VNP02IMG - VIIRS/NPP Imagery Resolution 6-Min L1B Swath 375m

VNP02IMG is the short-name for the Suomi National Polar-orbiting Partnership (SNPP) platform-based NASA Visible Infrared Imaging Radiometer Suite (VIIRS) Level-1B calibrated radiances product derived from the five image-resolution or I-bands, which have a 375-meter resolution at nadir. These I-bands comprise three reflective solar bands (RSB) and two thermal emissive bands (TEB). Each of the I-bands has 32 detectors in the along-track direction with 32 rows of pixels per scan that offer a resolution that is twice finer than that of the M- and Day-Night bands. Ranging in wavelengths from 0.6 µm to 12.4 µm, the I-bands are sensitive to visible/reflective, near-, shortwave-, mediumwave-, and longwave-infrared wavelengths. Derived from the NASA VIIRS Level-1A raw radiances, this product includes calibrated and geolocated radiance and reflectance data, quality flags, and granule- and collection-level metadata. In contrast to a MODIS Level-1B product, which temporally spans 5-minutes, the VIIRS Level-1B calibrated radiances product contains a nominal temporal duration of 6-minutes. The image dimensions of the 375 m swath product measure 6,464 lines by 6,400 pixels.

Traceability for Reference-based Instrument Calibration and Measurement Uncertainty
Traceability relates to how an instrument’s uncertainty measurements were calibrated using reference sources whose absolute radiometric performance is well-known and understood relative to the International System of Units (SI). This usually happens in the pre-launch calibration phase using a national laboratory’s standard sources, and later corroborated as part of the on-orbit validation activities in the post-launch phase.

The SNPP VIIRS instrument’s pre-launch radiometric calibration was accomplished through measurements that are traceable to the National Institute of Standards and Technology (NIST), and its post-launch on-orbit characterizations are based on data derived from the VIIRS’ on-board calibrators.

VIIRS Level-1B Measurement Uncertainty
The NASA VIIRS Characterization Support Team has developed VIIRS Level-1B measurement uncertainty algorithms that are designed to empirically derive measurement uncertainty values from the output Level-1B products to compare against the recommended values in the VIIRS Sensor Specifications that are detailed in the VIIRS Algorithm Theoretical Basis Document (ATBD).

Radiometric Accuracy
Radiometric accuracy forms a key requirement that enables us to derive good quality Level-2 retrievals, and provide the basis for higher-level products. The SNPP VIIRS instrument’s radiometric accuracy is characterized for each of its three spectral band groups:

Reflective Solar Bands: Based on the VIIRS sensor specifications, the VIIRS reflective solar bands’ calibration uncertainty for spectral reflectance over a scene with typical radiance is defined at less than 2%.

Thermal Emissive Bands: Given a uniform scene with 267 K brightness temperature (for image and emissive bands), the specified calibration uncertainty for spectral radiance is defined at 5% for Image band-4 and 2.5% for Image band-5.

Day-Night Band: The DNB’s defined radiometric calibration uncertainty for the effective in-band radiance over a uniform scene is gain-state dependent.