949
1 INTRODUCTION
In recent years, there has been a dynamic increase in
the use of unmanned aerial vehicles (UAVs),
commonly known as drones, in military operations.
Their role on the battlefield continues to evolvefrom
reconnaissance tools that support command and
observation to precise strike platforms with a high
degree of autonomy. Conflicts such as the 2020
Nagorno-Karabakh war and the ongoing war in
Ukraine clearly demonstrate how significantly drones
are reshaping the nature of modern warfare [1], [2]. The
growing availability of drone technology and the
relatively low cost of production have made these
systems increasingly attractive to both state actors and
irregular armed groups.
The application of UAVs that we are investigating
in several scientific research projects is the use of radio
emitters for localization. The method that we use is the
SDF (signal Doppler frequency) method. It has both
advantages and disadvantages. The aim of this article
is to examine the influence of selected parameters on
the accuracy of localization of radio emitters. The
conclusions from the article will allow us to focus on
the most important ones, which have the greatest
impact on the localization errors. They show directions
for further development of the method to improve its
accuracy.
The rest of the paper is organized as follows. Section
2 describes the SDF method and her parameters, that
influence the localization error. Simulation scenarios
and obtained results are described in Section 3. The
conclusions that are included in Section 4 concern the
recommendations and directions for further research
into the SDF method.
Study of Parameters Influencing the Accuracy
of the SDF Method Localization
K. Bednarz, C. Ziółkowski & J. Wojtuń
Military University of Technology, Warsaw, Poland
ABSTRACT: Modern military operations increasingly use unmanned aerial vehicles (UAVs) not only for
observation and reconnaissance, but also for active localization of radio emission sources. One of the methods
used for this purpose is the signal Doppler frequency method (SDF), based on the analysis of the frequency of the
signal received by the moving sensor. The paper presents a theoretical analysis and simulation studies aimed at
determining the effect of selected parameters on the accuracy of emitter localization using the SDF method. In
particular, the factors such as data acquisition time, accuracy of Doppler frequency estimation, carrier frequency
and the velocity of the moving sensor were considered. The aim of the work is to indicate which of these
parameters are crucial for the quality of localization. We formulate conclusions that can support the development
of the resistant to interference and more precise localization systems based on the SDF method. The presented
approach can be used both in real armed conflicts and in work on autonomous electronic reconnaissance systems.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 19
Number 3
September 2025
DOI: 10.12716/1001.19.03.29
950
2 SDF METHOD
2.1 SDF Method principles
The SDF method is a frequency method for locating
radio emitters. The basic parameter on which the
localization algorithms operate is the Doppler
frequency shift (DFS), which appears when the receiver
or transmitter is set in motion [3]. This frequency can
be expressed by the formula:
0
,
D
v
f f cos
c
=
(1)
where: v speed of change of position between the
signal source and the receiver, f0 frequency of the
emitted carrier wave, c- the speed of propagation of an
electromagnetic wave in a medium, γ- angle between
the direction of the velocity vector and the direction
determined by the position of the signal source and
receiver.
Assuming that we localize the stationary
transmitter using a sensor placed on a moving
platform, e.g. an unmanned aerial vehicle (UAV), we
can estimate the coordinates
of the localized
emitter in a two-dimensional plane using the equations
[4]:
( ) ( )
( ) ( )
1 1 2 2
12
t A t t A t
xv
A t A t
(2)
( ) ( ) ( )
( ) ( )
2
1 2 1 2
2
12
z
v t t A t A t
y
A t A t



(3)
where:
( )
( )
( )
( )
( )
2
0
1
, , , ,
max
max
D
D
D
Ft
ft
v
A t F t f kf k
F t f c
= = =
fDmax
maximum Doppler frequency, f0 - carrier frequency of
transmitted signal, z- constant height relative to the
receiver, v- velocity of receiver.
2.2 Parameters affecting the localization error
Analyzing equation (1), we can see that the
fundamental element influencing the Doppler
frequency fD value, apart from the carrier frequency f0
is the angle between the direction of the velocity vector
and the direction determined by the position of the
signal source and receiver γ. How the UAV flight
direction relative to the emitter location will affect the
nature of the Doppler frequency fD changes and the
SDF method location error is presented, among others,
in [5], [6]. Therefore, it is extremely important to select
the correct UAV flight direction, which is worth noting
here. For this reason, in further considerations
including research on other parameters, many
scenarios of UAV location relative to the emitter will be
taken to develop optimal solutions into account.
However, scenarios in which the Doppler frequency is
extremely low or its value is almost constant, will not
be considered.
An analysis of formulas (2) and (3) shows that the
accuracy of localization is influenced by the accuracy
of determination:
Doppler frequency fD,
carrier frequency of transmitted signal f0,
velocity of receiver v.
When spectrum analysis is used to estimate the
Doppler frequency fD, it can be expressed as [7]:
( ) ( )
0
,
D
f t f t f=−
(4)
where: f(t)- instantaneous frequency of received signal.
In this case, the accuracy of the carrier frequency f0
estimation of the emitted signal also affects the
accuracy of the Doppler frequency fD estimation. In the
following article, it is assumed that the Doppler
frequency fD is estimated using methods which do not
need information about the carrier frequency of the
signal. Consequently, carrier frequency estimation
error affects the accuracy of localization only in
formulas (2) and (3).
Formulas (2) and (3) allow for estimating the
coordinates (x,y) of the localized emitter in the case of
measuring the Doppler frequency fD at least at two
moments of time t1 and t2. Using a larger amount of
data, e.g. a ten-element vector, will also affect the
localization error. The fourth analyzed parameter will
therefore be:
the acquisition time t_A, reflecting the amount of
data (Doppler frequency shifts fD) used to determine
the coordinates (x,y) of the emitter.
As with the UAV velocity v, information about the
UAV location may also be subject to some error. The
SDF method determines the position relative to the
sensor position, and therefore it will also affect the
error in the radio emission location. For this reason, it
was decided to also examine the influence of
the UAV’s positioning accuracy.
In the case of performing localization procedures in
real time, we rely only on a part of the Doppler curve,
and we cannot select an arbitrary acquisition time tA.
However, it is necessary to determine when to perform
localization procedures so that the result is not
burdened with too large localization error r. The
solution to this problem may be the last parameter
studied in the publication, called:
the range of Doppler frequency changes fD.
3 SIMULATION STUDIES FOR TESTING THE
IMPACT OF SELECTED PARAMETERS ON
LOCLIZATION ACCURACY
3.1 Main assumptions for all scenarios
In order to investigate the influence of the parameters
listed in Section 2.2 on the localization accuracy of the
SDF method, a research scenario was adopted in which
the localization sensor was mounted on the UAV and
moved along the OX axis of the coordinate system
shown in Figure 1.
951
Figure 1. Spatial scenario for simulation studies.
Based on the arrangement of elements shown in
Figure 1, the following assumptions were made:
the emitter is located at point x0, y0, z0 of the
coordinate system,
the localized emitter transmits a harmonic signal at
the carrier frequency f0,
the carrier frequency f0 of the emitted signal is
determined by the sensor mounted on the non-
moving UAV No. 2, which is placed at coordinates
(xv, yv, zv)=(0,0,0)km,
the Doppler frequency fD is determined based on the
signal samples received by both sensors,
the carrier frequency f0 estimation error of the signal
does not affect the Doppler frequency fD estimation
error, and consequently, carrier frequency f0
estimation error affects the accuracy of localization
only in formulas (2) and (3),
UAV No. 1 moves along the OX axis over a distance
of S km with velocity v, at subsequent moments of
time its position coordinates are (xv, yv, zv)
=(vt,0,0)km,
the localization sensor estimates parameters (f0, fD,
v) every 1 s,
to determine the emitter coordinates (x,y) data
vectors (f0,fD,v) of length equal to the acquisition
time tA are taken,
the localization error r is determined according to
formula
= +
22
00
( ) ( )r x x y y
5
where x(t) and y(t) are the coordinates estimated
based on formulas (2) and (3).
3.2 The influence of the acquisition time
A similar analysis of this parameter was performed in
[8]. The authors of the article analyzed the acquisition
time tA for recorded signals burdened with large
oscillations. In this chapter, we would like to present
the trend of the localization error r in the case of the
selection of the acquisition time tA for ideal conditions.
3.2.1 Scenarios assumptions
The study was conducted taking the assumptions
from Section 3.1 into account. Additionally, the
following assumptions were made:
x0,y0,z0={(10,40,-0.1),(10,30,-0.1),(10,20,-0.1),
(10,10,-0.1),(10,5,-0.1),(10,2,-0.1),
(10,1,-0.1),
(5,20,-0.1),(5,15,-0.1),(5,10,-0.1),
(5,5,-0.1),(5,2.5,-0.1),(5,1.25,-0.1),
(5,0.5,-0.1),
(1.2,4.8,-0.1),(1.2,3.6,-0.1),(1.2,2.4,-0.1),
(1.2,1.2,-0.1),(1.2,0.6,-0.1),(1.2,0.2,-0.1),
(1.2,0.1,-0.1)} km,
f0={300,600,900,1200,1500,1800,2100,2400,2700,
3000} MHz,
v=15 m/s,
the selection of acquisition time tA and its maximum
value results from the selected scenarios. When the
path S=2∙x0 is 20 kilometers, at a speed of 15 m/s we
need 1334 seconds to complete the entire route.
When S=10 kilometers we need 667 seconds and for
S=2400 meters it is 161 seconds. It was therefore
decided to examine the acquisition time tA values
from 2 seconds to the total number of seconds
needed to cover the entire route tAmax, with a step of
1 s for all cases,
the emitter position coordinates are determined for
an analysis window of the acquisition time tA
length. Then, if the coordinate determination
counter k is lower than the maximum number of
localization procedure repetitions K defined as
= +
max
1,
AA
K t t
(6)
the analysis window is shifted by one second and
the coordinates are determined again. This
procedure is repeated K times. For this reason, the
first location result is obtained after a time equal to
the acquisition time tA.
for each value of the acquisition time tA, the mean
value μr and deviation σr of the localization error
r is determined according to formulas
=
=
Δ
1
1
Δ,
K
rk
k
μr
K
(7)
=
=−
2
ΔΔ
1
1
Δ,
1
K
r k r
k
σ r μ
K
(8)
where k=1,2,…,K, rk is a localization error defined
by Equation (5) for the kth estimation of emitter
coordinates (x(t),y(t)).
3.2.2 Results
Table 1 presents the mean value μr and standard
deviation σr of the localization error for each value of
the acquisition time tA. Due to the different number of
seconds needed to cover the entire route tAmax
depending on the length of the path S, the acquisition
time tA was expressed in percentage as:
% 100
A
A
Amax
t
t
t
=
(9)
The course of the mean localization error as a
function of acquisition time tA for different path lengths
is presented in Figure 2.
952
Table 1. The mean value μr and standard deviation σr
of the localization error for different path length S and
different value of the acquisition time tA.
S=20 km
S=10 km
S=2.4 km
tA [%]
Localization error [m]
μr
σr
μr
σr
μr
σr
10
1.471
3.356
0.684
1.612
0.160
0.321
20
1.114
2.316
0.524
1.119
0.124
0.225
30
0.836
1.499
0.396
0.723
0.096
0.148
40
0.632
0.881
0.304
0.428
0.075
0.090
50
0.500
0.454
0.243
0.222
0.062
0.051
60
0.440
0.231
0.216
0.116
0.056
0.031
70
0.442
0.198
0.216
0.101
0.056
0.027
80
0.466
0.213
0.228
0.108
0.059
0.029
90
0.491
0.220
0.240
0.111
0.063
0.031
100
0.530
0.245
0.258
0.123
0.069
0.037
Figure 2. The mean value of localization error μr as a
function of acquisition time tA for different path lengths S.
Analyzing the above results, we can see that the
lowest mean localization error μr is obtained in the
case when the acquisition time tA is about 65% of all
seconds needed to cover the entire route tAmax.
However, this value is difficult to achieve, especially in
the case of scenarios where there are more than 1300 of
them. The measurement time to the first localization
would reach more than 10 minutes. It can also be seen
that with the increase in the length of the measurement
path S, the difference between the localization errors
for individual acquisition times tA increases. However,
the trend itself is identical. In ideal simulation
conditions, we can see, however, that the selection of
the acquisition time tA does not have a critical
significance in the localization error.
3.3 The influence of the range of Doppler frequency
changes
As mentioned in Section 3.2, the accuracy of
localization is influenced by the acquisition time tA of
the signal, i.e. the number of fD values taken to calculate
the emitter coordinates (x,y). In general, the lowest
localization error was obtained when the acquisition
time tA was about 60% of the entire Doppler curve. In
real conditions, we do not always have the possibility
to collect data that will allow for the analysis of the full
Doppler curve and localization procedures must be
performed on its part. In such a case, a decision must
be made when to start determining the coordinates so
as not to burden the result with too large a localization
error r. For this purpose, another simulation study
was conducted, in which it was decided to analyze the
influence of the range of Doppler frequency changes
BfD on the localization error r. For assume that this
parameter has a constant value, the acquisition time tA
is changed dynamically by appropriately adding and
subtracting values from the fD vector, to maintain
a constant, previously determined the range of
Doppler frequency changes BfD.
3.3.1 Scenarios assumptions
The study was conducted taking the assumptions
from Section 3.1 into account. Additionally, the
following assumptions were made:
x0,y0,z0={(10,10,-0.1),(10,5,-0.1),(10,2,-0.1),
(10,1,-0.1),(1.2,1.2,-0.1),(1.2,0.6,-0.1)
(1.2,0.2,-0.1),(1.2,0.1,-0.1)} km,
f0={300,600,900,1200,1500,1800,2100,2400,2700,
3000} MHz,
v={15,20,30} m/s,
the range of Doppler frequency changes was
selected so that each scenario could meet the
requirements for its value, it was therefore decided
to test all possible BfD values in the range from 0.5
to 20 Hz with a step of 0.5 Hz,
the acquisition time tA is selected taking the range of
Doppler frequency changes BfD into account,
for each value of the range of Doppler frequency
changes BfD, the mean value μr and deviation σr
of the localization error ∆r is determined according
to formula (7) and (8).
3.3.2 Results
Figure 3 presents courses of the mean value μr and
standard deviation σr of the localization error as a
function of the range of Doppler frequency changes
BfD.
Figure 3. The mean value μr and standard deviation σr of
localization error as a function of the range of Doppler
frequency changes BfD.
Analyzing the obtained results, it can be noticed
that with small values of the range of Doppler
frequency changes BfD, the mean localization error μr
can reach almost 3 meters. By increasing the value of
the tested parameter, localization error begins to
decrease quickly. Assuming that the localization
procedure is to be carried out as quickly as possible and
the error cannot exceed 0.5 meters, localization can be
done on data for which the range of Doppler frequency
changes BfD equals 5 Hz. Further reduction of the value
of this parameter obviously causes a decrease in the
localization error and for BfD=20 Hz, the mean
localization error value μr=0.278 m. However, the
parameter study was performed for ideal conditions
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and in the case of real conditions, where the Doppler
frequency will oscillate, among others due to the
frequency stability of the SDR platform used [9], it will
be necessary to previously determine the value of this
parameter for the target solution.
3.4 The influence of the Doppler frequency estimation
error
The approximate analysis was carried out in [10]. The
ideal Doppler frequency courses as a function of time
were obtained using the following equation
( )
( )
( )( )
0
0
2
2
2 2 2
0 0 0
, ,
1
1
D
x vt
k
f t k f
k
x vt k y z


=+


+ +

x
where x=(x0,y0,z0).
In our consideration it was assumed, that the
estimated fD values oscillate and the oscillations follow
a normal distribution N(μfD, σfD).
3.4.1 Scenarios assumptions
The study was conducted taking into account the
assumptions from section 3.1. Additionally, the
following assumptions were made:
x0,y0,z0=(1.5,1.0,-0.1) km,
Doppler frequency fD oscillations have a normal
distribution N(μfD, σfD) = N(0, 0.001), N(0, 0.01), N(0,
0.1), N(0, 1), N(0, 10),
f0=1200 MHz,
v=15 m/s ,
the acquisition time tA=30 s,
the mean value μr and standard deviation σr of the
localization error r is determined according to
formula (7) and (8).
3.4.2 Results
Figure 4 shows the Doppler curves for all the
scenarios studied. Table 2 and Figure 5 show the
localization error for the given scenarios.
Figure 4. The Doppler curves for all the scenarios.
Figure 5. Localization error as a function of time for all
distributions of Doppler frequency f_D oscillations.
Table 2. The mean value μr and standard deviation σr of
the localization error for different distributions of Doppler
frequency fD oscillations.
Localization error [m]
N(μfD, σfD) [Hz]
μr
σr
N(0, 10)
857.08
1471.41
N(0, 1)
38.06
31.82
N(0, 0.1)
5.07
4.30
N(0, 0.01)
0.58
0.54
N(0, 0.001)
0.05
0.05
Analyzing the obtained results, it can be seen that
even small oscillations of the estimated Doppler
frequency fD lead to significant errors. In the case of
σfD=1 Hz, a satisfactory localization error can be
obtained. As can be seen, σfD=10 Hz disqualifies the
SDF method from practical use without prior filtering
of Doppler frequency curves.
3.5 The influence of the carrier frequency estimation error
As mentioned in Section 2.2 in the following article, it
is assumed that the Doppler frequency fD is estimated
using methods which do not need information about
the carrier frequency of the signal. Consequently,
carrier frequency estimation error affects the accuracy
of localization only in formulas (2) and (3).
3.5.1 Scenarios assumptions
The study was conducted taking the assumptions
from Section 3.1 into account. Additionally, the
following assumptions were made:
x0,y0,z0=(1.5,1.0,-0.1) km,
Doppler frequency fD is estimated without error,
carrier frequency of transmitted signal
f0=1200 MHz,
v=15 m/s ,
the acquisition time tA=30 s,
carrier frequency f0 is estimated with error
f0={0.01,0.1,1,10,100} MHz which is added to real
value of carrier frequency of transmitted signal f0,
the mean value μr and standard deviation σr of the
localization error r is determined according to
formula (7) and (8).
3.5.2 Results
Table 3 and Figure 6 show the localization error for
the given scenarios.
954
Figure 6. Localization error as a function of time for different
estimated carrier frequency (f_0=1200 MHz) .
Table 3. The mean value μr and standard deviation σr
of the localization error for different errors of carrier
frequency estimation.
Localization error [m]
Estimated f0 [MHz]
μr
σr
1300.00
238.03
145.09
1210.00
24.30
14.97
1201.00
2.39
1.48
1200.10
0.20
0.12
1200.01
0.02
0.02
Analyzing the above results, we can see that even a
carrier frequency estimation error f0 of 1 and 10 MHz
does not disqualify the SDF method from use. The
localization error does not exceed 2.5 and 25 meters in
this case, respectively. Only at f0=100 MHz does the
localization error reach hundreds of meters, which
would not allow for correct localization for a given
scenario.
3.6 The influence of the UAV’s velocity fluctuations
3.6.1 Scenarios assumptions
The study was conducted taking the assumptions
from Section 3.1 into account. Additionally, the
following assumptions were made:
x0,y0,z0=(1.5,1.0,-0.1) km,
Doppler frequency fD is estimated without error,
carrier frequency of transmitted signal f0=1200 MHz
and is estimated without error,
the acquisition time tA=30 s,
velocity v is estimated. Oscillations have a normal
distribution N(μv, σv) = N(0, 0.001), N(0, 0.01), N(0,
0.1), N(0, 1) and they are added to constant velocity
v=15 m/s,
the mean value μr and standard deviation σr of the
localization error r is determined according to
formula (7) and (8).
3.6.2 Results
Figure 7 shows the UAV velocity courses as a
function of time for all the scenarios studied. Table 4
and Figure 8 show the localization error for the given
scenarios.
Figure 7. The UAV velocity courses as a function of time for
all the scenarios studied.
Figure 8. Localization error as a function of time for all
distributions of velocity v oscillations.
Table 4. The mean value μr and standard deviation σr of
the localization error for different velocity v estimation
error.
Localization error [m]
N(μv, σv) [m/s]
μr
σr
N(0,1)
229.59
214.56
N(0, 0.1)
22.59
19.52
N(0, 0.01)
2.42
2.33
N(0, 0.001)
0.22
0.21
Analyzing the above results, we can see that an
error in determining the UAV speed of about 1 m/s
results in localization errors of several hundred meters.
Therefore, it is necessary to estimate this parameter as
accurately as possible. The distribution of the UAV
speed estimation error for which the localization error
is acceptable is N(0,0.1).
3.7 The influence of the UAV’s positioning accuracy
3.7.1 Scenarios assumptions
The study was conducted taking the assumptions
from Section 3.1 into account. Additionally, the
following assumptions were made:
x0,y0,z0=(1.5,1.0,-0.1) km,
Doppler frequency fD is estimated without error,
carrier frequency of transmitted signal f0=1200 MHz
and is estimated without error,
the acquisition time tA=30 s,
the determination of its own position by the UAV is
performed with an error whose values have a
normal distribution N(μP, σP) = N(0, 0.1), N(0, 1),
N(0, 2), N(0, 5), N(0, 10) m,
955
the velocity is obtained from the UAV and is equal
to v=15 m/s
the mean value μr and standard deviation σr of the
localization error r is determined according to
formula (7) and (8).
3.7.2 Results
Figure 9 shows an example of a UAV route used in
research with and without UAV location error. Table 5
show the localization error for the given scenarios.
Figure 9. Example of a UAV route used in research with and
without UAV location error.
Table 5. The mean value μr and standard deviation σr of
the localization error for different UAV location errors.
Localization error [m]
N(μP, σP) [m]
μr
σr
N(0, 0.1)
0.41
0.25
N(0, 1)
3.64
2.72
N(0, 2)
7.39
4.98
N(0, 5)
18.33
13.89
N(0, 10)
37.49
26.61
Analyzing the above results, we can see that an
error in determining the UAV location also has a
significant impact on accuracy of radio emissions
localization. However, it does not affect that
significantly as, for example, the Doppler frequency fD.
Considering the accuracy of available GNSS receivers,
whose worst-case location error is about 3-5 meters,
will still allow for obtaining effective location for which
the location error of the SDF method will increase by
only a few meters.
4 CONCLUSIONS
The aim of the article was to examine the influence of
parameters on the accuracy of localization of emission
sources using the SDF method. For this purpose,
a theoretical analysis of the SDF method and a series of
simulation studies were conducted.
Analyzing the obtained results, it can be seen that
in ideal conditions and taking all research assumptions
into account, the carrier frequency f0 estimation error
has the smallest impact on the accuracy of localization.
In its case, even an estimation error reaching tens of
megahertz allows for effective determination of the
position of the signal source. The selection of the
acquisition time tA has a slightly greater influence. In
extreme cases, for ideal conditions, its change allows
for a reduction of the localization error r by several
meters, which is not a significant value. The selection
of this parameter may become more important in the
case of an additional error in the estimation of the
Doppler frequency fD. However, the analysis
conducted in the article concerned ideal conditions and
only the change of the acquisition time tA value.
A much greater influence in the case of localization is
the precise determination of the velocity of the
localization sensor carrier, in our case UAV. In this
case, an incorrect determination of the speed differing
from the actual value by only 1 m/s can result in
localization errors reaching hundreds of meters for the
analyzed scenario. Also, the influence of the UAV’s
positioning accuracy is important in SDF method
location error. The scenarios tested show that the use
of commercial GNSS receivers with an error of several
meters should still allow for effective localization, and
the impact on the SDF method location error should be
of the order of several meters. However, the greatest
impact on the localization error can be observed in the
case of the Doppler frequency fD estimation. In the
assumed scenario, its value varied in the range from
about 60 Hz to -60 Hz. Errors in the estimation of this
parameter reaching tens of hertz completely disqualify
the method from practical use. Frequency estimation
with an error of single hertz, on the other hand,
translates into a localization error of several dozen
meters, which, however, for a given scenario allows for
the correct localization of the signal source.
To sum up, in the case of the SDF method, the
greatest impact is played by the Doppler frequency fD
estimation. Its determination is also the biggest
problem in the case of practical implementation,
especially when we are dealing with modulated signals
and non-line-of-sight (NLOS) conditions. Future
research will therefore focus on the most faithful
recovery of the Doppler frequency fD value using
different frequency estimators.
ACKNOWLEDGMENT
This work was developed within the framework of the grant
no. UGB/22-059/2025/WAT, sponsored by the Military
University of Technology (WAT), Poland.
ABBREVIATIONS
DFS Doppler frequency shift
GNSS global navigation satellite system
NLOS non-line-of-sight
SDF signal Doppler frequency
UAV unmanned aerial vehicle
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