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Description

The VNP18A2 Version 2 is a NASA/NOAA Suomi National Polar-orbiting Partnership (Suomi NPP) Visible Infrared Imaging Radiometer Suite (VIIRS) Photosynthetically Active Radiation (PAR) gridded Level 3 product. It is produced at 1 kilometer pixel resolution at daily intervals. PAR is the incident solar radiation in the visible spectrum (400-700 nanometers) and is a significant variable in land surface models (LSMs), receiving increased attention due to its importance for the management and operation of solar energy systems.

The VNP18 algorithm adapts the narrowband look-up table (LUT) approach to estimate PAR. The LUTs consider different types of loadings of aerosols and clouds at a variety of illumination and viewing geometry. The Algorithm Theoretical Basis Document (ATBD) is forthcoming and will provide additional details regarding the methodology used to create the data.

Provided in the VNP18A2 product are variables for instantaneous total, direct, and diffuse PAR, as well as 3-hour PAR, daily mean PAR, and a quality variable.

Version Description

Collection Version 2 Processing and Reprocessing

Product Summary

Platforms
Suomi-NPP
Instruments
VIIRS
Spatial Extent
N: 90 S: -90 E: 180 W: -180
Spatial Resolution
1000 Meters x 1000 Meters
Geographic Region
GLOBAL
Coordinate System
CARTESIAN
Granule Spatial Representation
GEODETIC
Temporal Extent
2012-01-19 to Present
Temporal Resolution
1 Day
Data Partner
Land Processes Distributed Active Archive Center (LP DAAC)
Land Science Investigator-led Processing System, Terrestrial Information Systems Laboratory, Earth Sciences Division, Sciences and Exploration Directorate, Goddard Space Flight Center, NASA (NASA/GSFC/SED/ESD/TISL/LandSIPS)
Concept ID
C2631841566-LPCLOUD
Data State
ACTIVE
Processing Level
3
Published
Updated
Science Keywords
Reflectance,
Albedo,
Anisotropy

Citation

Citation is critically important for dataset documentation and discovery. This dataset is openly shared, without restriction, in accordance with the EOSDIS Data Use and Citation Guidance.

Copy Citation

Wang, D. (2025). VIIRS/NPP Photosynthetically Active Radiation Daily L3 Global 1km SIN Grid V002 [Data set]. NASA Land Processes Distributed Active Archive Center. https://doi.org/10.5067/VIIRS/VNP18A2.002 Date Accessed: 2025-10-30

File Naming Convention

VNP18A2.A2024294.h08v09.002.2024311162006.h5

The file name begins with the Product Short Name (VNP18A2) followed by the Julian Date of Acquisition formatted as AYYYYDDD (A2024294), the Tile Identifier which is horizontal tile and vertical tile provided as hXXvYY (h08v09), the Version of the data collection (002), the Julian Date and Time of Production designated as YYYYDDDHHMMSS (2024311162006), and the Data Format (h5).

Documents

Variables

Variables are a set of physical properties whose values determine the characteristics or behavior of something. For example, temperature and pressure are variables of the atmosphere. Parameters and variables can be used interchangeably. Variable level attributes provide individual information for each variable.

The Name in this table is the variable name. Fill value indicates missing or undefined data points in a variable. Valid range is the range of values the variable can store. Scale factor is used to increase or decrease the size of an object and can be used to correct for distortion. For questions on a specific variable, please use the Earthdata Forum.

Name Description Units Data Type Fill Value Valid Range Scale Factor
3hour_PAR 3-hour mean PAR W/m² float32 -1 -1 to 700 N/A
Daily_Mean_PAR Daily mean PAR W/m² float32 -1 -1 to 700 N/A
Diffuse Instantaneous diffuse portion of PAR at VIIRS overpass W/m² float32 -1 -1 to 700 N/A
Direct Instantaneous direct portion of PAR at VIIRS overpass W/m² float32 -1 -1 to 700 N/A
PAR Instantaneous PAR at VIIRS overpass W/m² float32 -1 -1 to 700 N/A
PAR_Quality PAR quality flag N/A uint8 N/A N/A to 4 N/A
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