Abstract—Based on retrospective comparison with the data of ground-based spectroscopic measurements carried out in Peterhof by St. Petersburg State University (SPbSU) and aircraft measurements carried out in the area of the Novosibirsk Reservoir by the Zuev Institute of Atmospheric Optics in 2019–2022, results of application of a new version of the regression technique for determining the total carbon dioxide XCO2 content (the mole fraction of atmospheric CO2 in dry air) by measurements of the IKFS-2 infrared Fourier spectrometer of the Meteor-M No. 2 Russian meteorological satellite are analyzed. A description of changes made in the technique to improve the accuracy of satellite estimates is given. For example, to compensate for the influence of changes in IKFS-2 characteristics during a long flight on the XCO2 estimates, they are calibrated based on the results of ground measurements from the NOAA observatory at Mauna Loa volcano (the island of Hawai’i). After calibration and filtering of cloud scenes, the divergence of satellite estimates from ground and aircraft measurements is characterized by a mean square deviation of 4 ppm or 1

Current climate changes on Earth are caused by the violation of the planet’s radiation balance (RB). In this study, the changes in one component of the RB—yearly and monthly averaged global and regional outgoing thermal radiation of Earth, or the Earth’s own radiation (EOR), in a spectral range of 660–1300 cm–1 for 2015–2022 by an IKFS-2 IR Fourier spectrometer onboard the Meteor-M No. 2 satellite—are analyzed. It is shown that EOR on a global scale, falling in the range of 660–1300 cm–1, on average, decreased during the period of 2015–2022. The mean integral radiation in the same wavelength range decreased by 0.5 W m–2 in 2015–2022. The most pronounced decrease in EOR was found in the tropics, and the least pronounced was on polar latitudes. A negative trend of the integral EOR was found in the tropics (up to 0.95–1.3 ± 0.1 W m–2 for 8 years), with a relatively high coefficient of determination (0.46–0.57). At the same time, there is no pronounced trend of EOR on the polar and middle latitudes.

The results of determining the ozone total column (OTC) from the spectra of the outgoing thermal infrared radiation measured by the IKFS-2 instrument from the Meteor-M No. 2 spacecraft during 8 years of measurements are presented. The previously developed technique for the interpretation of spectral measurements made in 2015–2020 with a swath width (SW) of 1000 km is applied to the measurements in 2021–2022 with a SW of 1500 km. It is shown that the increase in the differences between the IKFS-2 data and the results of independent measurements is caused not by the expansion of the OTC variability statistics, but by the increase in the range of scanning angle variation. After a finalization of the technique for the measurements with a 1500-km SW, a comparison with independent data showed that the standard deviations of differences with the results of ground and satellite measurements for all 8 years do not exceed 3

Важной задачей в исследованиях современных изменениях климата Земли и факторов их определяющих, является регулярный мониторинг антропогенных эмиссий СО2. В настоящей работе проводится анализ сопоставления данных спутниковых измерений ХСО2 с помощью инфракрасного Фурье-спектрометра ИКФС-2, установленного на российском метеорологическом спутнике «Метеор-М» №2 и измеряющего уходящее тепловое ИК-излучение, и данных наземных измерений XCO2, полученных из спектров солнечного излучения в БИК диапазоне, осуществленных в Петергофе (СПбГУ) в период 2019-2022 гг. Фурье-спектрометром Bruker IFS 125НR высокого спектрального разрешения. Различия между величинами ХСО2, полученными по спутниковым и наземным данным, находятся в пределах ~ 1%. An important task in the research of modern changes in the Earth's climate and the factors determining them is the regular monitoring of anthropogenic CO2 emissions. This paper analyzes the comparison of data from satellite measurements of XCO2 using the infrared Fourier spectrometer IKFS-2 installed on the Russian meteorological satellite Meteor-M No. 2 and measuring outgoing thermal IR radiation, and data from ground-based measurements of XCO2 obtained from solar radiation spectra in the BIC range carried out in Peterhof (St. Petersburg State University) in the period 2019-2022 . The Bruker IFS 125HR Fourier spectrometer of high spectral resolution. The differences between the values of XCO2 obtained from satellite and ground data are in the range of ~ 1%.

The paper discusses the use of measurements of the IKFS-2 hyperspectral infrared sounder installed on Meteor-M polar-orbiting weather satellites for remote derivation of the atmospheric parameters related to so called essential climate variables (ECV) of the atmosphere, whose monitoring is necessary to characterize the climate system and its changes. The ECVs include the concentrations of the main atmosphere greenhouse gases (water vapor, carbon dioxide, methane, and ozone), characteristics of clouds and aerosols, as well as vertical temperature profiles, near-surface temperature, etc. A brief description of the IKFS-2 instrument and the results of its operation on board the Meteor-M spacecraft No. 2 during the period from the autumn of 2014 till now is given. The possibility of forming multiyear homogeneous series containing IKFS-2 measurements and satellite-based estimates of the aforementioned atmospheric ECVs is analyzed. An advanced method for deriving the total content of atmospheric carbon dioxide from IKFS-2 measurements is presented. The information on the errors of satellite-based ECV estimates obtained from their comparison with independent observations is provided.

The noise covariance matrix, whose diagonal square root is commonly referred to as radiometric noise (NESR), is one of the most important characteristics of hyperspectral infrared sounders measurements. It is used in spectral data inversion and in estimating the atmospheric state vector. This paper presents new results of noise covariance matrix characterization in measurements of the IKFS-2 infrared Fourier transform spectrometer, which has been successfully operating on board the Meteor-M No. 2 spacecraft for more than 6 years. The main factors leading to the interchannel noise correlation are considered. They are associated both with the properties of noise in the interferograms measured by the instrument and the specifics of the initial processing procedure. The noise covariance matrix in the IKFS-2 output spectra has been experimentally estimated in three different ways: (1) from measurements of reference radiation sources, (2) from measured atmospheric spectra, and (3) from the imaginary part of the calibrated atmospheric spectra. The results of the experimental assessment are consistent with the calculations and can be used in the problems of thematic processing and assimilation of IKFS-2 data in numerical weather prediction models of Roshydromet.

A ground-based spectroscopic method for determining the trichlorofluoromethane (CCl3F) content from measurements of IR spectra of solar radiation using an IFS-125HR Fourier spectrometer (FTIR method) is considered. A detector based on mercury-cadmium-tellurium (HgCdTe), which is used for measurements in the CCl3F absorption spectral region, was cooled by liquid N-2. An amorphous ice film grew on the detector crystal as the vacuum in the metal Dewar flask gradually deteriorated during cooling. The spectral absorption band of amorphous ice at liquid N-2 temperature overlapped the CCl3F absorption band. The variability of the ice film thickness added additional uncertainty to the estimates of the CCl3F atmospheric content. A technique has been developed to estimate the thickness of the ice film, to account for its spectral absorption in the algorithm for solving the inverse problem, and to eliminate this uncertainty. The technique was applied to measuring the atmospheric concentration of CCl3F in 2017-2019 over the NDACC St. Petersburg station. The results were compared with those obtained earlier using a technique in which the thickness of the ice film was treated as an unknown parameter adjusted during solution of the inverse problem. Previously obtained CCl3F atmospheric contents were refined using the proposed technique. The difference reached 10%.

The paper provides an overview of methods and technical devices for remote temperature and humidity sensing of the Earth’s atmosphere from satellites developed in Russia. A brief description of modern and forthcoming infrared and microwave atmospheric sounders installed on Meteor-M operational polar-orbiting weather satellites is given. The physical and mathematical base of interpreting measurements of atmospheric sounders (IKFS-2 infrared Fourier spectrometer and MTVZA-GYa microwave radiometer) is presented. The technologies for retrieving atmospheric temperature and humidity profiles are described. The results of retrieval validation as well as the prospects for further development of satellite remote temperature and humidity sensing systems are discussed.

A description is given of the method for the retrieval of atmospheric column-averaged dry-air mole fractions of carbon dioxide (XCO2) from the data of IKFS-2 infrared Fourier spectrometer on board the Meteor-M Russian meteorological satellites. The method is based on estimating XCO2 using a second-order regression, whose predictors are the effective spectral optical depths of the atmosphere in the infrared region of 8-14 μm. The optical depth is determined using spectral intensities of outgoing radiation measured by the IKFS-2 as well as the calculated intensities of the Earth’s surface or cloud top simulated as a gray body with temperature T s. The temperature T s is retrieved from IKFS-2 measurements within the atmospheric microwindow at the wave number equal to 900.1 cm-1. The reference XCO2 values for constructing the regression were the results of contact CO2 measurements on the tall tower at the ZOTTO international observatory (Central Siberia) and at the NOAA observatory on the Mauna Loa volcano (Hawaii) in 2015-2016. The methodology was validated by comparing the XCO2 retrieved from Meteor-M No. 2 IKFS-2 measurements with parallel measurements over Siberia by the OCO and CrIS satellite spectrometers on board the OCO-2 and NOAA-20 satellites (USA). The maximum discrepancies in the daily estimates of the spatially averaged XCO2 during October 9-19, 2021 derived from the IKFS-2 data do not exceed 2.3 ppm versus the OCO data and 5 ppm versus the CrIS data.

The method and algorithm for ozone total column (OTC) determining based on spectroscopic measurements of outgoing thermal radiation by IKFS-2 spectrometer (on-board “Meteor-M2 N 2” satellite) are described. Algorithm is based on an artificial neural network method and OMI satellite measurements. The results of comparison of OTC measurements by IKFS-2 spectrometer and by ground-based instruments (Dobson, Brewer, and M-124 ozonometer) are given. It is shown that systematic discrepancy between satellite and ground-based measurements in most cases is not higher than 1%, RMSD values are within 3.0–4.5%. The empirical assessment of retrieval errors demonstrates that Dobson and Brewer OTC measurement random total errors are 1% (in direct solar radiation measurements mode), OMI and IKFS-2 satellite measurements give 2.8 and 3.6% random errors, respectively.

The study of climate change based on spectral radiances of outgoing infrared radiation measured by different space-borne spectroradiometers, requires careful intercalibration of these instruments.The results of SI-1/Meteor-28 (-29) (1977, 1979) and IKFS-2/Meteor-M N2 (in orbit operation since 2015) FTIR spectrometers intercalibration are presented in this paper to clarify the results of IR atmospheric spectra changes over the past 40 years, previously obtained by authors.The double-difference method is applied due to the impossibility of direct (synchronous) comparisons.Calculations of the infrared atmospheric spectra based on the radiosonde data and carbon dioxide data carried out using the LBLTRM radiation code are used as reference measurements.It was found that both the mean and standard deviation for double differences after selecting the most reliable measurements do not exceed 1-2 mW/(m 2 •sr•cm -1 ) in almost the entire spectral range under consideration 660-1350 cm -1 , which indicates a good calibration agreement between two instruments.

The method and algorithm for determining total ozone column amounts (TOC) based on spectroscopic measurements of outgoing thermal radiation by IKFS-2 spectrometer (on-board ″Meteor-M No. 2″ satellite) are described. The algorithm is based on the artifi cial neural network method and satellite measurements of TOC using ozone monitoring instrumentation (OMI). Comparison of the results of TOC measurements by IKFS-2 spectrometer and by ground-based instruments (Dobson, Brewer, and M-124 ozonometers) are given. It is shown that systematic discrepancy between the results of satellite and ground-based measurements in most cases does not exceed 1%, and RMSD values are within 3.0–4.5%. The empirical assessment of random measurement errors in the determination of TOC demonstrates that Dobson and Brewer TOC measurement random total errors are ~1% (in direct solar radiation measurements mode), and OMI and IKFS-2 satellite measurements give 2.8 and 3.6% random errors, respectively.

The first Russian advanced infrared (IR) atmospheric sounder IKFS-2 was launched in July 2014 on the "Meteor-M" No. 2 meteorological satellite. It is planned that this instrument and similar devices will continue to operate until 2025 aboard the current and subsequent satellites of "Meteor-M" series. IKFS-2 is a Fourier transform spectrometer covering the spectral domain of 5-15 mu m. It belongs to a class of hyper-spectral IR sounders, designed to measure the outgoing IR radiance spectra and to provide information on the thermodynamic parameters and the composition of the atmosphere such as vertical temperature and humidity profiles, estimates of the ozone and other trace gases total column amounts. In the paper, the IKFS-2 operation on board "Meteor-M" No. 2 is analyzed, including the assessment of the measurements' quality (the errors of radiometric and spectral calibration) and their information content. Since launch, the instrument performance has been remained stable, and the actual IKFS-2 characteristics (threshold value of NESR, uncertainty of onboard radiometric and spectral calibrations, spectral resolution) meet the planned requirements. There is a good agreement between IKFS-2 measurements and measurements of independent satellite instruments (SEVIRI, IASI). The paper also provides an overview of the developed scientific basis for simulation and interpretation ("inversion") of satellite measurements. The examples of output IKFS-2 level 2 products (vertical profiles of temperature and humidity, total ozone content) are given together with the error analysis. The performance of atmospheric (temperature and humidity) profile retrievals and the feasibility of total ozone content estimates are evaluated by comparison with independent ground-based or satellite measurements. (C) 2019 The Authors. Published by Elsevier Ltd.

The accuracy of retrieving the profiles of temperature and relative humidity from data of IKFS-2 Russian satellite Fourier spectrometer installed onboard the Meteor-M No. 2 satellite is assessed. The retrieved data were compared with radiosonde data and with the results of numerical weather prediction. It was found that the root-mean-square error of the vertical distribution of temperature in the air column of 1000-100 hPa as compared with radiosonde data does not exceed 2.5 K near the Earth surface and is within 2 K at the other levels. The maximum error of relative humidity retrieval was registered in the tropopause area and made up 35%. The use of water vapor mixing ratio for calculating relative humidity reduced the maximum error to ∼25% in the tropopause area and to 15% at the other levels.

Abstract—Comparisons of outgoing IR radiation spectra measured bу Fourier SI-1 spectrometer in 1977 and 1979 from the Meteor-28 and -29 satellites to numerical calculations on the basis of the modern LBLRTM code and data of atmospheric radio sounding are carried out. In most cases, mean differences between measurements and calculations do not exceed 2 mW/(m2 sr cm–1) in the 660–1600 cm–1 spectral range. Standard deviations and mean square differences are, on average, 2–4 mW/(m2 sr cm–1). These values are greater bу about 1 mW/(m2 sr cm–1) than relevant differences between calculations and measurements for modern IKFS-2 spectrometer. Comparisons of experimental spectra of 1977, 1979 and 2015–2016 have shown that, on average, the intensity of outgoing IR radiation measured bу the IKFS-2 device, is bу 0.5–3.0 mW/(m2 sr cm–1) less than SI-1 radiation measurements onboard Meteor-28 and -29 satellites obtained 40 years ago. This effect may be associated with the СО2 increase in the atmosphere and the resulting raising of radiating atmosphere layers to tropospheric layers with а smaller temperature.