An Estimation of Rainfall Amounts Using Radar-Derived Z-R Relationships
Abstract
Directly-measured reflectivity values (Z) by radar and rainfall values (R) by rain gages are correlated over five-minutes intervals to a maximum of one hour for 260 rain gage points. A non-linear regression of the expression R = aZ sub b is performed, with Z the independent variable. This expression is solved for Z to obtain Z-R relationships of the form Z = AR sub B for each five minute period. A median value of the coefficient A and the exponent B is computed to represent the complete hour. Z-R relationships are then used to calculate estimates of average rainfall amount over a rain gage area. These radar-estimated values of average rainfall amount are then compared to the average rainfall amounts measured by the rain gages for dependent as well as independent data sets. The significant effect of hail is also examined. Results indicate that directly-measured Z-R relationships derived from data containing shallow precipitation gradients were the most accurate in estimating the average water amount for the rain gage network area. In contrast, Z-R relationships derived from data containing steeper gradients of precipitation were not as accurate in estimating the average rainfall amount. The Z-R relationships of Marshall-Palmer,Jones, and the NEXRAD relationship underestimated the average rainfall amount by almost 30% for the data set containing shallow gradients of precipitation. Keywords: Theses. (KR)
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 1989
- Accession Number
- ADA217950
Entities
People
- Richard M. Harter
Organizations
- Air Force Institute of Technology