| 04 Aug 2026
VIIRS Global Area Coverage (VGAC): A reduced resolution VIIRS dataset for climate data record continuity
Abstract. The Visible Infrared Imaging Radiometer Suite (VIIRS) instrument represents a significant change from the legacy weather satellite observations. For example, there are several differences in scanning strategy, channels, file structure, etc. from the Advanced Very High Resolution Radiometer (AVHRR) which has flown on low earth orbit satellites since the 1970s. Several longstanding climate data records were developed expressly using the AVHRR instrument’s Global Area Coverage (GAC) data. The VIIRS Global Area Coverage (VGAC) dataset is an attempt to more closely bridge the old GAC technology with the new. The VGAC data file provides one orbit of VIIRS observations that have been degraded in resolution to approximate the AVHRR GAC resolution by defining a swath projection model. Each channel is provided using a swath that simulates a scan at ~3.9 km resolution. VGAC provides mean and standard deviation values for each moderate resolution (750 m) VIIRS channel. Higher resolution VIIRS imaging channels (375 m) contain more information, including maximum and minimum radiances, which benefit algorithms like cloud and surface retrievals. The result is that VGAC data are 50 times smaller with 1800 fewer files than the original VIIRS data. The main purpose of VGAC data is to facilitate climate processing to continue the historic climate records from AVHRR and other satellites. VGAC data described here are available from NOAA via https://doi.org/10.25921/gsef-pg81 (Knapp et al., 2024).
Competing interests: Kenneth R. Knapp operates Knapp WeatherSat Services, an independent consultancy, and performed this work under contract with NC State. Yuhan (Douglas) Rao is a topic editor for the ESSD journal.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
Excellent paper.
Because the projection is generic to cross-track and push-broom (along-track) instruments on near-circular orbits, it is a strong candidate for standardization in the netCDF Climate and Forecast conventions, which at present have no analytic representation for swath geometry. I am pursuing that separately and would welcome the authors' involvement. Stating the conventions precisely in this manuscript, as suggested above, would make that work considerably easier for everyone who follows."
I have also attached a PDF as a 'technical annex' feedback.