A controlled decoherence environment is studied experimentally by free electron interaction with semiconducting and metallic plates. The results are compared with physical models based on decoherence theory to investigate the quantum-classical transition. The experiment is consistent with decoherence theory and rules out established Coulomb interaction models in favor of plasmonic excitation models. In contrast to previous decoherence experiments, the present experiment is sensitive to the onset of decoherence.

Radiometric intercomparison between satellite remote sensing instruments has become an increasingly common practice to monitor the stability and even the accuracy of their radiance products. The assessment also enables the evaluation of calibration improvements made to these products, as well as the identification and resolution of remaining calibration inadequacies. In this paper, the radiance products of the Cross-track Infrared Sounder (CrIS), an interferometer-based hyperspectral IR sounder in low Earth orbit (LEO), is compared with the level-1b (L1b) radiance products of the infrared (IR) bands of the Advanced Baseline Imager (ABI), an imaging radiometer in geostationary (GEO) orbit. Two CrIS instruments are currently in operation on S-NPP and NOAA-20 satellites, respectively, and two ABI instruments are in operation on GOES-16 and GOES-17 satellites, respectively. Radiometric intercomparisons are performed between each CrIS-ABI pair. An established procedure by GSICS for such GEO-LEO instrument comparison is principally followed to emulate the radiance of ABI IR bands from CrIS spectra of the collocated pixels to be compared with the actual ABI radiance. Results show that the long-term time series of CrIS-ABI radiance bias have been stable within 0.2 K for nearly all ABI IR bands within a spectral range from 3.7 $\mathsf{\mu }$m to 13.3 $\mathsf{\mu }$m, except those with known calibration issues. Miscellaneous calibration events that had occurred to either instrument and altered the biases are identified and explained. While the main goal of the work is to support the on-orbit Cal/Val of CrIS, including the future JPSS-2/3/4 CrIS, such observations can also be referenced to further improve the calibration of ABI.

This manuscript describes the major prelaunch and postlaunch calibration and validation activities, along with the methodologies developed and implemented to successfully demonstrate the operational capability of the NOAA-21 Cross-track Infrared Sounder (CrIS) sensor in space. These activities were essential for generating calibrated NOAA-21 CrIS observations suitable for numerical weather prediction (NWP) models and environmental monitoring applications. The NOAA-21 CrIS sensor was launched in November 2022, becoming the third operational CrIS sensor deployed in space within the same orbital plane, thereby supporting continuity across the Joint Polar Satellite System (JPSS). Following the reception of initial scientific data on February 10, 2023, intensive calibration and validation efforts were conducted to ensure that NOAA-21 CrIS observations meet the JPSS Level-1 requirements with ample margin by September 2023. The NOAA-21 CrIS observations were assimilated operationally at the NOAA National Centers for Environmental Prediction (NCEP) in December 2023 and at the European Centre for Medium-Range Weather Forecasts (ECMWF) in January 2024. As demonstrated in this manuscript, the NOAA-21 CrIS calibrated observations exhibit quality comparable to that of corresponding observations from the Suomi National Polar-orbiting Partnership (SNPP) and NOAA-20 CrIS sensors. NOAA-21 CrIS radiometric biases relative to SNPP and NOAA-20 CrIS are within ± 0.2 K, while spectral errors are within 2 ppm. The NOAA-21 CrIS has been declared the primary JPSS infrared sounder observatory since March 2024, serving as a critical NOAA asset that ensures continuity and redundancy within the global Earth-observing system through high-quality infrared observations characterized by high spectral resolution and global coverage.

The cross-track infrared sounder (CrIS) is an infrared Fourier transform spectrometer (FTS) hosted on the Joint Polar Satellite System (JPSS). To produce a CrIS sensor data record (SDR) with high-quality spectral calibration, it is necessary to accurately and periodically calibrate CrIS interferometer metrology laser wavelength over time (i.e., a spectral calibration reference). The current spectral calibration reference method makes use of a neon lamp’s highly stable gas emission spectral line processed through the FTS. Further improvements in spectral calibration reliability have been developed using alternative methods described in this article which provide redundancy to the in-orbit neon lamp spectral calibration reference. The first proposed redundancy method involves a real-time regression algorithm which uses the known correlation between the laser diode’s output wavelength and the laser diode temperature to provide updated estimates of the metrology laser wavelength. A second proposed method uses simulated atmospheric line absorption and emission radiances as a spectral reference to estimate the spectral changes in the FTS laser metrology wavelength. Starting with NOAA-21 CrIS and for all other future CrIS sensors, the periodicity of calibrating the laser’s wavelength was changed from approximately once per satellite orbit to once every seven orbits to extend the neon lamp’s useful lifetime. Here we present the estimated impact of changing the interval between neon lamp measurements of the CrIS metrology laser wavelength, along with studies of these two redundancy methods and their assessment in an operational environment.