In the present study we introduce an integrated approach called satellite and clutter absolute radar (SCAR) calibration to adjust the calibration of the reflectivity Z h. (2016), it is possible to retrieve additional information about calibration changes by combining different calibration techniques (the so-called integrated approaches). Radar calibration techniques are often evaluated separately. 2001) or other surrounding radars (e.g., Vukovic et al. Joint observations of precipitating systems can also be used, by comparing with spaceborne radars (e.g., Anagnostou et al. 1976) high reflectivity gradients ( Mueller 1977) ground clutter echoes ( Rinehart 1978) or, for dual-polarization radar only, the self-consistency of polarimetric variables ( Gorgucci et al. Over the years, many radar calibration techniques have been developed, using a fixed target ( Atlas and Mossop 1960) collocated disdrometer data ( Stout and Mueller 1968) solar interference ( Whiton et al. It is for these reasons that we decided to find external ways to monitor the radar calibration, to be able to adjust the calibration quickly and accurately, and to have a common procedure for the entire operational network. As a result, while exploring the dataset we found 1) an abrupt change in radar calibration, 2) a long period of time where the radar is miscalibrated, and 3) large differences between radars with overlapping areas. However, these tests are performed at most a few times per year, with no rigorous calibration monitoring the rest of the time. It is thus nearly impossible to estimate C without using an external source of information.ĬPOL, and all the radars of the Australian Bureau of Meteorology network, use a standard internal calibration procedure. These quantities can vary over time as a result of degradation or maintenance of radar hardware. It depends on a wide range of parameters, including wavelength, beamwidth, pulse length, transmitted power, and receiver gain. The challenge of radar calibration is to estimate this constant C for given radar settings and its variations in real time. Z m = 10 log C + 20 log r + 10 log P r, (2)where P r is the returned power by the target and C is the so-called radar constant. with a standard deviation of the canting angle of 12° best matches our dataset. We find that the drop-shape model of Brandes et al. Small changes in the self-consistency parameterization can lead to 5 dB of variation in the reflectivity calibration. Finally, we review the self-consistency technique and constrain its assumptions using results from the hybrid TRMM–GPM and ground echo technique. Using an iterative procedure and stable calibration periods identified by the ground echoes technique, we improve the accuracy of this technique to about 1 dB. To obtain an absolute calibration value, CPOL observations are compared to spaceborne radars on board TRMM and GPM using a volume-matching technique. It is remarkably stable to within a standard deviation of 0.1 dB. The ground clutter monitoring technique is applied to each radar volumetric scan and provides a means to reliably detect changes in calibration, relative to a baseline. These techniques are applied to a C-band polarimetric radar (CPOL) located in the Australian tropics since 1998. In this paper the following three techniques are used: 1) ground clutter monitoring, 2) comparisons with spaceborne radars, and 3) the self-consistency of polarimetric variables. Various radar calibration and monitoring techniques have been developed, but only recently have integrated approaches been proposed, that is, using different calibration techniques in combination. The stability and accuracy of weather radar reflectivity calibration are imperative for quantitative applications, such as rainfall estimation, severe weather monitoring and nowcasting, and assimilation in numerical weather prediction models. Integrated approach calibration framework Calibration using scattering simulations of Zh with permanent disdrometer observations Using the self-consistency curves to monitor Zdr Using the self-consistency curves to monitor Zh Parameterization of the T-matrix formulation using disdrometer data Comparison of TRMM–GPM and CPOL between 19 Calibrating CPOL reflectivities with spaceborne radars Seasonal monitoring of the radar calibration Impact of rain on ground clutter reflectivity The RCA technique: Using ground clutter to monitor reflectivity calibration
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