Vladimir S. Kostsov

Numerical investigations of the accuracy of the remote sensing of non-LTE atmosphere by space-borne spectral measurements of limb i.r. radiation: 15 μm CO2 bands, 9.6 μm O3 bands and 10 μm CO2 laser bands

Abstract Inverse problems of the remote sensing of the atmosphere are formulated for the general case of an optically thick atmosphere under non-local thermodynamic equilibrium condition for the space-borne spectral measurements of the limb i.r. radiation. A feasibility study of the retrieval of the vertical profiles of different atmospheric parameters [vibrational (Tν) and kinetic (Tkin) temperatures, concentration of the absorbing gases, pressure] has been carried out by means of the error matrix calculations (optimal estimation method) for different spectral intervals of measurements (15 μm CO2 bands, 9.6 μm O3 bands and 10 μm CO2 laser bands), different spectral resolutions Δν and wide range of noise equivalent radiance (NER) values. It has been shown that limb radiation spectral measurements, for example, in 15 μm CO2 band (Δν = 1 cm−1, NER corresponding to MIPAS interferometer) enable the retrieval of Tv for CO2 states 0110, 0200, 0220, 1000 with an error less than half of the a priori uncertainty up to 112.5, 100, 102.5 and 100 km, respectively. Limb radiation measurements in the 9.6 μm O3 band make it possible to retrieve, with an accuracy about 10–30% of the a priori uncertainty, the vertical profile of the ozone concentration up to 65–90 km depending on the NER value, Δν and atmospheric model. The lower limit retrieval errors for O3 vibrational temperatures strongly depend on NER, Δν and the vibrational state under consideration, especially in the layers higher than 65 km. More than 50% decrease of a priori uncertainties (an error less than 25 K) is observed for the states of O3 molecule 001, 100, 011, 003, 012 up to 102, 94, 93, 92, 90 km, respectively (for Δν = 2.5 cm−1 and NER 10 times lower than one for MIPAS). Limb radiation measurements yield a considerable decrease (50–80%) of the a priori uncertainty of the pressure profile in the height range 30–60 km. If Tkin is considered as an independent unknown variable, the considerable amount of information on Tkin (up to 90–95 km) can be obtained only when NER is low, which is characteristic, for example, for CLAES instrument. Different ideas concerning the improvement of the retrieval accuracy are discussed.

Study of the Factors Determining Anomalous Variability of Carbon Dioxide Total Column Amount over St. Petersburg

Results of spectroscopic measurements of the carbon dioxide total column amount near St. Petersburg during forest fires in the period from August to September 2002 are analyzed. The HYSPLIT model is used to calculate air-mass trajectories and CO distribution on a mesoscale in this period. The HYSPLIT model simulations and measurements of carbon dioxide total column amount yield an estimate of the specific intensity of CO emission in a Pskov forest fire on August 28–September 8, 2002, equal to 0.17–0.26 kg m2. This estimate can be used for an estimation of the integral CO emission from fires in northwestern Russian forests and for model simulations of atmospheric CO concentration fields. The estimate of the CO emission from forest fires that is obtained from ground-based measurements can also be made on the basis of satellite measurements if they contain information on CO in the lower tropospheric layers (0 to 2 km).

Comparison of radio sounding and ground-based remote measurements of temperature profiles in the troposphere

A ground-based experiment on microwave temperature sounding in the troposphere with a RPG-HATPRO instrument, which has been performed at the Faculty of Physics, St. Petersburg State University since June, 2012, is described. On the basis of comparison of the results with radio sounding data, the temperature retrieval errors have been estimated using an algorithm provided by the manufacturer of the instrument. The errors have been compared with corresponding values for similar instruments functioning abroad. The conclusion has been drawn about a need to develop specialized algorithms and data processing procedures which include adaptation and correction of algorithms accounting for peculiarities of a specific instrument and experimental conditions.

Retrieving cloudy atmosphere parameters from RPG-HATPRO radiometer data

An algorithm for simultaneously determining both tropospheric temperature and humidity profiles and cloud liquid water content from ground-based measurements of microwave radiation is presented. A special feature of this algorithm is that it combines different types of measurements and different a priori information on the sought parameters. The features of its use in processing RPG-HATPRO radiometer data obtained in the course of atmospheric remote sensing experiments carried out by specialists from the Faculty of Physics of St. Petersburg State University are discussed. The results of a comparison of both temperature and humidity profiles obtained using a ground-based microwave remote sensing method with those obtained from radiosonde data are analyzed. It is shown that this combined algorithm is comparable (in accuracy) to the classical method of statistical regularization in determining temperature profiles; however, this algorithm demonstrates better accuracy (when compared to the method of statistical regularization) in determining humidity profiles.

Multiparameter technique for interpreting ground-based microwave spectral measurements in the problem of ozone vertical profile retrieval

The algorithm for interpreting ground-based measurements of the brightness temperature of downwelling microwave radiation in absorption lines traditionally used for to retrieve ozone vertical profiles is described. The inverse problem is formulated as a multiparameter with respect to ozone vertical profile (target parameter), as well as vertical profiles of the temperature, pressure, water vapor content, and cloud liquid water (controlled parameters). This approach allows one to use independent measurements of atmospheric parameters in different altitude ranges (if available) in any combinations and accounting for physical relationships between the parameters (e.g., the hydrostatic equation for temperature and pressure). Error estimates for retrieving the mean ozone concentration in the 22–30-, 30–40-, 40–50-, and 50–60-km layers are presented for summer and winter conditions (for different tropospheric total water content) and different scenarios of interpreting the downwelling microwave radiation measurements in the 110-GHz ozone absorption line.

Global distributions of temperature, carbon dioxide, ozone, and non-LTE parameters in mesosphere and lower thermosphere (CRISTA-1 experiment)

High-altitude limb infrared radiance spectra (CO2 15μm and O3 9.6μm bands) registered during CRISTA-1 experiment in November 1994 were interpreted using multiparameter inversion algorithm accounting for the nonlocal thermodynamic equilibrium conditions (non-LTE). Global distributions of temperature in the altitude range 40-120 km were obtained simultaneously with the distributions of CO2 and O3 (40-90 km) and vibrational temperatures of the lower vibrational states of CO2 and O3 molecules. Mean zonal values of temperature agree with CIRA-86 and SMLTM models. The root mean square variability of temperature reaches its maximum of 45 K at 105 km. Mesospheric temperature inversions were detected in 85% of cases during observations. The retrieved CO2 profiles demonstrate that the altitude level, up to which CO2 is well mixed, is considerably lower (70-75km) than predicted by models (85-90 km). Maximal diurnal variations of ozone were observed at 90 km altitude, where the mean value of volume mixing ratio is close to 2 ppmv for daytime and 7 ppmv for nighttime. The altitude levels of the LTE breakdown for the vibrational states of CO2 and O3 molecules and also the magnitude and vertical behavior of the non-LTE effect are in good agreement with numerical models.

Application of the information approach to the analysis of two-year microwave observations of the atmosphere by the RPG-HATPRO radiometer at St. Petersburg University

ABSTRACT Since June 2012 the ground-based microwave (MW) radiometer RPG-HATPRO (Radiometer Physics GmbH – Humidity and Temperature Profiler) G3 (generation 3) has been operating at the Faculty of Physics of St. Petersburg State University in constant mode with sampling interval of 1–2 s. The results of MW radiation brightness temperature measurements in 14 spectral channels of the RPG-HATPRO radiometer have been analysed for the time period December 2012 to November 2014. Within this time period, different data ensembles are compiled that have different duration and describe the variety of atmospheric situations at the observational site. Two different approaches are used for the assessment of the information characteristics of MW measurements. The first one is based on calculation of Shannon’s information content that characterizes the number of atmospheric states distinguishable by measurements. We use the modification proposed by Kozlov – the ‘information volume’ approach. The second approach is based on calculation of the information quantity that characterizes the degree of correlation between measurements and atmospheric state parameter variations. The information quantities are calculated and analysed for the complete set of spectral channels and for two subsets that comprised seven so-called ‘temperature’ and seven so-called ‘humidity’ channels separately. Kozlov’s ‘information volume’ approach is also applied to the problem of estimation of the optimal sampling interval of MW measurements. It is shown that for St. Petersburg University observation site that represents subarctic region with maritime climate: (1) the information volume of MW measurements for a cold and dry season is significantly less than for a warm and humid season due to lack of information from ‘humidity channels’; (2) for stable atmospheric conditions the sampling interval of MW measurements should not be greater than 100–200 s; (3) the degree of correlation between MW measurements and atmospheric temperature and humidity does not considerably depend on season of observations.

General approach to the formulation and solution of the multi-parameter inverse problems of atmospheric remote sensing with measurements and constraints of different types

A general approach to the formulation and solution of the multi-parameter inverse problems of atmospheric remote sensing with measurements and constraints of different types is considered, which is based on the concept of the presentation of constraints as virtual measurements of finite accuracy. The advantages of the approach are (1) the possibility to account for all kinds of available information (remote and in situ measurements, physical constraints, model predictions); (2) the unified description of different measurements, a priori information and constraints in the retrieval algorithm; (3) the possibility to use measurements and a priori information of different types in any combination and to assess individual contributions to information content. The approach can be considered as a convenient tool for implementation of different synergistic remote-sensing schemes and for utilization of maximum available information on sought parameters for the purpose of increasing the accuracy of atmospheric remote sensing and providing self-consistency of sets of retrieved parameters. The known formulae for degrees of freedom for signal, averaging kernels, error components, and parameters describing spatial resolution are generalized to the case of multiple sought variables, measurements, and constraints, and the peculiar features of such generalization are discussed. The example is given of the application of the approach to the interpretation of the middle atmosphere limb infrared radiance data obtained in CRISTA (Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere) experiments with special emphasis on the constraints describing coupling of the parameters due to physical processes.

On the accuracy of the limb sounding of the atmosphere in the 10.4 μm, 15 μm CO2 and 9.6 μm O3 bands with account for non-LTE

Abstract Inverse problem of thermal radiation transfer accounting for non-LTE effects has been considered for limb geometry in the spectral region covering 10.4μm, 15μm CO 2 and 9.6μm O 3 bands. Limb radiance has been calculated line-by-line on the basis of the non-LTE model describing day-time non-equilibrium populations of the vibrational states of CO 2 and O 3 molecules which correspond to the bands under consideration. The inverse problem for the satellite limb radiance high resolution measurements in the spectral interval 540–1150 cm −1 has been posed with respect to the simultaneous retrieval of the vertical profiles of pressure, kinetic temperature, number density of main absorbers, and vibrational temperatures of the states mentioned above. For the estimation of the retrieval accuracy the optimal estimation method has been applied, and the calculations of error matrices have been performed. The influence of the spectral resolution of measurements on the retrieval accuracy has been investigated. The conclusion has been done on the applicability of measurements to be performed in future by instruments similar to MIPAS to the investigations of non-LTE effects in the middle atmosphere.

General approach to the formulation and solution of the multi-parameter inverse problems of atmospheric remote sensing

Inverse problems of atmospheric remote sensing can be formulated as multi-parameter problems in most cases. The parameters to be retrieved (the parameters of primary interest) are called the target parameters and the parameters which influence the retrieval are called the interfering parameters. The interfering parameters should be preset and controlled in one way or another or should be retrieved simultaneously with the target parameters. Very often the information about interfering parameters is available from different sources with different accuracy and, if vertical profiles are considered, in different altitude regions. Besides, often it is necessary to apply constraints or physical links to the parameters (for example, hydrostatic equilibrium equation for temperature and pressure profiles). The convenient way to account for all kinds of available information about target and interfering parameters and for all constraints is to combine these parameters in one joint vector and to formulate the inverse...