IEEE GEOSCIENCE AND REMOTE SENSING LETTERS, VOL. 9, NO. 4, JULY 2012 759
Three-Dimensional SAR Focusing via Compressive
Sensing: The Case Study of Angel Stadium
Sun Xilong, Yu Anxi, Dong Zhen, and Liang Diannong
Abstract—Recently, a synthetic aperture radar (SAR) tomo-
grahic focusing method based on compressive sensing was pro-
posed. This focusing method can reduce the required number of
measurements and achieve satisfying elevation resolving ability.
First, we briefly review this novel focusing method and prove the
applicability of compressed sensing (CS) for SAR tomography the-
oretically using the latest improvement of CS. Then, we apply this
focusing method to the 3-D reconstruction of Angel Stadium with
Envisat-ASAR data. Both the theoretical analysis and satisfying
results of real data processing confirmed the applicability of this
SAR tomograhic focusing method.
Index Terms—Compressive sensing (CS), Envisat-ASAR, syn-
thetic aperture radar (SAR), tomography.
I. INTRODUCTION
S
YNTHETIC aperture radar (SAR) tomography forms a
synthetic aperture along the normal-slant-range (nsr) direc-
tion to achieve resolving ability of multiple scatterers within
one range-azimuth resolution cell [1], [2]. SAR tomography
enables SAR to have the ability of 3-D imaging, so it has at-
tracted an explosion of interest in the last few years. At present,
the synthetic aperture along nsr direction of SAR tomography
is usually achieved by repeat-pass missions of single-antenna
SAR systems. In this data acquisition mode, particularly for
spaceborne SAR, the passes are unevenly spaced, and available
passes are much lower than that needed for a large synthetic
aperture. Hence, the urgent problem of SAR tomography is how
to achieve satisfying elevation resolution with a small number
of nonuniform passes.
Recently, a SAR tomograhic focusing method based on
compressive sensing, in which the inverse problem of SAR
tomography is solved by
1
-norm regularization, was proposed
in [3]–[5]. This SAR tomographic focusing method can reduce
the required number of measurements and achieve satisfying
elevation resolving ability with a given aperture in nsr direction.
In [3] and [4], the required number of measurements was
discussed, and experimental results of ERS1/2 data were pre-
sented. In [5], Super-resolution properties and point localization
Manuscript received May 11, 2011; revised October 19, 2011; accepted
December 2, 2011. Date of publication February 23, 2012; date of current
version May 7, 2012. This work is supported by the National Natural Science
Foundation of China (61002031, 61101187) and NUDT Research Foundation
(JC10-04-03).
The authors are with School of Electronic Science and Engineer-
ing, National University of Defense Technology, Changsha 410073, China
(e-mail: longlongsun@sohu.com; yu_anxi@sina.com; dongzhen@vip.sina.
com; 396576571@qq.com).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/LGRS.2011.2181321
Fig. 1. Multipass acquisition geometry of SAR tomography. For the sake of
simplicity, all the acquisitions are aligned along normal-slant-range direction.
accuracies of this focusing method were demonstrated using
simulations and real TerraSAR-X data.
In SAR tomography, the measurements are random sam-
ples of continuous frequency spectrum of the unknown sig-
nal, instead of random samples of discrete Fourier transform
(DFT). As a consequence, the sensing matrix is not obtained
by randomly sampling rows of an orthonormal matrix. The
theory of CS in [6]–[11] cannot provide a framework for this
measurement strategy perfectly. Recently, Candes introduced a
simple and very general theory of compressive sensing in [12]
that can provide a framework for the measurement strategy in
SAR tomography. In this letter, we will prove the applicability
of compressed sensing (CS) for SAR tomography theoretically
using the theory in [12]. Then, we will apply the CS-based
focusing method to real data to validate this method. The
Envisat -ASAR data over Angel Stadium between October 29th
2003 and November 7th 2007 are used.
II. F
ORMULATION OF SAR TOMOGRAPHY
To achieve resolving ability of multiple scatterers within one
azimuth-range resolution cell, a synthetic aperture along the nsr
direction is needed to form by repeat-pass missions of single-
antenna SAR system. Fig. 1 gives the multipass acquisition
geometry, for the sake of simplicity, all the acquisitions are
aligned along nsr direction. Let us refer to the condition that
M passes are acquired over the target with different baselines.
1545-598X/$31.00 © 2012 IEEE