1. WHOTS - ADCP Compass Calibration History
Version 4: November 9, 2016
By: Walt Deppe

2. File History Version 1 – Walt Deppe, 9/23/2014

3. Outline Background Things to look for & keep in mind
Switch from Snug to UH
Magnetic Anomaly Surveys
Things to look for & keep in mind
ADCP S/N & Deployment List
Individual Instrument Error Analysis
Observations
Recommendations

4. 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)

5. 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. “

6. Magnetic Anomaly Surveys
Snug Harbor
UH Lower Campus Soccer Field

7. 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

8. ADCP S/N & Deployment List
300 kHz
s/n 4891 (WHOTS – 1, 2, 4, 6, 8, 10,12)
s/n 7637 (WHOTS – 3, 5, 7, 9, 11,13)
600 kHz
s/n 1825 (WHOTS – 4, 6, 8, 10,12)
s/n (WHOTS – 7, 9, 11,13)
1200 kHz
s/n 2530 (WHOTS – 5)

9. 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

10. S/N 4891

11. 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)

12. s/n 4891

13. S/N 7637

14. s/n 7637 – 300 kHz
Instrument damaged during WHOTS-5. No post-deployment check.
No pre-deployment post-cal spin check errors available
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

15. s/n 7637

16. S/N 1825

17. 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)

18. s/n 1825

19. S/N 13917

20. s/n – 600 kHz
Instrument damaged during WHOTS-7. No post-deployment check.

21. s/n 13917

22. S/N 2530

23. s/n 2530 – 1200 kHz
Only one deployment

24. s/n 2530

25. 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

26. 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

27. Recommendations
Run new Matlab graphing scripts produced by Walt for each instrument after every calibration session (spin & stats)
Path: /export/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 cataloging of results for future deployments