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Leo J. Fritschen

Abstract

A sensitive cup-type anemometer was developed which is mechanically and electrically simple. The characteristics include a starting speed of 6 cm sec−1, distance constant (63%) of 90 cm, and a linear response.

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Leo J. Fritschen

Abstract

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Leo J. Fritschen

The details of construction and method of calibration of an instrument used to measure net radiation have been described.

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Leo J. Fritschen

Abstract

The miniature net radiometer was constructed by enclosing a blackened thermal transducer within four polystyrene radiation windows. The outer two radiation windows were hemispherically shaped (one-inch radius) so that the response to varying angles of incidence would follow the cosine law and precipitation runoff would be facilitated.

The miniature net radiometer was calibrated in the laboratory in a chamber capable of simulating both solar and terrestrial radiation, and was found to be equally sensitive to both. The response to varying angles of incidence follows the cosine law. The output is not affected by wind or ambient temperature, and the size of the instrument enables its use to measure net radiation close to a surface or within a, plant canopy without appreciably altering the net radiation by shading.

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Leo J. Fritschen

Abstract

An improved net radiometer was designed with increased sensitivity to match a ±5-mv potentiometer used in a multipoint recording system. Its sensitivity is sufficient to give a full-scale range of ±1.4 ly min−1, with a recording sensitivity and accuracy of 0.003 ly min−1. The radiometer sensor consists of a 22-junction manganin-constantan thermopile with compensating thermistor embedded in epoxy resin. Effects of ambient temperature from 11 to 54C are virtually eliminated by means of a circuit comprised of a shunt thermistor and micronminiature rheostat. The blackened surfaces of the transducer are shielded against the effects of wind by thin polyethylene hemispheres. The improvement also include uniform sensitivity among sensors, better spectral response, and relative ~ of construction.

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Leo J. Fritschen and Richard Hinshaw

Abstract

An anemometer housing design is described which utilizes readily available components. The unique feature of the design is the use of a magnetically activated reed switch set in an iron epoxy housing to provide indication of wind speed and yet maintain a low-threshold starting speed. The reed switch provides a positive off-on switch and requires only two wires. The response of this reed-switch anemometer is similar to that of photo-chopper anemometers having a starting speed of 12 cm sec−1 and a sensitivity of 0.026 rpm per msec−1.

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Leo J. Fritschen and James R. Simpson

Abstract

Surface evaluation of sensible and latent heat flux densities and the components of the radiation balance were desired for various vegetative surfaces during the ASCOT84 experiment to compare with modeled results and to relate these values to drainage winds. Five battery operated data systems equipped with sensors to determine the above values were operated for 105 station days during the ASCOT84 experiment. The Bowen ratio energy balance technique was used to partition the available energy into the sensible and latent heat flux densities. A description of the sensors and battery operated equipment used to collect and process the data is presented. In addition, improvements and modifications made since the 1984 experiments are given. Details of calculations of soil heat flow at the surface and an alternate method to calculate sensible and latent heat flux densities are provided.

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Leo J. Fritschen and R. H. Shaw

The details of construction of a thermocouple-type anemometer and results obtained by its use in measuring the wind profile of a micro-layer, within a crop cover, are presented.

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Leo J. Fritschen and C. H. M. Van Bavel

Abstract

During the spring of 1961, experiments were conducted at the U.S. Water Conservation Laboratory, Tempe, Ariz., to measure the magnitude of evaporation and related micrometeorological factors from isolated shallow water and an extended shallow water. The data obtained were analyzed using the energy balance equation

                R n+S+W+LE+A = 0,

where R n is the measured net radiation, S is the measured soil heat flux below the water layer, W is the calculated change in heat storage of the water layer, LE is evaporative flux determined from sensitive weighing lysimeters, and A is the sensible heat flux to the air obtained from the solution of the energy balance equation. The results of triplicate measurements made every 15 minutes for seven consecutive days indicate that the evaporative flux is larger from the isolated shallow water. The daily totals of the sensible heat flux to the air indicate that energy was derived from the air in all cases for the isolated shallow water, and energy was used to heat the air in the case of the extended shallow water.

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Leo J. Fritschen and C. H. M. Van Bavel

Abstract

The data handling system was designed to record sequentially on punched paper tape or typewriter listings up to 40 voltage and nine electrical pulse signals from micrometeorological sensors. The system consists of a self-balancing potentiometer with shaft encoder, four 10-channel scanners, programmer, translator, digital clock, and nine electromechanical counters. The components of the system, mode of operation, and desirable modifications are described.

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