Fundamentals of Bistatic Synthetic Aperture Radar

Spatial Resolution Improvement in GNSS-Based SAR Using Multistatic Acquisitions and Feature Extraction

“…Due to the limited transmitted bandwidth, the bistatic geometry and the consequent non-orthogonality between range and Doppler resolution directions [33], each ‫ܫ‬ is characterized by a coarse spatial resolution (generally resolution cell area in the order of 80-150 m 2 ), whose worst value coincides with the direction of the resolution ellipse. As an example, we consider a simulated scenario given by a ground-based receiver collecting the signals reflected by a point scatterer in the scene center illuminated by the P-codes transmitted by two GLONASS satellites (5.11 MHz bandwidth).…”

Effects of Orbit and Pointing Geometry of a Spaceborne Formation for Monostatic-Bistatic Radargrammetry on Terrain Elevation Measurement Accuracy

“…It is worth noting that the bistatic angle plays the same role in monostatic-bistatic radargrammetry as the stereo-intersection angle in monostatic repeat-pass one. A general analysis of bistatic SAR resolution is reported in [26, 27], based on the gradient method and on the derivation of bistatic ambiguity function; literature results will be used in the next sections, whereas simplified expressions, based on [23], will be introduced here in order to assess basic rules for mission design. Assuming two space platforms operating at the same altitude in parallel trajectories, the bistatic ground range, Δ r g ″ , and azimuth, Δ x ′ resolution can be related to the monostatic ones (Δ r g ′ and Δ x′ , respectively) [23, 25]: $\Delta {r^{″}}_g=\frac{2\Delta {r^{\prime }}_{g}sin{\eta }^{\prime }}{sin{\eta }^{\prime }+sin{\eta }^{″}}$ $\Delta x^{″}=\frac{2r^{″}}{r^{\prime }+r^{″}}\Delta x^{\prime }$where η′ and η″ are monostatic and bistatic incidence angles; r′ and r″ are monostatic and bistatic slant ranges.…”

“…The projection of bistatic parameters, such as baseline $\overrightarrow{B}$, slant range $\overrightarrow{r}″$, sensor position $\overrightarrow{R}″$, onto the range-elevation plane of the monostatic antenna allows three-dimensional monostatic-bistatic geometry to be accounted [32], and generates an explicit formulation for height determination [23]. The projection can be carried out considering the unit vector normal to the first antenna range elevation plane (Figure 5): $\overrightarrow{n}=\frac{\overrightarrow{R}\prime \times \left({\stackrel{\prime }{V^{\to }}}_{\oplus }\times \overrightarrow{R}\prime \right)}{\left|\overrightarrow{R}\prime \times \left({\stackrel{\prime }{V^{\to }}}_{\oplus }\times \overrightarrow{R}\prime \right)\right|}$and, by means of this vector, calculating the projected parameters as follows: $B_{\perp }=\sqrt{B^2-{\left(\overrightarrow{B}\cdot \overrightarrow{n}\right)}^2}$ ${r^{″}}_{\perp }=\sqrt{{r^{″}}^2-{\left({\overrightarrow{r}}^{″2}\cdot \overrightarrow{n}\right)}^2}$ ${R^{″}}_{\perp }=\sqrt{{|\overrightarrow{R}″|}^2-{\left(\overrightarrow{R}″\cdot \overrightarrow{n}\right)}^2}$where $\overrightarrow{R}\prime$ is the monostatic sensor position, ${{\overrightarrow{V}}^{\prime }}_{\oplus }$ is the monostatic antenna velocity with respect to the Earth-centred-Earth-fixed (ECEF) reference frame.…”

“…In a spaceborne monostatic-bistatic scenario further considerations are needed: the bistatic image quality in terms of resolutions, ambiguities, signal-to-noise-ratio (SNR) is greatly affected by the monostatic-bistatic configurations, even before stereo reconstruction, therefore the effect of the acquisition geometry on bistatic image parameters must be accounted for when selecting the optimum configuration for radargrammetric DEM generation; when a monostatic image and a bistatic one are adopted to form a stereoscopic pair, new relations are needed to define target height as a function of the peculiar parameters of monostatic-bistatic surveying geometry [ 23 ]. Namely, the models of classical stereo-radargrammetry can be specialized to the monostatic/bistatic configuration, but also new models can be developed [ 17 , 24 ].…”

“…when a monostatic image and a bistatic one are adopted to form a stereoscopic pair, new relations are needed to define target height as a function of the peculiar parameters of monostatic-bistatic surveying geometry [ 23 ]. Namely, the models of classical stereo-radargrammetry can be specialized to the monostatic/bistatic configuration, but also new models can be developed [ 17 , 24 ].…”