A global Land Surface Temperature image from the VNP21C2 product on May 10, 2020.
View full-size imageThe NASA/NOAA Suomi National Polar-orbiting Partnership (Suomi NPP) Visible Infrared Imaging Radiometer Suite (VIIRS) Land Surface Temperature and Emissivity (LST&E) 8-day Climate Modeling Grid Version 2 product (VNP21C2) combines the daily VNP21A1D and VNP21A1N products over an 8-day compositing period into a single product. The VNP21C2 dataset is an 8-day composite LST&E product at 0.05 degree (~5,600 meter) resolution that uses an algorithm based on a simple-averaging method and is formatted as a CMG for use in climate simulation models. The algorithm calculates the average from all the cloud-free VNP21A1D and VNP21A1N daily acquisitions from the 8-day period. Unlike the VNP21A1 datasets where the daytime and nighttime acquisitions are separate products, the VNP21C2 contains both daytime and nighttime acquisitions as separate science dataset (SDS) layers within a single Hierarchical Data Format (HDF) file.
The overall objective for NASA VIIRS products is to ensure the algorithms and products are compatible with the MODIS Terra and Aqua algorithms to promote the continuity of the Earth Observation System (EOS) mission. Additional details regarding the method used to create this Level 3 (L3) product are available in the Algorithm Theoretical Basis Document (ATBD).
The VNP21C2 product contains 25 Science Datasets (SDS): LST, quality control, view zenith angle, and time of observation for both day and night observations along with emissivity for bands M14, M15, and M16. Low-resolution browse images for day and night LST are also available for each VNP21C2 granule.
More details can be found in this VIIRS Land V2 Changes document.
Validation at stage 1 has been achieved for the VIIRS Land Surface Temperature and Emissivity product suite. Visit VIIRS Land Product Quality Assessment Product Maturity for information on product maturity status.
Characteristic | Description |
---|---|
Collection | Suomi NPP VIIRS |
DOI | 10.5067/VIIRS/VNP21C2.002 |
File Size | ~2.05 MB |
Temporal Resolution | Multi-Day |
Temporal Extent | 2012-01-19 to Present |
Spatial Extent | Global |
Coordinate System | Geographic Latitude and Longitude |
Datum | N/A |
File Format | HDF-EOS5 |
Geographic Dimensions | Global |
Characteristic | Description |
---|---|
Number of Science Dataset (SDS) Layers | 27 |
Columns/Rows | 7200 x 3600 |
Pixel Size | 5600 m |
SDS Name | Description | Units | Data Type | Fill Value | No Data Value | Valid Range | Scale Factor | Offset |
---|---|---|---|---|---|---|---|---|
Clear_sky_days | Bitmap of Clear Sky Days (1 = clear, LSB = 1st day) | N/A | 8-bit unsigned integer | 0 | N/A | 0 to 255 | N/A | N/A |
Clear_sky_nights | Bitmap of Clear Sky Nights (1 = clear, LSB = 1st day) | N/A | 8-bit unsigned integer | 0 | N/A | 0 to 255 | N/A | N/A |
Count_Day | Count of Daytime Input Values | N/A | 16-bit unsigned integer | 0 | N/A | 1 to 65535 | N/A | N/A |
Count_Night | Count of Nighttime Input Values | N/A | 16-bit unsigned integer | 0 | N/A | 1 to 65535 | N/A | N/A |
Day_view_angle | Average Daytime View Zenith Angle | Degree | 8-bit unsigned integer | 255 | N/A | 0 to 130 | N/A | -65 |
Day_view_time | Average Daytime View Time | Hours | 8-bit unsigned integer | 255 | N/A | 0 to 240 | 0.2 | N/A |
Emis_14_Day | Average Daytime Band 14 Emissivity | N/A | 8-bit unsigned integer | 0 | N/A | 1 to 255 | 0.002 | 0.49 |
Emis_14_Day_err | Root-mean-square-error Daytime Band 14 Emissivity | N/A | 16-bit unsigned integer | 0 | N/A | 1 to 65535 | 0.0001 | N/A |
Emis_14_Night | Average Nighttime Band 14 Emissivity | N/A | 8-bit unsigned integer | 0 | N/A | 1 to 255 | 0.002 | 0.49 |
Emis_14_Night_err | Root-mean-square-error Nighttime Band 14 Emissivity | N/A | 16-bit unsigned integer | 0 | N/A | 1 to 65535 | 0.0001 | N/A |
Emis_15_Day | Average Daytime Band 15 Emissivity | N/A | 8-bit unsigned integer | 0 | N/A | 1 to 255 | 0.002 | 0.49 |
Emis_15_Day_err | Root-mean-square-error Daytime Band 15 Emissivity | N/A | 16-bit unsigned integer | 0 | N/A | 1 to 65535 | 0.0001 | N/A |
Emis_15_Night | Average Nighttime Band 15 Emissivity | N/A | 8-bit unsigned integer | 0 | N/A | 1 to 255 | 0.002 | 0.49 |
Emis_15_Night_err | Root-mean-square-error Nighttime Band 15 Emissivity | N/A | 16-bit unsigned integer | 0 | N/A | 1 to 65535 | 0.0001 | N/A |
Emis_16_Day | Average Daytime Band 16 Emissivity | N/A | 8-bit unsigned integer | 0 | N/A | 1 to 255 | 0.002 | 0.49 |
Emis_16_Day_err | Root-mean-square-error Daytime Band 16 Emissivity | N/A | 16-bit unsigned integer | 0 | N/A | 1 to 65535 | 0.0001 | N/A |
Emis_16_Night | Average Nighttime Band 16 Emissivity | N/A | 8-bit unsigned integer | 0 | N/A | 1 to 255 | 0.002 | 0.49 |
Emis_16_Night_err | Root-mean-square-error Nighttime Band 16 Emissivity | N/A | 16-bit unsigned integer | 0 | N/A | 1 to 65535 | 0.0001 | N/A |
LST_Day | Average Daytime Land Surface Temperature | Kelvin | 16-bit unsigned integer | 0 | N/A | 7500 to 65535 | 0.02 | N/A |
LST_Day_err | Root-mean-square-error Daytime Land Surface Temperature | Kelvin | 8-bit unsigned integer | 0 | N/A | 1 to 255 | 0.04 | N/A |
LST_Night | Average Nighttime Land Surface Temperature | Kelvin | 16-bit unsigned integer | 0 | N/A | 7500 to 65535 | 0.02 | N/A |
LST_Night_err | Root-mean-square-error Nighttime Land Surface Temperature | Kelvin | 8-bit unsigned integer | 0 | N/A | 1 to 255 | 0.04 | N/A |
Night_view_angle | Average Nighttime View Zenith Angle | Degree | 8-bit unsigned integer | 255 | N/A | 0 to 130 | N/A | -65 |
Night_view_time | Average Nighttime View Time | Hours | 8-bit unsigned integer | 255 | N/A | 0 to 240 | 0.2 | N/A |
Percent_land_in_grid | Percent of Land Detections in Grid Cell | Percent | 8-bit unsigned integer | 255 | N/A | 0 to 100 | N/A | N/A |
QC_Day | Quality Control for Daytime LST and Emissivity | N/A | 8-bit unsigned integer | 0 | N/A | 0 to 255 | N/A | N/A |
QC_Night | Quality Control for Nighttime LST and Emissivity | N/A | 8-bit unsigned integer | 0 | N/A | 0 to 255 | N/A | N/A |
The final quality bit for the output product reflects the lowest quality values from all observations that went into the final average. The bit flags for the QC layer are defined in Table 9 of the User Guide.
The quality layer is stored in an efficient bit-encoded manner. The unpack_sds_bits executable from the LDOPE Tools is available to the user community to help parse and interpret the quality layer.
Quality assurance information should be considered when determining the usability of data for a particular science application. The ArcGIS MODIS-VIIRS Python Toolbox contains tools capable of decoding quality data layers while producing thematic quality raster files for each quality attribute.
For additional information on product quality, refer to the VIIRS Land Product Quality website.
Users of VIIRS and MODIS LST products may notice an increase in occurrences of extreme high temperature outliers in the unfiltered VNP21 and MxD21 products compared to the heritage MxD11 LST products. This can occur especially over desert regions like the Sahara where undetected cloud and dust can negatively impact MxD11, MxD21, and VNP21 retrieval algorithms.
In the MxD11 LST products, these contaminated pixels are flagged in the algorithm and set to fill values in the output products based on differences in the band 32 and band 31 radiances used in the generalized split window algorithm. In the VNP21 and MxD21 LST products, values for the contaminated pixels are retained in the output products (and may result in overestimated temperatures), and users need to apply Quality Control (QC) filtering and other error analyses for filtering out bad values. High temperature outlier thresholds are not employed in VNP21 and MxD21 since it would potentially remove naturally occurring hot surface targets such as fires and lava flows.
High atmospheric aerosol optical depth (AOD) caused by vast dust outbreaks in the Sahara and other deserts highlighted in the example documentation are the primary reason for high outlier surface temperature values (and corresponding low emissivity values) in the VNP21 and MxD21 LST products. Future versions of the VNP21 and MxD21 products will include a dust flag from the MODIS aerosol product and/or brightness temperature look up tables to filter out contaminated dust pixels. It should be noted that in the MxD11B day/night algorithm products, more advanced cloud filtering is employed in the multi-day products based on a temporal analysis of historical LST over cloudy areas. This may result in more stringent filtering of dust contaminated pixels in these products.
To mitigate the impact of dust in the VNP21 and MxD21 products, the science team recommends using a combination of the existing QC bits, emissivity values, and estimated product errors, to confidently remove bad pixels from analysis. For more details, refer to this dust and cloud contamination example documentation.
For complete information about known issues please refer to the MODIS/VIIRS Land Quality Assessment website.