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Extend progresses in synthetic aperture radar technology

ACRS 1999

Poster Session 2

Extend Progresses in Synthetic Aperture Radar Technology

Zhu Minhui, Wu yirong


Institute of Electronics, Chinese Academy of Sciences

E=Mail:[email protected],
[email protected]


Abstract

In the recent years, China pays much
attention into microwave remote sensing
application. Synthetic Aperture Radar (SAR)
sensor is being developed as a key geomatics
data source. This paper presents the main
R&D activities of SAR systems. It includes 4
parts of work on airborne SAR, spaceborne
SAR, ground SAR processor and new
generation’s SAR technologies. Some good
results are described.


1. Introduction

Synthetic Aperture Radar (SAR) is used
to acquire high-resolution large-scale
images of earth surface. The advantages
of a SAR device are operations in all
weather condition during the day and
night circles of an orbit in order to
complement the existing optical sensors.
At present SAR becomes an important
tool of active microwave remote
sensors for environment monitoring and
resource survey, military application in
the world.

Since the end of 70’s, institute of
Electronics, Chinese Academy of
Sciences (IECAS) started to study on
imaging radar technology for radar
system design and signal processing
methods as the main unit in China. As
technological progresses are rapidly
extended, SAR systems both airborne
and spaceborne platforms form the
major subjects in IECAS, not only to
demonstrate its technological feasibility,
but also to develop SAR engineering
projects and exploit some of the new
generation’s SAR technology. Technical
researchers have developed hardware
and software dealing with data
processing of high data rate. The
applied researches on a variety of fields
are widely extended such as Institute of
Remote Sensing Application and users
etc. Work on cartography, crop
monitoring, disaster detection and
monitoring, desertification assessment
and new geographical information
systems are increasingly involved.


2. The Airborne SAR System

Chinese organizations have bought
several plans devoted to airborne SAR
system. IECAS completed the first
operational X-band airborne SAR with
mono-polarization in early 80’s. Then
we produced the first multi-polarization
and multi-swath airborne SAR imaging
system, which got radar images
successfully, used for flood monitoring
in the early 90’s. In above system, SAR
raw data are gathered on-board the
aircraft and stored on optical film
recorder for subsequent data processing
using optical correlator on the ground.

The first real-time on-board SAR
imaging processor has been developed
in 1994 in order to meet time urgent
applications. It does SAR images
processing on board the aircraft. The
produced images can be displayed and
recorded immediately to verify the SAR
data acquired. In the same time a data
downlink communication system is
used, the produced images can be also
displayed on ground monitoring system
in time.

The radar system has worked very well
under severe service conditions and
produced a great number of mapping
area images. An example of the digital
images is shown in fig. 1. The
boundaries between water and land are
displayed very clearly. The river course,
bridges and other prevention
engineering works are also shown
clearly. By use of these images and
other known information, the scientists
on geology and water conservancy can
efficiently evaluate the effects of
flooding to agriculture and properties.


Fig. 1 Flooded Yangtze River. The Jiu-Jiang Area, 1998.

ACRS 1999

Poster Session 2

Extend Progresses in Synthetic Aperture Radar Technology


3. The spaceborne SAR system

At the end of 80’s, we received a strong
request of national high technology
program. It started our campaign work
on the spaceborne SAR system. IECAS
was arranged as the chief department in
the project and some other institutes
from industry units also take part in the
project. After the significant progresses
of its key techniques, IECAS complete
the design of L-SAR, resulting in
production of the major specification to
meet user’s requirement. Hardware
development is advanced. The
instrument comprises two major
functional groups, the central
electronics and an active phased array
antenna, which can be steered in one
axis. IECAS completed L-SAR central
electronics prototype in 1997. It was
developed a demonstration system and
got SAR digital image under the aircraft
tests. In meantime, it is intended to use
for a wide range of possible applied
researches. Fig.2 is its testing result.
China ancient great wall hidden under
dry soil is clearly shown. It was built in
northwest area about 1500 years ago.


Fig. 2 The Yan-Chi Area. Ancient Great Wall Built 1400 Years Before Was Discovered.


The active microstrip patch antenna
model with deployed units will be
verified in near future.

Upon user community’s request, the
planned Chinese SAR is designed L
band, HH polarization, changeable
incidence angle and two operating
modes. It will be carried on China made
satellite with a circular sun-synchronized
orbit.


4. SAR Ground Processor

SAR is the combination of coherent
radar and imaging processing technique.
The SAR processor must be designed to
be suitable to the SAR imaging
algorithm and deal with heavy
computation load and high throughput.
The high performance platforms such
as super-PC based processor;
workstation and the array processor are
successfully used for the different user’s
requests. The SPECAN algorithm,
Range/Doppler algorithm, Chirp-Scaling
algorithm and their revised
algorithms are developed in SAR
processing for the different operating
modes.

Presently Chinese receiving ground
station is up graded to meet wide users’
requirements in getting microwave
remote sensing data. Activities are now
conducted to get within a reasonable
time the capability to receive signals
from ERS-1/2, Spot, Landsat 7 and
Radarsat. SAR images are widely used
for economic oriented application.


5. The New generation’ SAR
Technology

The serial projects of developing new
generation’s SAR technology supported
by national high technology program
have been deployed. Latest trends in
SAR system are developing to new
operating modes in order to provide
more and more application.