale Factor|
|PAR||Instantaneous total PAR at MODIS overpass||W/m²||32-bit floating point||-1||N/A||0 to 700||N/A|
|Direct||Instantaneous direct PAR at MODIS overpass||W/m²||32-bit floating point||-1||N/A||0 to 700||N/A|
|Diffuse||Instantaneous diffuse PAR at MODIS overpass||W/m²||32-bit floating point||-1||N/A||0 to 700||N/A|
|GMT_0000_PAR||Total PAR at GMT 00:00||W/m²||32-bit floating point||-1||N/A||0 to 700||N/A|
|GMT_0300_PAR||Total PAR at GMT 03:00||W/m²||32-bit floating point||-1||N/A||0 to 700||N/A|
|GMT_0600_PAR||Total PAR at GMT 06:00||W/m²||32-bit floating point||-1||N/A||0 to 700||N/A|
|GMT_0900_PAR||Total PAR at GMT 09:00||W/m²||32-bit floating point||-1||N/A||0 to 700||N/A|
|GMT_1200_PAR||Total PAR at GMT 12:00||W/m²||32-bit floating point||-1||N/A||0 to 700||N/A|
|GMT_1500_PAR||Total PAR at GMT 15:00||W/m²||32-bit floating point||-1||N/A||0 to 700||N/A|
|GMT_1800_PAR||Total PAR at GMT 18:00||W/m²||32-bit floating point||-1||N/A||0 to 700||N/A|
|GMT_2100_PAR||Total PAR at GMT 21:00||W/m²||32-bit floating point||-1||N/A||0 to 700||N/A|
|ViewZenithAngle||View Zenith Angle of each MODIS overpass||Degree||32-bit floating point||-1||N/A||0 to 90||N/A|
See Table 2 in the User Guide for additional information on band dimensions.
For information about MCD18A2 product quality please refer to the MODIS Product Quality Documentation.
Known issues for MCD18A2 are available on the MODIS Land Quality Assessment website.