Abstract
A fully automated, National Institute of Standards and Technology (NIST)-traceable artificial light source called Terra Vega has been developed to radiometrically calibrate the Visible Infrared Imaging Radiometer (VIIRS) Day Night Band (DNB) working in high gain stage (HGS) mode. The Terra Vega active point source is a calibrated integrating sphere that is only a fraction in size of a VIIRS DNB pixel. As such, it can be considered analogous to a ground-based photometric reference star. Vicarious calibrations that employ active point sources are different than those that make use of traditional extended sources and can be applyed to quantify the brightness of artificial light sources. The active source is successfully fielded, and early results indicate that it can be used to augment and validate the radiometric calibration of the VIIRS DNB HGS sensor on both the Suomi National Polar-orbiting Partnership (NPP) and NOAA-20 satellites. The VIIRS DNB HGS sensor can benefit from this technology as on-board calibration is challenging and hinges on transferring low gain stage (LGS) calibration using a solar diffuser to the medium gain stage (MGS) and HGS via regions of overlap. Current vicarious calibration methods that use a lunar-illuminated extended source estimate the HGS radiometric accuracy to within 8-15%. By comparison, early results and analysis showed that Terra Vega is stable to about 1%. Under clear dark night conditions, predicted top-of-atmosphere radiance from Terra Vega ranged between 1–11% of VIIRS measured values. Terra Vega’s excellent stability opens up new opportunities to validate and develop nighttime imaging applications based on point sources.
Highlights
The Visible Infrared Imaging Radiometer (VIIRS) Day Night Band (DNB) is enabling a new generation of nighttime imaging applications because of its high spatial resolution and its extremeRemote Sens. 2019, 11, 710; doi:10.3390/rs11060710 www.mdpi.com/journal/remotesensing Remote RemoteSens.Sens.2019, 10,710 x FOR PEER REVIEW22ofof21 sensitivity in the high gain stage (HGS) mode
NASA Goddard Space Flight Center (GSFC) demonstrated that stellar photometry could be used to trend the National Polar-orbiting Partnership (NPP) VIIRS DNB HGS and medium gain stage (MGS) within 6%
There is a time period each year when DNB data from South Dakota are affected by stray light, DNB stray light correction is applied during the VIIRS sensor data record (SDR) processing and any residual is removed by the Terra Vega radiance retrieval algorithm during the background subtraction step
Summary
The Visible Infrared Imaging Radiometer (VIIRS) Day Night Band (DNB) is enabling a new generation of nighttime imaging applications because of its high spatial resolution and its extreme. These extended sources introduce errors associated with non-uniformity and sensor’s response to a point source target depends on the sensor’s point spread function and imperfect knowledge of surface reflectance properties, including the bidirectional reflectance ground sample distance, VIIRS DNB HGS radiometric calibrations that make use of point sources distribution function (BRDF) as well as atmospheric and illumination conditions. NASA Goddard Space Flight Center (GSFC) demonstrated that stellar photometry (stars as point radiance predictions from the South Dakota location are within 1–11% of measured VIIRS radiance, sources) could be used to trend the NPP VIIRS DNB HGS and medium gain stage (MGS) within 6%.
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