Geoscience Reference
In-Depth Information
The 3-D imaging technique is able to contribute to high-range-resolution wind
measurement. Yu and Brown (2004) proposed a technique named RIM-SA that calculates
wind velocity using both spaced antennas and multiple frequencies. In RIM-SA, first, RIM
was separately applied to signals received by each of spaced antennas in order to produce
high-range-resolution received signals. Next, SA technique was applied to the received
signals produced by RIM in order to calculate horizontal wind velocity with high range
resolution. Using data measured by MAPR, Yu and Brown (2004) produced profiles of
horizontal wind velocity with 100-m intervals from a RIM-SA measurement using 2-μs
transmitted pulse and four frequencies (914.667, 915.000, 916.000, and 916.667 MHz). Yu and
Brown (2004) showed that the horizontal wind produced by RIM-SA agrees well with both
wind velocity measured by a radiosonde and that measured by MAPR using the 0.67-μs
transmitted pulse (i.e., 100-m range resolution).
2.3.2 Assessment of wind velocity measurement
Because DBS has been widely used for wind profiling radars, accuracy of wind velocity
measured by DBS needs to be assessed. High resolution measurements using CRI
and RIM provide the opportunity to assess the accuracy of wind velocity measured by
DBS.
Wind field inhomogeneity within the scanning area of radar beams is a significant factor
that produces errors of wind velocity measured by DBS. Cheong et al. (2008) carried out CRI
measurement using TEP in order to obtain radial Doppler velocities from 490 beam
directions, and used the radial Doppler velocity data in order to estimate how the wind field
inhomogeneity affects the error of wind velocity measured by DBS. Cheong et al. (2008)
concluded that optimal zenith angle of off-vertical radar beams is approximately 9-10° for
minimizing the root-mean square (RMS) error in wind velocity measured by DBS, and that
increasing number of off-vertical radar beams significantly reduces the RMS error in wind
velocity measured by DBS.
Tilted refractive-index layers caused by KH instability deteriorate the measurement
accuracy of vertical wind velocity because the tilted refractive-index layers cause
contamination of horizontal wind velocity to the Doppler velocity of vertically-pointed
radar beam, from which vertical wind is calculated in DBS (Muschinski, 1996; Yamamoto
et al., 2003). Chen et al. (2008) applied the 3-D imaging to data collected by the MU radar
in order to investigate relations between angular distribution of clear-air echo power and
Doppler velocity measured by the vertically-pointed radar beam with improved range
resolution. Chen et al. (2008) successfully showed the clear relation between the Doppler
velocity bias measured by the vertically-pointed radar beam and the tilt of radar echo
layers.
Though multistatic radar technique is not CRI, it is useful for measuring 3-D distribution
of wind velocities. By installing two receiver arrays at approximately 1 km away from
the westward and southward of the main antenna of the EAR, Nishimura et al. (2006)
and (2010) realized the multistatic radar measurement of wind velocities. Their
measurement results revealed 3-D wind perturbations down to the horizontal scale of
500 m.
