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Example of the accuracy of data from RASS Search web site |
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Comparison of the accuracy of 1290 MHz RASS and met tower in an altitude of 100 m As an example of the accuracy Picture 1 shows a comparison between RASS instrumentation and an in-situ measurement with ventilated temperature probes at a tower site of the Meteorological Observatory Lindenberg. The altitude of the tower measurement was at 98 m above ground and the corresponding RASS altitude was 100 m above ground. The tower values were converted with the help of a humidity measurement into virtual temperatures Tv. With a correlation coefficient of 0.98 and the a slope of the regression curve of 1,00 one found a nearly perfect match of both measurements. Also for the height of 48 m above ground nearly identical values were found. Due to seasonable conditions within this example only weak developed thermal induced turbulence with small vertical wind was observed. This caused less scattering of the RASS-values.
Height availability RASS 1290 MHz The reachable height range of the RASS-measurement depends more on the driftage of the sound wave due to the wind influence than on the attenuation of the sound wave in the air. Atmospheric turbulent density fluctuations can compensate this effect by some kind of deformation of the sound wave. The reception area of the backscattering on the ground expands, so that the reception antenna will be within this reception area also for backscattering from greater altitudes.The place where the comparison of Picture 1 occurred can be identified by comparable high wind speed and plain terrain. These are disadvantageous properties for the height availability of a RASS measurement. For this comparison we found an availability of 70% for the height of 200 m. A campaign with duration of 4 weeks in the vicinity of Basel brought a significant more favourable availability, which is shown in Picture 2. Good conditions with strong mechanical and thermal induced turbulence at low mean wind speeds brought availabilities over 90% up to altitudes of 400 m. The significant decrease in availability for the lowest height was based on a disturbing signal. The missing values for an availability of 100% were caused by failures of the power supply and of the data recording. |
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Please click image to expand in new windowPic 2: Height Availability of Doppler-RASS 1290 MHz
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