Multi-Look Radiometric Correction of SAR Images
Deviations of the aircraft trajectory and instabilities of the aircraft orientation lead to non-uniform
 illumination of the ground by the antenna beam and, as a result, to radiometric errors in radar images
 obtained with airborne synthetic aperture radars (SAR). The clutter-lock te...
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| Опубліковано в: : | Радиофизика и радиоастрономия |
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| Дата: | 2011 |
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Радіоастрономічний інститут НАН України
2011
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| Назва журналу: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Цитувати: | Multi-Look Radiometric Correction of SAR Images / O.O. Bezvesilniy, I.M. Gorovyi, V.V. Vynogradov, D.M. Vavriv // Радиофизика и радиоастрономия. — 2011. — Т. 16, № 4. — С. 424-432. — Бібліогр.: 8 назв. — англ. |
Репозитарії
Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860243827919421440 |
|---|---|
| author | Bezvesilniy, O.O. Gorovyi, I.M. Vynogradov, V.V. Vavriv, D.M. |
| author_facet | Bezvesilniy, O.O. Gorovyi, I.M. Vynogradov, V.V. Vavriv, D.M. |
| citation_txt | Multi-Look Radiometric Correction of SAR Images / O.O. Bezvesilniy, I.M. Gorovyi, V.V. Vynogradov, D.M. Vavriv // Радиофизика и радиоастрономия. — 2011. — Т. 16, № 4. — С. 424-432. — Бібліогр.: 8 назв. — англ. |
| collection | DSpace DC |
| container_title | Радиофизика и радиоастрономия |
| description | Deviations of the aircraft trajectory and instabilities of the aircraft orientation lead to non-uniform
illumination of the ground by the antenna beam and, as a result, to radiometric errors in radar images
obtained with airborne synthetic aperture radars (SAR). The clutter-lock technique is commonly used
to avoid the radiometric errors. However, this approach leads to strong geometric distortions in SAR
images in the case of fast and significant instabilities of antenna orientation. Here we propose a multilook
radiometric correction technique which can be used instead of the clutter-lock. The proposed
approach has been tested by using a Ku-band airborne SAR system installed onboard a light-weight
aircraft.
Отклонения траектории самолета и нестабильности ориентации самолета приводят к неравномерной подсветке земной поверхности
лучом антенны и в результате к радиометрическим ошибкам на радиолокационных изображениях, полученных с помощью самолетных радиолокаторов с синтезированной апертурой
(РСА). Чтобы избежать радиометрических ошибок, обычно применяется техника слежения за
сигналом от местности. Однако такой подход
приводит к значительным геометрическим искажениям на РСА-изображениях в случае быстрых и значительных нестабильностей ориентации антенны. В этой статье мы предложили
технику многовзглядовой радиометрической коррекции, которую можно использовать вместо
слежения за сигналом от местности. Предложенный подход был испытан с помощью самолетного РСА 2-сантиметрового диапазона длин
волн, установленного на легком самолете.
Відхилення траєкторії літака та нестабільності
орієнтації літака призводять до нерівномірного
підсвічування земної поверхні променем антени
і, як наслідок, до радіометричних помилок на радіолокаційних зображеннях, отриманих за допомогою літакових радіолокаторів з синтезованою
апертурою (РСА). Аби уникнути радіометричних
помилок, звичайно використовується техніка
слідкування за сигналом від місцевості. Однак
такий підхід призводить до значних геометричних
спотворень РСА-зображень у випадку швидких
та значних нестабільностей орієнтації антени.
У цій статті ми пропонуємо техніку багатопоглядової радіометричної корекції, яку можна використовувати замість слідкування за сигналом
від місцевості. Запропонований підхід був випробуваний за допомогою літакового РСА 2-сантиметрового діапазону довжин хвиль, встановленого на легкому літаку.
|
| first_indexed | 2025-12-07T18:33:22Z |
| format | Article |
| fulltext |
Радиофизика и радиоастрономия, 2011, т. 16, №4, с. 424-432
ISSN 1027-9636 © O. O. Bezvesilniy, I. M. Gorovyi, V. V. Vynogradov, and D. M. Vavriv, 2011
Multi-Look Radiometric Correction of SAR Images
O. O. Bezvesilniy, I. M. Gorovyi, V. V. Vynogradov, and D. M. Vavriv
Institute of Radio Astronomy of the National Academy of Sciences of Ukraine,
4, Chervonopraporna St., Kharkiv, 61002, Ukraine
E-mail: vavriv@rian.kharkov.ua
Received August 25, 2011
Deviations of the aircraft trajectory and instabilities of the aircraft orientation lead to non-uniform
illumination of the ground by the antenna beam and, as a result, to radiometric errors in radar images
obtained with airborne synthetic aperture radars (SAR). The clutter-lock technique is commonly used
to avoid the radiometric errors. However, this approach leads to strong geometric distortions in SAR
images in the case of fast and significant instabilities of antenna orientation. Here we propose a multi-
look radiometric correction technique which can be used instead of the clutter-lock. The proposed
approach has been tested by using a Ku-band airborne SAR system installed onboard a light-weight
aircraft.
Keywords: synthetic aperture radar (SAR), airborne SAR, radiometric errors, radiometric correction,
multi-look processing
1. Introduction
Synthetic aperture radars (SAR) are capable of
obtaining high-resolution radar images of ground
surfaces by using a physically small antenna [1].
The radar is mounted onboard a moving platform
such as an aircraft or a satellite. Due to the plat-
form motion, the radar transmits and receives ra-
dar pulses at different positions on the trajectory.
By coherent processing of the collected radar data,
a synthetic aperture with a very narrow beam
is formed thus providing the high azimuth (cross-
range) resolution. The high range resolution is
achieved by using a common pulse compression
technique, for example, by transmitting pulses with
linear frequency modulation. The direction of the
synthetic aperture beam (the synthetic beam)
is fully controlled by the SAR data processing
algorithm. Usually, the synthetic beam is formed to
be in the elevation plane of the real antenna beam.
In other words, the synthetic beam is pointed at the
central line of the ground spot illuminated by the
real antenna. If the real antenna beam is wide
enough, then several independent synthetic beams
can be built within the main lobe of the real antenna
pattern. This technique is known as multi-look pro-
cessing [1]. Each synthetic beam forms an inde-
pendent radar image of the same ground scene
called “SAR look”. The non-coherent averaging of
the SAR looks into one multi-look SAR image
is used to suppress speckle noise.
Difficulties in data processing for airborne SAR
systems come from the platform motion errors [2].
Most of SAR processing algorithms imply the
straight-line aircraft motion with constant altitude,
velocity and orientation. Deviations of the aircraft
trajectory from a straight line and instabilities of the
aircraft orientation, if not being properly compen-
sated, lead to defocusing of SAR images as well as
to geometric distortions and radiometric (bright-
ness) errors in SAR images.
Assume that the problem of compensation
of phase errors and range migration errors caused
by trajectory deviations is solved. We expect that
the SAR processing algorithm is capable of pro-
ducing well-focused SAR images based on the real
flight trajectory measured by the SAR navigation
system. In this paper, we will consider the problem
of correction of radiometric errors which arise in
SAR images because of instabilities of the real
antenna beam orientation or, in other words, be-
cause of non-uniform illumination of the ground
scene by the real antenna beam.
Multi-Look Radiometric Correction of SAR Images
425Радиофизика и радиоастрономия, 2011, т. 16, №4
The problem of radiometric errors is illustrated
in Figs. 1(a) and 1(b). Without orientation errors,
the synthetic beam of the central look is directed to
the center of the real antenna beam, and all SAR
look beams are within the main lobe of the real
antenna pattern, as shown in Fig. 1(a). Antenna
orientation errors lead to the case when some of
the SAR beams are directed outside the real an-
tenna beam to non-illuminated ground areas, as
shown in Fig. 1(b), resulting in radiometric errors.
The clutter-lock technique [3] is usually used
to avoid radiometric errors in SAR images. Fol-
lowing this technique, the synthetic beams are
built adaptively to be directed according to the
variations of the real antenna beam orientation as
shown in Fig. 1(c). In order to do this, the mean
Doppler frequency (the Doppler centroid), which
is used to set the synthetic beam direction, is
estimated from the received radar data. As a result,
the Doppler frequency of the matched filter of
the synthetic beam is locked to the Doppler fre-
quency to the clutter signal, and the direction of
the synthetic beam is locked to the direction of
the real antenna beam.
However, the synthetic beam orientation varia-
tions due to the clutter-lock naturally lead to geo-
metric distortions in SAR images. The problem of
geometric distortions is vital for SAR systems in-
stalled onboard light-weight aircrafts because of
rough motion of such platforms [4]. The clutter
lock technique is effective if the antenna beam
orientation variations are slow in time. In this case,
the geometric distortions can be corrected by re-
sampling of the obtained SAR images to the cor-
rect rectangular grid on the ground plane. If orien-
tation instabilities are fast and significant, the clut-
ter-lock leads to strong geometric distortions in SAR
images which cannot be easily corrected by re-
sampling.
In this paper, we propose a multi-look radio-
metric correction technique which can be used
instead of the clutter-lock. The idea of the ap-
proach is to form an extended number of looks to
cover directions beyond the main lobe of the real
antenna pattern as illustrated in Fig. 1(d). In such
an approach, some of the SAR look beams are
always presented within the real antenna beam
despite of orientation errors. Now we describe
how to combine these extended SAR looks to
produce the multi-look SAR image without radi-
ometric errors. The proposed method of a radio-
metric error correction does not require accurate
measurements of the real antenna beam orienta-
tion variations. Suffice it to know the average
antenna beam orientation for the whole data frame
used to produce a SAR image with the accuracy
to half the antenna beam width.
The proposed approach has been successfully
tested by using a Ku-band airborne SAR system
[5] developed and manufactured at the Institute of
Radio Astronomy of the National Academy of
Sciences of Ukraine. Preliminary results have been
presented at conferences [6, 7]. In this paper, the
method is described in details.
Fig. 1. Multi-look processing without antenna orientation errors (a) and with orientation errors: without clutter-
lock (b), with clutter-lock (c), with extended number of looks (d)
O. O. Bezvesilniy, I. M. Gorovyi, V. V. Vynogradov, and D. M. Vavriv
Радиофизика и радиоастрономия, 2011, т. 16, №4426
2. Mathematical Model
of Radiometric Errors
Let us denote the error-free SAR image to be
reconstructed as ( , ),I x y where ( , )x y are the
ground coordinates of the image pixels. This image is
not corrupted by speckle noise and not distorted by
radiometric errors. The obtained SAR look images
( , , )LI n x y ( Ln being the index of the SAR looks)
are corrupted by speckle noise ( , , )LS n x y and
distorted by radiometric errors 0 ( , , ) 1LR n x y< ≤
so that
( , , ) ( , ) ( , , ) ( , , ).L L LI n x y I x y S n x y R n x y=
(1)
The speckle noise in a single-look SAR image
is a multiplicative noise [1] with the exponential
probability density function with the mean and
variance, correspondingly,
{ }( , , ) 1,LS n x yμ = { }( , , ) 1.LS n x yσ = (2)
The speckle noise is uncorrelated for all SAR looks
as indicated by the SAR look index .Ln
The radiometric errors caused by instabilities of
antenna orientation are the low-frequency multip-
licative errors. The highest spatial frequencies of the
radiometric error function ( , , )LR n x y typically
correspond to the spatial scale of about half the width
of the real antenna footprint in azimuth direction.
Similar to the speckle noise, the radiometric errors
are different for different SAR looks.
In order to compensate the radiometric errors
we should measure them first. For this purpose we
use a low-pass filter F to measure the local bright-
ness of the SAR images. This filter is designed
to pass the radiometric errors,
{ }( , , ) ( , , ),L LR n x y R n x y≈F (3)
and at the same time, to suppress the speckle noise
(2) to some extent:
{ }( , , ) 1.LS n x y ≈F (4)
According to assumptions (3) and (4), the
application of this filter to the SAR look image (1)
gives approximately:
{ }( , , ) ( , , ) ( , ) ( , , ).LF L L LF LI n x y I n x y I x y R n x y= ≈F
(5)
Here ( , )LFI x y is the low-frequency component of
the error-free SAR image to be reconstructed. The
low-frequency components of the SAR looks
( , , )LF LI n x y (5) contain information about the
radiometric errors and are almost not corrupted
by speckle noise. These images can be used to
compare radiometric errors on different SAR looks
and, though such comparison, to estimate and
compensate the radiometric errors as described
in the next section.
3. Multi-Look Radiometric Correction
3.1. Idea of the Method
The idea of radiometric correction by multi-look
processing with the extended number of looks
is based on the fact that the synthetic beam of one
of many looks is pointed very close to the center
of the real antenna beam. This look demonstrates
the maximum power (brightness) among all looks,
and this power is not distorted by radiometric errors.
The mathematical description is as follows.
For every point of the scene we may find the
brightest pixel among all SAR looks:
{ }
1, ...,
( , ) max ( , , ) .
ext
L L
max
LF LF L
n N
I x y I n x y
=
= (6)
By substituting (5) into (6) we obtain
{ }
1, ...,
( , ) ( , ) max ( , , ) .
ext
L L
max
LF LF L
n N
I x y I x y R n x y
=
≈
(7)
These brightness values are obtained with the
synthetic beams that are directed very close to the
center of the real beam. Therefore they are not
distorted by the radiometric errors:
{ }
1, ...,
max ( , , ) 1.
ext
L L
L
n N
R n x y
=
≈ (8)
Multi-Look Radiometric Correction of SAR Images
427Радиофизика и радиоастрономия, 2011, т. 16, №4
This means that the image ( , )max
LFI x y (7) gives the
estimate of the low-frequency component of the
error-free SAR image to be reconstructed:
( , ) ( , ).max
LF LFI x y I x y≈ (9)
This image can be used as the reference to
estimate radiometric error functions for all SAR
looks. From (5) and (9) we obtain
( , , )( , , ) .
( , )
LF L
L max
LF
I n x yR n x y
I x y
≈ (10)
By using the estimated radiometric error functions
we may correct radiometric errors for all SAR
looks before combining them into the multi-look
SAR image.
3.2. Implementation of the Method
Let us denote the number of looks to be summed
up into a multi-look image as .pro
LN This number
of looks should be slightly less than that within the
real antenna beam LN since the orientation insta-
bilities may corrupt the side looks considerably.
By using the low-pass filter we should select the
brightest (best-illuminated) parts of the scene
among all extended SAR looks with the indexes
1, ..., ext
L Ln N= and compose only pro
LN SAR looks
(called the composite looks) for further processing.
It is convenient to build the following sequence of
pairs of the composite looks and their low-frequen-
cy components:
{ }( , , ), ( , , ) ,pro pro pro pro
L LF LI n x y I n x y
1, ..., .pro pro
L Ln N=
This sequence is kept in the ascending order with
respect to the brightness:
( , , ) ( 1, , ).pro pro pro pro
LF L LF LI n x y I n x y≤ +
After processing of all the extended SAR looks,
the brightest composite look is the one with the
index .pro pro
L Ln N= This look gives the estimate (9)
of the low-frequency component of the error-free
SAR image to be reconstructed.
If the number of looks pro
LN is sufficiently large
(e.g. greater than 9), we may improve the estimate
(9) by averaging several brightest composite looks
(e.g. 3 looks) to suppress the residual speckle noise
which have leaked though the low-pass filter:
3
1
1( , ) ( 1, , ).
3
max pro pro
LF LF L
n
I x y I N n x y
=
= − +∑
The radiometric errors are corrected according
to (10) as follows:
( , )( , , ) ( , , ) .
( , , )
max
pro pro pro LF
RC L L pro pro
LF L
I x yI n x y I n x y
I n x y
=
Finally, applying the above radiometric correction,
we may build the multi-look SAR image as
1
1( , ) ( , , ).
pro
L
pro
N
pro pro pro
RC RC Lpro
nL
I x y I n x y
N =
= ∑ (11)
The main steps of the described algorithm are shown
in Fig. 2.
3.3. Some Practical Considerations
We may use the Doppler centroid values esti-
mated from the backscattered radar signal to pre-
vent the synthesis of those SAR look beams which
are obviously directed beyond the real antenna beam
at the moment. This allows to reduce the compu-
tation burden. It is especially important when the
variations of the real antenna beam orientation are
larger than the antenna beam width, and we have
to increase the number of the SAR looks consi-
derably, although just a few of the extended SAR
looks are illuminated simultaneously.
To improve the signal-to-noise ratio in the final
multi-look SAR image, we should not sum up those
SAR looks which are illuminated less than, for
example, –10 dB with respect to the maximum
illumination. Such poorly-illuminated SAR looks may
introduce significant additional receiver noise to the
final image. Actually, this threshold limits the pos-
sible number pro
LN of the composite SAR looks.
The low-frequency components of SAR look
images ( , , )LF LI n x y (5) can be obtained by using
O. O. Bezvesilniy, I. M. Gorovyi, V. V. Vynogradov, and D. M. Vavriv
Радиофизика и радиоастрономия, 2011, т. 16, №4428
a simple smoothing filter, but excluding from ave-
raging all bright points representing artificial objects.
The radar cross section of artificial targets may
demonstrate significant variations from one look to
another hampering the correct choice of the best
illuminated looks.
If the navigation system is capable of measu-
ring accurately the fast variations of the real anten-
na beam orientation, and if we know the real an-
tenna pattern, then we may calculate the radiomet-
ric error functions (10) directly from the relative
orientation of the synthetic beam and the real an-
tenna beam. This approach is more rigorous and
accurate than the above-described empirical one
with the image brightness estimation. Neverthe-
less, with this approach we still have to build the
extended number of SAR looks, select the best
parts of SAR images among all looks and form the
composite looks for multi-look processing (11).
4. Experimental Results
The proposed method of a multi-look radiomet-
ric correction has been tested experimentally by
using an airborne SAR system [5] installed on-
board an Antonov AN-2 aircraft. Characteristics
of the SAR system are listed in Table 1. The SAR
system operates at the wavelength around 2 cm.
The real antenna beam width is about 1° in azi-
muth and 40° in elevation. The slant range reso-
lution is 3 m. For the same azimuth resolution of 3
m, SAR images can be built of 9 half-overlapping
SAR looks under stable flight conditions.
Fig. 2. Main steps of the multi-look radiometric correc-
tion algorithm
Table 1. RIAN-SAR-Ku system characteristics
Transmitter
Transmitter type Traveling-wave
tube power amplifier
Operating frequency Ku-band
Transmitted peak power 100 W
Pulse repetition
frequency (PRF) 5 20− kHz
Pulse compression Binary phase codding
technique (M-sequences)
Pulse bandwidth 50 MHz
Pulse duration 5 µs
Receiver
Receiver bandwidth 100 MHz
Receiver noise figure 2.5 dB
ADC sampling frequency 100 MHz
ADC capacity 12 bit
Range sampling interval 1.5 m
Number of range gates 1024
Antenna
Antenna type Slotted-waveguide
Antenna beam width
in azimuth / elevation 1 40° °
SAR Platform
Aircraft flight velocity 30 80− m/s
Aircraft flight altitude 1000 5000− m
Aircrafts used Antonov AN-2
SAR images
Azimuth resolution 3 m
Range resolution 3 m
Range swath width 1536 m
Raw data recording Range-compressed,
7-times decimated
down from the PRF
Multi-Look Radiometric Correction of SAR Images
429Радиофизика и радиоастрономия, 2011, т. 16, №4
Light-weight aircraft platforms – such as the
AN-2 aircraft – suffer from significant trajectory
deviations and orientation instabilities. The inf-
luence of motion errors is illustrated in Fig. 3, where
you can see the coordinate grid in the radar coor-
dinates “slant range – azimuth” projected into the
ground plane. The horizontal curves are the curves
of the constant slant range from the aircraft. They
are curved because of deviations of the trajectory
from the straight line. The vertical lines are the
central lines of the antenna footprint (the Doppler
centroid lines) for the consequent aircraft positions
along the trajectory. As is seen, these central lines
are non-equidistant and non-parallel because of
variations of the antenna orientation.
If the clutter lock technique is applied, then the
ground scene is sampled on the above-described
radar coordinate grid, which is non-uniform with
respect to the ground coordinate system. As a
result, geometric distortions will appear in the SAR
image as illustrated in Fig. 4. The geometric
errors in this single-look SAR image built by
using the clutter lock are evidently represented
by the curved forest shelter belts between the
fields in the top-left corner of the image and the
curved road in the bottom-right corner of the image.
The size of the scene in the SAR images is about
1.5 km in range (the vertical bottom-top direction)
and about 2 km in azimuth (the horizontal left-
right direction). The resolution in range and in
azimuth is 3 m.
If we do not use the clutter-lock and if we do
build the multi-look image as usual by using 9 cen-
tral SAR looks, we will observe severe radiometric
errors in the SAR image as shown in Fig. 5. Note,
however, that the above-described geometric er-
rors have disappeared from this SAR image.
The SAR image in Fig. 6 was built without the
clutter-lock by simple averaging of all the extended
SAR looks. The image demonstrates good geo-
metric accuracy. You may compare now the top-
right corners of the images in Figs. 4 and 6. You
can see how the antenna beam movement “for-
ward-backward-forward” distorts the shape of the
forest area in Fig. 4 as compared to its correct
shape in Fig. 6.
The radiometric errors are still present in the
SAR image in Fig. 6. You can see dark and light
strips in the image caused by non-uniform illumi-
nation of the scene. The dark areas were illumi-
nated for shorter time, the SAR image was present
only on a few SAR looks, the real antenna foot-
print quickly moved to the neighbor areas of the
scene. The light areas were illuminated for longer
Fig. 3. Trajectory deviations and orientation instabilities illustrated by the coordinate grid in the radar coor-
dinates “slant range – azimuth” on the ground plane
O. O. Bezvesilniy, I. M. Gorovyi, V. V. Vynogradov, and D. M. Vavriv
Радиофизика и радиоастрономия, 2011, т. 16, №4430
time, the SAR image was present on many SAR
looks.
The SAR image shown in Fig. 7 was built with-
out clutter lock by using the proposed method of
multi-look radiometric correction with the exten-
ded number of looks. The image was formed of 5
composite SAR looks. One can see that the radio-
metric errors have been corrected.
The proposed method of multi-look radio-
metric correction has been successfully applied
in conjunction with the the two SAR processing
algorithms: 1) the algorithm with the built-in geo-
Fig. 4. Geometric distortions in a single-look SAR image built by using the clutter lock
Fig. 5. Radiometric errors in the SAR image built without the clutter lock by simple averaging of 9 central looks
Multi-Look Radiometric Correction of SAR Images
431Радиофизика и радиоастрономия, 2011, т. 16, №4
metric correction [6, 8], and 2) the well-known
range-Doppler algorithm [7]. It will be obser-
ved here that these SAR processing algorithms
cannot be combined with the clutter-lock tech-
nique.
5. Conclusions
The proposed method of multi-look radiometric
correction is an effective alternative to the clutter-
lock technique. The method can be used with the
Fig. 6. Radiometric errors in the SAR image built without the clutter lock by simple averaging of all
extended SAR looks
Fig. 7. Multi-look SAR image formed of 5 composite SAR looks by using the proposed radiometric correction
O. O. Bezvesilniy, I. M. Gorovyi, V. V. Vynogradov, and D. M. Vavriv
Радиофизика и радиоастрономия, 2011, т. 16, №4432
SAR processing algorithms that cannot be com-
bined with the clutter-lock. The proposed method
also allows correcting the radiometric errors in SAR
images if the accurate orientation of antenna is
unknown. The obtained experimental results have
demonstrated that the method is capable of pro-
ducing multi-look SAR images without geometric
and radiometric errors under unstable flight con-
ditions.
References
1. C. J. Oliver and S. Quegan, Understanding Synthetic
Aperture Radar Images. Boston, London: Artech House,
1998, 480 p.
2. S. Buckreuss, “Motion errors in an airborne synthetic
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A. A. Belikov, M. P. Vasilevskiy, and D. I. Zaikin, “Cost-
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Многовзглядовая радиометрическая
коррекция РСА-изображений
А. А. Безвесильный, Е. Н. Горовой,
В. В. Виноградов, Д. М. Ваврив
Отклонения траектории самолета и неста-
бильности ориентации самолета приводят к не-
равномерной подсветке земной поверхности
лучом антенны и в результате к радиометричес-
ким ошибкам на радиолокационных изображе-
ниях, полученных с помощью самолетных ра-
диолокаторов с синтезированной апертурой
(РСА). Чтобы избежать радиометрических оши-
бок, обычно применяется техника слежения за
сигналом от местности. Однако такой подход
приводит к значительным геометрическим ис-
кажениям на РСА-изображениях в случае бы-
стрых и значительных нестабильностей ориен-
тации антенны. В этой статье мы предложили
технику многовзглядовой радиометрической кор-
рекции, которую можно использовать вместо
слежения за сигналом от местности. Предло-
женный подход был испытан с помощью само-
летного РСА 2-сантиметрового диапазона длин
волн, установленного на легком самолете.
Багатопоглядова радіометрична
корекція РСА-зображень
О. О. Безвесільний, Є. М. Горовий,
В. В. Виноградов, Д. М. Ваврів
Відхилення траєкторії літака та нестабільності
орієнтації літака призводять до нерівномірного
підсвічування земної поверхні променем антени
і, як наслідок, до радіометричних помилок на ра-
діолокаційних зображеннях, отриманих за допо-
могою літакових радіолокаторів з синтезованою
апертурою (РСА). Аби уникнути радіометричних
помилок, звичайно використовується техніка
слідкування за сигналом від місцевості. Однак
такий підхід призводить до значних геометричних
спотворень РСА-зображень у випадку швидких
та значних нестабільностей орієнтації антени.
У цій статті ми пропонуємо техніку багатопог-
лядової радіометричної корекції, яку можна ви-
користовувати замість слідкування за сигналом
від місцевості. Запропонований підхід був випро-
буваний за допомогою літакового РСА 2-санти-
метрового діапазону довжин хвиль, встановлено-
го на легкому літаку.
|
| id | nasplib_isofts_kiev_ua-123456789-98239 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1027-9636 |
| language | English |
| last_indexed | 2025-12-07T18:33:22Z |
| publishDate | 2011 |
| publisher | Радіоастрономічний інститут НАН України |
| record_format | dspace |
| spelling | Bezvesilniy, O.O. Gorovyi, I.M. Vynogradov, V.V. Vavriv, D.M. 2016-04-10T19:24:57Z 2016-04-10T19:24:57Z 2011 Multi-Look Radiometric Correction of SAR Images / O.O. Bezvesilniy, I.M. Gorovyi, V.V. Vynogradov, D.M. Vavriv // Радиофизика и радиоастрономия. — 2011. — Т. 16, № 4. — С. 424-432. — Бібліогр.: 8 назв. — англ. 1027-9636 https://nasplib.isofts.kiev.ua/handle/123456789/98239 Deviations of the aircraft trajectory and instabilities of the aircraft orientation lead to non-uniform
 illumination of the ground by the antenna beam and, as a result, to radiometric errors in radar images
 obtained with airborne synthetic aperture radars (SAR). The clutter-lock technique is commonly used
 to avoid the radiometric errors. However, this approach leads to strong geometric distortions in SAR
 images in the case of fast and significant instabilities of antenna orientation. Here we propose a multilook
 radiometric correction technique which can be used instead of the clutter-lock. The proposed
 approach has been tested by using a Ku-band airborne SAR system installed onboard a light-weight
 aircraft. Отклонения траектории самолета и нестабильности ориентации самолета приводят к неравномерной подсветке земной поверхности
 лучом антенны и в результате к радиометрическим ошибкам на радиолокационных изображениях, полученных с помощью самолетных радиолокаторов с синтезированной апертурой
 (РСА). Чтобы избежать радиометрических ошибок, обычно применяется техника слежения за
 сигналом от местности. Однако такой подход
 приводит к значительным геометрическим искажениям на РСА-изображениях в случае быстрых и значительных нестабильностей ориентации антенны. В этой статье мы предложили
 технику многовзглядовой радиометрической коррекции, которую можно использовать вместо
 слежения за сигналом от местности. Предложенный подход был испытан с помощью самолетного РСА 2-сантиметрового диапазона длин
 волн, установленного на легком самолете. Відхилення траєкторії літака та нестабільності
 орієнтації літака призводять до нерівномірного
 підсвічування земної поверхні променем антени
 і, як наслідок, до радіометричних помилок на радіолокаційних зображеннях, отриманих за допомогою літакових радіолокаторів з синтезованою
 апертурою (РСА). Аби уникнути радіометричних
 помилок, звичайно використовується техніка
 слідкування за сигналом від місцевості. Однак
 такий підхід призводить до значних геометричних
 спотворень РСА-зображень у випадку швидких
 та значних нестабільностей орієнтації антени.
 У цій статті ми пропонуємо техніку багатопоглядової радіометричної корекції, яку можна використовувати замість слідкування за сигналом
 від місцевості. Запропонований підхід був випробуваний за допомогою літакового РСА 2-сантиметрового діапазону довжин хвиль, встановленого на легкому літаку. en Радіоастрономічний інститут НАН України Радиофизика и радиоастрономия Радиофизические аспекты радиолокации, радионавигации, связи и дистанционного зондирования Multi-Look Radiometric Correction of SAR Images Многовзглядовая радиометрическая коррекция РСА-изображений Багатопоглядова радіометрична корекція РСА-зображень Article published earlier |
| spellingShingle | Multi-Look Radiometric Correction of SAR Images Bezvesilniy, O.O. Gorovyi, I.M. Vynogradov, V.V. Vavriv, D.M. Радиофизические аспекты радиолокации, радионавигации, связи и дистанционного зондирования |
| title | Multi-Look Radiometric Correction of SAR Images |
| title_alt | Многовзглядовая радиометрическая коррекция РСА-изображений Багатопоглядова радіометрична корекція РСА-зображень |
| title_full | Multi-Look Radiometric Correction of SAR Images |
| title_fullStr | Multi-Look Radiometric Correction of SAR Images |
| title_full_unstemmed | Multi-Look Radiometric Correction of SAR Images |
| title_short | Multi-Look Radiometric Correction of SAR Images |
| title_sort | multi-look radiometric correction of sar images |
| topic | Радиофизические аспекты радиолокации, радионавигации, связи и дистанционного зондирования |
| topic_facet | Радиофизические аспекты радиолокации, радионавигации, связи и дистанционного зондирования |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/98239 |
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