Retrieval Of Profiles Research Articles

Winds of Change for Future Operational AMV at EUMETSAT

EUMETSAT, the European Organization for the Exploitation of Meteorological Satellites, is one of the key contributors to global atmospheric motion vector (AMV) production around the world. Its current contribution includes geostationary satellites at 0.0 and 41.5 degrees east, and several products extracted from the Metop low-orbit satellites. These last ones mainly cover high-latitude regions completing the observations from the geostationary ring. In the upcoming years, EUMETSAT will launch a new generation of geostationary and low-orbit satellites. The imager instruments Flexible Combined Imager (FCI) and METImage will take over the nominal AMV production at EUMETSAT around 2022 and 2024. The enhanced characteristics of these new-generation instruments are expected to increase AMV production and to improve the quality of the products. This paper presents an overview of the current EUMETSAT AMV operational production, together with a roadmap of the preparation activities for the new generation of satellites. The characteristics of the upcoming AMV products are described and compared to the current operational AMV products. This paper also presents a recent investigation into AMV extraction using the Sentinel-3 Sea and Land Surface Temperature Radiometer (SLSTR) instrument, as well as the retrieval of wind profiles from infrared sounders.

Ozone profile climatology for remote sensing retrieval algorithms

Abstract. New ozone (O3) profile climatologies are created from the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) O3 record between 2005 and 2016, within the period of Aura Microwave Limb Sounder (MLS) and Aura Ozone Monitoring Instrument (OMI) assimilation. These two climatologies consist of monthly mean O3 profiles and the corresponding covariances dependent on the local solar time, longitude (15∘), and latitude (10∘), which are parameterized by tropopause pressure and total O3 column. They are validated through comparisons, which show good agreements with previous O3 profile climatologies. Compared to a monthly zonal mean climatology, both tropopause- and column-dependent climatologies provide improved a priori information for profile and total O3 retrievals from remote sensing measurements. Furthermore, parameterization of the O3 profile with total column O3 usually reduces the natural variability of the resulting climatological profile in the upper stratosphere further than the tropopause parameterization, which usually performs better in the upper troposphere and lower stratosphere (UTLS). Therefore tropopause-dependent climatology is more appropriate for profile O3 retrieval for complementing the vertical resolution of backscattered ultraviolet (UV) spectra, while the column-dependent climatology is more suited for use in total O3 retrieval algorithms, with an advantage of complete profile specification without requiring ancillary information. Compared to previous column-dependent climatologies, the new MERRA-2 column-dependent climatology better captures the diurnal, seasonal, and spatial variations and dynamical changes in O3 profiles with higher resolutions in O3, latitude, longitude, and season. The new MERRA-2 climatologies contain the first quantitative characterization of O3 profile covariances, which facilitate a new approach to improve O3 profiles using the most probable patterns of profile adjustments represented by the empirical orthogonal functions (EOFs) of the covariance matrices. The MERRA-2 daytime column-dependent climatology is used in the combo O3 and SO2 algorithm for retrieval from the Earth Polychromatic Imaging Camera (EPIC) on board the Deep Space Climate Observatory (DSCOVR) satellite, the Ozone Mapping and Profiler Suite Nadir Mapper (OMPS-NM) on the Suomi National Polar Partnership (SNPP), and the Ozone Monitoring Instrument (OMI) on the Aura spacecraft.

Effectiveness of the MFAS Method for Determining the Wind Velocity Vector from Windcube 200s Lidar Measurements

The technique of the maximum of the function of accumulated spectra (MFAS) is used for the first time for estimating the wind velocity vector from measurements with a micropulsed coherent Doppler lidar (MPCDL) in the process of conical scanning by a probing beam. It is established in the experiment with the Windcube 200s MPCDL that MFAS technique makes it possible to increase the maximum altitude of retrieval of the vertical profiles of the wind speed and direction by 30% on average as compared to the filtered sine wave fitting.

Calculation of Pressure in Tropical Cyclones Using Satellite Data

The paper studies the possibility of using air temperature and humidity profiles for the determination of pressure in tropical cyclones (TC). The accuracy of air temperature and humidity profile retrieval from AMSU radiometer data is verified using direct radiosonde measurements together with weather station data for the Northwest Pacific. In total, 10 tropical cyclones are analyzed for the period of 2011–2012. The comparison of pressure values inside TC calculated from satellite profiles with weather station data demonstrated good agreement: the linear regression with a slope of 1.014 ± 0.073, a free term of −19 ± 73, and a coefficient of determination R2 = 0.73. TC central pressure values calculated from satellite data were compared with the estimates of the Japan Meteorological Agency exhibiting a satisfactory correspondence with a slope of 1.2. The comparison with the estimates of the Joint Typhoon Warning Center (USA) demonstrates worse agreement.

On the analysis of ground-based microwave radiometer data during fog conditions

Abstract The goal of this study is twofold. First, we verify the retrievals of temperature and humidity profiles from a ground-based microwave radiometer (MWR) using radiosonde soundings. Second, we assess the potential of the MWR to nowcast fog formation and dissipation in a hyper-arid environment through the analysis of its profiles. The MWR is installed and operated at Masdar Institute in Abu Dhabi, United Arab Emirates (UAE), adjacent to Abu Dhabi's International Airport. MWR observations collected from 18 February 2017 to 31 March 2019. A comparison with airport radiosonde data reveals a good agreement in particular for temperature, with the two measurements generally within 1 K from the surface to 10 km. For the specific humidity, the biases can reach 5 g kg−1 in the PBL. Biases can be attributed to errors in the radiosonde measurements and a non-optimized retrieval algorithm for the MWR. A total of 14 fog events are identified during the study period. A strong near-surface inversion with lapse rates in the lowest 250 m of up to 30 K km−1 is needed for fog to form. Subsidence warming and drying associated with the subtropical anticyclone can descend down to 500 m, aiding the formation of fog at night. Cloud base height retrievals from the infrared (IR) camera capture fog onset and dissipation and complement the MWR observations. A synergy of different instruments could allow for more accurate fog detection.

Extraction of electron density profiles with geostationary satellite-based GPS side lobe occultation signals

GPS radio occultation (RO) measurements recorded on the geostationary earth orbit (GEO) satellite TJS-2 have been investigated for electron density profile (EDP) retrieval. The total electron content derived from TJS-2 single-frequency excess phase is refined by a moving average filter to smooth high-frequency errors, which outperforms the single-difference technique. The side lobe GPS RO signals have been used to estimate electron densities up to several thousand kilometers in height for the first time. By comparison with the ground-based digisonde, the IRI 2016 model and the Constellation Observing System for Meteorology, Ionosphere, and Climate satellite (COSMIC) EDPs, the TJS-2 ionospheric EDPs show good agreement with correlation coefficients exceeding 0.8. The TJS-2 average NmF2 differences compared to digisondes and COSMIC results are 12.9% and 1.4%, respectively, while the hmF2 differences are 1.65 km and 1.76 km, respectively. Our results reveal that GEO-based RO signals can estimate EDPs to altitudes up to several thousand kilometers at specific locations with daily repeatability, which makes it a very suitable technique for routinely monitoring EDP variations.

Full-azimuthal imaging-DOAS observations of NO<sub>2</sub> and O<sub>4</sub> during CINDI-2

Abstract. A novel imaging-DOAS (differential optical absorption spectroscopy) instrument IMPACT (Imaging MaPper for AtmospheriC observaTions) is presented combining full-azimuthal pointing (360∘) with a large vertical coverage (∼41∘). Complete panoramic scans are acquired at a temporal resolution of ∼15 min, enabling the retrieval of NO2 vertical profiles over the entire panorama around the measurement site. IMPACT showed excellent agreement (correlation >99 %) with coincident multiaxis DOAS (MAX-DOAS) measurements during the Second Cabauw Intercomparison of Nitrogen Dioxide measuring Instruments (CINDI-2) campaign. The temporal variability of NO2 slant columns within a typical MAX-DOAS vertical scanning sequence could be resolved and was as large as 20 % in a case study under good viewing conditions. The variation of corresponding profiles and surface concentrations was even larger (40 %). This variability is missed when retrieving trace gas profiles based on standard MAX-DOAS measurements. The azimuthal distribution of NO2 around the measurement site showed inhomogeneities (relative differences) up to 120 % (on average 35 %) on short timescales (individual panoramic scans). This is more than expected for the semirural location. We explain this behavior by the transport of pollution. Exploiting the instrument's advantages, the plume's trajectory during a prominent transport event could be reconstructed. Finally, the potential for retrieving information about the aerosol phase function from O4 slant columns along multiple almucantar scans of IMPACT is demonstrated, with promising results for future studies.

Variations in the vertical profile of ozone at four high-latitude Arctic sites from 2005 to 2017

Abstract. Understanding variations in atmospheric ozone in the Arctic is difficult because there are only a few long-term records of vertical ozone profiles in this region. We present 12 years of ozone profiles from February 2005 to February 2017 at four sites: Summit Station, Greenland; Ny-Ålesund, Svalbard, Norway; and Alert and Eureka, Nunavut, Canada. These profiles are created by combining ozonesonde measurements with ozone profile retrievals using data from the Microwave Limb Sounder (MLS). This combination creates a high-quality dataset with low uncertainty values by relying on in situ measurements of the maximum altitude of the ozonesondes (∼30 km) and satellite retrievals in the upper atmosphere (up to 60 km). For each station, the total column ozone (TCO) and the partial column ozone (PCO) in four atmospheric layers (troposphere to upper stratosphere) are analyzed. Overall, the seasonal cycles are similar at these sites. However, the TCO over Ny-Ålesund starts to decline 2 months later than at the other sites. In summer, the PCO in the upper stratosphere over Summit Station is slightly higher than at the other sites and exhibits a higher standard deviation. The decrease in PCO in the middle and upper stratosphere during fall is also lower over Summit Station. The maximum value of the lower- and middle-stratospheric PCO is reached earlier in the year over Eureka. Trend analysis over the 12-year period shows significant trends in most of the layers over Summit and Ny-Ålesund during summer and fall. To understand deseasonalized ozone variations, we identify the most important dynamical drivers of Arctic ozone at each level. These drivers are chosen based on mutual selected proxies at the four sites using stepwise multiple regression (SMR) analysis of various dynamical parameters with deseasonalized data. The final regression model is able to explain more than 80 % of the TCO and more than 70 % of the PCO in almost all of the layers. The regression model provides the greatest explanatory value in the middle stratosphere. The important proxies of the deseasonalized ozone time series at the four sites are tropopause pressure (TP) and equivalent latitude (EQL) at 370 K in the troposphere, the quasi-biennial oscillation (QBO) in the troposphere and lower stratosphere, the equivalent latitude at 550 K in the middle and upper stratosphere, and the eddy heat flux (EHF) and volume of polar stratospheric clouds throughout the stratosphere.

A practical information-centered technique to remove a priori information from lidar optimal-estimation-method retrievals

Abstract. Lidar retrievals of atmospheric temperature and water vapor mixing ratio profiles using the optimal estimation method (OEM) typically use a retrieval grid with a number of points larger than the number of pieces of independent information obtainable from the measurements. Consequently, retrieved geophysical quantities contain some information from their respective a priori values or profiles, which can affect the results in the higher altitudes of the temperature and water vapor profiles due to decreasing signal-to-noise ratios. The extent of this influence can be estimated using the retrieval's averaging kernels. The removal of formal a priori information from the retrieved profiles in the regions of prevailing a priori effects is desirable, particularly when these greatest heights are of interest for scientific studies. We demonstrate here that removal of a priori information from OEM retrievals is possible by repeating the retrieval on a coarser grid where the retrieval is stable even without the use of formal prior information. The averaging kernels of the fine-grid OEM retrieval are used to optimize the coarse retrieval grid. We demonstrate the adequacy of this method for the case of a large power-aperture Rayleigh scatter lidar nighttime temperature retrieval and for a Raman scatter lidar water vapor mixing ratio retrieval during both day and night.

Linearization of the effect of slit function changes for improving Ozone Monitoring Instrument ozone profile retrievals

Abstract. We introduce a method that accounts for errors caused by the slit function in an optimal-estimation-based spectral fitting process to improve ozone profile retrievals from the Ozone Monitoring Instrument (OMI) ultraviolet measurements (270–330 nm). Previously, a slit function was parameterized as a standard Gaussian by fitting the full width at half maximum (FWHM) of the slit function from climatological OMI solar irradiances. This cannot account for the temporal variation in slit function in irradiance, the intra-orbit changes due to thermally induced change and scene inhomogeneity, and potential differences in the slit functions of irradiance and radiance measurements. As a result, radiance simulation errors may be induced due to convolving reference spectra with incorrect slit functions. To better represent the shape of the slit functions, we implement a more generic super Gaussian slit function with two free parameters (slit width and shape factor); it becomes standard Gaussian when the shape factor is fixed to be 2. The effects of errors in slit function parameters on radiance spectra, referred to as pseudo absorbers (PAs), are linearized by convolving high-resolution cross sections or simulated radiances with the partial derivatives of the slit function with respect to the slit parameters. The PAs are included in the spectral fitting scaled by fitting coefficients that are iteratively adjusted as elements of the state vector along with ozone and other fitting parameters. The fitting coefficients vary with cross-track and along-track pixels and show sensitivity to heterogeneous scenes. The PA spectrum is quite similar in the Hartley band below 310 nm for both standard and super Gaussians, but is more distinctly structured in the Huggins band above 310 nm with the use of super Gaussian slit functions. Finally, we demonstrate that some spikes of fitting residuals are slightly smoothed by accounting for the slit function errors. Comparisons with ozonesondes demonstrate noticeable improvements when using PAs for both standard and super Gaussians, especially for reducing the systematic biases in the tropics and midlatitudes (mean biases of tropospheric column ozone reduced from -1.4∼0.7 to 0.0∼0.4 DU) and reducing the standard deviations of tropospheric ozone column differences at high latitudes (by 1 DU for the super Gaussian). Including PAs also makes the retrievals consistent between standard and super Gaussians. This study corroborates the slit function differences between radiance and irradiance, demonstrating that it is important to account for such differences in the ozone profile retrievals.

Vertical profile of aerosol extinction based on the measurement of O4 of multi-elevation angles with MAX-DOAS**Project supported by the National Natural Science Foundation of China (Grant Nos. 41875040, 41705012, and 1605013).

A method for aerosol extinction profile retrieval using ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) is studied, which is based on a look-up table algorithm. The algorithm uses parametric method to represent aerosol extinction profiles and simulate different atmospheric aerosol states through atmospheric radiation transfer model. Based on the method, aerosol extinction profile was obtained during six cloud-free days. The O4 differential air mass factor (dAMF) measured by MAX-DOAS is compared with the corresponding model results under different atmospheric conditions (). The aerosol optical thickness, aerosol weight factor in boundary layer, and the height of the boundary layer are obtained after the process of minimization and look-up table method. The retrieved aerosol extinction in boundary layer is compared with PM2.5 data measured by ground point instrument. The diurnal variation trends of the two methods are in good agreement. The correlation coefficients of the two methods are 0.71 when the aerosol optical thickness is smaller than 0.5. The results show that the look-up table method can obtain the aerosol state of the troposphere and provide validation for other instrument data.

The Mineral Aerosol Profiling from Infrared Radiances (MAPIR) algorithm: version 4.1 description and evaluation

Abstract. The Mineral Aerosol Profiling from Infrared Radiances (MAPIR) algorithm retrieves vertical dust concentration profiles from cloud-free Infrared Atmospheric Sounding Interferometer (IASI) thermal infrared (TIR) radiances using Rodgers' optimal estimation method (OEM). We describe the new version 4.1 and evaluation results. Main differences with respect to previous versions are the Levenberg–Marquardt modification of the OEM, the use of the logarithm of the concentration in the retrieval and the use of Radiative Transfer for TOVS (RTTOV) for in-line radiative transfer calculations. The dust aerosol concentrations are retrieved in seven 1 km thick layers centered at 0.5 to 6.5 km. A global data set of the daily dust distribution was generated with MAPIR v4.1 covering September 2007 to June 2018, with further extensions planned every 6 months. The post-retrieval quality filters reject about 16 % of the retrievals, a huge improvement with respect to the previous versions in which up to 40 % of the retrievals were of bad quality. The median difference between the observed and fitted spectra of the good-quality retrievals is 0.32 K, with lower values over oceans. The information content of the retrieved profiles shows a dependence on the total aerosol load due to the assumption of a lognormal state vector. The median degrees of freedom in dusty scenes (min 10 µm AOD of 0.5) is 1.4. An evaluation of the aerosol optical depth (AOD) obtained from the integrated MAPIR v4.1 profiles was performed against 72 AErosol RObotic NETwork (AERONET) stations. The MAPIR AOD correlates well with the ground-based data, with a mean correlation coefficient of 0.66 and values as high as 0.88. Overall, there is a mean AOD (550 nm) positive bias of only 0.04 with respect to AERONET, which is an extremely good result. The previous versions of MAPIR were known to largely overestimate AOD (about 0.28 for v3). A second evaluation exercise was performed comparing the mean aerosol layer altitude from MAPIR with the mean dust altitude from Cloud–Aerosol LIdar with Orthogonal Polarization (CALIOP). A small underestimation was found, with a mean difference of about 350 m (standard deviation of about 1 km) with respect to the CALIOP cumulative extinction altitude, which is again considered very good as the vertical resolution of MAPIR is 1 km. In the comparisons against AERONET and CALIOP, a dependence of MAPIR on the quality of the temperature profiles used in the retrieval is observed. Finally, a qualitative comparison of dust aerosol concentration profiles was done against lidar measurements from two ground-based stations (M'Bour and Al Dhaid) and from the Cloud–Aerosol Transport System (CATS) instrument on board the International Space Station (ISS). MAPIR v4.1 showed the ability to detect dust plumes at the same time and with a similar extent as the lidar instruments. This new MAPIR version shows a great improvement of the accuracy of the aerosol profile retrievals with respect to previous versions, especially so for the integrated AOD. It now offers a unique 3-D dust data set, which can be used to gain more insight into the transport and emission processes of mineral dust aerosols.

Retrieval of Tropospheric Refractivity Profiles Using Slant Tropospheric Delays Derived From a Single Ground‐Based Global Navigation Satellite System Station

AbstractThe Global Navigation Satellite System (GNSS) has proved to be a powerful tool for applications in meteorology. In this study, we propose a novel slant tropospheric delay (STD) model to obtain the vertical distribution of atmospheric refractivity based on a single ground‐based GNSS receiver. The new model is used to convert the STD into a function of the vertical gradient of temperature, and it is divided into two layers (above and below the tropopause) for integration. The optical vertical gradient of temperature can be estimated according to the STD obtained from the GNSS observations from a higher satellite elevation angle. The distribution of atmospheric refractivity can then be derived from the vertical gradient of temperature and the surface atmospheric refractivity. Moreover, to further improve the accuracy of the STD model‐derived atmospheric refractivity, we correct it using a “theoretical retrieval” method based on the STDs obtained at a lower elevation angle. The optical ranges of theoretical retrieval are obtained above and below 5 km. Finally, a search is performed for the value of atmospheric refractivity that best fits the model equations, and this value is taken as the final inversion result. Data collected from eight GNSS stations and nearby radiosonde stations in 2016 were used to verify the new method. Using the radiosonde‐derived values as a reference, the accuracy of the STD model‐derived atmospheric refractivity was improved by 13.4% compared with the traditional technique. In addition, again using the radiosonde‐derived values as a reference, the accuracy of the atmospheric refractivity derived with the optically corrected method was improved by 20.4% compared with the uncorrected STD model.

Characterization of the atmospheric boundary layer in a narrow tropical valley using remote‐sensing and radiosonde observations and the WRF model: the Aburrá Valley case‐study

The spatiotemporal evolution of the atmospheric boundary layer (ABL), in a narrow, highly complex terrain located in the Colombian Andes, is studied using radiosondes and remote‐sensing equipment. Different techniques are implemented to automatically estimate the ABL height using ceilometer backscattering profiles and a combination of a radar wind profiler and microwave radiometer retrievals. The large aerosol load from anthropogenic emissions within the valley allows the use of ceilometer‐based ABL height detection methods, especially under stable atmospheric conditions. However, convective atmospheres favour aerosol dispersion, increasing the uncertainty associated with the estimation of the convective boundary layer using ceilometers. In contrast, the multisensor technique is more robust, performing better in stable and unstable conditions. All ceilometer‐based methods and the multisensor scheme capture the observed ABL height diurnal cycle. The main difference among ABL height retrievals occurs in the afternoon and during the night when Richardson number estimates tend to detect the top‐down contraction of the residual layer, while ceilometer‐based estimates detect the sudden bottom‐up onset of the nocturnal stable layer. The results also show that intra‐annual and annual variations of cloudiness strongly condition the ABL expansion, leading to a modulation of the ABL height diurnal cycle. The amount of aerosol particles near the surface is influenced by the evolution of the ABL, modifying the available control volume for the pollutants to interact and disperse. The evolution of ABL over the slopes and at the valley floor differs as a result of the local thickening associated with upslope winds. Weather Research and Forecasting model simulations, from a climatological point of view, skilfully simulate the observed ABL height for both the diurnal and annual cycles; the model skill is higher over the valley floor than over the slopes.

Observations and Modeling of Potassium Emission in the Terrestrial Nightglow

AbstractThe ablation of cosmic dust entering the atmosphere causes the formation of an atomic potassium (K) layer in the mesopause region. It can be studied via resonance fluorescence from the K(D1) line at 769.9 nm, stimulated by sunlight or a laser. In addition, the faint emission from a chemiluminescent cycle involving ozone and oxygen atoms has been observed with a nocturnal mean intensity of about 1 Rayleigh. In this study, the K nightglow is investigated in much greater detail, using 2,299 high‐resolution spectra taken with the astronomical echelle spectrograph Ultraviolet and Visual Echelle Spectrograph at Cerro Paranal in Chile (24.6°S) between 2000 and 2014. The seasonal variation is dominated by a maximum in June. During the night, the highest intensities are found close to sunrise. Moreover, there is a clear negative correlation with solar activity. These variations are very different from those of the well‐studied sodium (Na) nightglow. The K nightglow at Cerro Paranal was also simulated with the Whole Atmosphere Community Climate Model including K chemistry. The observed and modeled climatologies do not match well, largely because of unreliable Whole Atmosphere Community Climate Model ozone densities. Satellite‐based profile retrievals for ozone and temperature from Sounding of the Atmosphere using Broadband Emission Radiometry and K from Optical Spectrograph and Infrared Imaging System were then used to simulate the K nightglow and to derive the quantum yield of the K(D) emission with respect to the reaction of K with ozone. Considering that the obscured K(D2) line is expected on theoretical grounds to be 1.67 times brighter than K(D1), we find about 30% for this quantum yield, which is much higher than for Na(D) emission.

Sensitivity of aerosol radiative forcing to various aerosol parameters over the Bay of Bengal

In the shortwave solar spectrum ( $$0.25{-}5~\upmu \hbox {m}$$ ), radiation is affected by the change in various aerosol properties and also by water vapour and other gas molecules. The presence of a variety of aerosols over the Bay of Bengal (BoB) during different seasons results in a change in aerosol properties, including the aerosol layer height. The BoB is an integral part of the Indian monsoon, and hence it is essential to understand the radiation budget over the BoB. The sensitivity of the aerosol forcing due to the changes in aerosol properties and other parameters has been studied using the Santa Barbara discrete ordinates radiative transfer model. The aerosol forcing at the top of the atmosphere was found to depend on the aerosol loading (aerosol optical depth), aerosol type (single scattering albedo) and the angular distribution of the scattered radiation (asymmetry parameter). The analysis also shows the presence of a relationship between aerosol layer height and the total amount of water vapour present in the atmosphere. The present study highlights the need for better retrievals of vertical aerosol distribution and water vapour profiles for a better understanding of the role of aerosols in the climate.

Solar Occultation FTIR Spectrometry at Mars for Trace Gas Detection: A Sensitivity Study

AbstractA sensitivity study has been performed to estimate detection limits of various atmospheric trace gases achievable by a Mars‐orbiting solar occultation Fourier transform infrared (FTIR) spectrometer. This was accomplished by first computing realistic limb transmittance spectra based on a model (T, P, VMR, and dust profiles) of the Mars atmosphere and adding appropriate noise and systematic errors based on assumed instrument design/configuration/performance. We then performed spectral fits to the resulting synthetic spectra to derive slant column abundances and their uncertainties. A profile retrieval was performed to infer limits of detection. This methodology was applied to a Mars‐orbiting FTIR solar occultation spectrometer covering the 850–4,300 cm−1 spectral region at 0.025‐cm−1 resolution. We conclude that most gases can be retrieved with a single‐occultation sensitivity of 20–100 ppt. But this sensitivity varies considerably with the dust loading, especially for gases whose strongest absorption bands are toward higher wavenumbers where scattering is large. We conclude that for CH4, the ν4 band centered at 1,305 cm−1, despite being more than 2 times weaker than the ν3 band centered at 3,015 cm−1, offers better sensitivity due to its close spectral proximity to the dust extinction minimum. We also conclude that for the purpose of CH4 detection, a high‐resolution (0.025 cm−1) broadband instrument would have a substantial advantage over a medium‐resolution (0.15 cm−1) instrument, despite the latter having a much larger signal‐to‐noise ratio.

Physical Evaluation of GPM DPR Single- and Dual-Wavelength Algorithms.

A physical evaluation of the rain profiling retrieval algorithms for the Dual-Frequency Precipitation Radar (DPR) on board the Global Precipitation Measurement (GPM) Core Observatory satellite is carried out by applying them to the hydrometeor profiles generated from measured raindrop size distributions (DSD). The DSD-simulated radar profiles are used as input to the algorithms, and their estimates of hydrometeors' parameters are compared with the same quantities derived directly from the DSD data (or truth). The retrieval accuracy is assessed by the degree to which the estimates agree with the truth. To check the validity and robustness of the retrievals, the profiles are constructed for cases ranging from fully correlated (or uniform) to totally uncorrelated DSDs along the columns. Investigation into the sensitivity of the retrieval results to the model assumptions is made to characterize retrieval uncertainties and identify error sources. Comparisons between the single- and dual-wavelength algorithm performance are carried out with either a single- or dual-wavelength constraint of the path integral or differential path integral attenuation. The results suggest that the DPR dual-wavelength algorithm generally provides accurate range-profiled estimates of rainfall rate and mass-weighted diameter with the dual-wavelength estimates superior in accuracy to those from the single-wavelength retrievals.

Improvements to the AERIoe Thermodynamic Profile Retrieval Algorithm

Temperature and humidity profiles in the atmospheric boundary layer (i.e., from the surface to 3 km) can be retrieved from ground-based spectral infrared observations made by the atmospheric emitted radiance interferometer (AERI) at high temporal and moderate vertical resolution. However, the retrieval is an ill-posed problem, and thus there are multiple thermodynamic solutions that might satisfy the observed radiances. Previous work developed a physical-iterative method called AERIoe that retrieved temperature and water vapor mixing ratio profiles from these radiance observations in both clear and cloudy conditions. The AERIoe algorithm was modified to enforce two physical constraints, namely that the derived relative humidity must be less than 100% and that the potential temperature must be monotonically increasing with height above some thin potentially subadiabatic layer after each iteration. Furthermore, additional observations including in situ surface meteorology, numerical weather prediction model output, microwave brightness temperatures, and partial profiles of water vapor from a Raman lidar were incorporated into the observation vector of the retrieval along with the infrared radiance observations. The addition of these new observations markedly improved the accuracy of the temperature profiles, especially above 2 km, and the water vapor profiles relative to radiosondes. These improvements are seen using cases from the tropics, mid-latitudes, and Arctic.

Algorithm for supersonic gas jet density profile retrieval from interferometric measurement.

A novel algorithm developed for supersonic gas jet profile retrieval from interferometric measurement is presented. The algorithm uses the Fourier transform method for the phase map restoration and method based on radial profile approximation by a set of hyper-Gaussian functions and their forward Abel transform for 3D gas density profile restoration. The numerical algorithm of the 3D gas density profile restoration based on expansion of the density radial distribution by a basis of hyper-Gaussian functions is compared with algorithms of the inverse Abel transform. Examining accuracy of the algorithms shows that the developed approach is more stable than the inverse Abel transform, and, in the case of axisymmetric objects like supersonic gas jets, it provides higher accuracy. The developed technique was applied for studying the density profile of the pulsed nitrogen supersonic jet produced using a de'Laval nozzle with an exit diameter of 1.5mm. It is shown that the radial density distributions at distances of 10-700μm behind the nozzle exit have a hyper-Gaussian-like form with sharp boundaries and a jet top of ∼0.8 mm length, where gas density is about 5.5·1018 cm-3 and varies by no more than 10%.