X-Band Polarimetric Radar Measurements of Rainfall

• Published in: Journal of applied meteorology (1988) Vol. 41; no. 9; pp. 941 - 952
• Main Authors: Matrosov, Sergey Y., Clark, Kurt A., Martner, Brooks E., Tokay, Ali
• Format: Journal Article
• Language: English
• Published: Boston, MA American Meteorological Society 01-09-2002
• Subjects: Earth, ocean, space; Environmental technology; Estimators; Exact sciences and technology; External geophysics; Geophysics. Techniques, methods, instrumentation and models; Meteorological applications; Meteorology; Phase shift; Radar; Radar echoes; Rain; Reflectance; Superhigh frequencies; Transcriptional regulatory elements; Wavelengths; United States; North America; Virginia; America; Validation; Geometrical shape; Polarization; High resolution; Convection cell; Water drop; Disdrometer; Phase shift; X band; Bias; Equilibrium shape; Convective cloud; Radar polarimetry; Dimension spectrum; Rainfall rate; Reflectivity; Rain; Stratiform cloud; Radar observation; Attenuation; Rain gauge; Corrections
• ISSN: 0894-8763; 1520-0450
• DOI: 10.1175/1520-0450(2002)041<0941:xbprmo>2.0.co;2

A combined polarimetric estimator for rainfall rate (R) retrievals from polarimetric radar measurements at X band is proposed. This estimator uses the horizontal polarization radar reflectivityZₑ, differential reflectivityZ
DR, and specific differential phase shiftK
DP, and it intrinsically accounts for changes in how drop oblateness increases with size. Because this estimator uses power measurements (i.e.,ZₑandZ
DR), a procedure for correcting these measurements for effects of partial attenuation and differential attenuation using the differential phase measurement is suggested. An altitude correction for estimates of rainfall rates is also suggested. The proposed combined polarimetric estimator that usesK
DP,Z
DR, andZₑ, an estimator that usesK
DPalone for equilibrium drop shapes, and differentZₑ–Rrelations were applied to the 15 rain events observed with the NOAA X-band transportable polarimetric radar during the eight-week field campaign at the NASA Wallops Island facility in Virginia. The observed rains ranged from very light stratiform events to very heavy convective ones with cells producing rainfall rates in excess of 100 mm h−1. The three different ground validation sites were equipped with high-resolution (0.01 in.) tipping-bucket rain gauges. One of these sites also was equipped with disdrometers. In terms of the relative standard deviation, the combined polarimetric estimator provided the best overall agreement with gauge data (22%), closely followed by a case-tunedZₑ–Rrelation (23%) that was determined for each observational case from drop size distributions (DSD) measured in situ by a disdrometer and was available only a posteriori. The use of theK
DP-only estimator and a meanZₑ–Rrelation resulted in 30% and 32% relative standard deviations, correspondingly. The combined polarimetric estimator, theK
DP-only estimator, and the casetunedZₑ–Rrelation estimator provided about a 6%–9% negative bias in comparison with the gauge data; the meanZₑ–Rrelation estimator provided a larger negative bias (18%).