SouthStar Under Ice

Quick Start Guide

          For SCINI Survey Operations under Sea or Lake Ice 16OCT09

          #1: Assembly and Placement of the Baseline Stations

          How many Baseline Stations to Use
          • One station: Distance to target only. For limited navigation.

          • Two stations: Baseline ambiguity. Must specify position is to left or right of baseline. Target position dependent accuracy and jumpy due to no redundancy. For basic navigation and initial surveys only.

          • Three stations: Uniform positioning accuracy, and removal of bad fixes. Positioning precision indicator. For general surveying including point surveys, full coverage and linear transects.

          • Four stations: Best redundancy and position availability. Any three out of four stations will yield a position. Best precision. Recommended for grid surveys including photo mosaic.

          Selecting Baseline Station Locations:
          • Station separation at least 1.5x water depth, and…

          • Survey area should be encompassed by the by the baseline stations, and…

          • Stations should be placed approx. evenly (equilateral triangle, square).

          • Reliable observed distance in low to moderate noise environments (100-110dB detection threshold) is about 300m. Maximum observed is around 850m. Do not place stations further apart than good geometry demands.

          • In shallow water, do not exceed station spacing of 50x water depth.

          • Rule (3&4 baseline stations): When standing at #1 and looking at #2, #3 must be to your right and #4 to your left.

          • For 2 baseline stations: Accuracy is best in areas where the two baseline stations appear to be at 45 to 135 degrees from each other.

          Connecting baseline stations:
          • Check FRF-2 status LED through translucent top cover. Short green blinks mean GPS detected & OK. Short red blink means no GPS signal. Rapid red blink is low battery.

          • Apply thin layer of silicone grease to underwater connector on FRF-2 and TLT- 32. TLT-32 is powered by FRF-2. Connect smoothly for reliable power-up RESET. If connector is freezing, warm before mating.

          • Check TLT-32 status LED. It must blink. If static ON or OFF, repeat power-up byun-mating, waiting 2-5 min and mating again.

             

          #2: Setting up the Control & Tracking Station

          Control & Tracking Station Wiring
          1. Connect whip (rubber duck) or base-station vertical antenna to FRF-2. Place FRF-2, with antenna pointing up, at a high position such as a top shelf or an antenna pole.

          2. Connect FRF-2 via USB cable to PC. FRF-2 will be powered by PC USB power.

          Software Function & Connections

          Navbridge software controls the acoustic array, performs an acoustic baseline self-survey, obtains target range data and forwards it via a COM port to the DiveBase tracking software. Select array COM port, DiveBase (RangeNav) COM port. Depth Input COM port remains closed because NavBridge receives depth via a ‘data socket’ from PC Pilot.

          DiveBase accepts the target range and depth data from Navbridge. Baseline survey results must be hand-transferred from Navbridge prior to start of tracking. DiveBase computes, filters and displays target positions.

          Typical COM port configuration.


          NAVBRIDGE FUNCTION EXPLANATION 
          Depth

          Depth display. Depth is received automatically from PC-PILOT and shown in this field. You can also hand-enter depth if automatic depth should fail.

          Noise Test

          Click to measure underwater noise levels and set the signal detection thresholds for the baseline stations (see section #3).

          Display

          Click to display/hide the signal strength display.

          Comms

          Click to set COM ports for data input from the array and output to DiveBase. Use 115200 baud for the array port, and 4800 baud for the RangeNav (DiveBase) port. Keep the depth port closed for SCINI, as depth is received via a data socket from PC PILOT.

          Baseline Survey

          Click to self-survey the baseline station network prior to tracking.

          Target Distance from B1 display, Offset Adjust Button, Offset display

          To synchronize the pinger to the array, place at a known distance from baseline station B1, enter that distance and click the Offset Adjust button. The ping time in microseconds from the start of a GPS second is now displayed.

          Drift

          Enter the pinger clock drift relative to the GPS standard based on an observation; to minimize position drift.

          Status Lights

          From left to right: B1, B2, B3, B4.

          Red: Cannot talk to TLT-32 acoustic baseline station. Check link via antenna, FRF-2 pair and cabling. Make sure TLT-32 is blinking.

          NOTE: All station symbols remaining red can indicate a failed FRF-2 USB connection to the PC. Re-launch Navbridge and re-connect the FRF-2 via USB.

          Yellow: Communication with acoustic baseline station OK, but station does not detect acoustic signals. Normal status when target pinger is not yet in the water, or is shielded or out of range.

          Green: Target pinger signal detected. Normal status when target pinger is in the water. If target pinger is out of the water, green means noise triggers the receiver. If this happens frequently (once every five seconds or faster on a indicator), increase the detection threshold. 

          Soundspeed

          Enter the sound speed here. Accurate number required for accurate measurements. Default is 1440 meters/sec, for - 2 deg C water with 35 ppm salinity (typical Antarctica condition).

          Distance Fields

          Shows the target distance from the baseline stations. These numbers will only be accurate after pinger synchronization (section #5)

          #3: Conducting a Noise Test and Checking for Echoes


          Prior to baseline surveying or tracking, conduct a noise test and set the signal detection threshold for the baseline stations. 
           

          Noise Test Procedure
          1. Click Noise Test button

          2. Observe noise bars for ten seconds or more

          3. Right-click on detection threshold slider to adjust the thresholds for all stations to just above the prevalent noise levels. If infrequent (every five seconds or less) noise spikes occur, they can be ignored. If one baseline station sees more noise, its threshold can be individually adjusted. As the noise test tends to be more sensitive than the tracking mode, you can also adjust the detection threshold by up to about 6dB below the noise level. See the advise below for details.

          4. Click on the Noise Test button to end the test and accept the new detection thresholds.

          5. Software bug: Due to an apparent software bug in Navbridge V1.1, you must now start and end Noisetest once more (click the noise test button twice, with a 1 sec or more pause in between clicks). Otherwise, the new detection thresholds may not be accepted by the array.

          Advice on setting detection thresholds

          Noise rejection:Higher detection thresholds are required for noisier environments, but they also reduce the effective tracking range. If you experience too much signal loss, try reducing the detection thresholds even below the level indicated by the noise test. Next, watch the ranging displays and status lights. If no pinger is in the water, you are OK as long as the status lights stay normally yellow and the distance indicators remain at 0.00m. If a target pinger is active, you are OK as long as the indicated target distances for the most art steadily show the correct target distance. If the indicators jump a lot, then you are probably picking up noise and need to increase the detection threshold.

          Echo rejection: Target pinger signals may bounce-off reflective surfaces such as the sea-floor, sea-surface, rocks or ice bergs. Echoes may be the cause if you frequently see an obviously wrong but consistent distance indicator. You can increase the detection threshold which may reject an echo if it is weak. Using four baseline stations will also help in high-echo environments, as the software will reject an outlier range but still obtain positions.

          Effective Tracking Range

          The following are observation values for the Southstar system performance in Antarctica, 2009:

          At Arrival Heights, in about 25m to 65m of water, reliable operation up to about 330m from baseline stations with 120 dB detection threshold, and no signal detects with 130 dB detection thresholds.

          Near Tent Island in 300m of water or more. Pinger lowered to 300m, baseline station at 9m depth.

          • No signal with 110 dB at 1000m

          • Good signal with 105 dB at 850m

          • Reliable detection at 475m with 110dB detection threshold and pinger at 30m and 60m depth.

          Bay of Sails Noise and Echo Evaluation at iceberg BS1 in 32m of water

          • Noise around 95dB – 100dB

          • Reliable signal detection at 100dB to 130 dB for a pinger lowered to the sea floor.

          • Apparent echoes indicated by jump to approx. 118m for about 20% of the ranges. Seemed to get marginally better at higher detection thresholds.

          #4: Conducting a Baseline Survey

          Do a baseline survey to establish the relative location of the baseline stations, and then convert them to UTM (if desired).

          Procedure

          1. Click the Baseline Survey button in Navbridge to call up the baseline survey window.

          2. For UTM operation, enter the Easting and Northing coordinates of B1 and B2 as established by a GPS receiver or other means (matching to a point on Google Earth, etc.), and check Operate in UTM.

          3. Click the Start the Baseline Survey button. The baseline survey can take up to 40 seconds, progress indicated by bar.

          4. Read the results. Baseline station distances are indicated first. The Precision shows how much the measurement from station A to B varied from B to A. It should be a few centimeters or less. If precision is poor then the survey results are probably poor. If a distance measurement is not available, then a path blockage or excess baseline station range may be the problem.

          5. Re-try a poor survey to see if it improves. If no improvement is available, move the baseline station closer, deeper or away from a suspected blockage.

          6. Now manually transfer baseline survey results into DiveBase. In DiveBase, select Action→Register and Calibrate Baseline Stations.

            • Enter the Easting coordinates of the baseline stations into the ‘X’ fields in Divebase.

            • Enter the Northing coordinates of the baseline stations into the ‘Y’ fields in DiveBase

            • Enter the actual baseline station depths into the Depth field in DiveBase. (The Depth field in Navbridge is not currently used and can be left open).

            • Click the OK button in DiveBase

            • In DiveBase, select File→Save Current Record and select a name representative of the dive site such as BayOfSailsIceberg1.shr

           #5: Mounting, Activating and Synchronizing the Target Pingerx

          1. Mount the target pinger on the vehicle such as to minimize shadowing by components of the vehicle. An unobstructed line-of-sight to the baseline stations must be maintained. Ideally, the pinger should be mounted vertical, with transducer end up.

          2. Insert 9V battery. Alkaline battery will run approx. 5 hours; Ultralife lithium battery approx. 12 hours. Smoth insertion promotes a good power-up reset. If contact bounces occur, processor may crash indicate by LED constantly ON or OFF. In that case, wait 2-5 minutes with battery removed and re-try.

          3. Switch pinger ON prior to deployment by swiping the magnetic switch with a magnet.

          Pinger Synchronization Procedure

          The pinger must be synchronized to the baseline stations (GPS time signal) in order to obtain valid ranges.

          1. Place pinger suberged a known distance from baseline station #1, such as 0.1m. Ideally, the pinger and the baseline station will already be at ambient water temperature.

          2. In Navbridge, enter that distance into Target Dist. from B1 (m)

          3. Make sure B1 sees the pinger, and distance readings are consistent (although wrong, typically several hundred meters).

          4. Click the Offset Adjust button. Navbridge will now compute and display the ping offset. The distance reading to B1 should now be within a few centimeters of the value entered in step two. Pinger distance from other baseline stations (if available) will now also be correct.

          5. Compensate for clock drift by observing how much the indicated B1 distance changes over an observation period such as two or five minutes. Convert that number to meters per sec and enter in the Drift (m/s) field.

          6. Observe B1 to verify that the distance to the pinger is correctly indicated, and the drift over time is minimal.

          Drift Observation Numbers for SCINI Southstar System

          Distance error at 2.5 hrs after start of test:

          • With no drift compensation: 23.18m

          • With 5-minute initial observation: 0.83m

          • With 30-minute observation: 0.3m

          • With 1 hr observation: 0.16m

          #6: Target Tracking

          Tracking is done with the DiveBase Seafloor software. Operate the software as described in the DiveBase manual, except that baseline surveys are done in Navbridge rather than directly in DiveBase.

          Here is some general guidance for tracking and DiveBase use:

          • Use Item→Filter settings to set position filter or processing parameters as appropriate:

            • Set an averaging period of 3-10 seconds to smooth the trace. More averaging → smoother race → more position lag.

            • Set the visibility rating to influence the width of the position trace. Set to camera or sensory range to visualize search coverage.

            • Set the Maximum Error in 1m to 3m range to remove poor quality position fixes.

            • Set the Maximum Holiday higher to show more severe position jumps in the ROV track, or lower to leave a gap when successive positions are too far apart.

          • Set Options→Acoustic Navigation Com port to point to the data source from NavBridge

          • Define Options→Serial Output Com Port, Options→Serial Output Baudrate to pipe position data to another computer or application (such as Hyperterm) to export position data in real-time or replay operations. Can be captured with Hyperterm to generate a text file for use in ARCGIS. Recommended Options→Output Format is DSS (XYD)

          • Use the Chart Registration utility in the Seafloor folder to register an image for use as a chart background in DiveBase.

          • Watch the Current Error at the bottom of the tracking screen to QC the quality of positioning. A smaller error means the system is more precise.

          • Watch the Last Fix Time up-counter to see how long it has been since the last position fix. There is a position fix opportunity once a second.

          Diagnosing when DiveBase Does Not Track (no positions)
          • View the baseline status lights in NavBridge and DiveBase. At least three green lights (available range measurements) are required to obtain a position fix, except when operating with two baseline stations and clicking Options→Allow 2 Range Position Fixes

          • View the Position Signal light in the lower left corner of the DiveBase screen. If red but enough ranges have been received, then the range data could not be converted into a position fix of sufficient quality:

            • If the Current Error indicator is red, then the resulting position does have an error exceeding the value set in Items→Filter Settings, Maximum Error. This can be the result of poor quality ranging data due to acoustic conditions (such as noise causing many outliers – raise the detection threshold). It will also happen if a baseline station position is significantly incorrect, i.e by a few meters or more.

            • Well working navigation is indicated by current errors of <0.5m. 0.5m-1m is reasonable, above 1m is poor and above 3m should almost always be ignored.

            • It is also possible that a range is outside the boundaries specified by Minimum Range and Maximum Range. Verify these settings.

          #7: Procedure for Operating with Charts and Data Post-Processing

          To establish the original dive site information, including chart and baseline survey data

          1. Operate Southstar in UTM coordinates. Following a baseline survey in Navbridge, transfer the UTM coordinates of the baseline stations into DiveBase (see section #4).

          2. Use the Chart Registration utility to register your original map or chart image for the site. Chart Registration accepts .BMP files.

          3. Add the registered chart to DiveBase by selecting File→Load Map File.

          4. Save your site plan, including the baseline station locations and the background chart: File→Save Current Record. Give the file the name of your dive site. This generates a .SHR index text file that contains references to the map image and its registration information, the baseline survey data and other items.

          Just Prior to a dive

          The last map and baseline station information appears when you launch DiveBase. DiveBase gets this information from the mission.shr file, which it automatically generates. You can also choose any previous .shr file for use on the next dive by selecting File→Load Record. This process loads chart, baseline survey, waypoint and annotation information. It does not re-load the actual track data that might already be associated with the .shr file of a particular dive.

          You can now start tracking by selecting Action→Start Real-Time Tracking (see section #6).

          ARCGIS Processing of the Data Following a Dive

          Following a dive, you may want to export the track file to ARCGIS in order to establish a coverage map. You can also get bathymetry by associating depth with colors, for periods where SCINI was cruising the sea floor. All this data can now be combined into an updated background chart, containing coverage and bathymetry, for use on the next dive. Follow this procedure.

          • Outlier removal and filtering: Load and replay the record of the last dive by selecting Action→Replay Survey. Take a first look at it, by fast-forwarding through the record. It will show up once fast-forward is completed, or when you switch to play mode. Apply any smoothing and filtering as desired by selecting Item→Filter Settings and then re-playing the record again. Note that the original tracking data, which is in a .rec file will never be modified by filtering. So, you can adjust filters as you like and see the results without compromising the original track data. In fact, the .rec file is never modified by DiveBase following its original recording.

          • Track data export to a text file:

            • Establish a link to HyperTerm via a virtual COM port pair. In DiveBase, select Options→Serial Output COM Port to select one port of the pair. Select the DSS (XYD) data output format Options→Output Format→DSS (XYD). If using real instead of virtual COM ports (such as by piping the data to another computer, select a common baud rate for DiveBase and Hyperterm, such as 115200 baud. Options→Serial Output Baud Rate→115200. (Virtual ports by default don’t use baud rate, so this step is not needed.)

            • In HyperTerm, select the other port of the pair. Select data logging.

            • Rewind and then start replaying the record in DiveBase. You will see the track data in HyperTerm, expressed as Easting (E or X), Northing (N or Y) and Depth, with all units in meters. Replay to the end to obtain all data, or fast forward to any point and then replay if you just want a section.

            • End logging in HyperTerm to save the text record of the track.

          • Import the track record into ARCGIS, and process as appropriate to establish coverage, bathymetry and other information. Note that you can also import the DiveBase annotation and waypoint files, which can be found in the shipfiles/annotations and shipfiles/waypoints folders.

          Creating an updated map for the next dive
          1. Create a map in ARCGIS as desired. Save it as a .BMP file.

          2. Register the map for DiveBase, using the Chart Registration utility.

          3. Load the map in DiveBase using File→Load Map File

          4. Save the updates dive information, including the baseline positions previously established by selecting File→Save Current Record

           Appendix A: FRF-2 Repeater Blink Patterns

          During Baseline Station Operation
          BLINK PATTERN MEANING COMMENT
          blink
          PAUSE
          blink
          PAUSE...

          FRF-2 is active, but is not yet receiving GPS time signals.

          Must wait until it starts blinking in green before tracking and baseline survey operations can start.

          blink
          PAUSE
          blink
          PAUSE...

          FRF-2 is active and is receiving GPS time signals.

          Ready for tracking!

          blink
          blink

          blink
          blink...

          FRF-2 Battery is low

          Rapid red blinking means it’s time to charge the battery! When the low battery light occurs, you may have approx. two to five hours before the battery is dead.

          OFF

          The battery is dead, or FRF-2 is switched OFF.

          The FRF-2 is switched OFF by inserting a shorting plug. If its still inserted, remove it. If the LED remains OFF, charge the station.

          During Battery Charging
          BLINK PATTERN MEANING COMMENT
          blink
          PAUSE
          blink
          PAUSE...*

          Battery charging is in progress

          Will persist for 12-hours following start of charging. Feel the metal bracket on the FRF-2 to determine if a battery is fully charged earlier. If so, it will be slightly but noticeably warm.

          ON

          Battery charging is completed

          Lights 12 hours after start of charging, and stays ON until you connect the FRF-2 from the charger.

          During FRF-2 operation as the control station RF modem, connected to the navigation PC (notebook computer):

          BLINK PATTERNMEANINGCOMMENT
          blink
          PAUSE
          blink
          PAUSE...
          Battery charging is in progress

          Will persist for 12-hours following start of charging. Feel the metal bracket on the FRF-2 to determine if a battery is fully charged earlier. If so, it will be slightly but noticeably warm.