Measurements Of Atmospheric Water Vapor Research Articles

Measuring regional atmospheric water vapor using the Swedish Permanent GPS Network

We investigate the application of a geodetic network of ground‐based GPS receivers in Sweden to the measurement of atmospheric water vapor. Using data acquired during four days in December 1993, we show that it is possible to study the detailed motions of air mass systems. Estimates of water vapor from GPS data agree with those from radiosonde and microwave radiometer data to within 1 mm RMS.

Fiber amplification in the 940-nm water vapor absorption band using the /sup 4/F/sub 3/2/ /sup 4/I/sub 9/2/ transition in Nd

The measurement of atmospheric water vapor in the 940-nm absorption band may be accomplished using fiber amplifiers based on the /sup 4/F/sub 3/2//spl rarr//sup 4/I/sub 9/2/ transition in Nd. We report initial experimental results on the effects codopants have on the characteristics of this transition in Nd-doped fiber, and present modeled and experimental results of a fiber amplifier. To our knowledge, this is the first reported fiber amplifier employing this transition.

In place merging of satellite based atmospheric water vapour measurements

Atmospheric water vapour plays a key role in the climatology of the Earth. It has traditionally been measured using radiosondes for reasons of instrumental simplicity but these offer limited opportunities for spatial and continuous measurements of dynamic water vapour changes over large areas of the Earth's atmosphere. Efforts have recently turned to using satellite remote sensing instruments with different spectral and spatial capabilities to derive measurements of total water vapour content in atmospheric columns or simply precipitable water. The merging of remote sensing data with different spectral and spatial capabilities can result in large biases when independent measurements are not nested correctly to produce the final product. Consequently, such merging of data must take into account the intrinsic time dynamics of measured parameters. In this paper, the impact of atmospheric water vapour dynamics on the merging of satellite-based retrieval of precipitable water estimates is investigated by comparing independent measurements obtained at different spatial resolutions from the High Resolution Infrared Sounder (HIRS) and the Advanced Very High Resolution Radiometer (AVHRR). Correlations are used to infer optimal merging parameters depending on the observational conditions. The authors conclude that the merging technique reproduces HIRS-based retrievals in cloud-free and partly cloudy locations from AVHRR soundings.

Ground‐based measurements of middle atmospheric water vapor at 183 GHz

We present here the first ground‐based observations of stratospheric/mesospheric H2O emission at the 31,3 → 22,0 resonance (183.3101 GHz of central frequency). The spectra were obtained in January 1991 and January 1994 using the Institut de Radioastronomie Millimétrique (IRAM) 30‐m radiotelescope located on Pico Veleta, Spain, (altitude 2870 m, latitude 37°N), during very dry tropospheric conditions (total precipitable water within the range 0.2–0.3 mm above the observation site). Microwave studies of stratospheric and mesospheric H2O profile have been carried out so far mostly by means of observations of the weak 61,6 → 52,3 resonance at 22.2351 GHz. Some measurements at 183 GHz were previously obtained from airborne observations. The water vapor abundance in the troposphere is, in most cases, so high that the atmosphere appears optically thick at 183 GHz. However, we show that emission from the stratosphere and mesosphere can be sometimes detected from the ground (allowing upper stratospheric and mesospheric water vapor profiles to be obtained). We use a generalized non linear radiative transfer code in order to perform a least squares fit of the observed spectra. The derived H2O abundances are consistent with most measurements at 22 GHz. We suggest the possibility of carrying out this kind of observation in some selected sites during a significant fraction of the whole winter season. The required integration times to get a given signal‐to‐noise ratio are much shorter at 183 GHz than at 22 GHz.

Martian water vapor, 1988–1995

We report new measurements of Martian atmospheric water vapor for the period 1991–1995 and discuss implications of these and earlier measurements from 1988 to 1989. Our measurements indicate abundances (precipitable micrometers (pr μm)) that show some departures from those of the Viking Mars atmospheric water detector (MAWD) experiment and other ground‐based measurement programs. Variation of water abundance within Martian season is sometimes as large as a factor of 3 from one year to the next. However, the seasonal shifts and variations between hemispheres show the same trends as observed by MAWD. Column abundances of water vapor varied from barely detectable, <1 (at Ls 320–340) to 36.4 pr μm (Ls 100) at high northern latitudes. Strong latitude variations were observed for all Ls seasons, with late spring and summers wet in both hemispheres. Northern latitudes are up to 5 times wetter than southern latitudes. Equatorial regions (30°S–30°N) show a rather stable abundance of atmospheric water varying between 2 and 20 pr μm, while much larger variations are observed at high latitudes. Southern atmospheric water drops below 10 pr μm rapidly in early autumn and is below our measurement threshold by late autumn. Strong diurnal variations show lowest water column abundance near the evening terminator.

Measurements of water vapor in the middle atmosphere and implications for mesospheric transport

We present data obtained during more than 3 years of nearly continuous measurements of middle atmospheric water vapor. The data are obtained from ground‐based measurements at 22 GHz taken at two sites, one in each hemisphere, using the Naval Research Laboratory water vapor millimeter‐wave spectrometer (WVMS). With the construction of a second instrument, it has been possible to maintain continuous monitoring from both sites since January 1994. The measurements from both instruments show significant seasonal variability. There is a clear annual cycle, with the water vapor above ∼60 km increasing in summer and decreasing in winter. The observed amplitude of the annual oscillation is larger at 45.0°S than at 34.4°N, a result which is qualitatively consistent with the higher latitude of the southern hemisphere site. There is also an indication of a semiannual cycle, particularly at altitudes near 80 km. The annual cycle is consistent with transport due primarily to advection, while the weaker semiannual cycle may be indicative of the effect of gravity waves on diffusive transport.

An Airborne Millimeter-Wave Imaging Radiometer for Cloud, Precipitation, and Atmospheric Water Vapor Studies

Abstract A six-channel airborne total-power Millimeter-wave Imaging Radiometer (MIR) was recently built to provide measurements of atmospheric water vapor, clouds, and precipitation. The instrument is a cross-track scanner that has a 3-dB beamwidth of 3.5° and an angular swath of 100°. It measures radiation at the frequencies of 89, 150, 183.3 ± 1, 183.3 ± 3, 183.3 ± 7, and 220 GHz. The inclusion of the 220-GHz receiver makes this instrument unique; no other instrument has made atmospheric radiation measurements using this combination of frequencies. The temperature sensitivities ΔT, based on the actual flight data with a 6.8-ms integration time, are found to be 0.44, 0.44, 1.31, 1.30. 1.02, and 1.07 K. The instrument has two external calibration loads maintained at the temperatures of 330 and 250 K (the ambient temperature at an aircraft altitude of 20 km). These calibration load temperatures are monitored precisely so that the radiometric measurements of the instrument could be made to better than 1 K o...

The Promise of GPS in Atmospheric Monitoring

Abstract This paper provides an overview of applications of the Global Positioning System (GPS) for active measurement of the Earth's atmosphere. Microwave radio signals transmitted by GPS satellites are delayed (refracted) by the atmosphere as they propagate to Earth-based GPS receivers or GPS receivers carried on low Earth orbit satellites. The delay in GPS signals reaching Earth-based receivers due to the presence of water vapor is nearly proportional to the quantity of water vapor integrated along the signal path. Measurement of atmospheric water vapor by Earth-based GPS receivers was demonstrated during the GPS/STORM field project to be comparable and in some respects superior to measurements by ground-based water vapor radiometers. Increased spatial and temporal resolution of the water vapor distribution provided by the GPS/STORM network proved useful in monitoring the moisture-flux convergence along a dryline and the decrease in integrated water vapor associated with the passage of a midtropospheri...

Simultaneous Measurements of Atmospheric Water Vapor with MIR, Raman Lidar, and Rawinsondes

Abstract Simultaneous measurements of atmospheric water vapor were made by the Millimeter-wave Imaging Radiometer (MIR), Raman lidar, and rawinsondes. Two types of rawinsonde sensor packages (AIR and Vaisala) were carried by the same balloon. The measured water vapor profiles from Raman lidar, and the Vaisala and AIR sondes were used in the radiative transfer calculations. The calculated brightness temperatures were compared with those measured from the MIR at all six frequencies (89, 150, 183.3 ± 1, 183.3 ±3, 183.3 ±7, and 220 GHz). The results show that the MIR-measured brightness temperatures agree well (within ±K) with those calculated from the Raman lidar and Vaisala measurements. The brightness temperatures calculated from the AIR sondes differ from the MIR measurements by as much as 10 K, which can be attributed to low sensitivity of the AIR sondes at relative humidity less than 20%. Both calculated and the MIR-measured brightness temperatures were also used to retrieve water vapor profiles. These retrieved profiles were compared with those measured by the Raman lidar and rawinsondes. The results of these comparisons suggest that the MIR can measure the brightness of a target to an accuracy of at most ±K and is capable of retrieving useful water vapor profiles.

Airborne differential absorption lidar system for measurements of atmospheric water vapor and aerosols

An airborne differential absorption lidar (DIAL) system has been developed at the NASA Langley Research Center for remote measurements of atmospheric water vapor (H(2)O) and aerosols. A solid-state alexandrite laser with a 1-pm linewidth and > 99.85% spectral purity was used as the on-line transmitter. Solid-state avalanche photodiode detector technology has replaced photomultiplier tubes in the receiver system, providing an average increase by a factor of 1.5-2.5 in the signal-to-noise ratio of the H(2)O measurement. By incorporating advanced diagnostic and data-acquisition instrumentation into other subsystems, we achieved additional improvements in system operational reliability and measurement accuracy. Laboratory spectroscopic measurements of H(2)O absorption-line parameters were perfo med to reduce the uncertainties in our knowledge of the absorption cross sections. Line-center H(2)O absorption cross sections were determined, with errors of 3-6%, for more than 120 lines in the 720-nm region. Flight tests of the system were conducted during 1989-1991 on the NASA Wallops Flight Facility Electra aircraft, and extensive intercomparison measurements were performed with dew-point hygrometers and H(2)O radiosondes. The H(2)O distributions measured with the DIAL system differed by ≤ 10% from the profiles determined with the in situ probes in a variety of atmospheric conditions.

Raman Lidar Profiling of Atmospheric Water Vapor: Simultaneous Measurements with Two Collocated Systems

Raman lidar is a leading candidate for providing the detailed space- and time-resolved measurements of water vapor needed by a variety of atmospheric studies. Simultaneous measurements of atmospheric water vapor are described using two collocated Raman lidar systems. These lidar systems, developed at the NASA/Goddard Space Flight Center and Sandia National Laboratories, acquired approximately 12 hours of simultaneous water vapor data during three nights in November 1992 while the systems were collocated at the Goddard Space Flight Center. Although these lidar systems differ substantially in their design, measured water vapor profiles agreed within 0.15 g kg−1 between altitudes of 1 and 5 km. Comparisons with coincident radiosondes showed all instruments agreed within 0.2 g kg−1 in this same altitude range. Both lidars also clearly showed the advection of water vapor in the middle troposphere and the pronounced increase in water vapor in the nocturnal boundary layer that occurred during one night.

Coherent laser radar at 2 mu m using solid-state lasers

The development of a coherent laser radar system using 2- mu m Tm- and Tm, Ho-doped solid-state lasers, which is useful for the remote range-resolved measurement of atmospheric winds, aerosol backscatter, and differential absorption lidar (DIAL) measurements of atmospheric water vapor and CO/sub 2/ concentrations, is described. Measurements made with the 2- mu m coherent laser radar system, advances in the laser technology, and atmospheric propagation effects on 2- mu m coherent lidar performance are discussed. Results include horizontal atmospheric wind measurements to >20 km. vertical wind measurements to >5 km, near-horizontal cloud returns to 100 km, and hard target (mountainside) returns from 145 km.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Measurements of Atmospheric Water Vapor with an Alexandrite Lidar.

A differential absorption lidar (DIAL) for the detection of atmospheric water vapor was developed based on a tunable alexandrite laser. Theoretical estimation shows that the bandwidth of laser radiation and accuracy of the wavelength tuning critically affect detection errors. We propose a new accurate tuning method on the resonance line of H2O at 725.8 nm using the opto-galvanic effect in a Xe discharge tube, and compared it with an absorption method and a photo-acoustic method. The DIAL experiment demonstrates the detection range up to 9.5 km with a detection error of less than 50%. The H2O distributions measured were agreed with sonde data.

Atmospheric water vapor measurements: Comparison of microwave radiometry and lidar

The NASA/GSFC Crustal Dynamics Project microwave water vapor radiometer (J03) is evaluated in terms of measurements of the integrated precipitable water vapor content of a particular column of the troposphere. The measurements were taken during the Atmospheric Moisture Intercomparison Study (ATMIS) held at Wallops Island, Virginia, during April 1989. Various water vapor sensing instruments were used during ATMIS, including radiometers, radiosondes, and the NASA/GSFC Raman lidar. Comparisons between water vapor measurements by the radiometer and the lidar yielded a correlation coefficient of 0.998 and rms differences for three nights of −0.2±0.2mm (April 11–12, 1989), −0.8±0.5 mm (April 16–17, 1989), and −0.4±0.3 mm (April 17–18, 1989). The integrated precipitable water vapor measurements for these three nights were approximately 5, 10, and 21 mm, respectively. The first two periods had clear meteorological conditions, while clouds were present during the third period. The lidar results during the third period are augmented with radiosonde measurements above the cloud base. This study shows that the radiometer provides accurate, continuous measurements of the water vapor integrated through the depth of the atmosphere.

DIAL Measurements of Water Vapor with a Ti:Sapphire Laser.

A differential absorption lidar (DIAL) system based on a continuously tunable Ti : sapphire laser is described. The system is capable of range-resolved measurement of atmospheric water vapor with 720nm absorption lines. A simple and compact laser wavelength tuning system for the water-vapor 720nm absorption lines is presented. The tuning system makes use of a com-pact wavemeter calibrated by the neon resonance line (724.5167nm) of a hollowcathode lamp. An actual measurement of water vapor in the lower troposphere is achieved by using this DIAL system.

Tunable 21-μm Ho lidar for simultaneous range-resolved measurements of atmospheric water vapor and aerosol backscatter profiles

An eye-safe, tunable differential-absorption lidar system has been developed for the range-resolved measurement of aerosol backscatter and water vapor in the atmosphere. The lidar uses a flash-lamp-pumped, qswitched, 10-mJ solid-state Ho:YSGG laser that is continuously tunable over a 20cm(-1) wavelength range near 2.084 microm. Both path-averaged and range-resolved measurements were performed with the Ho differential-absorption lidar system. Preliminary measurements have been made of the temporal variation of atmospheric aerosol backscatter and water-vapor profiles at ranges out to 1 km. These results indicate that the Ho lidar has the potential for the eye-safe remote sensing of atmospheric water vapor and backscatter profiles at longer ranges if suitably enhanced in laser power and laser linewidth.

Double-pulse dual-wavelength alexandrite laser for atmospheric water vapor measurement

We describe a new alexandrite laser source arrangement designed to measure atmospheric water vapor using the differential absorption lidar technique. This laser is capable of emitting two pulses at two appropriately selected wavelengths within a single flash lamp discharge. A narrow spectral linewidth of Deltalambda < 1 pm is obtained for each pulse by intracavity filtering with a birefringent filter and two Fabry-Perot interferometers. Wavelength commutation between the two pulses is performed by electro-optically tuning the birefringent filter. The temporal separation between the two pulses can be chosen between 50 and 70 micros and each pulse duration is <250-ns (full width at half-maximum). Typical output energies of 50 mJ/pulse at each wavelength are obtained with this laser system at a 10-Hz repetition rate for a 1.3-kW input electrical power.

Satellite microwave measurements of atmospheric water vapour and marine wind speed: case study application

Vertically integrated atmospheric water vapour and surface wind speed over the oceans are derived from the SSM/I microwave sensor aboard the DMSP F8 satellite. A description of the sensor and its capabilities is provided. As an example, water vapour and wind fields surrounding southern Africa are analysed for anomaly structure over the period of the floods of 1988 from 16 January to 31 March. Positive anomalies of water vapour during the peak-flood episodes originate from the Mozambique Channel. Surface winds were particularly strong over the Agulhas Current. The spatial pattern points to a strengthening of the Hadley circulation cell and to west-moving convective systems which drew moisture from the south-western Indian Ocean to the central plateau of South Africa.

CO_2 DIAL measurements of water vapor

CO(2) lidars have heretofore been used to measure water vapor concentrations primarily using the 10R(20) line at 10.247 microm, which has a strong overlap with a water vapor absorption line. This paper discusses the use of that line as well as other CO(2) laser lines for which the absorption coefficients are weaker. The literature on measurement of water vapor absorption coefficients using CO(2) lasers is reviewed, and the results from four laboratories are shown to be generally consistent with each other after they are normalized to the same partial pressure, temperature, and ethylene absorption coefficient for the 1P(14) CO(2) laser line; however, the agreement with the Air Force Geophysics Laboratory's HITRAN and FASCOD 2 spectral data tapes is not good either for the water vapor absorption lines or for the water vapor continuum. Demonstration measurements of atmospheric water vapor have been conducted using the Mobile Atmospheric Pollutant Mapping System, a dual CO(2) lidar system using heterodyne detection. Results are discussed for measurements using three sets of laser line pairs covering a wide range of water vapor partial pressures.

Contribution to the Tritium Continental Effect

The results of tritium measurements of atmospheric water vapour and precipitation samples for 1982 and 1983 are presented. The data were used to establish a simple model describing the tritium continental effect taking into account re-evaporation of tritium from the continental land surfaces. Some comments on man made tritium are given.