| Autor: |
Meshkov, Andrey I., De Lucia, Frank C. |
| Předmět: |
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| Zdroj: |
Review of Scientific Instruments; Aug2005, Vol. 76 Issue 8, p083103, 10p |
| Abstrakt: |
An instrument for the measurement of continua effects in the millimeter and submillimeter (a.k.a. terahertz) spectral region for mixtures of gases is described. In addition to their scientific interest, these continua are important because they contribute more than 50% of the opacity in the atmospheric windows important in remote sensing and communications. The instrument is based upon a fast scanning cavity ringdown approach that makes possible the measurement of continua and broad line absorptions at ∼6000 distinct cavity frequencies from 170 to 260 GHz in ∼3 s. The instrument’s 10 m Fabry–Perot cavity (Q∼5×106) is in a chamber whose temperature can be controlled between -80 and +100 °C and whose pressure can be varied between ∼10-5 Torr and 10 atm. The 3 s scan results in statistical uncertainty in the absorptions of ∼2×10-7 cm-1 at each of the 6000 frequencies. From these data an uncertainty of less than 1% for the weakest atmospheric continua (the dry air continuum) can be determined. For comparison, the continuum parameters that might be considered for inclusion in atmospheric remote sensing retrievals vary over a range of 10% to more than 50%. This uncertainty significantly impacts quality and validity of atmospheric retrievals from a variety of remote sensing platforms. While much lower statistical uncertainties are achievable with modest additional observation times, it is much more important that the near simultaneous measurements at many frequencies produce a data set that contains, without the use of parameters from other experiments, all of the required experimental information. This approach significantly reduces systematic effects and makes possible more realistic assessment of uncertainties. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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