On the Challenges of Tomography Retrievals of a 2D Water Vapor Field Using Ground-Based Microwave Radiometers: An Observation System Simulation Experiment

2015 ◽  
Vol 32 (1) ◽  
pp. 116-130 ◽  
Author(s):  
Véronique Meunier ◽  
David D. Turner ◽  
Pavlos Kollias
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
Turbulent Boundary Layer ◽  
Covariance Matrix ◽  
A Priori ◽  
Simulated Data ◽  
Optimal Estimation ◽  
Estimation Algorithm ◽  
Observation System ◽  
Microwave Radiometers

AbstractTwo-dimensional water vapor fields were retrieved by simulated measurements from multiple ground-based microwave radiometers using a tomographic approach. The goal of this paper was to investigate how the various aspects of the instrument setup (number and spacing of elevation angles and of instruments, number of frequencies, etc.) affected the quality of the retrieved field. This was done for two simulated atmospheric water vapor fields: 1) an exaggerated turbulent boundary layer and 2) a simplified water vapor front. An optimal estimation algorithm was used to obtain the tomographic field from the microwave radiometers and to evaluate the fidelity and information content of this retrieved field.While the retrieval of the simplified front was reasonably successful, the retrieval could not reproduce the details of the turbulent boundary layer field even using up to nine instruments and 25 elevation angles. In addition, the vertical profile of the variability of the water vapor field could not be captured. An additional set of tests was performed using simulated data from a Raman lidar. Even with the detailed lidar measurements, the retrieval did not succeed except when the lidar data were used to define the a priori covariance matrix. This suggests that the main limitation to obtaining fine structures in a retrieved field using tomographic retrievals is the definition of the a priori covariance matrix.

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

2019 ◽  
Vol 12 (7) ◽  
pp. 3943-3961 ◽  
Author(s):  
Ali Jalali ◽  
Shannon Hicks-Jalali ◽  
Robert J. Sica ◽  
Alexander Haefele ◽  
Thomas von Clarmann
Keyword(s):  
Water Vapor ◽  
A Priori ◽  
Estimation Method ◽  
Optimal Estimation ◽  
Mixing Ratio ◽  
A Priori Information ◽  
Fine Grid ◽  
Large Power ◽  
Priori Information ◽  
Water Vapor Mixing Ratio

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.

scholarly journals Retrieval of temperature and water vapor profiles from radio occultation refractivity and bending angle measurements using an Optimal Estimation approach: a simulation study

2005 ◽  
Vol 5 (6) ◽  
pp. 1665-1677 ◽  
Author(s):  
A. von Engeln ◽  
G. Nedoluha
Keyword(s):  
Water Vapor ◽  
Radio Occultation ◽  
A Priori ◽  
Estimation Method ◽  
Lower Troposphere ◽  
Optimal Estimation ◽  
Pronounced Difference ◽  
Bending Angle ◽  
Advantages And Disadvantages ◽  
The Impact

Abstract. The Optimal Estimation Method is used to retrieve temperature and water vapor profiles from simulated radio occultation measurements in order to assess how different retrieval schemes may affect the assimilation of this data. High resolution ECMWF global fields are used by a state-of-the-art radio occultation simulator to provide quasi-realistic bending angle and refractivity profiles. Both types of profiles are used in the retrieval process to assess their advantages and disadvantages. The impact of the GPS measurement is expressed as an improvement over the a priori knowledge (taken from a 24h old analysis). Large improvements are found for temperature in the upper troposphere and lower stratosphere. Only very small improvements are found in the lower troposphere, where water vapor is present. Water vapor improvements are only significant between about 1 km to 7 km. No pronounced difference is found between retrievals based upon bending angles or refractivity. Results are compared to idealized retrievals, where the atmosphere is spherically symmetric and instrument noise is not included. Comparing idealized to quasi-realistic calculations shows that the main impact of a ray tracing algorithm can be expected for low latitude water vapor, where the horizontal variability is high. We also address the effect of altitude correlations in the temperature and water vapor. Overall, we find that water vapor and temperature retrievals using bending angle profiles are more CPU intensive than refractivity profiles, but that they do not provide significantly better results.

scholarly journals Use of a Maximum Entropy Method as a Regularization Technique during the Retrieval of Trace Gas Profiles from Limb Sounding Measurements

2006 ◽  
Vol 23 (12) ◽  
pp. 1657-1667 ◽  
Author(s):  
J. Steinwagner ◽  
G. Schwarz ◽  
S. Hilgers
Keyword(s):  
Maximum Entropy ◽  
Random Noise ◽  
A Priori ◽  
Michelson Interferometer ◽  
Simulated Data ◽  
Optimal Estimation ◽  
Initial Guess ◽  
Entropy Method ◽  
Trace Gas ◽  
Regularization Techniques

Abstract The retrieval of trace gas profiles from radiance measurements of limb sounding instruments represents an inverse problem: vertical profiles of mixing ratios have to be extracted from sequences of horizontally measured radiances recorded by a spectrometer. Typically, these retrievals are plagued by random noise and systematic errors, necessitating the use of regularization techniques during inversion calculations. In the following, the use of selected maximum entropy operators as a regularization tool is discussed and their performance with conventional optimal estimation and Tikhonov-type regularization techniques is compared. The main gain with the proposed maximum entropy operators is that no a priori knowledge is needed; a reasonable initial guess profile is fully sufficient. The approach is verified by using simulated data of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument, an infrared Fourier transform spectrometer flown on the European Envisat mission.

Joint probability density analysis of the structure and dynamics of the vorticity field of a turbulent boundary layer

1998 ◽  
Vol 367 ◽  
pp. 291-328 ◽  
Author(s):  
LAWRENCE ONG ◽  
JAMES M. WALLACE
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Probability Density ◽  
Velocity Gradient ◽  
Joint Probability ◽  
Simulated Data ◽  
Wall Region ◽  
Rate Of Increase ◽  
Density Analysis ◽  
Joint Probability Density

An experimental study of a turbulent boundary layer at Rθ≈1070 and Rτ≈543 was conducted. Detailed measurements of the velocity vector and the velocity gradient tensor within the near-wall region were performed at various distances from the wall, ranging from approximately y+=14 to y+=89. The measured mean statistical properties of the fluctuating velocity and vorticity components agree well with previous experimental and numerically simulated data. These boundary layer measurements were used in a joint probability density analysis of the various component vorticity and vorticity–velocity gradient products that appear in the instantaneous vorticity and enstrophy transport equations. The vorticity filaments that contribute most to the vorticity covariance Ω[bar]xΩ [bar]y in this region were found to be oriented downstream with angles of inclination to the wall, when projected on the streamwise (x, y)-plane, that decrease with distance moving from the buffer to the logarithmic layer. When projected on the planview (x, z)- and cross-stream (y, z)-planes, the vorticity filaments that most contribute to the vorticity covariances Ω [bar]xΩ [bar]z and Ω [bar]yΩ [bar]z have angles of inclination to the z-ordinate axis that increase with distance from it. All the elements of the ΩiΩj ∂Ui/∂xj term in the enstrophy transport equation, i.e. the term that describes the rate of increase or decrease of the enstrophy by vorticity filament stretching or compression by the strain-rate field, have been examined. On balance, the average stretching of the vorticity filaments is greater than compression at all y+ locations examined here. However, some individual velocity gradient components compress the vorticity filaments, on average, more than they stretch them.

scholarly journals A new scheme for sulphur dioxide retrieval from IASI measurements: application to the Eyjafjallajökull eruption of April and May 2010

2012 ◽  
Vol 12 (23) ◽  
pp. 11417-11434 ◽  
Author(s):  
E. Carboni ◽  
R. Grainger ◽  
J. Walker ◽  
A. Dudhia ◽  
R. Siddans
Keyword(s):  
Covariance Matrix ◽  
Sulphur Dioxide ◽  
Meteorological Data ◽  
Optimal Estimation ◽  
Estimation Algorithm ◽  
Phase Iii ◽  
Absorption Bands ◽  
Error Covariance Matrix ◽  
Error Covariance ◽  
Order Of Magnitude

Abstract. A new optimal estimation algorithm for the retrieval of sulphur dioxide (SO2) has been developed for the Infrared Atmospheric Sounding Interferometer (IASI) using the channels between 1000–1200 and 1300–1410 cm−1. These regions include the two SO2 absorption bands centred at about 8.7 and 7.3 μm (the ν1 and ν3 bands respectively). The retrieval assumes a Gaussian SO2 profile and returns the SO2 column amount in Dobson units and the altitude of the plume in millibars (mb). Forward modelled spectra (against which the measurements are compared) are based on the Radiative Transfer for TOVS (RTTOV) code. In our implementation RTTOV uses atmospheric profiles from European Centre for Medium-Range Weather Forecasts (ECMWF) meteorological data. The retrieval includes a comprehensive error budget for every pixel derived from an error covariance matrix that is based on the SO2-free climatology of the differences between the IASI and forward modelled spectra. The IASI forward model includes the ability to simulate a cloud or ash layer in the atmosphere. This feature is used to illustrate that: (1) the SO2 retrieval is not affected by underlying cloud but is affected if the SO2 is within or below a cloud layer; (2) it is possible to discern if ash (or other atmospheric constituents not considered in the error covariance matrix) affects the retrieval using quality control based on the fit of the measured spectrum by the forward modelled spectrum. In this work, the algorithm is applied to follow the behaviour of SO2 plumes from the Eyjafjallajökull eruption during April and May 2010. From 14 April to 4 May (during Phase I and II of the eruption) the total amount of SO2 present in the atmosphere, estimated by IASI measurements, is generally below 0.02 Tg. During the last part of the eruption (Phase III) the values are an order of magnitude higher, with a maximum of 0.18 Tg measured on the afternoon of 7 May.

scholarly journals Carbon monoxide mixing ratios over Oklahoma between 2002 and 2009 retrieved from Atmospheric Emitted Radiance Interferometer spectra

2010 ◽  
Vol 3 (2) ◽  
pp. 1263-1301 ◽  
Author(s):  
L. Yurganov ◽  
W. McMillan ◽  
C. Wilson ◽  
M. Fischer ◽  
S. Biraud
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
Great Plains ◽  
A Priori ◽  
Microwave Radiometer ◽  
Precipitable Water ◽  
Diurnal Cycles ◽  
Mixing Ratios ◽  
True Profile

Abstract. CO mixing ratios weighted over the bottom 2-km thick atmospheric layer between 2002 and 2009 were retrieved from downwelling infrared (IR) radiance spectra of the clear sky measured by a zenith-viewing Atmospheric Emitted Radiance Interferometer (AERI) deployed at the Southern Great Plains (SGP) observatory of the Atmospheric Radiation Measurements (ARM) Program near Lamont, Oklahoma. A version of the algorithm proposed by He at al. (2001) was significantly improved and validated. Essentially, the new algorithm retrieves a CO mixing ratio that is determined by the convolution of the a priori profile (assumed to be constant with altitude), the true profile, and the averaging kernel which maximizes near the surface. Approximately 70% of the CO signal comes from the boundary layer and the remaining 30% come from the lower part of the free troposphere. Archived temperature and water vapor profiles retrieved from the same AERI spectra through automated ARM processing were used as input data for the CO retrievals. We found the archived water vapor profiles required additional constraint using SGP Microwave Radiometer retrievals of total precipitable water vapor. Additionally, a correction for scattered solar light was developed. The retrieved CO was validated using simultaneous independently measured CO profiles. An aircraft supplied in situ CO measurements at altitudes up to 4572 m above sea level once or twice a week between March 2006 and December 2008. The aircraft measurements were supplemented with ground-based CO measurements at the SGP and retrievals from the Atmospheric IR Sounder (AIRS) above 5 km to create full tropospheric CO profiles. Comparison of the convolved profiles to the AERI CO retrievals found a squared correlation coefficient of 0.57, a standard deviation of ±11.7 ppbv, a bias of 16 ppbv, and a slope of 0.92. Averaged seasonal and diurnal cycles measured by AERI are compared with those measured continuously in situ at the SGP in the boundary layer. Monthly mean CO values measured by AERI between 2002 and 2009 are compared with those measured by AIRS over North America, the Northern Hemisphere mid-latitudes, and over the tropics.

scholarly journals Daytime HONO, NO<sub>2</sub> and aerosol distributions from MAX-DOAS observations in Melbourne

2018 ◽  
Author(s):  
Robert G. Ryan ◽  
Steve Rhodes ◽  
Matthew Tully ◽  
Stephen Wilson ◽  
Nicholas Jones ◽  
...  
Keyword(s):  
Nitrogen Oxides ◽  
A Priori ◽  
Optimal Estimation ◽  
Estimation Algorithm ◽  
Oxidative Capacity ◽  
Urban Environments ◽  
Vertical Profiles ◽  
Pollution Levels ◽  
The World ◽  
Gas Measurements

Abstract. Nitrogen oxides produced by high temperature combustion are prevalent in urban environments and toxic, contributing to a significant health burden. The chemistry of nitrogen oxides such as NO2 and HONO in pollution are important for hydroxyl radical production and overall oxidative capacity in urban environments, however current mechanisms cannot explain high daytime levels of HONO observed in many urban and rural locations around the world. Here we present HONO, NO2 and aerosol extinction vertical distributions retrieved from MAX-DOAS measurements in suburban Melbourne, which are the first MAX-DOAS results from Australia. Using the optimal estimation algorithm HEIPRO we show that vertical profiles for NO2 and HONO can be calculated with low dependence on the retrieval forward model and a priori parameters, despite a lack of independent co-located aerosol or trace gas measurements. Between December 2016 and April 2017 average peak NO2 values of 8 ± 2 ppb indicated moderate traffic pollution levels, and high daytime peak values of HONO were frequently detected, averaging 220 ± 30 ppt in the middle of the day. HONO levels measured in Melbourne were typically lower than those recorded in the morning in other places around the world, indicating minimal overnight accumulation, but peaked in the middle of the day to be commensurate with midday concentrations in locations with much higher NO2 pollution. Regular midday peaks in the diurnal cycle of HONO surface concentrations have only previously been reported in rural locations. The HONO measured represents an OH radical source in the middle of the day in Melbourne up to ten times stronger than from ozone photolysis. The dependence of the high HONO levels on time since rainfall, combined with the observed diurnal and vertical profiles, provide evidence for a strong photo-activated and ground-based daytime HONO source.

scholarly journals BOREAS – a new MAX-DOAS profile retrieval algorithm for aerosols and trace gases

2018 ◽  
Vol 11 (12) ◽  
pp. 6833-6859 ◽  
Author(s):  
Tim Bösch ◽  
Vladimir Rozanov ◽  
Andreas Richter ◽  
Enno Peters ◽  
Alexei Rozanov ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Trace Gases ◽  
A Priori ◽  
Estimation Method ◽  
Optimal Estimation ◽  
Radiative Transfer Model ◽  
Retrieval Algorithm ◽  
Transfer Model ◽  
Night Time ◽  
Near Surface

Abstract. We present a new MAX-DOAS profiling algorithm for aerosols and trace gases, BOREAS, which utilizes an iterative solution method including Tikhonov regularization and the optimal estimation technique. The aerosol profile retrieval is based on a novel approach in which the absorption depth of O4 is directly used in order to retrieve extinction coefficient profiles instead of the commonly used perturbation theory method. The retrieval of trace gases is done with the frequently used optimal estimation method but significant improvements are presented on how to deal with wrongly weighted a priori constraints and for scenarios in which the a priori profile is inaccurate. Performance tests are separated into two parts. First, we address the general sensitivity of the retrieval to the example of synthetic data calculated with the radiative transfer model SCIATRAN. In the second part of the study, we demonstrate BOREAS profiling accuracy by validating the results with the help of ancillary measurements carried out during the CINDI-2 campaign in Cabauw, the Netherlands, in 2016. The synthetic sensitivity tests indicate that the regularization between measurement and a priori constraints is insufficient when knowledge of the true state of the atmosphere is poor. We demonstrate a priori pre-scaling and extensive regularization tests as a tool for the optimization of retrieved profiles. The comparison of retrieval results with in situ, ceilometer, NO2 lidar, sonde and long-path DOAS measurements during the CINDI-2 campaign always shows high correlations with coefficients greater than 0.75. The largest differences can be found in the morning hours, when the planetary boundary layer is not yet fully developed and the concentration of trace gases and aerosol, as a result of a low night-time boundary layer having formed, is focused in a shallow, near-surface layer.

scholarly journals Comparison of Optimal Estimation HDO/H2O Retrievals from AIRS with ORACLES measurements

2019 ◽  
Author(s):  
Robert L. Herman ◽  
John Worden ◽  
David Noone ◽  
Dean Henze ◽  
Kevin Bowman ◽  
...  
Keyword(s):  
A Priori ◽  
Lower Troposphere ◽  
Optimal Estimation ◽  
Estimation Algorithm ◽  
Deuterium Content ◽  
Aircraft Measurements ◽  
State University ◽  
Atmospheric Infrared Sounder ◽  
Fractional Deviation ◽  
Oregon State University

Abstract. In this paper we evaluate new retrievals of the deuterium content of water vapor from the Aqua Atmospheric InfraRed Sounder (AIRS) with aircraft measurements of HDO and H2O from the ObseRvations of Aerosols above Clouds and their intEractionS (ORACLES) field mission. Single footprint AIRS radiances are processed with an optimal estimation algorithm that provides a vertical profile of the HDO/H2O ratio, characterized uncertainties, and instrument operators (or averaging kernel matrix). These retrievals are compared to vertical profiles of the HDO/H2O from the Oregon State University Water Isotope Spectrometer for Precipitation and Entrainment Research (WISPER) on the ORACLES NASA P-3B Orion aircraft. Measurements were taken over the Southeast Atlantic Ocean from 31 August to 25 September 2016. HDO/H2O is commonly reported in delta-D notation, which is the fractional deviation of the HDO/H2O ratio from the standard reference ratio. For collocated measurements, the satellite operator (averaging kernels and a priori constraint) is applied to the aircraft profile measurements. We find that AIRS delta-D bias relative to the aircraft is well within the estimated measurement uncertainty. In the lower troposphere, 1000 to 800 hPa, AIRS delta-D bias is −6.6‰ and the Root Mean Square (RMS) deviation is 20.9‰, consistent with the calculated uncertainty of 19.1‰. In the mid-troposphere, 800 to 500 hPa, AIRS delta-D bias is 6.8‰ and RMS 44.9‰, comparable to the calculated uncertainty of 25.8‰.

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