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Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop on Subaqueous Soils Rhode Island August 9-12, 2010

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Page 1: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

Bathymetry Data Collection for Subaqueous Soil Mapping

Maggie Payne2nd National Workshop on Subaqueous Soils

Rhode IslandAugust 9-12, 2010

Page 2: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

Overview of Method

• Collect tide data

• Collect bathymetry data in tracks

• Correct to a vertical datum (NAVD88)

• Correct bathymetry data to tides

• Export as a point file (x,y,z data)

Page 3: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

Tidal Datums

• Mean Sea Level (MSL)– The arithmetic mean of hourly heights observed

over the National Tidal Datum Epoch (19 yrs).• Shorter series are specified in the name; e.g. monthly

mean sea level and yearly mean sea level.

• Mean Lower Low Water (MLLW)– The average of the lower low water height of each

tidal day observed over the National Tidal Datum Epoch.

Page 4: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

Elevation Datums• Mean Sea Level

(MSL)– Topo maps

• Mean Lower Low Water (MLLW)– Navigation charts

• North American Vertical Datum 1988 (NAVD88)– Lidar, RTK GPS

NAVD88: 2.05 ft

MLLW: 0.00 ft

MSL: 1.74 ft (1983-2001)

Missing topography/

bathymetry data

Navigation Charts:Relative to MLLW

Topo maps:Relative to MSL

Page 5: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

Tidal Range = 8 inches

Tidal Range = 3 feet

Tidal Range = 2.5 feet

•MLLW datum is different for each coastal pond. •This creates a confusing set of data if presented all together.

Our Problem:

Page 6: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

NAVD88

• Seamless topo/bathy• Same datum from one water body to the next• BUT

– Maps NOT used for navigation– 0 feet NAVD88 ≠ 0 feet MSL

• Does not necessarily indicate intertidal above 0 ft.– The general public does not understand NAVD88, most

understand mean sea level• Depending on your user you may want to provide a map in MSL or

MLLW as well

• Inland and freshwater areas will need to be tied to an average water level

Page 7: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

1. Tides• Set tide gauges during the time

of bathymetry data collection• Be sure gauge will be

underwater through the entire tidal cycle

• Measure elevation of tide gauges to tie into NAVD88 datum

• Multiple tide gauges may be necessary depending on size and shape of water body– No more than 1 mile apart

• One month of tidal data is beneficial to determine MSL and MLLW for the area

• Some tide gauges require barometric pressure correction

Page 8: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

15

17

19

21

23

25

27

29

-80

-60

-40

-20

0

20

40

60

80

100

120

1 656 1311 1966 2621 3276 3931 4586 5241 5896 6551 7206 7861 8516 9171 9826 10481

degr

ees

c

cm

Stone Cove

tide level NAVD88 (cm)

temp ©

Page 9: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

fathometer reading = 8 ft

tide gauge reading= 2 ft

Tide gauge elevation = -1 ft

Zero elevationNAVD88

Tide elevation above zero NAVD88 = 2+(-1) = 1At 10:00, water depth beneath boat = 8 – 1 = 7 feet

below zero NAVD88

10:00 am

Page 10: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

fathometer reading = 8 fttide gauge reading= 0.5 ft

Tide gauge elevation = -1 ft

Zero elevationNAVD88

Tide elevation below zero NAVD88 = 0.5+(-1) = -0.5At 3:00, water depth beneath boat = 8 – (-0.5) = 8.5 feet

below zero NAVD88

3:00 pm

Page 11: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

2. Bathymetry data collection

• Sounder or Chartplotterwith GPS and data recording/transferring capabilities

• Record depth every 5 -10 seconds

• Travel at 4-6 mph

• Criss-cross pattern

Page 12: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop
Page 13: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

• Verify water depth manually and determine draft or offset– Preferably at data

collection speed and weighted with the data collection personnel

Page 14: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

Vegetation• Submerged aquatic vegetation (SAV)

interferes with acoustic depth measurements– If annual vegetation, perform data collection in

winter months when growth is minimal

– If persistent, manual measurements are necessary

Page 15: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

Data Download

• Bathymetry track lines– Mapsource software for

Garmin

• Tide gauge data– Levelogger software for

Levelogger and barrologger

• Tide gauge elevation – RTK download

15

17

19

21

23

25

27

29

-80

-60

-40

-20

0

20

40

60

80

100

120

1 6561311196626213276393145865241589665517206786185169171982610481

degr

ees

c

cm

Stone Cove

tide level NAVD88 …

Page 16: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

Correct tide data to NAVD88

time

tide gauge reading

(ft)decimal

time

RTK tide gauge

elevation

total tide elevation (NAVD88)

11:19:03 2.31 11.32 -0.693 1.617

11:25:03 2.47 11.42 -0.693 1.777

11:31:03 2.5 11.52 -0.693 1.807

11:37:03 2.5 11.62 -0.693 1.807

11:43:03 2.56 11.72 -0.693 1.867

11:49:03 2.51 11.82 -0.693 1.817

11:55:03 2.49 11.92 -0.693 1.797

12:01:03 2.51 12.02 -0.693 1.817

12:07:03 2.51 12.12 -0.693 1.817

12:13:03 2.49 12.22 -0.693 1.797

Page 17: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

timetide gauge reading (ft)

decimal time

RTK tide gauge

elevation

total tide elevation (NAVD88)

11:19:03 2.31 11.32 -0.693 1.617

11:25:03 2.47 11.42 -0.693 1.777

11:31:03 2.5 11.52 -0.693 1.807

11:37:03 2.5 11.62 -0.693 1.807

11:43:03 2.56 11.72 -0.693 1.867

11:49:03 2.51 11.82 -0.693 1.817

11:55:03 2.49 11.92 -0.693 1.797

12:01:03 2.51 12.02 -0.693 1.817

12:07:03 2.51 12.12 -0.693 1.817

12:13:03 2.49 12.22 -0.693 1.797

Tide elevation = 1.617 ft NAVD88 (2.31 + -0.693)

2.31 ft = tide gauge reading

Pressure sensor elevation = -0.693 ft NAVD88

Page 18: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

Graph corrected tide data• Convert times for tide gauges and mapping depths to decimal

hours using equation (time-INT(time))*24=decimal time. • Graph the decimal time and the water depth from the

corrected tide gauge information as an x-y graph. • Add a trendline and get the equation.

Wickford Tides 7/11/05

y = -0.2136x2 + 5.177x - 29.52R2 = 0.988

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15

Decimal Time

Feet

(NA

VD88

)

Page 19: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

Correct tracklog data for tide• Use the equation of the trendline and plug in decimal times of

each depth reading from the Garmin. This will give you the approximate tide height above or below zero at that time.

• Subtract this correction number from the depth reading from the Garmin. This should give you the corrected depth readings.

Wickford Tides 7/11/05

y = -0.2136x2 + 5.177x - 29.52R2 = 0.988

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15

Decimal Time

Feet

(NA

VD88

)

Page 20: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

Y_PROJ X_PROJdepth

reading (ft) DateDecimal

time

tide correction equation =

tide elevation at each time

correct depth

y = -0.2136x2 +

5.177x -29.52

y = depth reading -

tide correction

179313 343306 17.16 7/11/2005 11.11 1.630 15.53

179244 343355 17.78 7/11/2005 11.11 1.631 16.15

179173 343401 17.68 7/11/2005 11.11 1.633 16.05

179064 343433 16.63 7/11/2005 11.12 1.635 14.99

178412 342965 4.82 7/11/2005 11.50 1.768 3.05

178446 342960 5.48 7/11/2005 11.51 1.769 3.71

178474 342983 6.46 7/11/2005 11.51 1.770 4.69

Page 21: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop
Page 22: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

Other methods

• Hypack software

• Direct connection of fathometer to RTK

• Multibeam fathometer

• Survey using total station

Page 23: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

Freshwater

• No tides, but be aware of water fluctuations seasonally

• Determine a vertical datum that would work for you – (NAVD88 might

not be your answer)

Page 24: Bathymetry Collection for Subaqueous Soil Mappingnesoil.com/sas/15_Payne_Bathymetry.pdf · Bathymetry Data Collection for Subaqueous Soil Mapping Maggie Payne 2 nd National Workshop

Questions?