THE MEASUREMENT OF CLOUD LIQUID-WATER CONTENT BY RADAR

Ralph J. Donaldson Jr. Air Force Cambridge Research Center

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Abstract

The depth to which a liquid-water cloud may be detected has been computed as a function of liquid-water content for radars at wavelengths of 0.86, 1.25 and 3.2 cm, with use of Atlas' relationship for Z versus liquid-water content, and with account being taken of attenuation. An estimation is made of the effect of attenuation on calibration error; the resultant error in liquid-water content places a limit on the depth to which the liquid-water concentration in a cloud may be measured to a given accuracy by radar means. For the two shorter wavelengths and for relatively high liquid-water concentrations, error considerations, and not detectability, limit the measurement. The 0.86-cm radar is superior to the other two in cloud detectability for nearly all commonly encountered values of liquid-water content. For cases where an attenuation correction is desirable, a relatively simple method of making this correction is developed.

Abstract

The depth to which a liquid-water cloud may be detected has been computed as a function of liquid-water content for radars at wavelengths of 0.86, 1.25 and 3.2 cm, with use of Atlas' relationship for Z versus liquid-water content, and with account being taken of attenuation. An estimation is made of the effect of attenuation on calibration error; the resultant error in liquid-water content places a limit on the depth to which the liquid-water concentration in a cloud may be measured to a given accuracy by radar means. For the two shorter wavelengths and for relatively high liquid-water concentrations, error considerations, and not detectability, limit the measurement. The 0.86-cm radar is superior to the other two in cloud detectability for nearly all commonly encountered values of liquid-water content. For cases where an attenuation correction is desirable, a relatively simple method of making this correction is developed.

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