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.

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 Fourier Transform Michelson interferometer instrument launched on board the Suomi National Polar-Orbiting Partnership (Suomi NPP) satellite on 28 October 2011. CrIS provides measurements of Earth view interferograms in three infrared spectral bands at 30 cross-track positions, each with a 3x3 array of field of views. The CrIS ground processing software transforms the measured interferograms into calibrated and geolocated spectra in the form of Sensor Data Records (SDRs) that cover spectral bands from 650 to 1095cm(-1), 1210 to 1750cm(-1), and 2155 to 2550cm(-1) with spectral resolutions of 0.625cm(-1), 1.25cm(-1), and 2.5cm(-1), respectively. During the time since launch a team of subject matter experts from government, academia, and industry has been engaged in postlaunch CrIS calibration and validation activities. The CrIS SDR product is defined by three validation stages: Beta, Provisional, and Validated. The product reached Beta and Provisional validation stages on 19 April 2012 and 31 January 2013, respectively. For Beta and Provisional SDR data, the estimated absolute spectral calibration uncertainty is less than 3ppm in the long-wave and midwave bands, and the estimated 3 sigma radiometric uncertainty for all Earth scenes is less than 0.3K in the long-wave band and less than 0.2K in the midwave and short-wave bands. The geolocation uncertainty for near nadir pixels is less than 0.4km in the cross-track and in-track directions.

In mid-2009, the Radiative Heating in the Underexplored Bands Campaign II (RHUBC-II) was conducted from Cerro Toco, Chile, a high, dry, remote mountain plateau, 23 degrees S, 67.8 degrees W at 5.4km, in the Atacama Desert of Northern Chile. From this site, dominant IR water vapor absorption bands and continuum, saturated when viewed from the surface at lower altitudes, or in less dry locales, were investigated in detail, elucidating infrared (IR) absorption and emission in the atmosphere. Three Fourier Transform InfraRed (FTIR) instruments were at the site, the Far-Infrared Spectroscopy of the Troposphere (FIRST), the Radiation Explorer in the Far Infrared (REFIR), and the Atmospheric Emitted Radiance Interferometer (AERI). In a side-by-side comparison, these measured atmospheric downwelling radiation, with overlapping spectral coverage from 5 to 100 mu m (2000 to 100cm(-1)), and instrument spectral resolutions from 0.5 to 0.643cm(-1), unapodized. In addition to the FTIR and other ground-based IR and microwave instrumentation, pressure/temperature/relative humidity measuring sondes, for atmospheric profiles to 18km, were launched from the site several times a day. The derived water vapor profiles, determined at times matching the FTIR measurement times, were used to model atmospheric radiative transfer. Comparison of instrument data, all at the same spectral resolution, and model calculations, are presented along with a technique for determining adjustments to line-by-line calculation continuum models. This was a major objective of the campaign.

The Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) Sensor Module (SM) Engineering Demonstration Unit (EDU) is a high resolution spectral imager designed to measure infrared (IR) radiances using a Fourier transform spectrometer (FTS). The GIFTS instrument employs three focal plane arrays (FPAs), which gather measurements across the long-wave IR (LWIR), short/mid-wave IR (SMWIR), and visible spectral bands. The raw interferogram measurements are radiometrically and spectrally calibrated to produce radiance spectra, which are further processed to obtain atmospheric profiles via retrieval algorithms. This paper describes the GIFTS SM EDU Level 1B algorithms involved in the calibration. The GIFTS Level 1B calibration procedures can be subdivided into four blocks. In the first block, the measured raw interferograms are first corrected for the detector nonlinearity distortion, followed by the complex filtering and decimation procedure. In the second block, a phase correction algorithm is applied to the filtered and decimated complex interferograms. The resulting imaginary part of the spectrum contains only the noise component of the uncorrected spectrum. Additional random noise reduction can be accomplished by applying a spectral smoothing routine to the phase-corrected spectrum. The phase correction and spectral smoothing operations are performed on a set of interferogram scans for both ambient and hot blackbody references. To continue with the calibration, we compute the spectral responsivity based on the previous results, from which, the calibrated ambient blackbody (ABB), hot blackbody (HBB), and scene spectra can be obtained. We now can estimate the noise equivalent spectral radiance (NESR) from the calibrated ABB and HBB spectra. The correction schemes that compensate for the fore-optics offsets and off-axis effects are also implemented. In the third block, we developed an efficient method of generating pixel performance assessments. In addition, a random pixel selection scheme is designed based on the pixel performance evaluation. Finally, in the fourth block, the single pixel algorithms are applied to the entire FPA.

The geosynchronous imaging Fourier transform spectrometer (GIFTS) sensor module (SM) engineering demonstration unit (EDU) is a high resolution spectral imager designed to measure infrared (IR) radiances using a Fourier transform spectrometer (FTS). The GIFTS instrument employs three focal plane arrays (FPAs), which gather measurements across the long-wave IR (LWIR), short/mid-wave IR (SMWIR), and visible spectral bands. The raw interferogram measurements are radiometrically and spectrally calibrated to produce radiance spectra, which are further processed to obtain atmospheric profiles via retrieval algorithms. This paper describes the processing algorithms involved in the calibration stage. The calibration procedures can be subdivided into three stages. In the pre-calibration stage, a phase correction algorithm is applied to the decimated and filtered complex interferogram. The resulting imaginary part of the spectrum contains only the noise component of the uncorrected spectrum. Additional random noise reduction can be accomplished by applying a spectral smoothing routine to the phase-corrected blackbody reference spectra. In the radiometric calibration stage, we first compute the spectral responsivity based on the previous results, from which, the calibrated ambient blackbody (ABB), hot blackbody (HBB), and scene spectra can be obtained. During the post-processing stage, we estimate the noise equivalent spectral radiance (NESR) from the calibrated ABB and HBB spectra. We then implement a correction scheme that compensates for the effect of fore-optics offsets. Finally, for off-axis pixels, the FPA off-axis effects correction is performed. To estimate the performance of the entire FPA, we developed an efficient method of generating pixel performance assessments. In addition, a random pixel selection scheme is designed based on the pixel performance evaluation.

The Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) Sensor Module (SM) Engineering Demonstration Unit (EDU) is a high resolution spectral imager designed to measure infrared (IR) radiances using a Fourier transform spectrometer (FTS). The GIFTS instrument employs three Focal Plane Arrays (FPAs), which gather measurements across the long-wave IR (LWIR), short/mid-wave IR (SMWIR), and visible spectral bands. The raw interferogram measurements are radiometrically and spectrally calibrated to produce radiance spectra, which are further processed to obtain atmospheric profiles via retrieval algorithms. This paper describes the processing algorithms involved in the calibration stage. The calibration procedures can be subdivided into three stages. In the pre-calibration stage, a phase correction algorithm is applied to the decimated and filtered complex interferogram. The resulting imaginary part of the spectrum contains only the noise component of the uncorrected spectrum. Additional random noise reduction can be accomplished by applying a spectral smoothing routine to the phase-corrected blackbody reference spectra. In the radiometric calibration stage, we first compute the spectral responsivity based on the previous results, from which, the calibrated ambient blackbody (ABB), hot blackbody (HBB), and scene spectra can be obtained. During the post-processing stage, we estimate the noise equivalent spectral radiance (NESR) from the calibrated ABB and HBB spectra. We then implement a correction scheme that compensates for the effect of fore-optics offsets. Finally, for off-axis pixels, the FPA off-axis effects correction is performed. To estimate the performance of the entire FPA, we developed an efficient method of generating pixel performance assessments. In addition, a random pixel selection scheme is designed based on the pixel performance evaluation.

The Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) Sensor Module (SM) Engineering Demonstration Unit (EDU) is a high resolution spectral imager designed to measure infrared (IR) radiances using a Fourier transform spectrometer (FTS). The GIFTS instrument employs three focal plane arrays (FPAs), which gather measurements across the long-wave IR (LWIR), short/mid-wave IR (SMWIR), and visible spectral bands. The raw interferogram measurements are radiometrically and spectrally calibrated to produce radiance spectra, which are further processed to obtain atmospheric profiles via retrieval algorithms. This paper describes the GIFTS SM EDU Level 1B algorithms involved in the calibration. The GIFTS Level 1B calibration procedures can be subdivided into four blocks. In the first block, the measured raw interferograms are first corrected for the detector nonlinearity distortion, followed by the complex filtering and decimation procedure. In the second block, a phase correction algorithm is applied to the filtered and decimated complex interferograms. The resulting imaginary part of the spectrum contains only the noise component of the uncorrected spectrum. Additional random noise reduction can be accomplished by applying a spectral smoothing routine to the phase-corrected spectrum. The phase correction and spectral smoothing operations are performed on a set of interferogram. scans for both ambient and hot blackbody references. To continue with the calibration, we compute the spectral responsivity based on the previous results, from which, the calibrated ambient blackbody (ABB), hot blackbody (HBB), and scene spectra can be obtained. We now can estimate the noise equivalent spectral radiance (NESR) from the calibrated ABB and HBB spectra. The correction schemes that compensate for the fore-optics offsets and off-axis effects are also implemented. In the third block, we developed an efficient method of generating pixel performance assessments. In addition, a random pixel selection scheme is designed based on the pixel performance evaluation. Finally, in the fourth block, the single pixel algorithms are applied to the entire FPA.

[1] Comparisons of remote sensing stratospheric mixing ratio profiles for O 3 , H 2 O, N 2 O, HNO 3 , and NO 2 are shown between data (version 5.2) obtained by the Improved Limb Atmospheric Spectrometer (ILAS) on board the Japanese Advanced Earth Observing Satellite (ADEOS) and the Smithsonian Astrophysical Observatory farinfrared spectrometer (FIRS)-2 balloon-borne spectrometer from a flight on 30 April 1997 originating in Fairbanks, Alaska. Submillimeter wave remote sensing and UV in situ observations of mixing ratios of O 3 from Jet Propulsion Laboratory (JPL) instruments obtained on board the same balloon gondola are also used for comparison with ILAS mixing ratios of O 3 . The remote sensing balloon observations occurred roughly 5° latitude, and the in situ 2° latitude, north of the nearest ILAS observations and were taken between 0700 and 1300 local solar time (LST), while the ILAS data were taken at the previous local sunset (near 2100 LST). Back trajectories from the locations and times of balloon data sets to the prior local sunset were within 2° latitude and 10° longitude of the nearest ILAS occultation; the validation therefore effectively occurred in very nearly the same air mass as was observed with ILAS, and well within a 1-day time interval. The mixing ratio profiles of all of the compared molecules (O 3 , HNO 3 , N 2 O, H 2 O, and NO 2 ) agree to within the combined uncertainties with only minor systematic offsets.

The Improved Limb Atmospheric Spectrometer (ILAS), a solar occultation infrared satellite sensor, was launched in August 1996. The ILAS validation balloon campaigns were carried out from Kiruna, Sweden (68°N, 21°E), in February and March 1997 and Fairbanks, Alaska (65°N, 148°W), in April and May 1997. During these campaigns, measurements of nitric acid (HNO3) were made using infrared emission spectrometers (Cold Atmospheric Emission Spectral Radiometer, Michelson Interferometer for Passive Atmospheric Sounding‐Balloon‐Borne version 2, and farinfrared spectrometer) and infrared solar occultation spectrometers (Limb Profile Monitor of the Atmosphere and Mark IV interferometer). An in situ experiment (Chemiluminescence Detector) measured total reactive nitrogen (NOy,), from which HNO3 mixing ratios in the lower stratosphere were calculated. In addition, an in situ NOy, measurement was also made at 12 km altitude from the Deutsche Luft‐und Raumfahrt Falcon aircraft in January 1997. The ILAS version 3.10 HNO3 mixing ratios obtained at the nearest location and averaged ILAS mixing ratios obtained within certain criteria were compared with the balloon data. The precision of the ILAS measurements was estimated from the random differences to be 0.8 parts per billion by volume (ppbv), corresponding to about 35% at 15 km and 10–15% at 20–35 km. While the absolute accuracy estimated from the systematic differences was as good as 0.5 ppbv (5%) at 20 km, the ILAS HNO3 mixing ratios were systematically lower than the balloon values by 1 ppbv (15–20%) at 25–30 km. The error in the altitude registration in the ILAS retrieval algorithm is a possible cause for the negative bias at higher altitudes.

Measurements of HCl in the lower stratosphere (15-21 km) from aircraft, balloon, Space Shuttle, and satellite reveal a growth in its mean abundance relative to that of total inorganic chlorine (Cly) from HCl/Cly = 57(+/-5)% in early 1993 to 75(+/-7)% by the end of 1997.

The Smithsonian far‐infrared spectrometer is a remote sensing Fourier transform spectrometer that measures the mid‐ and far‐infrared thermal emission spectrum of the stratosphere from balloon and aircraft platforms. The spectrometer has had nine successful balloon flights from 1987 to 1994, flying at float altitudes of 36–39 km and collecting 131 hours of midlatitude stratospheric limb spectra. The spectrometer also flew on a NASA DC‐8 aircraft, as part of the second Airborne Arctic Stratospheric Expedition (AASE‐II), collecting 140 hours of overhead spectra at latitudes ranging from the equator to the north pole. We present here a brief description of the instrument, a discussion of data reduction procedures, an estimation of both random and systematic errors, an outline of the procedure for retrieving mixing ratio profiles, and an explanation of the method of deriving temperature and pressure from the far‐ and mid‐infrared spectra.

The FIRS-2 is a far- to mid-infrared Fourier transform spectrometer, designed and built at the Smithsonian Astrophysical Observatory for the purpose of measuring stratospheric emission spectra. The instrument and data reduction system have been described elsewhere [Johnson et al., 1994]. We present here the method we have developed for phase recovery from highly asymmetric interferograms in the presence of an out-of-phase background signal.

The FIRS-2 spectrometer system is used to make accurate measurements of many stratospheric molecular species. The experimental method is to measure mid-infrared and far-infrared thermal emission spectra of the stratosphere, from a balloon-borne platform, at a discrete number of limb elevation angles. The analysis technique is to do a least-squares fit of a theoretical spectrum (calculated from a model mixing-ratio profile) to each measured emission line spectrum.

The hydroperoxyl radical (HO2) plays a key role in stratospheric chemistry through the HOx catalytic cycle of ozone destruction. Earlier measurements of stratospheric HO2 have given mixed results; some measured mixing ratios greatly exceed theoretical predictions. Measurements of HO2 have now been made with a balloon-borne farinfrared spectrometer. The measured daytime profile is in excellent agreement with theory up to 40 kilometers; above this level the measurements exceed theory by 30 percent, perhaps because of underprediction of ozone at these altitudes. The nighttime HO2 profile is strongly depressed with respect to the daytime profile, in general agreement with theory.