Synthetic aperture radar interferometry(6)

Synthetic aperture radar interferometry is an imaging technique for measuring the topography of a surface, its changes over time, and other changes in the detailed characteristics of the surface. By exploiting the phase of the coherent radar signal, interf

Fig.13.Block diagram showing the major steps in interferometric processing to generate topographic maps.Data for each interferometric channel are processed to full resolution images using the platform motion information to compensate the data for perturbations from a straight line path.One of the complex images is resampled to overlay the other,and an interferogram is formed by cross-multiplying images,one of which is conjugated.The resulting interferogram is averaged to reduce noise.Then,the principal value of the phase for each complex sample is computed.To generate a continuous height map,the two-dimensional phase field must be unwrapped.After the unwrapping process,an absolute phase constant is determined.Subsequently,the three-dimensional target location is performed with corrections applied to account for tropospheric effects.A relief map is generated in a natural coordinate system aligned with the flight path.Gridded products may include the target heights,the SAR image,a correlation map,and a height error

map.

Fig.14.Sensitivity tree showing the sensitivity of target location

to various parameters used in interferometric height reconstruction.

See Fig.15for definitions of angles.orthogonal to the velocity vector,the velocity errors do not

contribute to target position errors.Fig.14graphically de-

picts the sensitivity dependencies,according to the geometry

defined in Fig.15.

To highlight the essential features of the interferometric

sensitivity,we simplify the geometry to a flat earth,with

the Fig.15.Baseline and look angle geometry as used in sensitivity

formulas.

baseline in a plane perpendicular to the velocity vector.With this geometry the baseline and velocity vectors are given

by

Synthetic aperture radar interferometry is an imaging technique for measuring the topography of a surface, its changes over time, and other changes in the detailed characteristics of the surface. By exploiting the phase of the coherent radar signal, interf

and

is baseline

length,

is the look angle,as shown in Fig.9.These formulas are

useful for assessing system performance or making trade

studies.The full vector equation however is needed for use

in system calibration.

The sensitivity of the target position to platform position

in the along-track

direction,and

vertical

direction

have larger cross track position errors

than vertical errors.

The sensitivity of the target position to errors in the base-

line length,and baseline roll angles are given

by

is1or2for single transmit or ping-pong modes.This

is inversely proportional to the perpendicular component of

the

baseline,

is obtained from the third component of(30).

Fig.16represents an example of an interferometric

SAR system for topographic mapping.Several parameters

defining the performance sensitivity,and therefore calibra-

tion of the interferometer,relate directly to radar hardware

observables.

•Baseline vector,including length and attitude,for

reduction of interferometric phase to height.This pa-

rameter translates to knowing the locations of the phase

centers of the interferometer antennas.

•Total radar range,

say

and

,between channels,for determi-

nation of the topography.This parameter translates to

knowing the phase delays through the receiver

chains,