<s>
CryoSat-2	B-Algorithm
is	O
a	O
European	O
Space	O
Agency	O
(	O
ESA	O
)	O
Earth	O
Explorer	O
Mission	O
that	O
launched	O
on	O
April	O
8	O
,	O
2010	O
.	O
</s>
<s>
CryoSat-2	B-Algorithm
is	O
dedicated	O
to	O
measuring	O
polar	O
sea	O
ice	O
thickness	O
and	O
monitoring	O
changes	O
in	O
ice	O
sheets	O
.	O
</s>
<s>
CryoSat-2	B-Algorithm
was	O
built	O
as	O
a	O
replacement	O
for	O
CryoSat-1	B-Algorithm
,	O
which	O
failed	O
to	O
reach	O
orbit	O
following	O
a	O
launch	O
failure	O
in	O
October	O
2005	O
.	O
</s>
<s>
CryoSat-2	B-Algorithm
was	O
successfully	O
launched	O
five	O
years	O
later	O
in	O
2010	O
,	O
with	O
upgraded	O
software	O
aiming	O
to	O
measure	O
changes	O
in	O
ice	O
thickness	O
to	O
an	O
accuracy	O
of	O
~	O
10%	O
of	O
the	O
expected	O
interannual	O
variation	O
.	O
</s>
<s>
Unlike	O
previous	O
satellite	O
altimetry	O
missions	O
,	O
CryoSat-2	B-Algorithm
provides	O
unparalleled	O
Arctic	O
coverage	O
,	O
reaching	O
88˚N	O
(	O
previous	O
missions	O
were	O
limited	O
to	O
81.5	O
˚N	O
)	O
.	O
</s>
<s>
The	O
primary	O
payload	O
of	O
the	O
mission	O
is	O
a	O
synthetic	B-Application
aperture	I-Application
radar	I-Application
(	O
SAR	B-Application
)	O
Interferometric	O
Radar	O
Altimeter	O
(	O
SIRAL	O
)	O
,	O
which	O
measures	O
surface	O
elevation	O
.	O
</s>
<s>
CryoSat-2	B-Algorithm
is	O
part	O
of	O
ESA	O
's	O
wider	O
CryoSat	B-Algorithm
mission	O
in	O
the	O
Living	O
Planet	O
Programme	O
.	O
</s>
<s>
On	O
22	O
October	O
2010	O
,	O
CryoSat-2	B-Algorithm
was	O
declared	O
operational	O
following	O
six	O
months	O
of	O
on-orbit	O
testing	O
.	O
</s>
<s>
The	O
initial	O
proposal	O
for	O
the	O
CryoSat	B-Algorithm
programme	O
was	O
submitted	O
as	O
part	O
of	O
a	O
call	O
for	O
proposals	O
in	O
July	O
1998	O
for	O
Earth	O
Explorer	O
missions	O
as	O
part	O
of	O
the	O
European	O
Space	O
Agency	O
's	O
Living	O
Planet	O
programme	O
.	O
</s>
<s>
Due	O
to	O
the	O
importance	O
of	O
the	O
CryoSat	B-Algorithm
mission	O
for	O
understanding	O
global	O
warming	O
and	O
reductions	O
in	O
polar	O
ice	O
caps	O
,	O
a	O
replacement	O
satellite	O
was	O
proposed	O
.	O
</s>
<s>
The	O
development	O
of	O
CryoSat-2	B-Algorithm
was	O
authorised	O
in	O
February	O
2006	O
,	O
less	O
than	O
five	O
months	O
after	O
the	O
failure	O
.	O
</s>
<s>
Like	O
its	O
predecessor	O
,	O
CryoSat-2	B-Algorithm
was	O
constructed	O
by	O
EADS	O
Astrium	O
,	O
with	O
its	O
main	O
instrument	O
being	O
built	O
by	O
Thales	O
Alenia	O
Space	O
.	O
</s>
<s>
The	O
Project	O
Manager	O
for	O
the	O
CryoSat-2	B-Algorithm
mission	O
was	O
Richard	O
Francis	O
,	O
who	O
had	O
been	O
the	O
Systems	O
Manager	O
on	O
the	O
original	O
CryoSat	B-Algorithm
mission	O
.	O
</s>
<s>
CryoSat-2	B-Algorithm
is	O
an	O
almost-identical	O
copy	O
of	O
the	O
original	O
spacecraft	O
,	O
however	O
modifications	O
were	O
made	O
including	O
the	O
addition	O
of	O
a	O
backup	O
radar	O
altimeter	O
.	O
</s>
<s>
The	O
aim	O
of	O
the	O
CryoSat	B-Algorithm
mission	O
is	O
to	O
determine	O
ice	O
thickness	O
variations	O
on	O
Earth	O
's	O
ice	O
sheets	O
and	O
marine	O
ice	O
cover	O
.	O
</s>
<s>
CryoSat	B-Algorithm
achieved	O
its	O
initial	O
mission	O
objectives	O
following	O
the	O
launch	O
of	O
CryoSat-2	B-Algorithm
,	O
and	O
therefore	O
the	O
mission	O
was	O
extended	O
with	O
new	O
objectives	O
.	O
</s>
<s>
When	O
it	O
was	O
approved	O
in	O
February	O
2006	O
,	O
the	O
launch	O
of	O
CryoSat-2	B-Algorithm
was	O
planned	O
for	O
March	O
2009	O
.	O
</s>
<s>
The	O
Dnepr	O
rocket	O
assigned	O
to	O
launch	O
CryoSat-2	B-Algorithm
arrived	O
at	O
the	O
Baikonur	O
Cosmodrome	O
by	O
train	O
on	O
29	O
December	O
2009	O
.	O
</s>
<s>
Following	O
the	O
completion	O
of	O
its	O
construction	O
,	O
CryoSat-2	B-Algorithm
was	O
placed	O
into	O
storage	O
to	O
await	O
launch	O
.	O
</s>
<s>
During	O
final	O
testing	O
,	O
engineers	O
detected	O
that	O
the	O
spacecraft	O
's	O
X	B-Algorithm
band	I-Algorithm
(	O
NATO	O
H/I/J	O
bands	O
)	O
communications	O
antenna	O
was	O
transmitting	O
only	O
a	O
tiny	O
fraction	O
of	O
the	O
power	O
that	O
it	O
should	O
.	O
</s>
<s>
On	O
4	O
February	O
,	O
the	O
CryoSat-2	B-Algorithm
spacecraft	O
was	O
fuelled	O
for	O
launch	O
.	O
</s>
<s>
CryoSat-2	B-Algorithm
was	O
launched	O
at	O
13:57:04	O
UTC	O
on	O
8	O
April	O
2010	O
.	O
</s>
<s>
Following	O
a	O
successful	O
launch	O
,	O
CryoSat-2	B-Algorithm
separated	O
from	O
the	O
upper	O
stage	O
of	O
the	O
Dnepr	O
into	O
a	O
low	O
Earth	O
orbit	O
.	O
</s>
<s>
The	O
primary	O
payload	O
onboard	O
CryoSat-2	B-Algorithm
is	O
the	O
SAR	B-Application
Interferometric	O
Radar	O
Altimeter	O
(	O
SIRAL	O
)	O
,	O
operating	O
in	O
the	O
Ku-band	B-Algorithm
(	O
13.6	O
GHz	O
)	O
.	O
</s>
<s>
Unlike	O
the	O
original	O
CryoSat	B-Algorithm
,	O
two	O
SIRAL	O
instruments	O
are	O
installed	O
aboard	O
CryoSat-2	B-Algorithm
,	O
with	O
one	O
serving	O
as	O
a	O
backup	O
in	O
case	O
the	O
other	O
fails	O
.	O
</s>
<s>
The	O
instrument	O
combines	O
a	O
pulse-limited	O
radar	O
altimeter	O
and	O
a	O
second	O
antenna	O
with	O
synthetic	B-Application
aperture	I-Application
and	O
interferometric	O
signal	O
processing	O
.	O
</s>
<s>
The	O
instrument	O
operates	O
in	O
three	O
modes	O
depending	O
on	O
the	O
surface	O
type	O
being	O
measured	O
;	O
low	O
resolution	O
mode	O
,	O
synthetic	B-Application
aperture	I-Application
radar	I-Application
(	O
SAR	B-Application
)	O
mode	O
,	O
and	O
SAR	B-Application
interferometric	O
(	O
SARIn	O
)	O
mode	O
.	O
</s>
<s>
Low	O
resolution	O
mode	O
is	O
used	O
over	O
ice	O
sheet	O
interiors	O
and	O
oceans	O
,	O
SAR	B-Application
is	O
used	O
over	O
sea	O
ice	O
and	O
possible	O
oceanographic	O
areas	O
,	O
and	O
SARIn	O
is	O
used	O
around	O
the	O
ice	O
sheet	O
margins	O
and	O
mountain	O
glaciers	O
.	O
</s>
<s>
In	O
SAR	B-Application
mode	O
,	O
SIRAL	O
emits	O
a	O
burst	O
of	O
64	O
pulses	O
,	O
separated	O
into	O
narrow	O
along-track	O
beams	O
by	O
exploiting	O
the	O
Doppler	O
Effect	O
.	O
</s>
<s>
The	O
SAR	B-Application
footprint	O
is	O
approximately	O
0.31	O
km	O
along-track	O
and	O
1.67	O
km	O
across-track	O
.	O
</s>
<s>
The	O
Doppler	O
Orbit	O
and	O
Radio	O
Positioning	O
Integration	O
(	O
DORIS	O
)	O
is	O
the	O
second	O
instrument	O
on	O
CryoSat-2	B-Algorithm
,	O
and	O
calculates	O
precisely	O
the	O
spacecraft	O
's	O
orbit	O
.	O
</s>
<s>
Following	O
launch	O
,	O
CryoSat-2	B-Algorithm
was	O
placed	O
into	O
a	O
low	O
Earth	O
orbit	O
with	O
a	O
perigee	O
of	O
,	O
an	O
apogee	O
of	O
,	O
92	O
degrees	O
of	O
inclination	O
and	O
an	O
orbital	O
period	O
of	O
99.2	O
minutes	O
.	O
</s>
<s>
CryoSat	B-Algorithm
successfully	O
achieved	O
its	O
mission	O
objectives	O
following	O
the	O
launch	O
of	O
CryoSat-2	B-Algorithm
.	O
</s>
<s>
Data	O
from	O
CryoSat-2	B-Algorithm
has	O
shown	O
25,000	O
seamounts	O
,	O
with	O
more	O
to	O
come	O
as	O
data	O
is	O
interpreted	O
.	O
</s>
<s>
It	O
was	O
clear	O
from	O
the	O
beginning	O
of	O
the	O
CryoSat	B-Algorithm
programme	O
that	O
an	O
extensive	O
series	O
of	O
measurements	O
would	O
be	O
needed	O
,	O
both	O
to	O
understand	O
interaction	O
of	O
the	O
radar	O
waves	O
with	O
the	O
surface	O
of	O
the	O
ice	O
caps	O
and	O
to	O
relate	O
the	O
measured	O
freeboard	O
of	O
floating	O
sea	O
ice	O
with	O
its	O
thickness	O
.	O
</s>
<s>
For	O
sea	O
ice	O
,	O
which	O
moves	O
as	O
it	O
is	O
blown	O
by	O
the	O
wind	O
,	O
it	O
was	O
also	O
necessary	O
to	O
develop	O
techniques	O
which	O
could	O
give	O
consistent	O
results	O
when	O
measured	O
from	O
platforms	O
travelling	O
at	O
different	O
speed	O
(	O
scientists	O
on	O
the	O
surface	O
,	O
helicopter-towed	O
sounders	O
,	O
aircraft-borne	O
radars	O
and	O
CryoSat	B-Algorithm
itself	O
)	O
.	O
</s>
<s>
These	O
campaigns	O
continued	O
through	O
the	O
development	O
of	O
the	O
original	O
CryoSat	B-Algorithm
and	O
were	O
planned	O
to	O
continue	O
after	O
its	O
launch	O
.	O
</s>
<s>
Following	O
the	O
announcement	O
that	O
CryoSat-2	B-Algorithm
would	O
be	O
built	O
the	O
CRYOVEX	O
programme	O
was	O
extended	O
.	O
</s>
<s>
Additional	O
snow	O
measurements	O
were	O
provided	O
by	O
the	O
Arctic	O
Arc	O
Expedition	O
,	O
and	O
the	O
Alfred	O
Wegener	O
Institute	O
's	O
Airborne	O
Synthetic	B-Application
Aperture	I-Application
and	O
Interferometric	O
Radar	O
Altimeter	O
System	O
(	O
ASIRAS	O
)	O
instrument	O
,	O
mounted	O
aboard	O
a	O
Dornier	O
228	O
aircraft	O
.	O
</s>
