Vertical Profiles Of Water Vapor Research Articles

WINTERTIME PROFILES OF TEMPERATURE, CO2, AND WATER VAPOR AND LOCAL COLD-AIR SUBSIDENCE IN A RESIDENTIAL AREA

In this study we focused on the relationships between the vertical profiles of scalar within and above a suburban canopy and the cold-air subsidence locally generated within the canopy. The results were derived from the wintertime field measurements of the vertical profiles of CO2, air temperature, water vapor, and turbulent flows, which were conducted in a residential area (the mean height of canopy is 7.3 m) of Tokyo, Japan. Under stably stratified conditions, the CO2 concentration above the canopy decreased with height, while that within the canopy kept almost same level. This indicates that the CO2 emitted from the houses accumulated within the canopy. Such behavior was not found in H2O profile. The vertical profile of air temperature and observations on the surface temperature using a thermal infrared camera suggested that the cold air generated at roof level moved down to the ground level. The effect of ‘cold air subsidence’ within the canopy is the most plausible reason for the nighttime vertical profiles of CO2 and H2O.

Retrieval of Optical Thickness and Effective Particle Radius of Thin Low-Level Water Clouds using the Split Window of Meteosat-8

We developed a method to retrieve the optical thickness (τ) and effective particle radius (re) of water clouds using the split-window channels and the 8.7-µm channel of Meteosat-8. Valid ranges are approximately from 1 to 9 for τ and smaller than 18 µm for re. Water clouds were first identified using 8.7-µm and 11-µm data. The retrieval used the brightness temperature (TBB) and brightness temperature difference (BTD) between the split windows, as computed with the radiation code RSTAR5b for various properties of water clouds and vertical profiles of temperature and water vapor. Arch-shaped curves in the TBB and BTD domains resembled those for ice clouds, depending on τ and re. The retrieved cloud parameters were then compared to those retrieved by the solar reflection method, which uses the 0.6-, 3.9-, and 11-µm channels of Meteosat-8. Comparison of the two methods revealed that the split-window technique could capture spatial features for both τ and re, showing some agreement with re for the solar reflection but needing more improvement for τ in the current case study.

Analysis of atmospheric and ionospheric structures using the GPS/MET and CHAMP radio occultation database: a methodological review

Since 1995, the global positioning system (GPS) has been exploited by the means of the radio occultation (RO) method to obtain the vertical profiles of refractivity, temperature, pressure, and water vapor in the neutral atmosphere and electron density in the ionosphere. Applying the RO method to the study of the Earth’s atmosphere was demonstrated for the first time with the GPS/MET experiment. Since then, several satellites with GPS receivers, suitable for RO experiments, have been launched including Oersted, SUNSAT, CHAMP, SAC-C, and GRACE. Future RO investigations that are planned now include FORMOSAT3/COSMIC and Terra-SAR missions. New elements in the RO technology are required to meet the goals of improving the accuracy and broadening the potential of the RO method. In this paper, a methodological review of RO investigations is presented to emphasize new directions in applying the RO method: measuring the vertical gradients of the refractivity in the atmosphere and electron density in the lower ionosphere, determination of the temperature regime in the upper stratosphere, investigation of the internal wave activity in the atmosphere, and study of the ionospheric disturbances on a global scale. These new directions may be relevant for investigating the relationships between processes in the atmosphere and mesosphere, the study of thermal regimes in the intermediate heights of the upper stratosphere—lower mesosphere, and the analysis of the influence of the space weather phenomena on the lower ionosphere.

Analysis of Relative Humidity Sensors at the WMO Radiosonde Intercomparison Experiment in Brazil

Abstract The quality of the vertical distribution measurements of humidity in the atmosphere is very important in meteorology due to the crucial role that water vapor plays in the earth’s energy budget. The radiosonde is the humidity measurement device that provides the best vertical resolution. Also, radiosondes are the operational devices that are used to measure the vertical profile of atmospheric water vapor. The World Meteorological Organization (WMO) has carried out several intercomparison experiments at different climatic zones in order to identify the differences between the available commercial sensors. This article presents the results of an experiment that was carried out in Brazil in 2001 in which major commercial radiosonde manufacturers [e.g., Graw Radiosondes GmbH & Co., KG (Germany); MODEM (France); InterMet Systems (United States); Sippican, Inc. (United States); and Vaisala (Finland)] were involved. One of the main goals of this experiment was to evaluate the performance of the different humidity sensors in a tropical region. This evaluation was performed for different atmospheric layers and distinct periods of the day. It also considers the computation of the integrated water vapor (IWV). The results showed that the humidity measurements achieved by the different sensors were quite similar in the low troposphere (the bias median value regarding the RS80 was around 1.8%) and were quite dispersed in the superior layers (the median rms regarding the RS80 was around 14.9%).

Atmospheric temperature sounding on Mars, and the climate sounder on the 2005 reconnaissance orbiter

Detailed measurements of the vertical profiles of atmospheric temperature, water vapour, dust and condensates in the Martian atmosphere are needed to characterize the present-day Martian climate and to understand the intricately related processes upon which it depends. Among the most important of these are accurate and extensive temperature measurements. Progress to date, key problems still to be addressed and upcoming new approaches to the measurement task are briefly reviewed, and expectations for the Mars Climate Sounder experiment on the 2005 Mars Reconnaissance Orbiter are described. Some even more advanced methods for temperature, humidity and condensate sounding in the decade beyond MCS/MRO, and promising approaches to achieving these are also considered.

Remote Sensing of Cirrus Optical and Microphysical Properties From Ground-Based Infrared Radiometric Measurements—Part II: Retrievals From CRYSTAL-FACE Measurements

The ground-based infrared radiance measurements acquired on July 14, 20, and 28, 2002 during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers Florida Area Cirrus Experiment (CRYSTAL-FACE) campaign have been used for simultaneously retrieving the optical thickness and effective particle size on the basis of the retrieval algorithm reported in the preceding counterpart of this paper. The corresponding ice water path is derived from the retrieved optical thickness and effective particle size. Specifically, the data used for the retrieval include: 1) the infrared radiance spectrum observed by an atmospheric emitted radiance interferometer at the surface; 2) the sky condition and cloud height determined from a sky imager and a micropulse lidar; and 3) the sounding data for the profiles of temperature, pressure, and relative humidity. For these three case studies, the retrieved cirrus optical thickness, effective particle size, and ice water path are in the range of 0.2-1.5, 18-42 /spl mu/m, and 2-15 g /spl middot/ m/sup -2/, respectively. Furthermore, error analyses show that the retrieval uncertainties of the optical thickness and effective particle size are less than 15% if the uncertainty of water vapor vertical profile is within 5%. The retrieval errors are within 10% if the uncertainty of cloud temperature is within 7 K.

A Sensitivity Study of Regional Climate Simulation to Convective Parameterization Schemes for the 1998 East Asian Summer Monsoon

A sensitivity study of regional climate simulations over East Asia to three convective parameterization schemes (CPSs), the Grell, Kain-Fritsch, and Anthes-Kuo schemes, was conducted using a regional climate model, SNURCM with a 60 km horizontal resolution. Nesting experiments with a 20 km horizontal resolution were also performed in order to investigate the sensitivity of CPSs to horizontal resolution. In all runs with 60 km horizontal resolution, seasonal mean precipitation, low-and upper-level wind, and temporal and spatial variation of monsoon fronts over East Asia were simulated with a certain difference between CPSs. With higher horizontal resolution, all the schemes were likely to increase slightly the total precipitation amount and the precipitation intensity due to the increase of convective rain, but differences in the spatial distribution of precipitation between CPSs were relatively small. There were prominent differences in vertical profiles of wind, temperature, water vapor, and atmospheric hydrometeors amongst CPSs, although the vertical structures of those in GR and KF runs were similar to each other. Sensitivities of the vertical structure of most atmospheric variables to horizontal resolution were relatively smaller than they were to CPSs except for cloud water. Surface energy fluxes, in particular incoming solar radiation and latent heat between CPSs were different to each other because of differences in the vertical structure of atmospheric hydrometeors. Diurnal variation of precipitation was also sensitive to not only CPSs but also horizontal resolution. In this study, the AK scheme reproduced the East Asian Summer precipitation properly because of intrinsic triggering assumptions and the spectral nudging technique. The GR scheme was on the whole suitable to simulate the general features of East Asian summer monsoon in 1998 such as heavy precipitation, atmospheric vertical structure, and temporal evolution of the East Asian Summer monsoon. The KF scheme had the worst statistics in precipitation simulation due to large convective precipitation portion. Consequently, the AK and GR schemes simulated more reasonably the 1998 summer flood over East Asia which was affected by anomalous large-scale conditions.

Aerosol Characterization and Direct Radiative Forcing Assessment over the Ocean. Part I: Methodology and Sensitivity Analysis

Abstract A method based on the synergistic use of low earth orbit (LEO) and geostationary earth orbit (GEO) satellite data for aerosol-type characterization, as well as aerosol optical thickness (AOT) retrieval and monitoring over the ocean, is presented. These properties are used for the estimation of the direct shortwave aerosol radiative forcing at the top of the atmosphere. The synergy serves the purpose of monitoring aerosol events at the GEO time and space scales while maintaining the accuracy level achieved with LEO instruments. Aerosol optical properties representative of the atmospheric conditions are obtained from the inversion of high-spectral-resolution measurements from the Global Ozone Monitoring Experiment (GOME). The aerosol optical properties are input for radiative transfer calculations for the retrieval of the AOT from GEO visible broadband measurements, avoiding the use of fixed aerosol models available in the literature. The retrieved effective aerosol optical properties represent an essential component for the aerosol radiative forcing assessment. A sensitivity analysis is also presented to quantify the effects that changes on the aerosol model may have on modeled results of spectral reflectance, AOT, and direct shortwave aerosol radiative forcing at the top of the atmosphere. The impact on modeled values of the physical assumptions on surface reflectance and vertical profiles of ozone and water vapor are analyzed. Results show that the aerosol model is the main factor influencing the investigated radiative variables. Results of the application of the method to several significant aerosol events, as well as their validation, are presented in a companion paper.

Single frequency processing of atmospheric radio occultations

Tracking of the radio signals broadcast by the Global Positioning System (GPS) satellites as they are occulted from a GPS receiver by the Earth's atmosphere can provide high resolution vertical profiles of atmospheric refractivity, temperature and water vapour. Most implementations of this radio occultation technique use two GPS frequencies to correct for ionospheric effects. However, during most soundings, one of the frequencies is degraded by the introduction of the so-called Anti-Spoofing (AS) encryption mode. A retrieval method is discussed in this work for periods when only one of the two frequency signals has good quality. This method uses only the frequency with higher signal-to-noise ratio. We illustrate the quality of the atmospheric profiles obtained from such single frequency retrievals using GPS/MET data from the periods where the AS was turned off and the two frequencies were available. The results enable us to ensure the quality of a climate record of thousands of radio occultations collected by GPS/MET during the period with AS encryption, and the data processing of future missions with similar constraints, like IOX, can be performed.

Data Assimilation of GPS Precipitable Water Vapor into the JMA Mesoscale Numerical Weather Prediction Model and its Impact on Rainfall Forecasts

Precipitable water vapor (PWV), which was obtained from the nation wide GPS (Global Positioning System) network over Japan, operated by the Geographical Survey Institute (GSI), was assimilated into the meso data assimilation (DA) system of the Japan Meteorological Agency (JMA). Two different methods were examined; one is an optimum interpolation (OI) method, and the other is a 4-dimensional variational (4D-Var) method. Using the analysis data derived from both systems, a number of forecast experiments for rainfall events in Baiu and summer seasons were carried out using the JMA meso scale numerical weather prediction model (MSM). Remarkable improvements in rainfall forecast were seen in several cases, both for the OI and 4D-Var experiments. A statistical score of the 4D-Var experiments, however, showed that the impact of GPS PWV was almost neutral for rainfall forecast, and no substantial improvements were obtained. One of the reasons might be that GPS sites used for the experiments were too few, and sparsely distributed compared to the rainfall systems. Another reason specific for the 4D-Var is that, although the 4D-Var improved PWV analyses, it sometimes modified vertical profiles of water vapor significantly, which brought about different static stability from the first guess of the model (MSM) or from the observations. These results suggested the importance of correct assimilation of vertical profiles of water vapor.

The Radio Occultation Experiment aboard CHAMP: Operational Data Analysis and Validation of Vertical Atmospheric Profiles

The operational data analysis of the GPS radio occultation experiment aboard the German CHAMP (CHAllenging Minisatellite Payload) satellite mission is described. Continuous Near-Real-Time processing with average time delay of ∼5 hours between measurement and provision of analysis results is demonstrated. A delay of less than 3 hours is reached for individual events. This is made possible by using an operationally operated ground infrastructure, consisting of a polar downlink station, a globally distributed fiducial GPS ground network, a precise orbit determination facility, an automated occultation processing system and an advanced data center (the Information System and Data Center at GFZ, ISDC). The infrastructure was installed within the CHAMP and the German GPS Atmosphere Sounding Project (GASP). More than 120,000 globally distributed occultation measurements were automatically analysed during 2001 and 2002. A set of∼46,000 vertical profiles of refractivity, temperature and water vapor is validated with meteorological analyses from the European Centre for Medium-Range Weather Forecasts (ECMWF) and data from the global radiosonde network. The mean temperature bias in relation to the analyses is less then 0.4 K between 10 and 35 km, the mean deviation of the refractivity is <0.5%. A height dependent standard deviation of ∼1 K at 10 km and ∼2 K at 30 km is observed. This result is confirmed by comparing ∼6,000 CHAMP occultations with corresponding radiosonde measurements. A negative bias of the refractivity in relation to the analyses up to ∼5% in the Tropics is found in the lower troposphere. It corresponds to mean meridional dry biases of the specific humidity up to ∼30%. It is shown, that the application of a heuristic retrieval method, based on the Canonical Transform method and the sliding spectral approach, reduces the refractivity bias on average by a factor of ∼2. The corresponding bias in the specific humidity is reduced by a factor of ∼3. In mid-latitudes almost no more refractivity bias out of the planetary boundary layer is observed. This is shown by a comparison of CHAMP refractivity and water vapor profiles with radiosonde data. More than 50,000 globally distributed electron density profiles were automatically derived during 2001/2002. A validation study including 1,004 comparisons with corresponding ionosonde data yields a bias of 0.18 MHz and 13.4 km for foF2 and hmF2 respectively. The standard deviation is 1.28 MHz (foF2) and 46.8 km (hmF2).

Reason for the Failure of the Simulation of Heavy Rainfall during X-BAIU-01—Importance of a Vertical Profile of Water Vapor for Numerical Simulations—

A heavy rainfall band was observed over southern Kyushu on 23 June 2001. This heavy rainfall was not predicted by a nonhydrostatic model (NHM) that was operated twice a day to support the field experiment of X-BAIU-01. The reason for this failure was examined in comparison with X-BAIU-01 special observation and satellite data. The maritime wind convergence zone was retrieved over the sea southwest of Kyushu Island from NASA QuickSCAT data, before the heavy rainfall system formed. This wind convergence was also found in the initial field of NHM. The lower atmosphere observed by aerosondes was very humid, while that simulated by NHM was considerably drier. The existence of this low-level humid air was also supported by total precipitable water (TPW) data derived from Tropical Rainfall Measuring Mission Microwave Imager (TMI) and Defense Meteorological Satellite Program Special Sensor Microwave/Imager (SSM/I). These comparisons indicate that the fact that the lower atmosphere was drier than it is in reality, was the reason that the NHM failed to simulate the heavy rainfall. This indication was ascertained by humidifying the lower atmosphere of NHM to correspond to the observation (MOD), and applying the four-dimensional variational data-assimilation technique to TMIderived TPW data (4DV). For MOD, the band-shaped rainfall was reproduced successfully. For 4DV, the simulated precipitation intensity was not strong enough to forecast a heavy rainfall, because 4DV could not retrieve the vertical profile of water vapor by using only the TMI-derived TPW data. Humid air concentrated in the lower atmosphere is necessary to induce heavy rainfall over the Baiu frontal zone.

Dry Bias and Variability in Vaisala RS80-H Radiosondes: The ARM Experience

Thousands of comparisons between total precipitable water vapor (PWV) obtained from radiosonde (Vaisala RS80-H) profiles and PWV retrieved from a collocated microwave radiometer (MWR) were made at the Atmospheric Radiation Measurement (ARM) Program's Southern Great Plains Cloud and Radiation Testbed (SGP CART) site in northern Oklahoma from 1994 to 2000. These comparisons show that the RS80-H radiosonde has an approximate 5% dry bias compared to the MWR. This observation is consistent with interpretations of Vaisala RS80 radiosonde data obtained during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). In addition to the dry bias, analysis of the PWV comparisons as well as of data obtained from dual-sonde soundings done at the SGP show that the calibration of the radiosonde humidity measurements varies considerably both when the radiosondes come from different calibration batches and when the radiosondes come from the same calibration batch. This variability can result in peak-to-peak differences between radiosondes of greater than 25% in PWV. Because accurate representation of the vertical profile of water vapor is critical for ARM's science objectives, an empirical method for correcting the radiosonde humidity profiles is developed based on a constant scaling factor. By using an independent set of observations and radiative transfer models to test the correction, it is shown that the constant humidity scaling method appears both to improve the accuracy and reduce the uncertainty of the radiosonde data. The ARM data are also used to examine a different, physically based, correction scheme that was developed recently by scientists from Vaisala and the National Center for Atmospheric Research (NCAR). This scheme, which addresses the dry bias problem as well as other calibration-related problems with the RS80-H sensor, results in excellent agreement between the PWV retrieved from the MWR and integrated from the corrected radiosonde. However, because the physically based correction scheme does not address the apparently random calibration variations observed, it does not reduce the variability either between radiosonde calibration batches or within individual calibration batches.

Large‐scale air mass characteristics observed over the remote tropical Pacific Ocean during March‐April 1999: Results from PEM‐Tropics B field experiment

Eighteen long‐range flights over the Pacific Ocean between 38°S to 20°N and 166°E to 90°W were made by the NASA DC‐8 aircraft during the NASA Pacific Exploratory Mission (PEM) Tropics B conducted from March 6 to April 18, 1999. Two lidar systems were flown on the DC‐8 to remotely measure vertical profiles of ozone (O3), water vapor (H2O), aerosols, and clouds from near the surface to the upper troposphere along their flight track. In situ measurements of a wide range of gases and aerosols were made on the DC‐8 for comprehensive characterization of the air and for correlation with the lidar remote measurements. The transition from northeasterly flow of Northern Hemispheric (NH) air on the northern side of the Intertropical Convergence Zone (ITCZ) to generally easterly flow of Southern Hemispheric (SH) air south of the ITCZ was accompanied by a significant decrease in O3, carbon monoxide, hydrocarbons, and aerosols and an increase in H2O. Trajectory analyses indicate that air north of the ITCZ came from Asia and/or the United States, while the air south of the ITCZ had a long residence time over the Pacific, perhaps originating over South America several weeks earlier. Air south of the South Pacific Convergence Zone (SPCZ) came rapidly from the west originating over Australia or Africa. This air had enhanced O3 and aerosols and an associated decrease in H2O. Average latitudinal and longitudinal distributions of O3 and H2O were constructed from the remote and in situ O3 and H2O data, and these distributions are compared with results from PEM‐Tropics A conducted in August‐October 1996. During PEM‐Tropics B, low O3 air was found in the SH across the entire Pacific Basin at low latitudes. This was in strong contrast to the photochemically enhanced O3 levels found across the central and eastern Pacific low latitudes during PEM‐Tropics A. Nine air mass types were identified for PEM‐Tropics B based on their O3, aerosols, clouds, and potential vorticity characteristics. The data from each flight were binned by altitude according to air mass type, and these results showed the relative observational frequency of the different air masses as a function of altitude in seven regions over the Pacific. The average chemical composition of the major air mass types was determined from in situ measurements in the NH and SH, and these results provided insight into the origin, lifetime, and chemistry of the air in these regions.

Study of atmospheric water in gaseous and. liquid state by using combined elastic-Raman. depolarization lidar

A combined elastic–Raman lidar system based on a tripled Nd:YAG laser is used for the separate detection of elastic backscatter and Raman signals from atmospheric nitrogen, water vapor and liquid water and for their depolarization measurement. Vertical profiles of water-vapor and liquid-water content measured under clear-sky conditions behave differently: inside the boundary layer the ratio of liquid-water to water-vapor Raman backscatters rises with altitude. The depolarization measurements bring additional information about atmospheric scattering. The observed depolarization ratio of the water-vapor Raman signal is about 14%, while for liquid water this ratio varies in the 30–75% range, which exceeds the depolarization of bulk water and is attributed to the water-aerosol effects. Raman contours of water vapor and liquid water are partially overlapped, and bleed-through of liquid-water Raman backscatter leads to enhancement of depolarization of the water-vapor Raman signal. This parameter may be used as a convenient indicator of liquid-water interference in water-vapor measurements.

A Near-Infrared Diode Laser Spectrometer for the In Situ Measurement of Methane and Water Vapor from Stratospheric Balloons

The Spectrometre a Diodes Laser Accordables (SDLA), a balloonborne near-infrared diode laser spectrometer, was developed to provide simultaneous in situ measurements of methane and water vapor in the troposphere and the lower stratosphere. The instrument was flown several times from stratospheric balloons operated by the Centre National d'Etudes Spatiales within the framework of the Third European Stratospheric Experiment on Ozone in 1998–2000. The SDLA is based on a multipass optical cell open to the atmosphere. Two near-infrared telecommunication-type laser diodes are connected with optical fibers to the cell to take in situ absorption spectra of methane (in the 6047 cm−1 spectral region) and water vapor (in the 7181 cm−1 spectral region) at 1-s intervals. Mixing ratios are obtained, with a precision error of within 5%–10%, from a nonlinear fit to the full molecular line shape in conjunction with in situ pressure and temperature measurements. The SDLA is described, and achieved atmospheric methane and water vapor vertical concentration profiles are reported.

Balloon-borne near-infrared diode laser spectroscopy for in situ measurements of atmospheric CH 4 and H 2O

Absorption spectroscopy with near-infrared telecommunication laser diodes is a very convenient technique to measure in situ methane and water vapor in both the troposphere and the lower stratosphere (LS) and thereby to address many topics in the science of the atmosphere. This technique offers a high temporal resolution that ranges from 10 ms to 1 s, a precision error in the concentration retrieval of within a few percents and a dynamic range for the measurements of four orders of magnitude. A balloon-borne near-infrared diode laser spectrometer is described that provides simultaneous in situ methane (in the 1.65-μm region) and water vapor (in the 1.39-μm region) measurements at 1 s intervals. Tropospheric and stratospheric vertical concentration profiles of methane and water vapor are reported.

Ozone and water-vapor measurements by Raman lidar in the planetary boundary layer: error sources and field measurements

A new lidar instrument has been developed to measure tropospheric ozone and water vapor at low altitude. The lidar uses Raman scattering of an UV beam from atmospheric nitrogen, oxygen, and water vapor to retrieve ozone and water-vapor vertical profiles. By numerical simulation we investigate the sensitivity of the method to both atmospheric and device perturbations. The aerosol optical effect in the planetary boundary layer, ozone interference in water-vapor retrieval, statistical error, optical cross talk between Raman-shifted channels, and optical cross talk between an elastically backscattered signal in Raman-shifted signals and an afterpulse effect are studied in detail. In support of the main conclusions of this model study, time series of ozone and water vapor obtained at the Swiss Federal Institute of Technology in Lausanne and during a field campaign in Crete are presented. They are compared with point monitor and balloon sounding measurements for daytime and nighttime conditions.

A Global Determination of Cloud Microphysics with AVHRR Remote Sensing

An algorithm is developed for determining the cloud optical thickness and effective particle radius simultaneously on a global scale using Advanced Very High Resolution Radiometer (AVHRR) multispectral radiance data. In the algorithm, the treatment of thermal radiation in Nakajima and Nakajima is improved by reformulating the thermal emission in the atmospheric layers. At the same time, the lookup table for thermal emission is parameterized in terms of the equivalent water vapor path in order to include the effect of various vertical water vapor profiles. The algorithm is applied to AVHRR radiance data corresponding to reported aircraft and balloon measurements of cloud microphysical parameters. A comparison shows a good agreement between in situ and satellite-retrieved values thus obtained. The algorithm is further applied to 4-month Global Area Coverage data of 1987 to generate global distributions of the cloud optical thickness and effective particle radius for every 0.5 83 0.58 box in a 2608‐608 latitudinal region. Similarities and differences in the global features of the effective particle radius and the optical thickness are found as compared with the previous studies.

Microwave attenuation measurements in satellite-ground links: the potential of spectral analysis for water vapor profiles retrieval

The authors address the problem of estimating vertical profiles of atmospheric water vapor by means of attenuation measurements simultaneously made at different frequencies along a vertical satellite-ground link. The operating frequencies selected are those around the spectral absorption lines of water vapor at 22.235 GHz. A simulation is presented of multifrequency attenuation measurements, based on an atmospheric propagation model and on radiosonde data providing true profiles of temperature, pressure, and water vapor. The results indicate that such multifrequency measurements are correlated to variations of the vertical profiles of water vapor. It is therefore expected that vertical detail of such profiles depends on number and position of the frequencies utilized.