Citation
Abstract
Unmodeled electrical path delay from atmospheric water vapor is a limiting error source in geodetic measurements made with very long baseline interferometry and in radio ranging to spacecraft. A dual channel water vapor radiometer, operating near the 22.235-GHz water vapor line, is capable of measuring water vapor-induced delay with good accuracy under most weather conditions. Theory shows that water vapor path delay AL, is proportional to a linear combination of saturation-corrected sky brightness temperatures, measured on and off the water vapor line. The second, off-line, channel removes the effects of emission from liquid water droplets in clouds as well as most of the oxygen emission. Tipping curves remove instrumental error. Sky brightness temperatures are saturation-corrected or “linearized” using estimates of effective sky temperature made from surface temperature. Coefficients in the expression for path delay AL, are functions of surface temperature, pressure, and water vapor density, allowing use of our data reduction algorithm at any altitude and in any climate. Coefficients are found by two methods: (1) from a regression analysis of measured brightness temperatures versus radiosonde measured delay, and (2) from a regression of theoretical brightness temperatures versus radiosonde measured delay. Regression solutions are constrained to remove liquid water contributions and to give the correct slope (i.e., one) for radiometer versus radiosonde path delay.
Details
- Volume
- 42-48
- Published
- December 15, 1978
- Pages
- 22–30
- File Size
- 818.8 KB