Problem Gallery. 
The vertical dBZ profile.
The Vertical profile of reflectivity is the main factor in the
accurancy of precipitation measurements at distances of 50250 km. The
origins of large bias of 220 dB are based on the difference between the
actual reflectivity of ground level and in the contribution volume
aloft. 

Attenuation by precipitation.
dBZc = dBZ
+ 2C*r*sum(Z^{E} ) this equation is used for getting
corrected values of attenuation by precipitation.
. 

Total beam overshooting.
Total beam overshooting influences the range limit of radar. This
range limit depends on elevation angle and cloud top height. It is worth
sitting radar to place, that gives lower elevation angle. 

Sea clutter.
Sea clutter is a spesific form of spurious echo feature. The main
reason of its formation is partial radar beam anomalous propagation above water
bodies, i.e. ducting. The method that is able to treat sea clutter, is successful, if
only it can identify multiple modes of the reflictivity spectrum and
treat each mode differently. 

Ground clutter.
It occurs independently of propagation conditions. It can be
permanent and severe. Its occurance depends on radar location and on its
scan strategy configuration. Minimization of ground clutter effects
depends upon intelligent siting and signal processing. 

AP clutter.
AP (anomalious propagetion) is a mirage on a radar. Ground clutter, high
superrefraction, echos beyond max unumbiguous range and biolife,
mountains are common AP signatures. If there are data
from more than one radar, AP and false echos are easy to identify,
because the neighboring radars generally won't see the same thing. If
there is the only radar but it is possible to look at different
elevation angles, it can be found that AP tends to be confined to the
lowest elevation angle. 

Hail.
Hail is one of problems in precipitation measurements.
There is a method for detection summer hail, developed by Waldvogel.
The matter is that the presence of hail is likely, when radar
reflectivities of 45 dBZ are observed at 1.4 km above
freezing level. The probability of hail presence increases, when high
reflectivity is even higher above freezing level. 

Beam propagation changes. Vertical
profiles of temperature, pressure and humidity affect radar beam
propagation, especially when there is low elevation angle at the radar
site. Actually, normal propagation conditions are dominant but there are
also significant seasonal variations in the median and monthly
dispersion of the vertical refrectivity gradient. 
Beam blockage.
There are many methods, e. g. the Norwegian one documented in Gjertsen and Dahl (2002),
for the blockage correction. In this method the number of beam traces
are determined using altitude vertical angle, refractivity, atmosferic
pressure, temperature data and data of water vapour partial pressure.
This computed beam trace is used in a distributed model, where each
point is taken in cylindrecal coordinate system, if a point on the
topografic map is higher than a computed one. The precalculated beam
closest to the topografic data is used as min measurement height in that
point. 

Radar siting.
National radar network consists of many radars located all over the
country. The radar horizon should be unobscured to the extent possible
determined by the local orography. If the surface of the country is
flat, one can avoid blocked sectors and to find the location that is not
far from the optimal location. In the mountaneous regions such locations
are found only on mountain tops. But this location is problematic for
many points considered below. Thus an
unobscured horizon is only one of the things which determine the radar
location. Location at the airport should be avoided, because this
location is not the best one to support the aviation. 

Suboptimal compositing algorithms.
There are several different principles of choosing
the data (compositing algorithm). Problems of cartezian product
themselves cause information loss or bias, but it is obvious that
quality indicator fields are necessary when calculating the optimal
values of data from two or more radars. There are principles of data
choosing based on choosing the nearest radar, closest to earth,maximume
and average. All of them have some problems but the worst choise is
connected with average one. In any case to use these principles
information of elevation angles and radar heights should be available.
One possible solution was developed at FMI. It is based on generating so
called seek matrix. This matrix is a kind of pointer table. Every point
gives a lot of information. The advantage of this method is the fastness
of getting information. But it is suitable for supercomputers only,
because of considerable large amount of memory required by matrix and
data. 
Availability of polar data.
The problem connected with polar data is access to it. In many radar
networks polar data are the lowest level potensially available. But due
to radical change data's charakteristics, when transforming them to
cartezian grids, many algorithms perform best in polar space. Further
improvement the data quality comes with international exchange of polar
volume data. 
Orographic enhancement.
The precipitation process can be enhanced by the seederfeeder
mechanizm. Convective cells aloft can produce large precipitation
particles, falling through a lower cloud layer, grow at the expense of
the water content at the lower cloud. 
Gauge adjustment.
Gauge adjustment is a solution of problems connected with range
effects, calibration level, and limited extent effects. Gauge adjustment
can be found as a term which helps to describe any procedure according
to which characteristics of radar data are made partial changes such
that they correspond to the quantity given by gauge measurements. 