The VNP46A1 Daily At-sensor TOA Nighttime Radiance Product


VNP46 DNB Flow Chart
Algorithm processing cycle and ancillary parameters used by NASA's Black Marble product suite (VNP46)


Both VNP46 products use the standard suite of VIIRS land products as input and are integrated as part of NASA's Black Marble processing chain which contains both daytime and nighttime branches. For the daytime branch, a modified version of the operational VIIRS surface reflectance algorithm (Roger et al., 2016; Vermote et al., 2014) is used to generate the DNB surface bidirectional reflectance factor (BRF) using NASA's Level 1B calibrated radiance product as input (i.e., 6-minute granules, or 2366 km along track and ~3100 km across-track). Level 2G DNB surface reflectance is then generated by performing spatial and temporal aggregation to 500 m grid cells over daily time periods (Campagnolo et al., 2016; Pahlevan et al., 2017; Wolfe et al., 1998; Yang and Wolfe, 2001). Daily Level 3 DNB BRDF/Albedo data are then retrieved using the heritage MODIS/VIIRS algorithm (MCD43/VNP43) (Liu et al., 2017, Liu et al., 2017; Wang et al., 2018), and corresponding snow flags are estimated using the VIIRS Normalized Difference Snow Index (NDSI) algorithm (VNP10) (Riggs et al., 2016, Riggs et al., 2017). The NDVI and NDSI values are used to determine the growing, dormant, and snow periods to routinely update the a priori global database of the DNB BRDF product (Cescatti et al., 2012; Liu et al., 2017, Liu et al., 2017; Román et al., 2009). Surface bidirectional reflectance factor from the VIIRS I1 (red) and I2 (NIR) channels is used to obtain daily estimates of LAI (Knyazikhin et al., 1999; Park et al., 2017; Xiao et al., 2016). The retrieved leaf area index and clumping index values are then used to calculate the gap fraction probability (Pgap).

Black Marble VNP46A1 product input files
Input File Description
VNP02DNB VIIRS/NPP Day/Night Band 6-Min L1B Swath 750m (L1B DNB)
VNP02MOD VIIRS/NPP Moderate Resolution 6-Min L1B Swath 750m (L1B moderate bands)
NPP DNBN VIIRS L2G DNB radiance
NPP DNBN angles VIIRS L2G DNB angles
NPP MOD VIIRS L2G moderate bands M10, M11, M12, M13, M15, M16
NPP PTDN VIIRS DNB pointer files
The standard VIIRS Cloud Mask (VCM) VIIRS cloud mask


The nighttime branch is the path that actually generates the final VNP46 products. We begin with the at-sensor TOA nighttime radiance (VNP46A1), along with the corresponding nighttime cloud mask, multiple solar/viewing/lunar geometry values (including moon-illuminated fraction and phase angles), and the daily snow and aerosol status flags. These science data sets (SDS) enable open access to the primary inputs used to generate the NASA Black Marble NTL time series record, thus ensuring reproducibility of the final outputs. A series of temporal and spatial gap-filling techniques are also employed to improve the coverage of the VNP46 NTL product.

The NASA Black The daily at-sensor TOA nighttime radiance product (VNP46A1) is available at 500m resolution from January 2012 onward. The 500m VNP46A1 product contains 26 SDS layers, including sensor radiance, zenith and azimuth angles at sensor, solar, and lunar, cloud mask flag, time, shortwave IR radiance, brightness temperatures, VIIRS quality flags, moon phase angle, and moon illumination fraction. The table below details the information within the product layers.

Scientific datasets included in the VNP46A1 daily at-sensor TOA nighttime radiance product
Scientific Datasets
(SDS HDF Layers)
Units Description Bit Types Fill Value Valid Range Scale Factor Offset
DNB_At_Sensor_Radiance_500m nW cm-2 sr -1 At-sensor DNB radiance 16-bit unsigned integer 65535 0 - 65534 0.1 0.0
Sensor_Zenith Degrees Sensor zenith angle 16-bit signed integer -32768 -90 - 90 0.01 0.0
Sensor_Azimuth Degrees Sensor azimuth angle 16-bit signed integer -32768 -180 - 180 0.01 0.0
Solar_Zenith Degrees Solar zenith angle 16-bit signed integer -32768 0 - 180 0.01 0.0
Lunar_Zenith Degrees Lunar zenith angle 16-bit signed integer -32768 -180 - 180 0.01 0.0
Lunar_Azimuth Degrees Lunar azimuth angle 16-bit signed integer -32768 0 - 180 0.01 0.0
Glint_Angle Degree Moon glint angle 16-bit signed integer -32768 -180 - 180 0.01 0.0
UTC_Time Decimal hours UTC time 32-bit floating point -999.9 0-24 1.0 0.0
QF_Cloud_Mask Unitless Cloud mask status 16-bit unsigned integer 65535 0 - 65534 N/A N/A
QF_DNB Unitless DNB quality flag 16-bit unsigned integer 65535 0 - 65534 N/A N/A
Radiance M_10 Wm-2 μm-1 sr-1 Radiance in band M10 16-bit unsigned integer 65535 0 - 65534 0.0013045005 -0.04
Radiance M_11 Wm-2 μm-1 sr-1 Radiance in band M11 16-bit unsigned integer 65535 0 - 65534 1.0 -0.4
Brigthness Temperature M_12 Kelvin Brigthness Temperature of band M12 16-bit unsigned integer 65535 0 - 65534 0.002518946 203.0
Brigthness Temperature M_13 Kelvin Brigthness Temperature of band M13 16-bit unsigned integer 65535 0 - 65534 0.002518946 203.0
Brigthness Temperature M_15 Kelvin Brigthness Temperature of band M15 16-bit unsigned integer 65535 0 - 65534 0.004120439 111.0
Brigthness Temperature M_16 Kelvin Brigthness Temperature of band M16 16-bit unsigned integer 65535 0 - 65534 0.004257787 103.0
QF_VIIRS_M10 Unitless Quality flag of band M10 16-bit unsigned integer 65535 0 - 65534 N/A N/A
QF_VIIRS_M11 Unitless Quality flag of band M11 16-bit unsigned integer 65535 0 - 65534 N/A N/A
QF_VIIRS_M12 Unitless Quality flag of band M12 16-bit unsigned integer 65535 0 - 65534 N/A N/A
QF_VIIRS_M13 Unitless Quality flag of band M13 16-bit unsigned integer 65535 0 - 65534 N/A N/A
QF_VIIRS_M15 Unitless Quality flag of band M15 16-bit unsigned integer 65535 0 - 65534 N/A N/A
QF_VIIRS_M16 Unitless Quality flag of band M16 16-bit unsigned integer 65535 0 - 65534 N/A N/A
Moon_Phase_Angle Degrees Moon ohase angle 16-bit signed integer -32768 0 - 180 0.01 0.0
Moon_Illumination_Fraction Percentage Moon ilumination fraction 16-bit signed integer -32768 0 - 100 0.01 0.0
Granule Unitless Nunber of selected granule 8-bit unsigned integer 255 0 - 254 1.0 0.0


VNP46 product suite components for a 10° x 10° Level 3 tile over Sweden and Finland (h20v02; DOY 2013-080). The half-moon-illuminated and 30% cloud-contaminated scene is shown to capture extraneous light emissions north of the Gulf of Bothnia caused by the Aurora Borealis.
VNP46 product suite components for a 10 ° X 10 ° Level 3 tile over Sweden and Finland (h20v02; DOY 2013-080). The half-moon-illuminated and 30% cloud-contaminated scene is shown to capture extraneous light emissions north of the Gulf of Bothnia caused by the Aurora Borealis.