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