Synthetic aperture radar interferometry(11)

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.21.Baseline decorrelation for various point target response functions.The solid line is for standard sinc response with no weighting.The dashed,dotted–dashed,dotted,and triangled lines are weightings of half-cosine,Hanning,Hamming,and optimized cosine,respectively.

It was shown in[23]

that

(63)

provided the scattering volume could be regarded as homo-

geneous in the range direction over a distance defined by the

range resolution.The

function

is the effective normalized backscatter cross sec-

tion per unit height.The term“effective”is used to indicate

that is the intrinsic cross section of the medium atten-

uated by all propagation losses through the medium.The

specific form

for depends on the scattering medium.

Models for this term,and its use in the remote sensing of

vegetation height,will be discussed in the applications sec-

tion of this paper.

In repeat-pass systems,there is another source of decor-

relation.Temporal

decorrelation

(shaded boxes)

as scattering from the volume contributes within a resolution

cell.

,the correlation due to thermal noise alone,can be written

as

(65)

where channel.In addi-

tion to thermal noise,which is additive,SAR returns also

have other noise components,due to,for example,range

and Doppler ambiguities.An expression for the decorrela-

tion due to this source of error can only be obtained for ho-

mogeneous scenes,since,in general,the noise contribution

is scene dependent.Typically for simplicity these ambigui-

ties are treated as additive noise as part of the overall system

noise floor.

In general,the full correlation will comprise contribution

from all these

effects

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.23.(a)Correlation image in radar coordinates of Algodones Dunefield,CA,measuring the sameness of the two images acquired one day apart used to form an ERS-1/2radar interferogram.Blue denotes low correlation,purple moderate correlation,and yellow-green high correlation.Salton Sea decorrelates because water changes from one second to the next.Some agricultural fields and dune areas decorrelate from over the one day period.Mountains decorrelate from baseline decorrelation effects on high slopes rather than temporal effects.Dunes remain well correlated in general over one day.(b)Five month correlation map showing large decorrelation in the unvegetated Algodones dunes but significantly less in much of the vegetated area to the west(in box).(c)Ground photo of vegetated dune area in box.

Rodríguez and Martin[23]presented the analytic expression

for the Cramer–Rao bound[54]on the phase variance

(67)

The variable

200m/s)and

spaceborne platforms(

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

platforms are limited in their ability to repeat their flight track

spatially with sufficient control.For a given image resolu-

tion and wavelength,the critical baseline for spaceborne plat-

forms is longer than airborne platforms by the ratio of their

target ranges,typically a factor in the range of20–100.For

example,a radar operating at C-band at40-MHz range band-

width looking at35

denote

the range-compressed presummed signal data for a pulse,

with.The motion

compensated signal is given by

(68)

where is

the range component of the displacement from the reference

path to the actual antenna location.This is denoted and

in Fig.24for the two interferometric antennas and is

given by

(69)

where