Synthetic aperture radar interferometry

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

Synthetic Aperture Radar Interferometry

PAUL A.ROSEN,SCOTT HENSLEY,IAN R.JOUGHIN,MEMBER,IEEE,FUK K.LI,FELLOW,IEEE, SØREN N.MADSEN,SENIOR MEMBER,IEEE,ERNESTO RODRÍGUEZ,AND

RICHARD M.GOLDSTEIN

Invited Paper

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,interferom-etry has transformed radar remote sensing from a largely inter-pretive science to a quantitative tool,with applications in cartog-raphy,geodesy,land cover characterization,and natural hazards. This paper reviews the techniques of interferometry,systems and limitations,and applications in a rapidly growing area of science and engineering.

Keywords—Geophysical applications,interferometry,synthetic aperture radar(SAR).

I.I NTRODUCTION

This paper describes a remote sensing technique gener-ally referred to as interferometric synthetic aperture radar (InSAR,sometimes termed IFSAR or ISAR).InSAR is the synthesis of conventional SAR techniques and interfer-ometry techniques that have been developed over several decades in radio astronomy[1].InSAR developments in recent years have addressed some of the limitations in conventional SAR systems and subsequently have opened entirely new application areas in earth system science studies.

SAR systems have been used extensively in the past two decades for fine resolution mapping and other remote sensing applications[2]–[4].Operating at microwave frequencies, Manuscript received December4,1998;revised October24,1999.This work was supported by the National Imagery and Mapping Agency,the De-fense Advanced Research Projects Agency,and the Solid Earth and Natural Hazards Program Office,National Aeronautics and Space Administration (NASA).

P.A.Rosen,S.Hensley,I.R.Joughin,F.K.Li,E.Rodríguez,and R. M.Goldstein are with the Jet Propulsion Laboratory,California Institute of Technology,Pasadena,CA91109USA.

S.N.Madsen is with Jet Propulsion Laboratory,California Institute of Technology,Pasadena,CA91109USA and with the Technical University of Denmark,DK2800Lyngby,Denmark.

Publisher Item Identifier S0018-9219(00)01613-3.SAR systems provide unique images representing the elec-trical and geometrical properties of a surface in nearly all weather conditions.Since they provide their own illumina-tion,SAR’s can image in daylight or at night.SAR data are increasingly applied to geophysical problems,either by themselves or in conjunction with data from other remote sensing instruments.Examples of such applications include polar ice research,land use mapping,vegetation,biomass measurements,and soil moisture mapping[3].At present,a number of spaceborne SAR systems from several countries and space agencies are routinely generating data for such re-search[5].

A conventional SAR only measures the location of a target in a two-dimensional coordinate system,with one axis along the flight track(“along-track direction”)and the other axis defined as the range from the SAR to the target(“cross-track direction”),as illustrated in Fig.1.The target locations in a SAR image are then distorted relative to a planimetric view, as illustrated in Fig.2[4].For many applications,this alti-tude-dependent distortion adversely affects the interpretation of the imagery.The development of InSAR techniques has enabled measurement of the third dimension.

Rogers and Ingalls[7]reported the first application of in-terferometry to radar,removing the“north–south”ambiguity in range–range rate radar maps of the planet Venus made from Earth-based antennas.They assumed that there were no topographic variations of the surface in resolving the ter,Zisk[8]could apply the same method to mea-sure the topography of the moon,where the radar antenna directivity was high so there was no ambiguity.

The first report of an InSAR system applied to Earth observation was by Graham[9].He augmented a conven-tional airborne SAR system with an additional physical antenna displaced in the cross-track plane from the conven-tional SAR antenna,forming an imaging interferometer. By mixing the signals from the two antennas,the Graham interferometer recorded amplitude variations that repre-sented the beat pattern of the relative phase of the signals.

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