observing sea level
DESCRIPTION
Presentation given by Roland Klees at the symposium on Sea Level Rise by TU Delft Climate Institute http://bit.ly/Y5dPvYTRANSCRIPT
11/29/12
Challenge the future Delft University of Technology
Observing Sea Level
R Klees Department of Geoscience & Remote Sensing Delft University of Technology
2 Observing Sea Level
What is sea level?
• Distance of water level from some reference point • Absolute and relative sea level • (Global) Mean sea level
fixed point on land
relative sea level
absolute sea level
3 Observing Sea Level
How is sea level measured?
Tide gauge Satellite radar altimetry Floats + satellite gravimetry
4 Observing Sea Level
Tide gauge measurement system Basic principle
Ruler edged staff
5 Observing Sea Level
Tide gauge technical realizations
Classical float gauge (from ~1832)
Radar gauge @ Liverpool
Acoustic gauge @ Hamburg
6 Observing Sea Level
25 well-selected tide gauge records
-20
-15
-10
-5
0
5
10
15
20
1900 1920 1940 1960 1980 2000
ΔSL
(mm
)
Year
-20
-15
-10
-5
0
5
10
15
20
1900 1920 1940 1960 1980 2000
ΔSL
(mm
)
Year
Rate ~ 1.8 ± 0.1 mm/yr
Nerem 2005
7 Observing Sea Level
Satellite radar altimetry
8 Observing Sea Level
MSL from satellite radar altimetry 10-day coverage of Topex & Jason
-100
0
100
1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012
TOPEXERS-2
GFOJason-1
EnvisatJason-2
-100
0
100
Ch
an
ge
in
me
an
se
a l
ev
el
[mm
]
1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012
North Sea mean sea level
seasonal signals removedtrend: 1.7 ± 0.4 mm/year
Laboratory for Satellite AltimetryNOAA•NESDIS•STAR
NOAA) ) ) ) ) )))
9 Observing Sea Level
Observing changes in the volume of ocean water …
… due to changes in total ocean water mass
…due to changes in ocean water density
+
ARGO GRACE
10 Observing Sea Level
Observing ocean water temperature
Profile data
Surface Pressure
ARGO floats
11 Observing Sea Level
ARGO network
12 Observing Sea Level
Changes in the volume of ocean water
GRACE
RA versus ARGO+GRACE
ARGO versus RA-GRACE
ARGO
GRACE versus RA-ARGO
Leuliette & Miller 2009
13 Observing Sea Level
Some issues with sea level records • Vertical land movement
GPS
Abs grav
2000-2050
Geology or GIA models
14 Observing Sea Level
• Uneven geographic distribution
Some issues with sea level records
PSMSL stations
Woodworth et al 2011
15 Observing Sea Level
• Uneven geographic distribution
Some issues with sea level records
PSMSL stations with record > 60 yrs
Woodworth et al 2011
16 Observing Sea Level
Regional mean sea level trends (Jan 1993 – April 2012)
• Uneven geographic distribution
Some issues with sea level records
17 Observing Sea Level
• Calibration of radar altimeters
Some issues with sea level records
• ± 0.4 mm/yr tide gauge calibration error
• dominated by errors in vertical land movement from GPS data
Nerem 2005
18 Observing Sea Level
Predicted present-day impact of GIA…
… on relative sea level change measured by tide gauges
… on absolute sea level change measured by radar altimetry
… on change in water mass measured by GRACE Tamisiea 2011
19 Observing Sea Level
New techniques for sea level measurements
Waverider GPS buoy, University of Tasmania
GNSS altimetry (PARIS concept)
Spar buoy, NOAA