JPSS-4 VIIRS prelaunch calibration performance and assessment

The Visible Infrared Imaging Radiometer Suite (VIIRS), a key instrument in the Joint Polar Satellite System constellation, generates high fidelity land, ocean, and atmospheric data for a suite of science products that include monitoring of vegetation, algal blooms, wildfires, drought, flooding etc. There are three VIIRS instruments on orbit, one on each of the following: Suomi National Polar-orbiting partnership, NOAA-20 (formerly JPSS-1), and NOAA- 21 (formerly JPSS-2) spacecraft. Starting March 2024, NOAA-21 and NOAA-20 are the primary and secondary satellites of the constellation and providing meteorologists detailed information on severe weather events. In addition to the 21 spectral bands, covering the wavelength range from 0.41 to 12.2 μm, VIIRS has a day-night band (DNB) that collects valuable daytime and nighttime measurements at three different gain stages. The VIIRS instrument on the JPSS-4 spacecraft, scheduled to launch in 2027, recently (in Fall 2023) underwent sensor thermal vacuum (TVAC) environmental testing. Several key performance parameters such as the instrument gains, detector SNR or NEdT, dynamic range, relative spectral response, response versus scan angle, polarization sensitivity, stray light, and nearfield response were characterized during the various testing phases. In this paper, we provide an overview of the JPSS- 4 VIIRS prelaunch calibration activities, with a focus on radiometric performance assessments and their comparisons with previous VIIRS instruments.