UNOLS Ocean Surveyor ADCPOverview

Julia Hummon, Eric Firing

hummon@hawaii.edu, efiring@hawaii.edu

UNOLS Ocean Surveyor ADCP Overview – p. 1/22

Outline

ADCP: recent history

Installations surveyed

Data and conditions

PerformanceInstallationDepth coverageSide lobesErrors in velocity

Specific problems

Conclusions and Recommendations

UNOLS Ocean Surveyor ADCP Overview – p. 2/22

ADCP: Recent History

4 acoustic beams; interpret Doppler shift

Use heading and position to remove ship motion

1980’s: Narrowband (150KHz)

1990’s: Broadband

2000: Phased Array (150KHz, 75KHz, 38KHz)

Comparison: NB150 vs OS75 (Hummon and Firing,JTECH 2003)

UNOLS Ocean Surveyor ADCP Overview – p. 3/22

Acknowledgements:

Sandy Shor, andScientists and Techs who provided data

This work was supported by NSF grant numberOCE03-09966

This report is online at:http://currents.soest.hawaii.edu/reports

UNOLS Ocean Surveyor ADCP Overview – p. 4/22

Installations Surveyed150KHz 75KHz 38KHz

UNOLS Barnes Endeavor

Walton Smith Knorr

Oceanus

Pelican

Seward Johnson II Seward Johnson I

Wecoma

SEA C. Cramer

R.C. Seamans

USCG Healy

NOAA Sette

LoveBoat Explorer of the Seas Explorer of the Seas

JAMSTEC Kaiyo

UNOLS Ocean Surveyor ADCP Overview – p. 5/22

Data Description

Conditions varied:Acquisition mode (nb or bb, cell size)Water depth, topographic slopeSpeed of ship (many or no stations, transit, ice)Weather conditions

specific comparisonsDepth coverage in different modesBottom return shape from OS vs BB, OS vs NBSame instrument, two different installationsSame instrument and ship, with and without window

UNOLS Ocean Surveyor ADCP Overview – p. 6/22

Performance: Installation

50

100

150

200

284.6 284.8 285 285.2 285.4

5

10

15

20

25

30

35

40

45

50AMPLITUDE

ACG, WITH WINDOW

0

20

40

60

80

100

284.6 284.8 285 285.2 285.4

5

10

15

20

25

30

35

40

45

50PERCENT GOOD

PGOOD, WITH WINDOW

0 50 100 150 200

0

10

20

30

40

50

ACG, WITH WINDOW

ON STATION

UNDERWAY

50

100

150

200

298.6 298.8 299 299.2 299.4

5

10

15

20

25

30

35

40

45

50

55AMPLITUDE

ACG, WITHOUT WINDOW

0

20

40

60

80

100

298.6 298.8 299 299.2 299.4

5

10

15

20

25

30

35

40

45

50

55PERCENT GOOD

PGOOD, WITHOUT WINDOW

Knorr: AGC and Percent Good in two installations

0 50 100 150 200

0

10

20

30

40

50

60

ACG, WITH WINDOW

ON STATION

UNDERWAY

UNOLS Ocean Surveyor ADCP Overview – p. 7/22

Depth coverage summary

best worst(bubbles)

150KHzup to 230m (NB8) 0mup to 200m (BB8)

75KHzup to 750m (NB16, NB8) 0mup to 600m (BB10, BB8) 0m

38KHzup to 1200m (NB16, NB24) 0m

UNOLS Ocean Surveyor ADCP Overview – p. 8/22

Performance: Depth coverage ...

... depends on signal/noise:

Number of scatterersLocation: biological activity variesDiurnal cycle: up at night, deep during dayDepth of scattering layers, some strong

Ambient noiseFaster ship increases ambient noiseFaster ship in heavy weather increases bubbles

UNOLS Ocean Surveyor ADCP Overview – p. 9/22

Performance: Side lobes

AGC bottom return shape shows OS side lobes worse thanNB or BB:

Shows up in all frequencies, (least evident in 38KHz)

Difficult to compare between instruments

Visible as “shoulder” or increased thickness

velocity effect is visible

UNOLS Ocean Surveyor ADCP Overview – p. 10/22

Performance: Errors in velocity

Cross-track error:1 degree heading error at 10kts gives 10cm/s error

Use gyro as the primary heading source (reliable)GPS-aided heading should go into serial port

along-track error:Top bin bias:(up to 1+ m/s) edit out bins or fix installationAnomalous shear:(5-15cm/s) from scattering layers: BE AWAREUnflagged bad bins:(5-15cm/s) EDIT prior to averaging

UNOLS Ocean Surveyor ADCP Overview – p. 11/22

Performance Concerns

All ADCPs:

Bubbles

Ringing

No gps-aided heading

Ocean Surveyor

Increased sidelobe strength (vs NB or BB)

UNOLS Ocean Surveyor ADCP Overview – p. 12/22

Acquisition concerns

Concerns:

Bottom track bug (fixed in firmware version XX?)

Problems with serial inputs:Binary garbage in serial dataBinary message in serial dataToo many unnecessary messages

File names not consistent

Heading comes in through serial port (versus chassis)

Timeserver problems

Thermistors can fail

UNOLS Ocean Surveyor ADCP Overview – p. 13/22

Conclusions (I)

Combination of VmDAS and Ocean Surveyor works

Increased depth range of OS75 and OS38 will be veryvaluable for scientific studies

So far, no ambiguity wraps in velocity

UNOLS Ocean Surveyor ADCP Overview – p. 14/22

Conclusions (II)

Beam side lobesOS sidelobes higher than BB and NBDifficult to compare between instruments(installations)

Velocity errors (all ADCPs)Averaged data can include obvious and subtlebiasesScattering layers do cause a visible effect in velocity

Installation quality is criticalGyro errors induce cross-track velocity errorsRinging causes bias in top binsBubbles are BAD, affecting depth penetration andaccuracy

UNOLS Ocean Surveyor ADCP Overview – p. 15/22

Recommendations

Every installation needs oversight

Designate a central repository of ADCP installationinformation

Deep water installations (frequently out of bottomtrackrange) should have gps-aided heading

Improved automated editing needed

Monitor instrument quality over time and compareinstruments with each other. Need to:

Determine data parameters, site characteristics, testprocedureIdentify locations and manage scheduling

UNOLS Ocean Surveyor ADCP Overview – p. 16/22

Gulf Stream Cross-section

simultaneously logged

NB150 (8m bins) OS75 (BB, 8m) OS75 (NB, 16m)

37.5°N 38°N 38.5°N

0

100

200

300

400

500

600

700 (OSB, ping−edited)

−0.5

0

0.5

1

1.5

2

37.5°N 38°N 38.5°N

0

100

200

300

400

500

600

700 (OSN, ping−edited)

37.5°N 38°N 38.5°N

0

100

200

300

400

500

600

700 (allNB, ping−edited)

met

ers

UNOLS Ocean Surveyor ADCP Overview – p. 17/22

side lobes←−

0 20 40 60 80 100 120 140 160 180

200

220

240

260

280

300

320

340

360

AGC counts

met

ers

Endeavor NB150, OS75

OS75 (8m)

NB150 (8m)

85% of water depth

side lobesdiffer

UNOLS Ocean Surveyor ADCP Overview – p. 18/22

side lobes affect velocity←−←−

40 50 60 70 80 90

200

250

300

350

400

450

500

550

on station

underway

ACG countsde

pth,

met

ers

LIDEX: AGC bump causes "S" in velocity−10 −8 −6 −4 −2

200

250

300

350

400

450

500

550

on station

underway

southward ocean velocity

cm/s

UNOLS Ocean Surveyor ADCP Overview – p. 19/22

heading error←−

170 175 180 185 190 195 200 205 210 215 220

−2°

0°

2°

4°

decimal day

gyro

err

or

gyro error (compared to Seapath)

RB0304, A16N CLIVAR repeat line

170 175 180 185 190 195 200 205 210 215 220−20

−10

0

10

20

30

decimal day

cm/s

cross−track velocity error

UNOLS Ocean Surveyor ADCP Overview – p. 20/22

top bin bias←−

UNOLS Ocean Surveyor ADCP Overview – p. 21/22

edit before averaging←−

360.32 360.34 360.36 360.38 360.4 360.42 360.44 360.46 360.482

3

4

5

6

7

8

9

10averaged data

averaged data

bias in averaged data

no biasm

/s

EX0251 bin 3 abs measured velocity: underway bias towards zero

360.32 360.34 360.36 360.38 360.4 360.42 360.44 360.46 360.480

2

4

6

8

10single−ping data

m/s

single−ping data

bias in raw data

no bias

UNOLS Ocean Surveyor ADCP Overview – p. 22/22