System-Level Calibration of VIIRS
In collaboration with National Oceanic and Atmospheric Administration (NOAA), NIST scientists have achieved the first-of-the-kind system-level calibration of a satellite sensor. The sensor, known as the Visible Infrared Imager Radiometer Suite (VIIRS), is scheduled to be flown on the next generation of weather and climate satellites, the Joint Polar Satellite System (formerly known as the National Polar-orbiting Operational Environmental Satellite System).
VIIRS operates from the infrared to the visible and is the primary sensor responsible for producing environmental data products. Of particular interest is ocean color, which provides an assessment of ocean health and ocean organic carbon storage. The measurement requirements for ocean color are stringent, and testing of the sensor at the component level in 2008 raised concerns about the ability of VIIRS to meet the accuracy requirements required for continuing the 20-year remote sensing ocean-color climate data record.
As a result, NOAA scientists requested system-level testing of VIIRS using Optical Technology Division’s portable calibration system, “Travelling SIRCUS.” It is a portable version of the Division’s facility for the Spectral Irradiance and Radiance Responsivity Calibrations using Uniform Sources (SIRCUS). The system generates tunable monochromatic radiation of known spectral radiance, and it was used to determine the spectral responsivity of the VIIRS system in the visible and near-infrared bands.
Testing confirmed that VIIRS had small leaks of radiometric flux between its sensor bands, a phenomenon known as crosstalk. However, the amount of crosstalk was low enough that VIIRS scientists will be able to extract the necessary spectral information from the data set.
In a separate test, Traveling SIRCUS was employed to study the internal, on-orbit calibration system used by VIIRS. While the data analysis is still in progress, the comparison between measured and predicted signals will provide critical information about its performance.
This testing demonstrates a fruitful collaboration between different government agencies, satellite sensor companies, and data product analysts. Additionally, it demonstrates the potential for tunable laser systems, like NIST’s Travelling SIRCUS, to improve the calibration and characterization of satellite sensors, and with reduced testing time and cost.