Browsing by Autor "David N. Whiteman"

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Airborne and Ground-Based Measurements Using a High-Performance Raman Lidar
(American Meteorological Society, 2010) David N. Whiteman; Kurt Rush; Scott D. Rabenhorst; Wayne Welch; Martin Cadirola; Gerry McIntire; Felicita Russo; Mariana Adam; D. D. Venable; R. Connell
Abstract A high-performance Raman lidar operating in the UV portion of the spectrum has been used to acquire, for the first time using a single lidar, simultaneous airborne profiles of the water vapor mixing ratio, aerosol backscatter, aerosol extinction, aerosol depolarization and research mode measurements of cloud liquid water, cloud droplet radius, and number density. The Raman Airborne Spectroscopic Lidar (RASL) system was installed in a Beechcraft King Air B200 aircraft and was flown over the mid-Atlantic United States during July–August 2007 at altitudes ranging between 5 and 8 km. During these flights, despite suboptimal laser performance and subaperture use of the telescope, all RASL measurement expectations were met, except that of aerosol extinction. Following the Water Vapor Validation Experiment—Satellite/Sondes (WAVES_2007) field campaign in the summer of 2007, RASL was installed in a mobile trailer for ground-based use during the Measurements of Humidity and Validation Experiment (MOHAVE-II) field campaign held during October 2007 at the Jet Propulsion Laboratory’s Table Mountain Facility in southern California. This ground-based configuration of the lidar hardware is called Atmospheric Lidar for Validation, Interagency Collaboration and Education (ALVICE). During the MOHAVE-II field campaign, during which only nighttime measurements were made, ALVICE demonstrated significant sensitivity to lower-stratospheric water vapor. Numerical simulation and comparisons with a cryogenic frost-point hygrometer are used to demonstrate that a system with the performance characteristics of RASL–ALVICE should indeed be able to quantify water vapor well into the lower stratosphere with extended averaging from an elevated location like Table Mountain. The same design considerations that optimize Raman lidar for airborne use on a small research aircraft are, therefore, shown to yield significant dividends in the quantification of lower-stratospheric water vapor. The MOHAVE-II measurements, along with numerical simulation, were used to determine that the likely reason for the suboptimal airborne aerosol extinction performance during the WAVES_2007 campaign was a misaligned interference filter. With full laser power and a properly tuned interference filter, RASL is shown to be capable of measuring the main water vapor and aerosol parameters with temporal resolutions of between 2 and 45 s and spatial resolutions ranging from 30 to 330 m from a flight altitude of 8 km with precision of generally less than 10%, providing performance that is competitive with some airborne Differential Absorption Lidar (DIAL) water vapor and High Spectral Resolution Lidar (HSRL) aerosol instruments. The use of diode-pumped laser technology would improve the performance of an airborne Raman lidar and permit additional instrumentation to be carried on board a small research aircraft. The combined airborne and ground-based measurements presented here demonstrate a level of versatility in Raman lidar that may be impossible to duplicate with any other single lidar technique.
Breakdown of a Nocturnal Inversion Measured with a Low-Cost Tethersonde System: A High School Student Experiment
(American Meteorological Society, 2022) David N. Whiteman; Kofi Boateng; Sara Harbison; Hadijat Oke; Audrey Rappaport; Monique Watson; Ayomiposi Ajayi; Oluwafisayo Okunuga; Ricardo Forno; Marcos Andrade
Abstract For the past 4 years, four different cohorts of students from the Science and Technology program at Eleanor Roosevelt High School in Greenbelt, Maryland, have performed their senior research projects at the Howard University Beltsville Research Campus in Beltsville, Maryland. The projects have focused generally on the testing and correction of low-cost sensors and development of instrumentation for use in profiling the lower atmosphere. Specifically, we have developed a low-cost tethersonde system and used it to carry aloft a low-cost instrument that measures particulate matter (PM) as well as a standard radiosonde measuring temperature, pressure, and relative humidity. The low-cost PM sensor was found to provide artificially high values of PM under conditions of elevated relative humidity, likely due to the presence of hygroscopic aerosols. Reference measurements of PM were used to develop a correction technique for the low-cost PM sensor. Profiling measurements of temperature and PM during the breakdown of a nocturnal inversion were performed using the tethersonde system on 30 August 2019. The evolution of temperature during the breakdown of the inversion was studied and compared with model forecasts. The attempt to measure PM during the tethersonde experiment was not successful, we believe, due to the packaging of the low-cost sensor. Future cohorts of students from Eleanor Roosevelt High School students will work on improving the instrumentation and measurements shown here as we continue the collaboration between the Howard University Beltsville Campus and the local school system.
CAMPAÑA DE MEDICIONES ATMOSFÉRICAS EN LOS ANDES BOLIVIANOS REALIZADA POR EQUIPO ESTUDIANTIL BOLIVIANO-ESTADOUNIDENSE
(2024) David N. Whiteman; Marcos Andrade; Ricardo Forno; MAMANI-PACO; BLACUTT; René Gutierrez; Decker Guzmán Zabalaga
A student-focused field measurement campaign was held in the vicinity of Mt. Chacaltaya in the Bolivian Andes near the city of La Paz on May 24, 2022. The campaign was part of a program funded by the US Department of State, the main goal of which was to foster cultural and scientific exchange among Bolivian and US students. As part of this exchange, a group of eight Bolivian and four U.S. students worked together to plan and execute measurements which focused on quantifying the flow of particulate matter from the city of La Paz toward the summit of Mt. Chacaltaya, where the world’s highest elevation Global Atmosphere Watch site is located. Measurements were performed at three locations along a canyon that leads toward the summit of Mt. Chacaltaya and is a natural pathway for city-generated pollutants to travel toward the GAW station. The measurements indicated the presence of regular, solarheating-generated, downslope/upslope wind flow that aids the movement of particles near the mountain surface. The development of convection during the afternoon regularly decreased the concentrations measured at the surface and thus complicated the interpretation of particle flows. A novel, low-cost tethersonde apparatus was developed by members of the Laboratory for Atmospheric Physics (LFA) at the Universidad Mayor de San Andres (UM- ´ SA). Use of this tethersonde permitted vertical profiles of winds, temperature, pressure and relative humidity to be acquired thus allowing the investigation of the vertical structure of the transition between downslope and upslope flow. Outside of the measurement campaign, the students engaged in cultural activities together to enjoy local Bolivian sites and get to know each other better. One of the goals of the experiment was to increase interest in the atmospheric sciences among UMSA students. The results of a post-campaign survey indicate that participation in this joint field campaign has increased the number of physics students participating in the activities of the LFA at UMSA
Comment on egusphere-2025-5035
(2026) Arlett Díaz-Zurita; Daniel Pérez-Ramírez; David N. Whiteman; Onel Rodríguez-Navarro; Víctor Manuel Naval-Hernández; Jorge Andrés Muñiz-Rosado; María Soledad Fernández-Carvelo; Jesús Abril-Gago; Ana del Águila; Pablo Ortiz-Amezcua
<strong class="journal-contentHeaderColor">Abstract.</strong> This study presents a hybrid methodology to obtain high temporal resolution calibration constants for water vapour Raman lidar measurements, and posteriorly retrieve high accuracy water vapour mixing ratio profiles. The hybrid method combines correlative measurements of collocated precipitable water vapour and Numerical Weather Prediction data to reconstruct the profile within the incomplete overlap region. The hybrid methodology is applied to the MULHACEN Raman lidar system, which operated at the EARLINET/ACTRIS station of the University of Granada, Spain for the period 2009–2022. The system has been continuously updated to meet EARLINET/ACTRIS requirements for aerosol measurements, but the hybrid method has allowed tracking the impact of these changes on calibration constants for water vapour retrievals, and consequently to exploit water vapour mixing ratio profiles that were previously unavailable. The hybrid method was optimised for the Granada station by selecting Global Navigation Satellite System precipitable water vapour data as the most appropriate due to its better agreement with collocated and simultaneous radiosonde data (coefficient of determination of 0.95). Furthermore, the ERA5 reanalysis model was selected as the most appropriate because of its better temporal and spatial resolution and its accuracy when evaluated against radiosonde data. The advantages of the hybrid methodology were evaluated in comparison to traditional calibration methods such as those based on radiosondes or precipitable water vapour data assuming a constant water vapour mixing ratio in the incomplete overlap region. Although all methods generally provided good calibration constants, the hybrid method presented the best assessments under conditions where atmospheric layers were not well-mixed. Comparison with radiosonde data revealed excellent agreement, with a mean bias of -0.1 ± 0.3 g/kg, a standard deviation of 1.0 ± 0.4 g/kg and a coefficient of determination of 0.87 across the entire period and vertical range (0–6 km agl). The most important result of this study is the ability to continuously evaluate calibration constants in a system that has been changing its configuration over 14 years of operation. This new methodology expanded the dataset from 31 initial cases using collocated radiosondes to more than 2000 values through the hybrid methodology. The posterior application of the hybrid methodology to all MULHACEN measurements enabled the generation of a comprehensive database of water vapour mixing ratio profiles for the entire period 2009–2022. Illustrative cases under different atmospheric conditions are presented to showcase the potential of MULHACEN measurements in monitoring water vapour and to investigate its role in climate dynamics and weather prediction.
Comparison of Tropospheric Emission Spectrometer nadir water vapor retrievals with in situ measurements
(American Geophysical Union, 2008) Mark W. Shephard; R. L. Herman; B. Fisher; Karen Cady‐Pereira; S. A. Clough; Vivienne H. Payne; David N. Whiteman; Joseph Comer; Holger Vömel; Larry M. Miloshevich
Comparisons of Tropospheric Emission Spectrometer (TES) water vapor retrievals with in situ measurements are presented. Global comparisons of TES water vapor retrievals with nighttime National Centers for Environmental Prediction RS90/RS92 radiosondes show a small (<5%) moist bias in TES retrievals in the lower troposphere (standard deviation of ∼20%), increasing to a maximum of ∼15% bias (with standard deviation reaching ∼40%) in the upper troposphere. This moist bias with respect to the sonde bias increases to a maximum of ∼15% in the upper troposphere between ∼300–200 hPa. The standard deviation in this region reaches values of ∼40%. It is important to note that the TES reported water vapor comparison statistics are not weighted by the water vapor layer amounts. Global TES/radiosonde results are comparable with the Atmospheric Infrared Sounder reported unweighted mean of 25% and root‐mean‐square of ∼55%. While such global comparisons help to identify general issues, inherent sampling errors and radiosonde measurement accuracy can limit the degree to which the radiosonde profiles alone can be used to validate satellite retrievals. In order to characterize the agreement of TES with in situ measurements in detail, radiance closure studies were performed using data from the Water Vapor Validation Experiment – Satellites/Sondes campaign from July 2006. Results indicate that estimated systematic errors from the forward model, TES measurements, in situ observations, retrieved temperature profiles, and clouds are likely not large enough to account for radiance differences between TES observations and forward model calculations using in situ profiles as input. Therefore, accurate validation of TES water vapor retrievals requires further campaigns with a larger variety of water vapor measurements that better characterize the atmospheric state within the TES field of view.
Evaluation of AERONET precipitable water vapor versus microwave radiometry, GPS, and radiosondes at ARM sites
(Wiley, 2014) Daniel Pérez‐Ramírez; David N. Whiteman; A. Smirnov; H. Lyamani; B. N. Holben; R. T. Pinker; Marcos Andrade; Lucas Alados‐Arboledas
Abstract In this paper we present comparisons of Aerosol Robotic Network (AERONET) precipitable water vapor ( W ) retrievals from Sun photometers versus radiosonde observations and other ground‐based retrieval techniques such as microwave radiometry (MWR) and GPS. The comparisons make use of the extensive measurements made within the U.S. Department of Energy Atmospheric Radiation Measurement Program (ARM), mainly at their permanent sites located at the Southern Great Plains (Oklahoma, U.S.), Nauru Islands, and Barrow (Alaska, U.S.). These places experience different types of weather which allows the comparison of W under different conditions. Radiosonde and microwave radiometry data were provided by the ARM program while the GPS data were obtained from the SOUMINET network. In general, W obtained by AERONET is lower than those obtained by MWR and GPS by ~6.0–9.0% and ~6.0–8.0%, respectively. The AERONET values are also lower by approximately 5% than those obtained from the numerous balloon‐borne radiosondes launched at the Southern Great Plains. These results point toward a consistent dry bias in the retrievals of W by AERONET of approximately 5–6% and a total estimated uncertainty of 12–15%. Differences with respect to MWR retrievals are a function of solar zenith angle pointing toward a possible bias in the MWR retrievals. Finally, the ability of AERONET precipitable water vapor retrievals to provide long‐term records of W in diverse climate regimes is demonstrated.
Hybrid methodology for optimised water vapour mixing ratio profiles from Raman lidar measurements
(2026) Arlett Díaz-Zurita; Daniel Pérez-Ramírez; David N. Whiteman; Onel Rodríguez-Navarro; Víctor Manuel Naval-Hernández; Jorge Andrés Muñiz-Rosado; María Soledad Fernández-Carvelo; Jesús Abril-Gago; Ana del Águila; Pablo Ortiz-Amezcua
Abstract. This study presents a hybrid methodology to obtain high temporal resolution calibration constants for water vapour Raman lidar measurements, and posteriorly retrieve high accuracy water vapour mixing ratio profiles. The hybrid method combines correlative measurements of collocated precipitable water vapour and Numerical Weather Prediction data to reconstruct the profile within the incomplete overlap region. The hybrid methodology is applied to the MULHACEN Raman lidar system, which operated at the EARLINET/ACTRIS station of the University of Granada, Spain for the period 2009–2022. The system has been continuously updated to meet EARLINET/ACTRIS requirements for aerosol measurements, but the hybrid method has allowed tracking the impact of these changes on calibration constants for water vapour retrievals, and consequently to exploit water vapour mixing ratio profiles that were previously unavailable. The hybrid method was optimised for the Granada station by selecting Global Navigation Satellite System precipitable water vapour data as the most appropriate due to its better agreement with collocated and simultaneous radiosonde data (coefficient of determination of 0.95). Furthermore, the ERA5 reanalysis model was selected as the most appropriate because of its better temporal and spatial resolution and its accuracy when evaluated against radiosonde data. The advantages of the hybrid methodology were evaluated in comparison to traditional calibration methods such as those based on radiosondes or precipitable water vapour data assuming a constant water vapour mixing ratio in the incomplete overlap region. Although all methods generally provided good calibration constants, the hybrid method presented the best assessments under conditions where atmospheric layers were not well-mixed. Comparison with radiosonde data revealed excellent agreement, with a mean bias of -0.1 ± 0.3 g/kg, a standard deviation of 1.0 ± 0.4 g/kg and a coefficient of determination of 0.87 across the entire period and vertical range (0–6 km agl). The most important result of this study is the ability to continuously evaluate calibration constants in a system that has been changing its configuration over 14 years of operation. This new methodology expanded the dataset from 31 initial cases using collocated radiosondes to more than 2000 values through the hybrid methodology. The posterior application of the hybrid methodology to all MULHACEN measurements enabled the generation of a comprehensive database of water vapour mixing ratio profiles for the entire period 2009–2022. Illustrative cases under different atmospheric conditions are presented to showcase the potential of MULHACEN measurements in monitoring water vapour and to investigate its role in climate dynamics and weather prediction.
Integrated Water Vapour (IWV) trend analysis from GNSS and NWP reanalyses: a homogenised long-term analysis over Granada
(2026) V. Hernandez; Arlett Díaz Zurita; Onel Rodríguez Navarro; Jorge Andrés Muñiz Rosado; Daniel Pérez Ramírez; David N. Whiteman; Lucas Alados Arboledas; Francisco Navas Guzmán
In a context of climate change and global warming, the characterisation and operational monitoring of greenhouse gases is of uppermost importance for implementing mitigation strategies that could help to reduce the impact of the current climatic emergency in the surrounding ecosystems and society. Among these gases, water vapour can contribute to almost a 60% of the total greenhouse effect. Moreover, its interaction with solar and infrared radiation or its main role in cloud formation, make water vapour a key driver of most atmospheric thermodynamic processes and a crucial component of the Earth's radiative budget. Nevertheless, the large spatial and temporal variability of water vapour hinders the acquisition of reliable operational measurements. Remote sensing techniques such as the Global Navigation Satellite System (GNSS) have been proven to be an accurate and trustworthy alternative for integrated water vapour (IWV) retrievals, providing a valuable platform for continuous operational monitoring and thus enabling long-term characterisation. To further address this challenge, reanalysis data from Numerical Weather Prediction (NWP) models can significantly increase the temporal and spatial coverage of atmospheric variables datasets. In particular, ERA5 (fifth generation of European Centre for Medium-Range Weather Forecasts reanalysis) and MERRA-2 (Modern-Era Retrospective Analysis for Research and Applications, version 2) provide validated data for the city of Granada, in southeastern Spain, since 1980.The current study presents a comprehensive analysis of IWV trends retrieved from a 15-year GNSS database and an extended 45-year reanalysis dataset. Special attention is paid to time-series quality control and homogenisation. Small jumps or discontinuities due to GPS receiver updates or changes in the data assimilation strategies of NWP models, can introduce artificial artifacts in the time series and consequently lead to biased or misleading trend esimates. A modified Mann-Kendall test proposed by Coen et al. (2020) that applies a Variance-Corrected Trend-Free Pre-Whitening approach is evaluated against a General Least Square method with a full custom covariance matrix accounting for residual heteroscedasticity and autocorrelation. While both methodologies agree on the sign and uncertainties of the retrieved trends, some discrepancies are found in the magnitudes, reflecting the different nature of both algorithms and highlighting the sensibility of trend detection techniques. Positive increasing IWV trends of a 3% per decade on average were obtained from both datasets and algorithms, being significant to a 95% level when analysing the 45-year time series. Nonetheless, relevant behaviour differences are found between the 1980-2000 and 2000-2024 periods, unveiling the pronounced increasing in IWV experimented during the last 25 years. The results obtained are consistent with previous studies, both regarding the trend magnitude and the uncertainty range, reinforcing the capability of the GNSS technique and NWP models as robust tools for environmental and atmospheric monitoring of complex variables such as water vapour (Parracho et al., 2018; Yuan et al., 2023). However, they also unveil trend discrepancies which are inherent to the chosen retrieval methodologies and that must always be assessed.
Long-term analysis of Raman lidar water vapour profiles over the ACTRIS AGORA Granada station
(2026) Arlett Díaz Zurita; V. Hernandez; David N. Whiteman; Onel Rodríguez Navarro; Jorge Andrés Muñiz Rosado; Daniel Pérez Ramírez; Lucas Alados Arboledas; Francisco Navas Guzmán
Water vapour is a crucial and highly variable greenhouse gas in the Earth's atmosphere that plays a major role in the radiative balance, energy transport and photochemical processes. It can also affect the radiative budget indirectly through cloud formation and by altering the size, shape, and chemical composition of aerosol particles. Moreover, monitoring water vapour remains challenging due to its high temporal and spatial variability. Consequently, systematic and accurate observations of water vapour are essential to improve our understanding of its role at both local and global scales and for enhancing climate projections.Advances in remote sensing techniques have enabled continuous acquisition of precipitable water vapour (PWV) measurements using sun/star photometry, microwave radiometry and the Global Navigation Satellite System (GNSS). Nevertheless, none of these instruments provides information on the vertical distribution of water vapour, a critical information considering that water vapour concentrations typically vary by up to three orders of magnitude between the surface and the upper troposphere. In this context, Raman lidar has demonstrated its ability to capture the spatial and temporal evolution of water vapour in the troposphere. Accurate retrievals of the water vapour mixing ratio from Raman lidar measurements rely on robust and well-characterised calibration procedures as well as on an accurate estimation of the differential atmospheric transmission term, which accounts for extinction differences between the molecular reference (nitrogen and oxygen) and water vapour wavelengths.In this study, the lidar calibration constant was determined using a hybrid calibration method, which combines correlative PWV measurements for lidar calibration with Numerical Weather Prediction (NWP) data to reconstruct the water vapour profile within the incomplete overlap region of the lidar system. The differential transmission was estimated using an automated method to account for the aerosol contribution, based on sun photometer Aerosol Optical Depth (AOD) measurements and an exponential decay function with attitude to model aerosol extinction (Díaz-Zurita et al., 2025). Subsequently, a long-term database of water vapour profiles over the period 2009-2022 was generated, providing high vertical and temporal resolution measurements of water vapour over the city of Granada, in Southern Spain. A comprehensive statistical analysis was conducted to characterise the vertical distribution of water vapour over a 14-year period, representing the first long-term vertical characterisation of water vapour in this region. Mean interannual and seasonal water vapour profiles were derived for the entire study period, and trend analyses were performed to assess long-term variations in water vapour content in the lower troposphere. Additionally, lidar-derived PWV values were compared with those obtained from microwave radiometer and GNSS observations.This research was funded by Grant PID2021-128008OB-I00 funded by MICIU/AEI/ 10.13039/501100011033 by ERDF/EU European Union, and by the Spanish national projects CNS2023-145435, PID2023-151817OA-I00 and Marie Skłodowska-Curie Staff Exchange Actions with the project GRASP-SYNERGY (grant agreement no. 10113163). Diaz-Zurita et al. (2025). Remote Sens. 2025, 17(20), 3444; https://doi.org/10.3390/rs17203444
Multi year aerosol characterization in the tropical Andes and in adjacent Amazonia using AERONET measurements
(Elsevier BV, 2017) Daniel Pérez‐Ramírez; Marcos Andrade; T. F. Eck; Ariel Stein; Norman T. O’Neill; H. Lyamani; Santiago Gassó; David N. Whiteman; Igor Veselovskii; Fernando Velarde
Sensitivity Analysis of the Differential Atmospheric Transmission in Water Vapour Mixing Ratio Retrieval from Raman Lidar Measurements
(Multidisciplinary Digital Publishing Institute, 2025) Arlett Díaz-Zurita; Víctor Manuel Naval-Hernández; David N. Whiteman; Onel Rodríguez Navarro; Jorge Muñiz-Rosado; Daniel Pérez‐Ramírez; Lucas Alados‐Arboledas; Francisco Navas-Guzmán
This study assesses the effect of the differential atmospheric transmission term in Raman lidar water vapour mixing ratio retrievals. Such issue is evaluated for two optical configurations: the first is a vibrational–rotational Raman nitrogen (∼387 nm) and the second is a pure–rotational Raman molecular reference near 354 nm (nitrogen and oxygen). Both optical configurations use a vibrational–rotational water vapour channel at ∼408 nm. More than 300 aerosol profiles acquired by the University of Granada Raman lidar over the period 2010–2016 enabled the calculation of the aerosol contribution of the differential atmospheric transmission term, indicating that neglecting the total differential atmospheric transmission term can introduce systematic uncertainties in water vapour mixing ratio retrievals of approximately 5.1% and 15% (18% under high-aerosol conditions) at 6 km for the first and second configuration, respectively. Subsequently, in order to apply automatic differential transmission calculations, we developed a technique for estimating the aerosol contribution from sun photometer AOD measurements, yielding relative deviations in water vapour mixing ratio of 0.10% and 0.40% for ∼387 nm and ∼354 nm configurations when compared with cases where Raman lidar aerosol profiles were available. This approach transforms systematic uncertainties into random ones that can be reduced by increasing the number of measurements.
The Water Vapor Variability - Satellite/Sondes (WAVES) Field Campaigns
(2008) David N. Whiteman; Mariana Adam; C. Barnet; Bojan Bojkov; Rubén Delgado; Belay Demoz; J. Fitzgibbon; Ricardo Forno; R. L. Herman; Erik A. Hoff
Three NASA-funded field campaigns have been hosted at the Howard University Research Campus in Beltsville, MD. In each of the years 2006, 2007 and 2008, WAVES field campaigns have coordinated ozonesonde launches, lidar operations and other measurements with A-train satellite overpasses for the purposes of satellite validation. The unique mix of measurement systems, physical location and the interagency, international group of researchers and students has permitted other objectives, such as mesoscale meteorological studies, to be addressed as well. We review the goals and accomplishments of the three WAVES missions with the emphasis on the nonsatellite validation component of WAVES, as the satellite validation activities have been reported elsewhere.