Geoscience Reference
In-Depth Information
A larger data set of six months (January to July 2007) using the SMC Vallirana radar provided
additional insight to the performance of this correction technique of AP echoes. It also allowed
to evaluate the performance of the technique applied by Bøvith et al. (2006) which made use of
cloud type information (SAF, 2011) as precipitating echo mask. A parallax correction (Vicente
et al., 2002) was introduced in the mask in order to improve the matching between the two
data types and, as seen in Table 5, substantial changes were found for some of the cloud types.
Uncorrected
Corrected
Precipitation
fr equency(%)
Precipitation
fr equency(%)
Cloud type
Cloud type
01.- Cloud fr ee land
0.64
01.- Cloud fr ee land
0.30
02.- Cloud fr ee sea
0.62
02.- Cloud fr ee sea
0.40
03.- Snow/ice land
0.41
03.- Snow/ice land
0.40
06.- Ver y low Cu.
0.77
06.- Ver y low Cu.
0.60
08.- Low St .
3.60
08.- Low St .
3.48
10.- Medium St .
15.30
10.- Medium St .
16.38
12.-High & opaque St .
29.18
12.-High & opaque St .
30.85
14.- Ver y High & opaque St .
31.90
14.- Ver y High & opaque St .
32.76
15.- Thin Ci.
0.79
15.- Thin Ci.
0.99
16.-Moderate thick Ci.
1.53
16.-Moder at e t hick Ci.
1.68
17. Ci. above lower cloud
6.80
17. Ci. above lower cloud
6.62
19.- Fractional cloud
1.40
19.- Fractional cloud
0.63
20.-Holes
0.00
20.-Holes
0.85
Table 5. Precipitation frequency for Cloud type product using the parallax corrected (left)
and uncorrected products (right), both generated using six months of SMC radar data
(January-July 2007).
7. Final remarks
In this chapter, an overview of the effects of radio propagation conditions upon radar
observations has been given. Though we have focused in ground-based weather radar systems,
many of the concepts presented apply as well to other types of radar and applications.
Particular emphasis has been given to aspects with potential impact on radar quantitative
precipitation estimates, considering beam blockage corrections or anomalous propagation
echoes detection and removal. These items should be considered in quality control for weather
radars, particularly those operating in complex topography environments and located near the
coast where anomalous propagation may affect dramatically radar observations.
8. Acknowledgments
Part of the results presented here were obtained by the authors in research projects made in
collaboration with a number of individuals including Uta Gjertsen (formerly at met.no and
now at the Norwegian Defence Research Establishment, Norway), Günther Haase and Anke
