Coupling GPROF precipitation estimates and DPR reflectivity profiles
over the Netherlands to (reflectivity) observations obtained from
ground-based dual-polarization radars.
Abstract
Radiance measurements from several types of passive microwave (PMW)
sensors are combined in the Global Precipitation Measurement mission
(GPM) to increase the temporal and spatial coverage of precipitation
observations. The measurements of these sensors are converted to
precipitation estimates by the GPM Profiling Algorithm (GPROF). High
frequency PMW-channels are used to retrieve precipitation estimates over
land, as these frequencies can measure the radiance scattered by ice
particles in rain clouds. Scattering related to shallow and
low-intensity precipitation events, however, is limited. Hence,
radiometric signals associated with these events are hard to distinguish
from the naturally emitted radiation from the Earth’s surface,
especially since this so-called background radiation is dependent on the
surface type. A better understanding of the physical processes that
occur during precipitation events can help to identify possible
weaknesses in the GPROF algorithm. Hence, this study couples overpasses
of GPM radiometers over the Netherlands to two dual-polarization radars
from the Royal Netherlands Meteorological Institute (KNMI) in 2019. All
rainy overpasses (>0.1 mm/hr) within a 75 km radius around
one of the radars are selected. This coupling provides the opportunity
to relate GPROFs performance to physical characteristics of
precipitation events, such as the vertical reflectivity profile and
dual-polarization information on the melting layer. Additionally,
simultaneous observations from both the PMW sensor and the
dual-frequency precipitation radar (DPR, used as a-priori database in
GPROF) aboard the GPM core satellite are available. Hence, space-based
and ground-based reflectivity profiles can be compared and coupled to
discrepancies of the GPROF algorithm.