Digital Signal Processing Reference
In-Depth Information
Fig. 8.11
Sinc function in Eq.
8.7
corresponding to a coherent integration time of
i
= 0.001 s,
for the LEO scenario in the
bottom-right panel
of Fig.
8.10
.(
left
) Correlation frequency set to the
frequency of the specular point f
central
f
spec
.(
right
) Correlation frequency centered with an
offset of 2 kHz with respect to the specular one, f
central
D
D
f
spec
C
2 kHz
Fig. 8.12
Sketch of informational content of the delay-Doppler waveforms. Correlations per-
formed at different f
central
frequency capture the reflected power from different Doppler belts on
the surface (
left
). These produce different delay waveforms (
right
), with lower power levels and
further delayed peaks as the frequency differs from the specular one. The
grey shaded areas
on
the basis of the
right panel
correspond to the contour plot of the complete set of delay-Doppler
waveforms, also called delay-Doppler map, DDM
8.5
Reflectivity Levels and Polarization Issues
The detailed formulation of the polarimetric behavior of the GNSS reflected signals
is embedded in the theories listed under Sect.
8.6
. However, the details of these
theories are not required to understand some general polarization aspects of the
reflectometry GNSS:
The GNSS signals are transmitted at right-hand circular polarization (RCHP).
The dielectric properties of the reflecting surface, together with the geometry (inci-
dence angle) determine which amount of RHCP signal is reflected as RHCP, and
which one is reflected as left-hand circular (LHCP) in specular-like contributions. It
follows the Fresnel reflectivity relationship:
Search WWH ::
Custom Search