WHOTS - ADCP Compass Calibration History Version 5: January 18, 2017 By: Walt Deppe

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

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

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, 10,12) s/n 7637 (WHOTS – 3, 5, 7, 9, 11,13) 600 kHz s/n 1825 (WHOTS – 4, 6, 8, 10,12) s/n 13917 (WHOTS – 7, 9, 11,13) 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

S/N 7637

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

s/n 7637

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

S/N 13917

s/n 13917 – 600 kHz Instrument damaged during WHOTS-7. No post-deployment check.

s/n 13917

S/N 2530

s/n 2530 – 1200 kHz Only one deployment

s/n 2530

Summary of RDI Overall Errors

Heading comparison for same session Differences between mean offsets from spin checks for 2 ADCPs during same compass assessment session (top): pre-deployment, after calibration (bottom): post-deployment *Pre-dep WHOTS-11 had ~4° mean offset, but consistent between two ADCPs, therefore, likely bad N-S line setup that time

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: /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