Validation of GOMOS/Envisat High-Resolution Temperature Profiles (HRTP) Using Spectral Analysis
The GOMOS (Global Ozone Monitoring by Occultation of Stars) instrument on board the Envisat satellite is equipped with two fast photometers operating at 1 kHz sampling frequency in blue and red wavelengths. The bi-chromatic scintillations recorded by the photometers allow the determination of refractive angle, which is proportional to the time delay between the photometer signals. The high resolution density and temperature profiles can be reconstructed (with a vertical resolution of about 200 m) from these data in the altitude range ∼15–35 km. The validation of small-scale fluctuations in HRTP requires a very close collocation in time and space with high-quality data having comparable or better vertical resolution. Comparing spatial spectra of temperature profile fluctuations requires less strict collocation criteria. In this paper, we compared vertical wavenumber spectra of temperature fluctuations in HRTP and in collocated radiosonde data. We found that the vertical wavenumber spectra of HRTP and radiosonde temperature fluctuations are very similar in case of vertical occultations of bright stars. In case of oblique occultations or of dim stars, the HRTP fluctuations often have a larger spectral magnitude, despite of several good agreements. The spectral analysis has confirmed that the actual resolution of HRTP is 150–200 m.
KeywordsVertical Resolution Horizontal Wind Radio Occultation Internal Gravity Wave Bright Star
This work has been performed within the scope of the ESA funded project “Algorithms for the estimation of high resolution temperature and density profiles from GOMOS measurements” (Contract number 17895/04/I-LG). The authors thank ESA and the GOMOS team for the GOMOS data. The authors greatly appreciate the use of correlative data from the ENVISAT Cal/Val database at NILU, and thank the principal investigators of the radiosondes and SHADOZ sondes. The work of V.F. Sofieva was supported by the Academy of Finland (postdoctoral researcher project).
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