WHOTS - ADCP Compass Calibration History

Version 1: September 23, 2014By: Walt Deppe

File History

• Version 1 – Walt Deppe, 9/23/2014

Outline

1. Background Switch from Snug to UH Magnetic Anomaly Surveys

2. Things to look for & keep in mind3. ADCP S/N & Deployment List4. Individual Instrument Error Analysis5. Observations6. Recommendations

Background• Snug Harbor: initial compass calibration location• Between WHOTS-1 and -2, turnaround & compass

calibration done at sea• Some early compass calibration spin data not recorded

(and s/n 1825 originally prepared by WHOI)• Switched calibration location from Snug to UH after

large magnetic anomalies detected at Snug• Calibration frame changed over years– Trash can– Wooden frame– Aluminum frame (current)

Switch from Snug to UH• Following WHOTS-7 compass calibration and before WHOTS-6 post-

deployment check, compass-spin location switched from Snug Harbor to UH Lower Campus Soccer Field after large magnetic field anomalies detected at Snug

• Magnetic Anomaly Surveys (August 2010)– Located on OHU in ‘C:\Users\Craig\Documents\WHOTS\

Compass_Calibs’– Snug Harbor Analysis (Aug 24th): magnetic_survey.doc– UH Soccer Field Analysis (Aug 27th): magnetic_survey2.doc

• “The manufacturer of the compass used for the survey did not list accuracy specifications but given the compass does not appear to be crafted with precision tools and given the very poor eyesight of the surveyor, it is possible that the +/- 1.5 differences seen could be considered “in the noise”.

• “If/when the Lower Campus site is used for compass calibrations, it would be advisable to perform the calibrations at the midpoint of the 100 point reference line outlined in this survey as it appears to have the smallest mean differences from magnetic north and the smallest standard deviations. “

Magnetic Anomaly Surveys

Snug Harbor UH Lower Campus Soccer Field

Things to look for & keep in mind• Differences between calibrations done at Snug (worse) and

UH (better)• Tightening of error amplitude after calibration during pre-

deployment observations• Comparison between spin error amplitudes & RDI “Overall

Error” output• Calibration purpose: reducing error around compass rows

due to battery interference signature• Pre-deployment, pre-calibration spin is using calibration

matrix determined for previous battery pack before last deployment

• Spin errors currently not used in any data processing, only RDI calibration matrix affects data

ADCP S/N & Deployment List

• 300 kHz– s/n 4891 (WHOTS – 1, 2, 4, 6, 8, 10)– s/n 7637 (WHOTS – 3, 5, 7, 9, 11)

• 600 kHz– s/n 1825 (WHOTS – 4, 6, 8, 10)– s/n 13917 (WHOTS – 7, 9, 11)

• 1200 kHz– s/n 2530 (WHOTS – 5)

Individual Instrument Error Analysis

• For Each ADCP:– Compass spin error plots by deployment– Compass spin error stats over time– Comparison of spin stats w/ RDI output

• ADCPs– s/n 4891– s/n 7637– s/n 1825– s/n 13917– s/n 2350

S/N 4891

s/n 4891 – 300 kHz• No spin errors recorded for

WHOTS-1 pre-deployment (Snug) or post-deployment (@ sea) or WHOTS-2 pre-deployment (@ sea)

• Note WHOTS-6 post-deployment mean error (performed at UH soccer field) does not reflect large pre-deployment offset (performed at Snug)

s/n 4891

RDI Estimate RDI Estimate RDI EstimateMean Min-Mean Max-Mean Overall Error(±) Mean Min-Mean Max-Mean Overall Error(±) Mean Min-Mean Max-Mean Overall Error(±)

1 Snug 3.10 Snug 0.32 Sea n/a2 Sea n/a Sea n/a Snug -3.06 -1.59 2.36 1.924 Snug -8.96 -1.94 2.41 4.29 Snug -0.38 -0.52 0.38 0.61 Snug -3.22 -1.78 2.22 1.726 Snug -11.30 -4.00 3.45 3.95 Snug -14.08 -0.47 0.68 0.83 UH -1.78 -1.22 1.78 2.288 UH -2.39 -1.81 1.89 1.97 UH -0.39 -0.11 0.19 0.70 UH -0.66 -2.14 1.76 1.75

10 UH -0.77 -3.13 2.47 3.08 UH -0.60 -0.30 0.40 0.35 UH -0.49 -2.56 1.59 2.06

Snug -10.13 ± 2.95 3.78 Snug -7.23 ± 0.51 0.59 Snug -3.14 ± 1.99 1.82UH -1.58 ± 2.33 2.53 UH -0.50 ± 0.25 0.53 UH -0.98 ± 1.84 2.03

ALL -5.86 ± 2.64 3.28 ALL -3.86 ± 0.38 0.56 ALL -1.84 ± 1.90 1.95

Mean

Mean

Mean

s/n WHOTS

4891

n/an/a

Before Cal

@ Spin Data Errors

n/a

Post DeploymentPre Deployment Pre Deployment

n/an/a

Spin Data Errors Spin Data ErrorsAfter Cal

@ @

S/N 7637

s/n 7637 – 300 kHz• Instrument damaged during

WHOTS-5. No post-deployment check.

• Note WHOTS-7 post-deployment mean error (performed at UH soccer field) does not reflect large pre-deployment offset (performed at Snug)

• A boat docked 60 m. away half-way through pre-deployment calibration for WHOTS-7

s/n 7637

RDI Estimate RDI Estimate RDI EstimateMean Min-Mean Max-Mean Overall Error(±) Mean Min-Mean Max-Mean Overall Error(±) Mean Min-Mean Max-Mean Overall Error(±)

3 Snug -0.52 -3.28 2.72 3.07 Snug -1.92 -3.09 2.69 0.26 Snug -7.50 -2.69 3.10 2.885 Snug -4.64 -1.76 1.64 1.61 Snug -4.36 -0.49 0.66 0.49 Snug

7 Snug -12.37 -1.18 1.87 1.70 Snug -8.66 -1.19 1.21 1.50 UH 0.99 -0.79 0.71 0.549 UH -2.03 -6.67 8.93 8.23 UH 0.61 -0.91 2.39 0.48 UH 1.83 -1.33 1.27 1.22

11 UH 4.71 -2.11 3.29 2.29 UH 4.33 -0.33 0.42 0.59 UH

Snug -5.84 ± 2.08 2.13 Snug -4.98 ± 1.56 0.75 Snug -7.50 ± 2.90 2.88UH 1.34 ± 5.25 5.26 UH 2.47 ± 1.01 0.54 UH 1.41 ± 1.03 0.88

ALL -2.97 ± 3.35 3.38 ALL -2.00 ± 1.34 0.66 ALL -1.56 ± 1.65 1.55Mean

Mean

Mean

@ Spin Data Errors @ Spin Data Errors @ Spin Data Errors

7637

s/n WHOTS

Pre Deployment Pre Deployment Post DeploymentBefore Cal After Cal

damaged

in water

S/N 1825

s/n 1825 – 600 kHz• WHOTS-4, prepared by WHOI (no

cal records available)• Note WHOTS-6 post-deployment

mean error (performed at UH soccer field) does not reflect large pre-deployment offset (performed at Snug)

s/n 1825

RDI Estimate RDI Estimate RDI EstimateMean Min-Mean Max-Mean Overall Error(±) Mean Min-Mean Max-Mean Overall Error(±) Mean Min-Mean Max-Mean Overall Error(±)

4 Snug Snug Snug

6 Snug 4.34 Snug -10.23 -1.62 1.13 1.03 UH 0.67 -1.67 1.33 0.998 UH -1.31 -0.89 1.81 1.48 UH 1.09 -0.59 0.31 0.22 UH -1.06 -1.24 1.06 1.15

10 UH -0.72 -2.48 2.72 2.81 UH -0.91 -0.39 0.31 0.18 UH -3.16 -0.89 0.76 0.76

Snug 4.34 Snug -10.23 ± 1.38 1.03 Snug

UH -1.02 ± 1.98 2.15 UH 0.09 ± 0.40 0.20 UH -1.18 ± 1.16 0.97

ALL -1.02 ± 1.98 2.88 ALL -3.35 ± 0.73 0.48 ALL -1.18 ± 1.16 0.97

Mean

Mean

s/n WHOTS

Pre Deployment Pre Deployment Post Deployment

1825

Mean

n/a

whoiwhoi

n/a

whoin/a

@ Spin Data ErrorsBefore Cal After Cal

@ Spin Data Errors @ Spin Data Errors

S/N 13917

s/n 13917 – 600 kHz• Instrument damaged during

WHOTS-7. No post-deployment check.

s/n 13917

RDI Estimate RDI Estimate RDI EstimateMean Min-Mean Max-Mean Overall Error(±) Mean Min-Mean Max-Mean Overall Error(±) Mean Min-Mean Max-Mean Overall Error(±)

7 Snug -7.72 -0.88 1.27 0.42 Snug -10.09 -0.81 0.94 0.64 UH

9 UH -2.57 -2.13 2.47 2.49 UH -0.02 -0.48 0.22 0.23 UH 2.16 -2.96 2.34 2.8711 UH 3.50 -2.30 2.45 2.84 UH 3.62 -0.32 0.38 0.54 UH

Snug -7.72 ± 1.08 0.42 Snug -10.09 ± 0.88 0.64 Snug

UH 0.47 ± 2.34 2.67 UH 1.80 ± 0.35 0.39 UH 2.16 ± 2.65 2.87

ALL -2.26 ± 1.64 1.92 ALL -2.16 ± 0.45 0.47 ALL 2.16 ± 2.65 2.87

s/n WHOTS

Pre Deployment Pre DeploymentBefore Cal After Cal

@ Spin Data Errors @ Spin Data Errors @

13917

Mean

Mean

Mean

in water

Spin Data Errors

Post Deployment

n/a

damaged

S/N 2530

s/n 2530 – 1200 kHz• Only one deployment

s/n 2530

RDI Estimate RDI Estimate RDI EstimateMean Min-Mean Max-Mean Overall Error(±) Mean Min-Mean Max-Mean Overall Error(±) Mean Min-Mean Max-Mean Overall Error(±)

2530 5 Snug -3.32 -5.88 3.12 5.16 Snug -0.20 -0.80 0.70 0.84 Snug -10.24 -1.66 1.24 1.91

Snug -3.32 ± 4.50 5.16 Snug -0.20 ± 0.75 0.84 Snug -10.24 ± 1.45 1.91Mean

s/n WHOTS

Pre Deployment Pre DeploymentBefore Cal After Cal

@ Spin Data Errors @ Spin Data Errors @ Spin Data Errors

Post Deployment

Observations• Calibrations done at Snug have mostly larger mean errors

(offsets) but similar error amplitudes to UH calibrations• Pre-Deployment, After Calibration consistently smallest

error amplitude• Spin error amplitudes & RDI Overall Error very similar, as

expected• Not large enough sample size at any calibration location to

conclude that offsets based on mean error should be applied at this time

• Large mean errors (offsets) could be a product of magnetic anomalies at calibration site or inconsistencies/errors in setup of N-S reference line

Recommendations• Continue doing calibrations at UH Soccer field– Find cross-references (E/W) for calibration stand location

along N-S reference line in order to keep consistency between calibrations

• Most important thing to check for– Low pre-deployment after-cal “overall error”/spin error

amplitude (<2°)• Apply no corrections/offsets based on spin-mean– Calibration purpose: reducing error around compass rows

due to battery interference signature– Large spin-mean offsets likely due to magnetic anomalies

at cal site (Snug) or inconsistencies/inaccuracies in setting up N-S line

Recommendations• Run new Matlab graphing scripts produced by Walt for each

instrument after every calibration session (spin & stats)– Path: /home/aina1/whots/ADCP_cmpscals/– Create new text files for each spin session according to templates

• template_adcpSNNUMcmpss_eval_PRE_whotsDEPNUM.txt• template_adcpSNNUMcmpss_eval_POST_whotsDEPNUM.txt

– plot_adcp_cmpscal.m – By-deployment/instrument compass spin error plots

– stats_adcp_cmpscal.m – By-instrument compass spin error stat plots over time

– Use as sanity check and to follow history for each instrument– These scripts will make for more consistent cataloguing of results for

future deployments