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  • Author or Editor: Belay B. Demoz x
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Belay B. Demoz, Arlen W. Huggins, Joseph A. Warburton, and Richard L. Smith

Abstract

In the winter of 1986, two microwave radiometers were operated side by side at a high-altitude weather observation site in the central Sierra Nevada for the purpose of comparing measurements in a variety of ambient weather conditions. The instruments continuously recorded measurements of vertically integrated water vapor and liquid water during storms affecting the area. One radiometer was designed with a spinning reflector to shed precipitation particles while the other radiometer's reflector was fixed. Temporal records of the data show periods of wet weather contamination for the fixed reflector radiometer. The absence (presence) of these contaminated periods is mainly explained by the difference in the design of the radiometers. These contaminated periods led to larger standard deviation in the data from the fixed-reflector radiometer and lower correlation coefficients between the two instruments. Correlation coefficients of 0.83 for the liquid and 0.68 for the vapor values were found for the radiometer-radiometer comparisons. When some of the points suspected of contamination were removed, the correlation coefficients improved to 0.87 and 0.71 for the liquid and vapor channels, respectively. The standard deviations were 0.1 mm and 0.12 cm for the liquid and vapor channels, respectively, of the spinning reflector radiometer. For the fixed-reflector design radiometer, a standard deviation of 0.1 mm for the liquid and 0.26 cm for the vapor was found. Comparison of radiometer vapor and rawinsonde precipitable water resulted in a correlation coefficient of 0.97 for the spinning-reflector radiometer and 0.8 for the fixed-reflector radiometer.

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Andreas Behrendt, Volker Wulfmeyer, Hans-Stefan Bauer, Thorsten Schaberl, Paolo Di Girolamo, Donato Summa, Christoph Kiemle, Gerhard Ehret, David N. Whiteman, Belay B. Demoz, Edward V. Browell, Syed Ismail, Richard Ferrare, Susan Kooi, and Junhong Wang

Abstract

The water vapor data measured with airborne and ground-based lidar systems during the International H2O Project (IHOP_2002), which took place in the Southern Great Plains during 13 May–25 June 2002 were investigated. So far, the data collected during IHOP_2002 provide the largest set of state-of-the-art water vapor lidar data measured in a field campaign. In this first of two companion papers, intercomparisons between the scanning Raman lidar (SRL) of the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC) and two airborne systems are discussed. There are 9 intercomparisons possible between SRL and the differential absorption lidar (DIAL) of Deutsches Zentrum für Luft- und Raumfahrt (DLR), while there are 10 intercomparisons between SRL and the Lidar Atmospheric Sensing Experiment (LASE) of the NASA Langley Research Center. Mean biases of (−0.30 ± 0.25) g kg−1 or −4.3% ± 3.2% for SRL compared to DLR DIAL (DLR DIAL drier) and (0.16 ± 0.31) g kg−1 or 5.3% ± 5.1% for SRL compared to LASE (LASE wetter) in the height range of 1.3–3.8 km above sea level (450–2950 m above ground level at the SRL site) were found. Putting equal weight on the data reliability of the three instruments, these results yield relative bias values of −4.6%, −0.4%, and +5.0% for DLR DIAL, SRL, and LASE, respectively. Furthermore, measurements of the Snow White (SW) chilled-mirror hygrometer radiosonde were compared with lidar data. For the four comparisons possible between SW radiosondes and SRL, an overall bias of (−0.27 ± 0.30) g kg−1 or −3.2% ± 4.5% of SW compared to SRL (SW drier) again for 1.3–3.8 km above sea level was found. Because it is a challenging effort to reach an accuracy of humidity measurements down to the ∼5% level, the overall results are very satisfactory and confirm the high and stable performance of the instruments and the low noise errors of each profile.

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