Uncertainties Associated with Combining Airborne and Ground-Based Doppler Radar Data

Abstract

Observations with airborne Doppler radar can expand the area of coverage and extend the time a moving weather system can remain under observation. Also, additional analysis methods are possible with the increase in independent estimates of the wind field that can be provided by an airborne sampling system. However, the advantages of airborne Doppler sensing are constrained by the geometry in which the data are collected, as well as errors introduced by uncertainties in the sampling platform location and orientation. Finally, a longer time required to sample a region than is typical for ground-based radar results in increased uncertainties due to the field's evolution and advection during the sampling interval. Uncertainties related to geometry are examined for flight patterns which are for aircraft alone and for those which also utilize data from one and two ground-based radars. These illustrate the distribution and relative magnitude of uncertainty expected for each type of flight pattern and data analysis method. Both the NOAA P?3, and the NCAR ELDORA scanning methodologies are examined. To evaluate the different flight patterns, a relative quality index is used. It is defined as the reciprocal of the vertical velocity error variance integrated over the analysis domain. This normalized relative quality index is a mean value over the sampled volume. Flight patterns that utilize a single ground-based radar provide coverage over ? ten times the area in about one-half the time, and with relative quality about ten times better than that by aircraft alone. Data collection, particularly aircraft data collection, often involves real-time decision making, and storms frequently are not in an ideal location relative to fixed ground-based radars. The best operational decisions require knowledge of eventual synthesis capabilities and the location of the volume to be interrogated relative to those facilities. These concepts are illustrated in a case example. Airborne Doppler and ground-based radar synthesis results are compared and discussed.