Oceanetic Model 406 Ice tracking Buoy Manual

Transcription

1 Oceanetic Model 406 Ice tracking Buoy Manual (1989) Limited Oceanographic Consulting and Technical Support 1695 Mills Road, Hangar 38, V8L 3S1 Tel. (250) , Fax -0533, 03/11/2004

2 Oceanetic Model 406 Ice tracking Buoy Manual...1 Introduction...3 Theory of operation...3 Deployment...5 Ideas for deployment...7 * Important Note *...7 Appendix...9 Argos Message Format...9 Table 1- Data format of Argos message packed into 31 bytes Table 2- Converting Argos message data...11 Message Priority Levels...12 Communications Interface...13 Downloaded Data Format...14 Table 3- Converting downloaded data...14 Mechanical Specifications...16 Electrical specifications...16

3 Introduction This model 406 Ice Tracking buoy is a low cost custom designed platform designed for the International Arctic Research Center at the University of Alaska Fairbanks. It has been designed to provide Global Positioning System (GPS) data both through the Argos satellite network and to internally record data in nonvolatile memory. Originally, the proposal for this buoy included very low cost, small size and low weight for storage aboard an MBB 105 helicopter. Theory of operation The model 406 Ice tracking buoy was designed to provide 10 minute sampling of GPS data to provide high resolution ice drifting information. The data is compressed and sent through the Argos satellite system and simultaneously stored into non-volatile memory. In order to compress the data to fit the 31 Byte Argos data message, the positions have been shortened. The first position is the full lat/long with UTC time from the GPS GGA NMEA string. The subsequent 5 positions contained in the message are relative positions to the first (absolute) position. The relative positions are shortened to the difference in the minutes from the latitude and longitude of the absolute position. The relative positions are taken to 3 decimal places, and can be a maximum of +/ minutes. Details for calculating the relative position can be found in the appendix. On start-up, the controller will turn on the GPS and try to acquire a position. Typically, under a cold boot condition, new position acquisition will take 2-5 minutes. The Argos PTT will transmit every 180s after start-up. The controller will pass the PTT a message for transmitting that will include the GPS absolute and relative data. The GPS sensor is set up to produce two standard NMEA formatted strings. The GPGGA and PGRMF strings are sent at 4800 baud, and used to determine the GPS position, time, date and it's quality. The Garmin receiver sends positions in degrees plus decimal minutes format and the controller stores and sends position data in the same format. Although the Garmin receiver gives minutes to four decimal places, the last decimal place is truncated and is not stored or sent. The fourth decimal place is equivalent to 20 cm accuracy which is only possible using differential GPS and post processing. GPS positions are validated and filtered according to how many satellites the GPS receiver is picking up, and it's Horizontal Dilution of Precision (HDOP). Upon acquiring a valid position, the controller then checks to see that at least three satellites are in view, then verifies that the HDOP variable is less than 7. Once a valid GPS position has been received the position is written into an Argos message. The Argos data message (see appendix for details) includes an

4 absolute GPS position with a time and date stamp. The following portions of the message contain the relative position information and a checksum. Every 10 minutes the controller adds relative position information to the absolute position in the message. Every hour from start-up a new message is created while old ones continue to be sent. Every three hours the oldest message is restarted with a fresh absolute position. The data is stored simultaneously in non-volatile memory for later recovery. If the buoy is recovered intact, the data can be downloaded using a terminal program (i.e. Terra Term, HyperTerminal etc.). Details of this recovery are in the appendix. Because the buoy is collecting GPS data, it must be deployed in a location where the sky is not obscured by surrounding topography. This means that the buoy should be placed on a level patch of ice away from high-pressure ridges if possible.

5 Deployment The model 406 buoy has been designed to require minimum set-up in the field. All sampling parameters have been set-up by the manufacturer. It should require only connecting of power and a brief confirmation of operation, then it is ready to deploy. 1. The buoy has been built using a standard polyethylene 20 gallon container for the hull. The buoy must be opened to connect the power to be turned on. Remove the nylon strap from the lid and turn the lid counter clockwise to open. 2. Undo the two ¼" wing nuts that hold the aluminium ground plane in the buoy. Ground Plane Argos Antenna Wingnuts GPS Receiver

6 3. Gently lift one side of the ground plane to lift the plane off the ¼ studs. Care must be taken with this as the Argos and GPS antennas are both hardwired to the controller and the short cables and their terminations can easily be damaged by excessive force. Ground Plane Argos PTT Controller Box Battery Harness 4. Check all other connectors on the PTT and controller box. DB9 and DB15 serial connectors should have the locking screws checked and tightened if necessary. The BNC connector to the Argos antenna must be secure before power up. 5. Find the power bridle and attach first to the 5 20 Ah battery connectors coming through the blue foam. 6. Place the Oceanetic passive Argos beeper within 3 metres of the Argos antenna. It will beep loudly when the buoy transmits. 7. Turn on the Telonics TSUR-400 uplink receiver and have handy nearby. It should be able to receive the buoy from over 20 m, but obstructions will limit its range. In particular steel structures such as ship bulkheads will interfere with reception. 8. Plug in the last connector on the bridle to the connector on the controller box. The buoy should transmit in 180 s. Check a watch for the time and listen for the beep from the OML beeper and the tone from the Telonics TSUR-400.

7 The Telonics set should display the time of transmission, PTT ID and any data sent. Refer to the appendix and the TSUR manual for details. The GPS will require 2-5 minutes to acquire a good position so it will not appear in the data until that time. 9. Press ground plane back into position, do up the wing nuts and replace the lid. The buoy should now be placed on deck where it can acquire a GPS signal and start collecting data. The TSUR-400 can be used to view received data. See TSUR-400 manual for set-up information. 10. Once the buoy has been powered up and routine operation has been confirmed, it is ready for deployment. It is recommended that you start up the buoy 1-2 days before deployment to check operation. There is sufficient battery to cover a generous test period and a 2-month deployment with a good safety margin. 11. On recovery, the battery connectors in the buoys should be disconnected immediately to prevent memory overwrites and further Argos transmissions. Refer to the Communications Interface section for data download instructions. Ideas for deployment 1. Line of sight Both Argos and GPS rely on satellites for communication by radio. It is important that the buoy have an unobstructed view of the sky for operation. Avoid placing next to pressure ridges or operating inside labs or hangars on the ship. 2. Ice ablation A typical problem of placing instrumentation on ice or snow covered surfaces is that the instrument may absorb more solar radiation than the surrounding white surface. The result of this is that it may cause increased snow or ice melt under the buoy. Since the buoy is yellow, this should be less of a problem than with darker colours. It is a good idea to place a ¼ sheet, 2 x 2 piece of white painted plywood under the buoy at the deployment site. This will also reduce the effect of wind scouring if the buoy is placed on a layer of snow. * Important Note * The 6 buoys to be deployed from the Polarstern in November 2004 have a programmed feature that requires another step in set-up. The controller has been programmed to not use up battery power if GPS reception is not found within 5 minutes. The controller will go into a sleep mode and try again in 10 minutes. The GPS however needs to have a position received within 2 weeks to act as a seed position for calculating its position. If it does not have a recent position, it will go through a set-up period that may take more than 5 minutes. It is necessary

8 therefore to turn the buoys on and acquire a GPS position within 2 weeks of 25 October (before 8 November) to provide the needed recent seed position. Alternatively, the GPS must be started independently and a new position acquired. The DB9 connector on the GPS is not a standard serial connector and has power on pins that may damage a PC if connected. It requires the special interface connector made of a DB9F and DB9M with the power leads brought out. The interface can either be used with the spare 20 Ah alkaline buoy battery or other 12 V (6-40 VDC) source. The interface requires a standard serial cable to the PC.

9 Appendix Argos Message Format The model 406 Ice tracking buoy was designed to provide 10 minute sampling of GPS data to facilitate high resolution ice tracking. The data is in hexadecimal format, compressed and sent to the Argos satellite system. In order to compress the data to fit the 31 Byte Argos data message, the positions have been packed together. The first position is the full lat/long with UTC time from the GPS GGA NMEA string. The subsequent 5 positions contained in the message are relative positions to the first (absolute) position. The 5 relative positions have been shortened to the difference in the minutes of the latitude and longitude of the absolute position. This relative position is taken to 3 decimal places. See Table 1 for a description on how each byte is packed into the message. See Table 2 for details on how to extract the Argos data to usable data. Using the Telonics Receiver The Telonics TSUR-400 uplink receiver is used to receive Argos PTT transmissions in a local area. When the uplink receiver is in split bit mode it will display the buoy data with each field separated as shown in this table. When viewing on the screen, note must be made that the display can scroll down but not up again. If a lot of data is desired for converting, it is best to set up a log on the uplink receiver and then download to a computer. The Telonics receiver has already been set up in split bit mode for the 406 buoy. When a message is received, you will see the buoy PTT id number appear on the screen. When using the scroll down button, two columns of decimal numbers will appear. The leftmost column is the field number, and the one to the right is the data in that field. The first field is the message identification number, the second field is battery Voltage (unused at this time), the third field is UTC day, etc. Refer to table 2 for more details.

10 Packed Argos Message Description msg id- 2 Field Description- # of bits voltage- 7 day- 5 mth- 4 year- 6 hours- 5 minutes- 6 Byte Contents m m v v v v v v v d d d d d m m m m y y y y y y h h h h h m m m Byte Number Field Description- # of bits seconds- 6 lat degrees- 7 minutes- 16 Byte Contents m m m s s s s s s d d d d d d d m m m m m m m m m m m m m m m m Byte Number Field Description- # of bits long degrees- 8 minutes- 16 relative minutes lat 1-14 Byte Contents s d d d d d d d d m m m m m m m m m m m m m m m m s s m m m m m Byte Number Field Description- # of bits relative minutes long 1-14 relative minutes lat 2-14 Byte Contents m m m m m m m m m s m m m m m m m m m m m m m m s m m m m m m m Byte Number Field Description- # of bits relative minutes long 2-14 relative minutes lat 3-14 Byte Contents m m m m m m m s m m m m m m m m m m m m m m s m m m m m m m m m Byte Number Field Description- # of bits relative minutes long 3-14 relative minutes lat 4-14 Byte Contents m m m m m s m m m m m m m m m m m m m m s m m m m m m m m m m m Byte Number Field Description- # of bits relative minutes long 4-14 relative minutes lat 5-14 Byte Contents m m m s m m m m m m m m m m m m m m s m m m m m m m m m m m m m Byte Number Field Description- # of bits relative minutes long 5-14 chksum- 8 Byte Contents m s m m m m m m m m m m m m m m c c c c c c c c reserved by PTT Byte Number Table 1- Data format of Argos message packed into 31 bytes.

11 Argos data will come separated in bytes either in decimal or hexadecimal. A decimal number will range from 000 to 255 and a hexadecimal number will range from 00 to FF. Both should be padded with leading zeroes. Starting at the most significant bit of the Argos data (in the first byte), GPS data is decoded into a number of fields as follows: Table 2- Converting Argos message data Field Number Field description Field Range Field Conversion Number of bits 1 2 Message range 0 to 2 (decimal) Convert to decimal identification 2 7 Voltage Unused in this version Convert to decimal of firmware 3 5 UTC day 0 to 31 (decimal) Convert to decimal 4 4 UTC month 0 to 12 (decimal) Convert to decimal 5 6 UTC year 0 to 63 (decimal) Convert to decimal 6 5 UTC hours 0 to 23 (decimal) Convert to decimal 7 6 UTC minutes 0 to 59 (decimal) Convert to decimal 8 6 UTC seconds 0 to 59 (decimal) Convert to decimal 9 7 Absolute degrees latitude Absolute minutes latitude 11 1 Absolute latitude sign 12 8 Absolute degrees longitude Absolute minutes longitude 14 1 Absolute longitude sign 15 1 relative latitude minutes (1) sign relative latitude minutes (1) 17 1 relative longitude minutes (1) sign relative longitude minutes (1) 19 1 relative latitude minutes (2) sign relative latitude minutes (2) 21 1 relative longitude minutes (2) sign 0 to 89 (decimal) Convert to decimal 0 to 59,999 (decimal) Convert to floating point (3 0 to 1 1 = North 0 = South 0 to 179 (decimal) Convert to decimal 0 to 59,999 (decimal) Convert to floating point (3 0 to 1 1 = East 0 = West

12 Field Number Field description Field Range Field Conversion Number of bits relative longitude minutes (2) 23 1 relative latitude minutes (3) sign relative latitude minutes (3) 25 1 relative longitude minutes (3) sign relative longitude minutes (3) 27 1 relative latitude minutes (4) sign relative latitude minutes (4) 29 1 relative longitude minutes (4) sign relative longitude minutes (4) 31 1 relative latitude minutes (5) sign relative latitude minutes (5) 33 1 relative longitude minutes (5) sign relative longitude minutes (5) 35 8 message checksum 0 to 1 Convert to decimal. This is the 8 bit arithmetic sum of all 31 bytes in the Argos message Message Priority Levels It is desirable in an Argos Application to have has as much data overlap as possible to ensure that the data is received by satellite. The following message sending protocol has been developed in an attempt to get a high level of confidence in receiving all data, given that the longest interval between satellite passes may be as much as 3 hours, with an average of 1.5 hours.

13 Communications Interface The buoy controller has a limited capability to communicate with a dumb terminal or a terminal emulator running on a Personal Computer (PC). This interface enables the user to download stored data (to be logged to a file for example), dump memory contents at various addresses, or begin the data acquisition cycle. PC/terminal interface requirements are as follows: PC or terminal with an RS-232 compatible interface 19,200 baud 8 data bits no parity 1 stop bit Hardware/Software handshaking disabled RS-232 extension cable (straight-through cable). Should be no more than regular length (a few feet or so). PC Connetor (RS-232) GPS Connector (not RS-232) PTT Connector To communicate with the controller: 1. Set-up your PC with a terminal emulator such as Hyperterminal with the communication settings listed above. Set up the program to log incoming data to a file. 2. Connect the RS-232 cable to the PC, but do not connect it to the controller yet. Make sure the battery connector is detached from the controller box. Leave it disconnected for at least seconds to allow the circuit time to discharge. 3. Refer to the above picture to help locate the PC connector on the controller. Connect the RS-232 cable to it.

14 To download data: 1. With the Terminal emulator program running, plug the battery connector into the controller box. Hit any key within 5 seconds of powering up the controller. The controller will go into communication mode when it detects a keystroke within the first 5 seconds of power-up. After that, it will enter its acquisition mode. 2. A prompt will pop up on the terminal display: Command: go dp dl > If the terminal emulator is logging data to a file, you are ready to download the memory contents. Type in the letters dl (lower case) to begin. The controller will send the contents of the first memory chip. When the first chip is done it will prompt to download the second then the third memory chip. At these prompts, you will have the opportunity to log to a new file. To resume a download hit any key. Note: The dl utility in the controller is provided as a simple way to obtain data from the internal memory. No method of error checking is implemented with it, so we do not guarantee the accuracy of the data. The user should look over the following section and scan the data for anomalies that may appear. Downloaded Data Format Data is downloaded from controller memory in a Comma Separated Value format. As hexadecimal values are pulled from memory they are formatted and printed to the terminal as decimal numbers. Each row represents a time/date stamped GPS position. The first row of characters are abbreviated field titles only. Here is an example of the first couple of lines of a CSV output: Command: go dp dl > Hit Backspace to pause download, hit Enter to restart Rec#,Date,Time,LatD,LatM,LatM,LatS,LonD,LonM,LonM,LonS,SIV,HDOP 00000,012,010,004,000,015,004,075,000,000,000,120,005,255,001,003,001 The last row of characters is the first data set from memory. The leftmost value is the five-digit record number. It ranges from 0 to 4096 (decimal), and is padded with leading zeroes. The following 16 values are the decimal representation of GPS data, range in value from 0 to 255 and are also padded with leading zeroes. In the above example the values 00000,012,010,004 represent record number 0 and a three number date code (dd/mm/yy) of 12-October-04. The table below describes the 16 data values: Table 3- Converting downloaded data Field Field description Number 1 record number none Field Conversion

15 2 UTC day none 3 UTC month none 4 UTC year none 5 UTC hours none 6 UTC minutes none 7 UTC seconds none 8 Absolute degrees latitude none 9 Absolute minutes latitude (upper byte) convert to 16 bit unsigned integer, multiply by Absolute minutes latitude (lower byte) add to field 9, then divide this result by to get decimal minutes 11 Absolute latitude sign 1 = North 0 = South 12 Absolute degrees longitude none 13 Absolute minutes longitude (upper byte) convert to 16 bit unsigned integer, multiply by Absolute minutes longitude (lower byte) Add to field 13, then divide this result by to get decimal minutes 15 Absolute longitude sign 1 = North 0 = South 16 Satellites in view none 17 HDOP none

16 Mechanical Specifications Physical dimensions Maximum diameter: cm (23 ) Height: cm (19 ) Weight: approx 16 kg (35 lbs) Electrical specifications Battery capacity Approx. 100 Ah (at 0C) 12V alkaline battery Argos PTT Seimac Wildcat 1.1 W output 180 s transmission repetition rate GPS Sensor Garmin 16 (12-channel receiver) Sampling rate GPS positions are taken every 10 minutes and stored and transmitted via Argos in messages of 6. The latest 3 complete messages are sent in rotation to ensure reception during a pass of the satellite. Endurance EEPROM memory is capable of holding 85 days sampling at the above rate. Battery estimated to be sufficient for up to 85 days (at 0C).