Alamelu Kilambi

On the Extraction of Near-Surface Index of Refraction Using Radar Phase Measurements from Ground Targets

The authors consider the simplest radar equation involving the index of refraction n: the time t taken by electromagnetic waves to reach a target at range r and return to the radar is r=2rn/c/sub 0/, with c/sub 0/, being the speed of light in a vacuum. For fixed targets, r is constant and only n varies; hence if t could be measured precisely for such targets, the average value of the refractive index over the path between the radar and these targets could be determined. Unfortunately, most radars cannot measure t and site surveys are not accurate enough to determine r with the part-per-million accuracy required to obtain useful information about n. However, if the range to the target is fixed, but only known to a fair accuracy, say better than 1%, it would be enough to allow us to relate changes in t to changes in n; the absolute calibration would then have to be done by other means. With this scheme, we are only required to determine changes in t that can be obtained by measuring the phase of the target.

Real-Time Comparisons of VPR-Corrected Daily Rainfall Estimates with a Gauge Mesonet

Abstract The relative skill of two vertical-profile-of-reflectivity (VPR) correction techniques for daily accumulations on a selected dataset and a real-time dataset has been verified. The first technique (C1) adjusts the 1-h rainfall amounts already derived on a Cartesian CAPPI map at an altitude of 1.5 km in a “one step” procedure using the range-dependent space–time-averaged VPR over the 1-h interval. The C2 technique corrects the nonconvective polar reflectivity measurements of each 5-min radar cycle that are also centered at a height of 1.5 km according to a VPR that is similarly derived but over a shorter time interval. The results emphasize the importance of applying a VPR correction scheme—in particular, in a climatic regime in which most of the liquid precipitation falls from stratiform echoes. The crucial importance of the choice of datasets is also underlined, causing differences in the final assessment that may be greater than those between the various algorithms. Both techniques perform well ...

Extraction of near-surface index of refraction using radar phase measurements from ground targets

The authors consider the simplest radar equation involving the index of refraction n: the time t taken by electromagnetic waves to reach a target at range r and return to the radar is r=2rn/c/sub 0/, with c/sub 0/, being the speed of light in a vacuum. For fixed targets, r is constant and only n varies; hence if t could be measured precisely for such targets, the average value of the refractive index over the path between the radar and these targets could be determined. Unfortunately, most radars cannot measure t and site surveys are not accurate enough to determine r with the part-per-million accuracy required to obtain useful information about n. However, if the range to the target is fixed, but only known to a fair accuracy, say better than 1%, it would be enough to allow us to relate changes in t to changes in n; the absolute calibration would then have to be done by other means. With this scheme, we are only required to determine changes in t that can be obtained by measuring the phase of the target.

A Simple and Effective Method for Separating Meteorological from Nonmeteorological Targets Using Dual-Polarization Data

AbstractTo satisfy the needs of the meteorological and aeroecological communities wanting a simple but effective way of flagging each other’s unwanted echo for a variety of different operational ra...