This paper presents the development of an independent algorithm at NOAA/STAR for processing radio occultation (RO) bending angle and refractivity data from RO observations explicitly designed for multi-GNSS RO missions. The primary aim is to understand the uncertainties introduced in the processing, from excess phase data to bending angle and refractivity profiles. This study investigates three algorithms that convert RO excess phases to bending angles. These three algorithms are full spectrum inversion (FSI), canonical transform type 2 (CT2), and phase matching (PM). The STAR-developed FSI algorithm has been fully integrated into the Radio Occultation Processing Package (ROPP) version 10.0. This integration provides users with an alternative to wave optics and geometry optics through configurable settings. A detailed comparison of bending angle and refractivity results generated by these three algorithms, explicitly focusing on COSMIC-2 and Spire data, is presented. The analysis highlights discrepancies and uncertainties inherent in bending angle and refractivity processing, providing valuable insights into the performance of each algorithm.

Since early 2012, the cross-track infrared sounder (CrIS) on board the Suomi National Polar-orbiting Partnership (S-NPP) satellite has continually provided the hyperspectral infrared observations for profiling atmospheric temperature, moisture, and greenhouse gases. In this study, the CrIS sensor data record (SDR) data are improved for climate applications with its fine-tuning of calibration coefficients in an NOAA reprocessing project. A specific software system was developed to reprocess the CrIS SDR. This software system was updated with a new calibration algorithm, nonlinearity, and geolocation to improve the SDR data quality and long-term consistency. The calibration coefficients are refined with the latest updates, which were used to calibrate the latest operational SDR products and replace those in the engineering packet (EP) in the raw data record (RDR) data stream. The resampling wavelength was updated based on the metrology laser wavelength and resulted in zero sampling error in the spectral calibration. All the historical SDRs (from February 2012 to March 2017) were generated with the same calibration coefficients and same version of the processing software system, resulting in improved accuracy and stability in terms of spectral and radiometric calibration during the CrIS lifetime mission. The quality of the reprocessed CrIS SDR data at nominal spectral resolution (NSR) is assessed in terms of its radiometric and spectral calibration. Comparisons against the operational SDR data are carried out to demonstrate the improved long-term stability of the reprocessed CrIS SDR data. Overall radiometric biases are found to be small and highly stable over the instrument mission, the FOV-to-FOV differences are less than ~10 mK, and much better than that from the operational SDR data. It is shown that the CrIS metrology laser wavelength varies within 4 ppm as measured by the neon calibration system. The reprocessed SDR data have spectral errors less than 0.5 ppm, which is much better than the operational SDR data with about 4 ppm. This baseline version of the reprocessed SNPP CrIS SDR data is suitable for long-term climate monitoring and model assessments and can provide an infrared reference observation to assess other narrow- or broadband infrared instruments’ calibration accuracy.

The Suomi National Polar-orbiting Partnership (SNPP) cross-track infrared sounder (CrIS) has provided critical observations for environmental applications for nearly ten years. However, on 26 March 2019, the Joint Polar Satellite System (JPSS) interface data processing segment (IDPS) stopped producing the operational SNPP CrIS sensor data record (SDR) product due to a failure of the midwave infrared (MWIR) band. Following a comprehensive risk assessment, the switch from primary Side-1 to redundant Side-2 electronics was made on 24 June 2019, successfully recovering the full capabilities of the sensor. Comprehensive assessment results demonstrate the high quality of the CrIS SDR product resulting from the sensor recalibration, thus meeting the JPSS Level-1 requirements with margin. The spectral calibration prioritized consistency with the CrIS SDR product prior to the side switch to minimize the impact on users. The results show that the radiometric impact on the CrIS SDR product resulting from the side switch is not significant and is within the calibration radiometric uncertainty. It is demonstrated that after instrument restoration, the SNPP CrIS SDR product recovers the quality needed to be used as radiometric reference for calibration and validation of infrared remote sensing instruments. The recovery of the SNPP CrIS MWIR band is expected to support improvements in numerical weather forecasting by restoring the MWIR band channels sensitive to tropospheric water vapor. This should also help maintain continuity and redundancy of one of the backbone observations of the global observing system.

The Cross-track Infrared Sounder (CrIS) is a Michelson-type Fourier Transform Spectrometer. The CrIS flight module 2 instrument was launched into orbit on November 18, 2017, onboard the NOAA-20 satellite as part of the United States (US) Joint Polar Satellite System (JPSS). The CrIS instrument measures the top-of-atmosphere upwelling spectral radiance in the thermal infrared (IR) spectrum. These measurements provide critical information for medium-range weather forecasting, and the retrieval of atmospheric profiles of temperature, water vapor, and other trace gases. The instrument noise equivalent radiance differential (NEdN) estimates are used by the weather forecasting systems, the trace gas atmospheric retrieval algorithms, and for trending the health and stability of the instrument over time. The current operational NEdN estimate is calculated using instrument observations from the deep space (DS) view and the internal calibration target (ICT). Two alternative methodologies are described here based on the principal component analysis (PCA) of an ensemble of calibrated Earth scene (ES) spectra. The NEdN calculation methods show that the instrument meets the specifications with a margin for all 27 detectors with an exception of one midwave IR (MWIR) field-of-view (FOV) 9, which is borderline. The PCA analysis shows that warmer ES spectra have higher noise, known as scene shot, for the short-wave IR (SWIR) band. Using the PCA analysis, the NEdN for the long-wave IR FOV 5 is 30% higher than the NEdN calculated by the operational algorithm. Correlated noise is also found due to the effect of the instrument self-apodization correction.

The Cross-track Infrared Sounder (CrIS) [1] is currently undergoing Thermal Vacuum Testing (TVAC) before integration with the Joint Polar Satellite System-2 (JPSS-2) satellite prior to the planned launch in 2022. During these tests, the NOAA/CrIS Sensor Data Record (SDR) team aims to independently evaluate the performance of the new CrIS instrument. Here, we will present our work assessing the instrument noise and the brightness temperature measurement from external calibration targets (ECTs) as a function of its stepped temperature. The latter test will be used to calculate the radiometric nonlinearity correction applied to the complex spectra. Additional tests that will take place during TVAC include the evaluation of noise during vibration testing, analyzing slit scan data to determine the Field-Of-View (FOV) crosstalk, processing gas cell data to derive the spectral calibration coefficients, and measuring ECTs to validate the radiometric calibration of CrIS.

The Cross-track Infrared Sounder (CrIS) on board the Suomi National Polar-Orbiting Partnership (S-NPP) Satellite, NOAA-20, and future Joint Polar Satellite System (JPSS) satellites J2 to J4 provide the hyperspectral infrared observations for profiling atmospheric temperature, moisture and greenhouse gases globally. In this study, the J2 CrIS prelaunch spectral calibration parameters including detector focal plane geometry (FOV size and offset angles, referred to as instrument line shape (ILS)) and Neon lamp effective wavelength are derived from the thermal vacuum (TVAC) gas cell test data. These derived parameters are evaluated using the spectral cross-correlation method by comparing with the simulated spectral lines from the line-by-line radiative transfer model (LBLRTM).

As one of the calibration reference targets used to calibrate the cross-track infrared sounder (CrIS) earth scene (ES) measurements, the stable deep space (DS) reference spectrum in the 30-scan DS calibration moving window is very important for the accuracy of the calibrated ES radiances. The DS view changes when the lunar radiation intrudes into the observation field of view (FOV). In the original CrIS lunar intrusion (LI) detection algorithm implemented in the operational ground processing system, the contaminated DS spectra were not effectively removed from the DS moving window due to large threshold values and the assumption that the first DS spectrum in the moving window was not contaminated. As a result, inaccurate, degraded, or invalid ES radiances were produced in the operational CrIS sensor data record (SDR) during LI events. In this article, an improved LI detection algorithm is developed and implemented into the operational system. First, the new algorithm efficiently finds a contamination-free DS spectrum in the DS 30-scan calibration moving window to use as the reference spectrum. Second, based on the phase characteristics of the complex raw DS spectra during LI events, the LI band-dependent thresholds were derived to effectively reject the contaminated DS spectra and to make the valid DS window size consistent among the three CrIS bands. The new LI algorithm implemented in the operational system shows a successful detection and removal of all the lunar-contaminated DS spectra in the DS moving window, resulting in an improved calibration of ES radiances during LI events.

In this work, the current performance of the calibrated Joint Polar Satellite System (JPSS) Cross-track Infrared Sensor (CrIS) observations is reported. The CrIS instrument is currently on-board the Suomi National Polar-orbiting Partnership (SNPP) and NOAA-20 spacecraft, and planned for the JPSS-2, -3 and -4 satellites. Presently, calibrated and validated CrIS observations, in the form of sensor data record (SDR) products, are being assimilated by operational NWP models and atmospheric retrieval systems. CrIS measurements from SNPP and NOAA-20 are expected to improve our understanding of the dynamics of the atmosphere due to the higher temporal and spatial coverage resulting from optimally blending the hyperspectral Earth observations. This work also reports recent improvements performed on the CrIS SDR products, including: 1) the implementation of the polarization correction, 2) the optimization of the spike detection and correction algorithm, and 3) the optimization of the lunar intrusion algorithm.

The cross-track infrared sounder (CrIS) is a hyper-spectral infrared sounder with 2211 (full-spectral resolution) channels over three wavelength ranges. Due to its excellent calibration and high spectral resolution, CrlS radiances are also used as an infrared reference to check calibration accuracy of other narrow- or broadband instruments. However, there are spectral gaps between the CrlS bands, which impact the accuracy of intercomparison between CrlS and other instruments. To fill up the spectral gaps, this paper develops a new method to predict the CrlS gap channels. A training data set was first built based on the spectra selected from different seasons to represent different atmospheric and surface conditions. The principal component regression method is then developed to derive the prediction coefficients between the CrlS measured and the gap channel spectra. The prediction accuracies are around 0.005 K ± 0.18 mK, 0.06 K ± 0.45 mK, and 0.05 K ± 0.71 mK for the long-, middle-, and short-wave gap channels, respectively. It should note that the predicted channels are intended to be only used in the intercomparison purposes instead of providing exact information of these gap channels. When comparing the CrlS gap radiances with atmospheric infrared sounder and infrared atmospheric sounding interferometer, consistent results are observed between CrIS and other sounders. The further intercomparison results with visible infrared imaging radiometer suite and advanced baseline imager suggest that the predicted gap radiances are good enough for the intercalibration purposes and this method can be confidently applied in global space-based intercalibration system community.

The cross-track infrared sounder has been operated in the full spectral resolution (FSR) mode since December 4, 2014. To provide the FSR radiance spectra with a spectral resolution of 0.625 cm-1for all the three bands, a new calibration algorithm has been developed and implemented for operational uses. The algorithm is an improvement over the previous algorithm that had been operationally used until March 2017. Major changes include the calibration equation, self-apodization correction and resampling matrices, and calibration filter. Compared to the previous algorithm, the improvement reduces the calibration inconsistencies among the nine fields of view and between the forward and reverse interferometer sweep directions by up to 0.5 K, and the differences between observed and simulated spectra by up to 0.4 K.

Since early 2012, the Cross-track Infrared Sounder (CrI)S on board the Suomi National Polar-Orbiting Partnership (S-NPP) Satellite has continually provided the hyperspectral infrared observations for profiling atmospheric temperature, moisture and greenhouse gases. In this study, the CrIS Sensor Data Record (SDR) data are improved for climate applications with its fine-tuning of calibration coefficients in NOAA reprocessing project. One specific code for CrIS SDR reprocessing was developed. This code was updated with calibration algorithm, non-linearity, and geolocation to improve the scientific results. The calibration coefficients are refined with the latest updates based on the work from CrIS science team, and are inserted in the Engineering Packet (EP) in the Raw Data Record (RDR) data stream. The resampling wavelength was updated based on the metrology laser wavelength and resulting in zero sampling error in the spectral calibration. All the SDRs are generated with the same calibration coefficients, resulting in improved consistency during the CrIS lifetime mission. The reprocessed SDRs are essential for deriving the long-term climate trending such as tropical sea surface temperature trends and CO2trends. Evaluation of CrIS reprocessed SDR in term of spectral, and radiometric long-term accuracy and stability are presented.

Since early 2012, the cross-track infrared sounder (CrIS) onboard the Suomi National Polar-Orbiting Partnership satellite has continually provided the hyperspectral infrared observations for profiling atmospheric temperature, moisture, and greenhouse gases. The CrIS radiance data are also directly assimilated into global numerical weather prediction models to improve the medium-range forecasts. These important applications require accurate CrIS calibration. Since CrIS radiometric accuracy depends on the accurate spectral calibration, it is important to reduce the spectral uncertainty and increase the calibration stability for weather and climate applications. In this paper, the accuracy of CrIS spectral calibration and its stability are assessed using the operational sensor data record (SDR) data generated by the interface data processing segment (IDPS). A spectral validation method is developed and applied to clear scene data over ocean from September 22, 2012, to April 19, 2016. It is shown that CrIS metrology laser wavelength varies within 3 ppm, as measured by the Neon calibration subsystem. While the current CrIS operational algorithm is designed to have a spectra error less than 2 ppm, the actual spectral errors are about 4 ppm due to the IDPS software bugs. A new correction method is applied to fix the bugs and to further improve CrIS spectral calibration. It is found that the CrIS spectral calibration accuracy is less than 1 ppm in both normal and full spectral resolution SDR data sets.

Given the fact that Cross-track Infrared Sounder (CrIS) and the Visible Infrared Imaging Radiometer Suite (VIIRS) currently are onboard the Suomi National Polar-orbiting Partnership (Suomi NPP) satellite and will continue to be carried on the same platform of future Joint Polar Satellite System (JPSS) satellites for the next decade, it is desirable to develop a fast and accurate collocation scheme to collocate VIIRS products and measurements with CrIS to facilitate the applications that need to combine measurements from two sensors such as inter-calibration, geolocation assessment, and cloud detection. In this paper, we will discuss the potential applications to demonstrate the benefits of combination of VIIRS with CrIS as well as an accurate and fast collocation method to collocate VIIRS measurements within CrIS instantaneous field of view (IFOV).

The Cross-track Infrared Sounder (CrIS) on Suomi National Polar-orbiting Partnership Satellite (S-NPP) is a Fourier transform spectrometer and provides a total of 1305 and 2211 channels in normal spectral resolution (NSR) mode and full spectral resolution (FSR) mode, respectively, for sounding the atmosphere. NOAA operated CrIS in FSR mode on December 4, 2014 for S-NPP, and will operate CrIS in FSR mode for the Joint Polar Satellite System (JPSS). Based on CrIS Algorithm Development Library (ADL), CrIS full resolution processing system (CRPS) has been developed to generate the FSR Sensor Data Record (SDR). This code can also be run for normal mode and truncation mode SDRs. In order to select the best calibration algorithm for JPSS-1, four different calibration approaches are being implemented in the ADL full resolution code. In this study, evaluation results from different calibration approaches are presented and the ringing features observed in CrIS unapodized spectra are discussed.

The Defense Meteorological Satellite Program's (DMSP) F-18 Special Sensor Microwave Imager/Sounder (SSMIS) brightness temperature difference (O-B) between observations and simulations from the Community Radiative Transfer Model (CRTM) based on 6 hour forecast fields of the National Centers for Environmental Prediction (NCEP) Global Forest System (GFS) are analyzed in this paper. It shows that after the current GSI bias correction, the O-B from SSMIS F-18 lower atmospheric sounding (LAS) channels are still significant and depend on nodes, seasons, latitudes and channels.

The Community Radiative Transfer Model (CRTM), developed at U.S. Joint Center for Satellite Data Assimilation (JCSDA), has been used for infrared and microwave satellite radiance simulations and their derivatives to the surface/atmospheric parameters in data assimilation, physical retrieval, and many others. The CRTM has also been applied visible sensors and visible channel radiance/reflectance is simulated for studying aerosol and cloud effect. Together with the CRTM aerosol optical depth (AOD) module, the MODIS AOD satellite products can be assimilated and enhance air quality forecasting. This paper gives an overview of the CRTM developments and functionalities as well as its applications.

InfraRed Atmospheric Sounder (IRAS) instruments were successfully launched onboard the FengYun-3A (FY3A) and FengYun-3B (FY3B) satellites on May 27, 2008, and November 5, 2010, respectively. They aim at providing multichannel radiances within the spectral range of visible to infrared (IR) wavelengths for many environmental applications, including data assimilation and retrievals of global atmospheric temperature and humidity profiles. However, the velocity of the filter wheel of the first IRAS onboard FY3A is unstable and, therefore, induced a discontinuity in the measurement. The IRAS onboard FY3B works well in normal and stable operational mode since its launch without any anomaly. A variety of postlaunch calibration/validation tasks are conducted using on-orbit data during a period of three months. This paper presents on-orbit verification of IRAS instrument performance, including long-term trends of the space and warm calibration counts and noise equivalent delta radiance. The Earth scenes observed simultaneously by IRAS and Meteorological Operational Satellite Programme (METOP)/Infrared Atmospheric Sounding Interferometer were obtained and compared to demonstrate a close similarity between the two measurements. Furthermore, the IR channel observations from FY3B/IRAS are compared with those from National Oceanic and Atmospheric Administration-19/High Resolution Infrared Radiation Sounder (HIRS) equivalent channels and simulations from a radiative transfer model. The results show that some of IRAS IR channels perform very well, particularly for channels 1-10, 15, 19, and 20, compared to those of HIRS. Several channels, such as 13, 16, and 18, however, display some large biases. The causes of these increased biases are still under investigation.

The Community Radiative Transfer Model (CRTM) has been implemented in the Gridpoint Statistical Interpolation (GSI) system at the National Center for Environmental Prediction (NCEP) to simulate microwave and infrared radiances. We investigate impacts on analysis from a recent sensor, Special Sensor Microwave Imager Sounder (SSMIS). Both retrievals and radiance assimilation using the SSMIS show that SSMIS is unique in precisely determining stratospheric temperatures. We also utilize the SSMIS radiance for studying Hurricane Katrina. A "control-run" using current NCEP analysis field and a "test-run" using additional SSMIS data are compared. It shows again that the SSMIS radiance assimilation is helpful for hurricane forecasting.