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- Author or Editor: P. G. Mestayer x
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Abstract
A prototype system for the measurement and computation of air–sea fluxes in realtime was tested in the Humidity Exchange Over the Sea (HEXOS) main experiment, HEXMAX. The system used a sonic anemometer/thermometer for wind speed, surface stress and sensible heat flux measurements and a Lyman-α fast hygrometer for latent beat flux. A small desktop computer combining both fast analog to digital (A/D) capabilities, external bus (IEEE-488) operation of a slow voltmeter/scanner unit, and a plug-in board for computation of turbulence spectra by Fast Fourier Transform was used for acquisition of 17 channels of data. At the end of a ten-minute averaging period, air–sea fluxes were computed from the velocity, temperature, and humidity variance spectra using the inertial-dissipation method. A second computer and data acquisition system was used for simultaneous computations of covariance fluxes for comparison.
The sonic anemometer/thermometer proved to be well suited for this application: the velocity data appear to be of good quality and the temperature data wore unaffected by salt contamination. We suggest an infrared hygrometer as a replacement for the Lyman-α. For the six week HEXMAX period the inertial-dissipation flux estimates agreed with covariances computed from the same instruments with a typical average root-mean-square difference of ± 10% for stress and ± 25% for sensible and latent heat.
Abstract
A prototype system for the measurement and computation of air–sea fluxes in realtime was tested in the Humidity Exchange Over the Sea (HEXOS) main experiment, HEXMAX. The system used a sonic anemometer/thermometer for wind speed, surface stress and sensible heat flux measurements and a Lyman-α fast hygrometer for latent beat flux. A small desktop computer combining both fast analog to digital (A/D) capabilities, external bus (IEEE-488) operation of a slow voltmeter/scanner unit, and a plug-in board for computation of turbulence spectra by Fast Fourier Transform was used for acquisition of 17 channels of data. At the end of a ten-minute averaging period, air–sea fluxes were computed from the velocity, temperature, and humidity variance spectra using the inertial-dissipation method. A second computer and data acquisition system was used for simultaneous computations of covariance fluxes for comparison.
The sonic anemometer/thermometer proved to be well suited for this application: the velocity data appear to be of good quality and the temperature data wore unaffected by salt contamination. We suggest an infrared hygrometer as a replacement for the Lyman-α. For the six week HEXMAX period the inertial-dissipation flux estimates agreed with covariances computed from the same instruments with a typical average root-mean-square difference of ± 10% for stress and ± 25% for sensible and latent heat.
Abstract
The integration of plug-in Fast Fourier Transform (FFT) boards in data acquisition computers allows a considerable development in the dynamic calibration of turbulence sensors. The spectral transfer function of a fast and sensitive turbulence sensor can be obtained in situ from a slow sensor having an absolute calibration, by computing in real time either the power spectra of the two signals or their complex cross-spectrum. The real-time spectral method allows calibration of sensors with relatively complex responses and, in most cases, nonlinear transfer functions. When used in conjunction with appropriate control and correction algorithms, this method can take care of numerous sources of error such as electronic noise, line pickup, and sensor malfunctions. This study shows that it can be extended to sensor arrays, including X-wire dual-component anemometers.
Abstract
The integration of plug-in Fast Fourier Transform (FFT) boards in data acquisition computers allows a considerable development in the dynamic calibration of turbulence sensors. The spectral transfer function of a fast and sensitive turbulence sensor can be obtained in situ from a slow sensor having an absolute calibration, by computing in real time either the power spectra of the two signals or their complex cross-spectrum. The real-time spectral method allows calibration of sensors with relatively complex responses and, in most cases, nonlinear transfer functions. When used in conjunction with appropriate control and correction algorithms, this method can take care of numerous sources of error such as electronic noise, line pickup, and sensor malfunctions. This study shows that it can be extended to sensor arrays, including X-wire dual-component anemometers.
Abstract
The response of a Kaijo Denki DAT 300 ultrasonic anemometer-thermometer is analyzed with respect to temperature and vertical velocity. The effects of the emitting-receiving cycle of the transducer array on w, T, and CowT spectra are considered. The resulting relations are used to interpret temperature spectra obtained during the HEXMAX (Humidity Exchange over the Sea, Main Experiment) measuring campaign.
Abstract
The response of a Kaijo Denki DAT 300 ultrasonic anemometer-thermometer is analyzed with respect to temperature and vertical velocity. The effects of the emitting-receiving cycle of the transducer array on w, T, and CowT spectra are considered. The resulting relations are used to interpret temperature spectra obtained during the HEXMAX (Humidity Exchange over the Sea, Main Experiment) measuring campaign.
Abstract
Accurate measurement of fluctuations in temperature and humidity are needed for determination of the surface evaporation rate and the air-sea sensible heat flux using either the eddy correlation or inertial dissipation method for flux calculations. These measurements are difficult to make over the ocean, and are subject to large errors when sensors are exposed to marine air containing spray droplets. All currently available commercial measurement devices for atmospheric humidity require frequent maintenance. Included in the objectives of the Humidity Exchange over the Sea program were testing and comparison of sensors used for measuring both the fluctuating and mean humidity in the marine atmosphere at high wind speeds and development of techniques for the protection of these sensors against contamination by oceanic aerosols. These sensors and droplet removal techniques are described and comparisons between measurements from several different systems are discussed in this paper.
To accomplish these goals, participating groups devised and tested three methods of removing sea spray from the sample airstream. The best performance was given by a rotating semen device, the “spray Ringer.” Several high-frequency temperature and humidity instruments, based on different physical principles, were used in the collaborative field experiment. Temperature and humidity fluctuations were measured with sufficient accuracy inside the spray removal devices using Lyman-α hygrometers and a fast thermocouple psychrometer. Comparison of several types of psychrometers (using electric thermometers) and a Rotronic MP-100 humidity sensor for measuring the mean humidity illustrated the hysteresis of the Rotronic MP-100 device after periods of high relative humidity. Confidence in the readings of the electronic psychrometer was established by in situ calibration with repeated and careful readings of ordinary hand-held Assman psychrometers (based on mercury thermometers). Electronic psychrometer employing platinum resistance thermometers perform very well.
Abstract
Accurate measurement of fluctuations in temperature and humidity are needed for determination of the surface evaporation rate and the air-sea sensible heat flux using either the eddy correlation or inertial dissipation method for flux calculations. These measurements are difficult to make over the ocean, and are subject to large errors when sensors are exposed to marine air containing spray droplets. All currently available commercial measurement devices for atmospheric humidity require frequent maintenance. Included in the objectives of the Humidity Exchange over the Sea program were testing and comparison of sensors used for measuring both the fluctuating and mean humidity in the marine atmosphere at high wind speeds and development of techniques for the protection of these sensors against contamination by oceanic aerosols. These sensors and droplet removal techniques are described and comparisons between measurements from several different systems are discussed in this paper.
To accomplish these goals, participating groups devised and tested three methods of removing sea spray from the sample airstream. The best performance was given by a rotating semen device, the “spray Ringer.” Several high-frequency temperature and humidity instruments, based on different physical principles, were used in the collaborative field experiment. Temperature and humidity fluctuations were measured with sufficient accuracy inside the spray removal devices using Lyman-α hygrometers and a fast thermocouple psychrometer. Comparison of several types of psychrometers (using electric thermometers) and a Rotronic MP-100 humidity sensor for measuring the mean humidity illustrated the hysteresis of the Rotronic MP-100 device after periods of high relative humidity. Confidence in the readings of the electronic psychrometer was established by in situ calibration with repeated and careful readings of ordinary hand-held Assman psychrometers (based on mercury thermometers). Electronic psychrometer employing platinum resistance thermometers perform very well.
