In addition to a proper radar calibration, quantitative estimation of precipitation from VHF radars requires the extraction of the precipitation signal out of the Doppler spectra. It also requires the proper conversion of this precipitation signal into a reflectivity factor. / This research develops a multi-faceted approach for the calibration of VHF vertically-pointing radars, by combining a first calibration method that compares the recorded VHF signal to power coming from a noise generator and a second calibration method that compares recorded VHF signal to cosmic radiation. This approach allows the retrieval of antenna and receiver parameters (such as noise levels, efficiency, and gain), and four other equations for the corresponding errors. In addition, we develop an equation for calibrating Doppler spectra. / The analysis is focused on rain observations with VHF radar. We verify the hypothesis that |K|2 = 0.93 for most of the rain observations at VHF band. A signal-processing algorithm for extracting the rain signal out of the VHF power spectra is then presented. This work also derives a general version of the radar equation valid for vertically pointing radars, as well as a particular version of this equation valid for the McGill VHF radar. The study then makes numerical simulations of several profiles of precipitation signal at VHF band, by combining high-resolution profiles of precipitation signal (from a calibrated X-band radar) and the VHF antenna pattern in our general version of the radar equation. The analyses indicate that VHF reflectivity at gates above the melting layer is artificially enhanced by the precipitation signal collected from the side lobes. / This work also studies the effect of precipitation in the scattering properties of clear air. We analyze several cases of stratiform and convective rain, occurring in a continental mid-latitude environment (Montreal, Lat.45.41°N, Long.73.94°W). For these cases, Doppler spectra taken by a VHF vertically-pointing radar were used to retrieve simultaneous co-located values of precipitation intensity (rainrates) and degrees of refractive index fluctuation (structure-function parameter for refractivity turbulence, Cn2). We validated these retrievals using co-located, calibrated measurements of precipitation signal at X-band. The comparison between equivalent reflectivity factors at X and VHF bands agrees within 1 dB. The study includes rainrates between 0.3 and 78 mm/h, and Cn2 values between 10-16 and 10-12 m-2/3 , retrieved from the VHF spectra at 2.5 km height. The study finds that the occurrence of rain is associated with distinctive changes in the structure of air refractive index fluctuations, and that these changes are of a turbulent nature for the most intense rainrates.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.102965 |
| Date | January 2006 |
| Creators | Campos Ortega, Edwin F., 1972- |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Atmospheric and Oceanic Sciences.) |
| Rights | © Edwin F. Campos Ortega, 2006 |
| Relation | alephsysno: 002590114, proquestno: AAINR32161, Theses scanned by UMI/ProQuest. |
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