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© 2
014
Airb
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ce a
nd S
pace
– A
ll rig
hts
rese
rved
. The
rep
rodu
ctio
n, d
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and
utili
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unic
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cont
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rs w
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pres
s au
thor
izat
ion
is p
rohi
bite
d. O
ffend
ers
will
be
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or t
he p
aym
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el o
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.
The Ocean Surface Current Mission (OSCM)Earth Observation for Ocean Atmosphere Interactions Science, ESRIN, Frascati, Italy28th-31st of October 2014
Benjamin Dobke – Airbus Defence & Space, ESA OSCM Study
© 2
014
Airb
us D
efen
ce a
nd S
pace
– A
ll rig
hts
rese
rved
. The
rep
rodu
ctio
n, d
istr
ibut
ion
and
utili
zatio
n of
thi
s do
cum
ent
as w
ell a
s th
e co
mm
unic
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its
cont
ents
to
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rs w
ithou
t ex
pres
s au
thor
izat
ion
is p
rohi
bite
d. O
ffend
ers
will
be
held
liab
le f
or t
he p
aym
ent
of d
amag
es. A
ll rig
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in t
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of
the
gran
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a p
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.
Ocean Surface Current Mission (OSCM) Study
Outline Aim: to give an overview of some of the issues and options within and Ocean
Surface Current Mission (OSCM)
Science Motivation
Measurement Principle
Key Mission Drivers
Key Sensitivities
Instrument Configuration Options
Orbital Options and Regions-of-Interest
Data Processing and Downlinking Options
Estimated Performance
Mass, Power and Launcher
Summary
© 2
014
Airb
us D
efen
ce a
nd S
pace
– A
ll rig
hts
rese
rved
. The
rep
rodu
ctio
n, d
istr
ibut
ion
and
utili
zatio
n of
thi
s do
cum
ent
as w
ell a
s th
e co
mm
unic
atio
n of
its
cont
ents
to
othe
rs w
ithou
t ex
pres
s au
thor
izat
ion
is p
rohi
bite
d. O
ffend
ers
will
be
held
liab
le f
or t
he p
aym
ent
of d
amag
es. A
ll rig
hts
rese
rved
in t
he e
vent
of
the
gran
t of
a p
aten
t, u
tility
mod
el o
r de
sign
.
Ocean Surface Current Mission (OSCM) Study
Science Motivation
Have known for centuries the large scale ocean currents that traverse the world
Have also known about smaller surface currents (~1-100 km) called the mesoscale and sub-meso scale.
Unable to measure currents globally
Eddies, jets, fronts and filaments are ubiquitous and account for over 50% of the oceans’ kinetic energy
OSCM is a science mission, but could also help inform multiple users, e.g. global shipping routes.
Motivation Measurement Drivers Sensitivities Instrument Orbit/Data Performance Launcher
© 2
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Airb
us D
efen
ce a
nd S
pace
– A
ll rig
hts
rese
rved
. The
rep
rodu
ctio
n, d
istr
ibut
ion
and
utili
zatio
n of
thi
s do
cum
ent
as w
ell a
s th
e co
mm
unic
atio
n of
its
cont
ents
to
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rs w
ithou
t ex
pres
s au
thor
izat
ion
is p
rohi
bite
d. O
ffend
ers
will
be
held
liab
le f
or t
he p
aym
ent
of d
amag
es. A
ll rig
hts
rese
rved
in t
he e
vent
of
the
gran
t of
a p
aten
t, u
tility
mod
el o
r de
sign
.
Ocean Surface Current Mission (OSCM) Study
Measurement Principle The focus of the OSCM will be to attain Total Surface Current Velocites (TSCV)
This is performed by measuring phase differences in via Along Track Interferometry (ATI)
Area of ocean is illuminated with a radar swath at time t=0, and later at t=1.
All else being constant, the phase difference between the two received signals will be due to ocean currents
T = 0 T = 1
Motivation Measurement Drivers Sensitivities Instrument Orbit/Data Performance Launcher
© 2
014
Airb
us D
efen
ce a
nd S
pace
– A
ll rig
hts
rese
rved
. The
rep
rodu
ctio
n, d
istr
ibut
ion
and
utili
zatio
n of
thi
s do
cum
ent
as w
ell a
s th
e co
mm
unic
atio
n of
its
cont
ents
to
othe
rs w
ithou
t ex
pres
s au
thor
izat
ion
is p
rohi
bite
d. O
ffend
ers
will
be
held
liab
le f
or t
he p
aym
ent
of d
amag
es. A
ll rig
hts
rese
rved
in t
he e
vent
of
the
gran
t of
a p
aten
t, u
tility
mod
el o
r de
sign
.
Ocean Surface Current Mission (OSCM) Study
Key Mission Drivers
Key mission drivers, or requirements, broadly fall into four catagories:
Measurement Instrument Orbital System
• 5 cm/s accuracy• Wind removal
• Try to provide raw data
• 200km swath (split/non-split)
• Ambiguity control
• 2-10 day repeat• Global coverage
• VEGA class LV• Size, mass, power• Sufficient data
downlinking• Baseline control
A number of these requirements are being re-informed by the OSCM studies
Motivation Measurement Drivers Sensitivities Instrument Orbit/Data Performance Launcher
© 2
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Airb
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efen
ce a
nd S
pace
– A
ll rig
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rese
rved
. The
rep
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ctio
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and
utili
zatio
n of
thi
s do
cum
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as w
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s th
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mm
unic
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its
cont
ents
to
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rs w
ithou
t ex
pres
s au
thor
izat
ion
is p
rohi
bite
d. O
ffend
ers
will
be
held
liab
le f
or t
he p
aym
ent
of d
amag
es. A
ll rig
hts
rese
rved
in t
he e
vent
of
the
gran
t of
a p
aten
t, u
tility
mod
el o
r de
sign
.
Ocean Surface Current Mission (OSCM) Study
Key Sensitivites
We measure the phase, which can be related to the baseline, the surface current velocity, and the velocity of the satellite
When measuring phase, the unknown position and lengths of the baseline can introduce phase errors that dominate the signal you try to measure in diffferent ways.
Putting in representative numbers show that the across-track is negligable, the alongtrack is important, but that the line-of-sight dominates.
dxdβ
B
B’
Motivation Measurement Drivers Sensitivities Instrument Orbit/Data Performance Launcher
© 2
014
Airb
us D
efen
ce a
nd S
pace
– A
ll rig
hts
rese
rved
. The
rep
rodu
ctio
n, d
istr
ibut
ion
and
utili
zatio
n of
thi
s do
cum
ent
as w
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s th
e co
mm
unic
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its
cont
ents
to
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rs w
ithou
t ex
pres
s au
thor
izat
ion
is p
rohi
bite
d. O
ffend
ers
will
be
held
liab
le f
or t
he p
aym
ent
of d
amag
es. A
ll rig
hts
rese
rved
in t
he e
vent
of
the
gran
t of
a p
aten
t, u
tility
mod
el o
r de
sign
.
Ocean Surface Current Mission (OSCM) Study
Instrument Configuration Options
For the ESA OSCM study, we are focusing on single platform solutions.
The focus is also exclusively on ATI rather than XTI (i.e. sea surface heights)
Implies two high-level configuration restrictions.
1. A transmitter and receiver pair that must be separated by a significant distance (of the order of 10m)2. A single, medium-sized platform
Due to the VEGA class launcher, will most likely need a folding antenna to achieve acceptable performance
antenna
boom
3.3m
4.5m
0.7m
antenna support tapers in depth
Motivation Measurement Drivers Sensitivities Instrument Orbit/Data Performance Launcher
© 2
014
Airb
us D
efen
ce a
nd S
pace
– A
ll rig
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rese
rved
. The
rep
rodu
ctio
n, d
istr
ibut
ion
and
utili
zatio
n of
thi
s do
cum
ent
as w
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s th
e co
mm
unic
atio
n of
its
cont
ents
to
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ithou
t ex
pres
s au
thor
izat
ion
is p
rohi
bite
d. O
ffend
ers
will
be
held
liab
le f
or t
he p
aym
ent
of d
amag
es. A
ll rig
hts
rese
rved
in t
he e
vent
of
the
gran
t of
a p
aten
t, u
tility
mod
el o
r de
sign
.
Ocean Surface Current Mission (OSCM) Study
Orbital Options and Regions of Interest
There are specific highly dynamic regions that are of most interest to oceanographers.
Raw data and fast, good area coverage should prioritise these areas.
Open ocean can fill up remaining data allowance
Sun-Synchronous orbit performs best for coverage, thermal, and power
Fixed and drifting orbits at altitudes between 400-600km are being explored
Motivation Measurement Drivers Sensitivities Instrument Orbit/Data Performance Launcher
© 2
014
Airb
us D
efen
ce a
nd S
pace
– A
ll rig
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rese
rved
. The
rep
rodu
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n, d
istr
ibut
ion
and
utili
zatio
n of
thi
s do
cum
ent
as w
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s th
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mm
unic
atio
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its
cont
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to
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rs w
ithou
t ex
pres
s au
thor
izat
ion
is p
rohi
bite
d. O
ffend
ers
will
be
held
liab
le f
or t
he p
aym
ent
of d
amag
es. A
ll rig
hts
rese
rved
in t
he e
vent
of
the
gran
t of
a p
aten
t, u
tility
mod
el o
r de
sign
.
Ocean Surface Current Mission (OSCM) Study
Data Processing and Downlinking Options
Depending on the number of polarisations used, data from a single receiver is of the order of 1.4Gbit/s
Depending on number of receivers and orbital duty cycle, total data per orbit can be ~5-10Tbits
A few downlinking options:
Relying solely on X-band implies that an OSCM would require fully compressed data.
Raw SLC data can be provided with K-band / EDRS. Assuming a likely 1st generation K-band, ~3 minutes of raw data could be provided per orbit in selected areas
Lossless BAQ is also a help (factor of ~2), but could be is not ‘noiseless’ compression.
An on-board data compression could reduce data rate to 30kbit/s allowing high level of coverage at X-band
Motivation Measurement Drivers Sensitivities Instrument Orbit/Data Performance Launcher
© 2
014
Airb
us D
efen
ce a
nd S
pace
– A
ll rig
hts
rese
rved
. The
rep
rodu
ctio
n, d
istr
ibut
ion
and
utili
zatio
n of
thi
s do
cum
ent
as w
ell a
s th
e co
mm
unic
atio
n of
its
cont
ents
to
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rs w
ithou
t ex
pres
s au
thor
izat
ion
is p
rohi
bite
d. O
ffend
ers
will
be
held
liab
le f
or t
he p
aym
ent
of d
amag
es. A
ll rig
hts
rese
rved
in t
he e
vent
of
the
gran
t of
a p
aten
t, u
tility
mod
el o
r de
sign
.
Ocean Surface Current Mission (OSCM) Study
Estimated Performance
Starlab Ltd. and Airbus DS have tools to help estimate expected performance.
Ongoing refininment in design understanding of the complexities of performance
Swath Position in Y [km]
Sw
ath
Pos
ition
in X
[km
]
Varience of Surface Velocity [cm/s]
120 140 160 180 200 220160
165
170
175
180
185
190
195
200
0
5
10
15
20
25
30
35
40
45
50
Error on the current retrieval can be considered as two separate factors:
1. Bias errors: a fixed error dependant upon baseline and spacecraft attitude errors. Can be measured and removed by calibration although residual error will remain
2. Variance: error dependant upon instrument performance and surface decorrelation time
Working on making the performance as compliant as possible
Motivation Measurement Drivers Sensitivities Instrument Orbit/Data Performance Launcher
© 2
014
Airb
us D
efen
ce a
nd S
pace
– A
ll rig
hts
rese
rved
. The
rep
rodu
ctio
n, d
istr
ibut
ion
and
utili
zatio
n of
thi
s do
cum
ent
as w
ell a
s th
e co
mm
unic
atio
n of
its
cont
ents
to
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rs w
ithou
t ex
pres
s au
thor
izat
ion
is p
rohi
bite
d. O
ffend
ers
will
be
held
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le f
or t
he p
aym
ent
of d
amag
es. A
ll rig
hts
rese
rved
in t
he e
vent
of
the
gran
t of
a p
aten
t, u
tility
mod
el o
r de
sign
.
Ocean Surface Current Mission (OSCM) Study
Mass, Power and Launcher
Mass, volume and power are other critical areas for the missionVEGA
PSLV
Mass capacity reduces with altitude, power increases with altitude for the same SNR.
But performance not necessarily better at lower altitudes. Trade-off…
Motivation Measurement Drivers Sensitivities Instrument Orbit/Data Performance Launcher
© 2
014
Airb
us D
efen
ce a
nd S
pace
– A
ll rig
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rese
rved
. The
rep
rodu
ctio
n, d
istr
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and
utili
zatio
n of
thi
s do
cum
ent
as w
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s th
e co
mm
unic
atio
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its
cont
ents
to
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ithou
t ex
pres
s au
thor
izat
ion
is p
rohi
bite
d. O
ffend
ers
will
be
held
liab
le f
or t
he p
aym
ent
of d
amag
es. A
ll rig
hts
rese
rved
in t
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vent
of
the
gran
t of
a p
aten
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tility
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sign
.
Ocean Surface Current Mission (OSCM) Study
Summary1) Strong science motivation to measure un-observed global currents
5) Configuration will most likely need folding antenna. In an in-line ‘Sentinel-1’ style configuration
2) There are key mission drivers that influence mission design
6) Data rates are extremely large. X-band only enabled through compression, 1st Gen K-band offers minutes of raw data
3) Errors in the phase are central to the instrument design issues and performance. Arrise due to baseline knowledge.
7) Performance is continually being refined. Bias dominate but calibration should be able to remove most. Low wind performance a challenge
4) Coverage will likely focus on key dynamic areas with open ocean coverage secondary
8) Launch dictates mass and size. Vega is prefered, PSLV can provide a higher mass alternative.
Measurement Instrument Orbital System
Swath Position in Y [km]
Sw
ath
Pos
ition
in X
[km
]
Varience of Surface Velocity [cm/s]
120 140 160 180 200 220160
165
170
175
180
185
190
195
200
0
5
10
15
20
25
30
35
40
45
50
