Synthetic aperture radar interferometry(5)

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

facing toward the radar and is less on slopes facing away from the radar.Also from(16),the fringe frequency is inversely proportional

to

(20)

These equations appear to be nonlinear,but by choosing an

appropriate local coordinate basis,they can be readily solved

for[48].To illustrate,we

let be the platform

position vector and specialize to the two-dimensional case

where

is measured and relates the platform posi-

tion to the target(range sphere)through extension of the unit

look vector.The look

angle

estimated,can be constructed.

It is immediate from the above expressions that re-

construction of the scatterer position vector depends on

knowledge of the platform location,the interferometric

baseline length,orientation angle,and the interferometric

phase.To generate accurate topographic maps,radar inter-

ferometry places stringent requirements on knowledge of

the platform and baseline vectors.In the above discussion,

atmospheric effects are neglected.Appendix B develops

the correction for atmospheric refraction in an exponential,

horizontally stratified atmosphere,showing that the bulk of

the correction can be made by altering the effective speed

of light through the refractive atmosphere.Refractivity

fluctuation due to turbulence in the atmosphere is a minor

effect for two-aperture single-track interferometers[24].

To illustrate these theoretical concepts in a more concrete

way,we show in Fig.13a block diagram of the major steps

in the processing data for topographic mapping applica-

tions,from raw data collection to generation of a digital

topographic model.The description assumes simultaneous

collection of the two interferometric channels;however,

with minor modification,the procedure outlined applies to

processing of repeat-track data as well.

B.Sensitivity Equations and Accuracy

1)Sensitivity Equations and Error Model:In design

tradeoff studies of InSAR systems,it is often convenient to

know how interferometric performance varies with system

parameters and noise characteristics.Sensitivity equations

are derived by differentiating the basic interferometric height

reconstruction equation(6)with respect to the parameters

needed to determine,,

and

,baseline

length

,and position,assuming

that,yields

[24]

,and velocity errors result in position

errors on a vector parallel

to.Since the look vector

in an interferometric mapping system has components both

parallel and perpendicular to nadir,baseline and phase errors

contribute simultaneously to planimetric and height errors.

For broadside mapping geometries,where the look vector is PROCEEDINGS OF THE IEEE,VOL.88,NO.3,MARCH2000341