Global Positioning System Navigation Option OPERATION MANUAL

Clearwater Instrumentation, Inc.
304 Pleasant Street
Watertown, MA 02181
924-2708 Tel (617) 924-2724 Fax

CAUTION!

NEVER HANDLE DRIFTER BY ANTENNA. HANDLING DRIFTER BY THE
ANTENNA WILL DAMAGE ANTENNA SPRING AND MAY CAUSE IRREPARABLE
DAMAGE TO SEALS, RESULTING IN LEAKING AND EXTENSIVE INTERNAL
DAMAGE. ANTENNA DAMAGE WILL INVALIDATE ALL WARRANTIES!

TABLE OF CONTENTS CLEARSAT-1 SURFACE DRIFTER. ClearSat-1 Design. ClearSat-GPS Argos PTT (OPTION). OPERATION. Starting and Stopping Buoy Transmissions. GPS (OPTION) Sampling Interval Adjustment. DEPLOYING THE CLEARSAT-1. Unpacking the ClearSat-1. Deploying the ClearSat-1. CLEARSAT-1 ARGOS DATA FORMAT. GPS (OPTION) OPERATION. GPS Page 0 (Table 2 PAGE 0 BYTE NUMBER-DATUM.) GPS Page 1 (Table 3 GPS Data Page 1). GPS Page 2, 3, 4 (Table 4 GPS Data Page 2, 3, 4). Argos GPS Data Optional Format. PARSE GPS/Argos decoding software. WARRANTY

Figures

Tables

1. ClearSat-1 Surface Drifter.

The ClearSat-1 is an Argos Satellite-tracked surface drifter designed to accurately follow water movement in the upper meter of the ocean. Optional equipment can include GPS (Global Positioning System) instrumentation to provide highly accurate, on-demand location for tracking rapidly varying surface currents, air deployment system for rapid, convenient dispersing of the instruments, and conductivity-temperature probe for surface salinity measurement. Data are accessible throughout the world from the Argos system. In addition, Argos equipment location services can provide tracking and positioning sufficient to locate the drifter.

Argos PTT radio transmission can be received by a CLS/Argos uplink receiver on NOAA Tiros satellites when they pass within line-of-site of a buoy. CLS/Argos decodes the radio message, computes the location of the equipment, then makes the information available to the user who may select from a variety of methods including e-mail and public telephone accessible database. the computed location are evaluated statistically and classed according to an estimate of the accuracy. Location quality, or class, is affected by radio signal strength and quality, number of messages received during the satellite pass and satellite altitude (angle above the horizon). Location classes vary from 3 to 1. Location 3, the most accurate position estimate, has a precision of 150 meters (two standard deviations); class 2, 350 meters; and class 3, 1 kilometer.

NOAA Tyros satellites are in near-polar orbits at 300 to 400 miles altitude. They complete an orbit around the earth once every 90 minutes. There are usually a minimum of two Tyros satellites receiving Argos PTT signals at any time. Under ideal conditions, equipment fitted with an Argos PTT may be located six to eight times per day; more with locations may be expected as the latitudes approach polar regions.

1.a ClearSat-1 Design.

The ClearSat-1 drifter has a slightly negatively buoyant spar buoy suspended from the surface on four float attached to the ends of the upper drogue spar; it was specifically designed to accurately follow the mean current between the surface and 1 meter depth. The four vertical sails measure 1 meter from side to side enhance its water-following ability by limiting rectification of wave motion (drift relative to the mean current when a buoyant object oscillates wildly around its static buoyant point.

The four floats maintain the drifter at the surface with the antenna out of the water. In addition, its symmetric design assures that the wetter area and drag coefficient of the drifter remains essentially constant during a wave cycle. Wave force approximately integrate to zero and drift is minimized. The upper half of the floats and the active portion of the Argos PTT antenna are the only parts of the buoy that project into the air to be exposed to wind. This minimizes leeway.

The ClearSat-1 surface drifter includes many enhancements which facilitate the use of the CODE drifter¹, yet preserves its excellent water-following characteristics. An ArgFigure 1. ClearSat-1 Surface Drifter.os PTT allows the Argos system to provide location and data collection anywhere in the world and eliminated the need to maintain 24-hour observation for obtaining locations and data through a microwave link. With the option of GPS positioning equipment, highly accurate locations can be obtained at half-hour intervals. For compact storage and ease of deployment the sail spars supporting the drogue planes are spring-loaded and can be retracted and laid alongside the body of the drifter. Being able to break down the drifter into a compact forms permits the drifter to be deployed from and aircraft at speed up to 160 kts using a specially designed deployment system.

1.b ClearSat-GPS Argos PTT (OPTION). The Clearwater Instrumentation, Inc. ClearSat-GPS

Argos PTT is a satellite tracked instrument with Argos positioning is augmented, or replaced with GPS positioning to improve accuracy of locations which are reported to +/- 0.0001 degree latitude and longitude, and to allow acquisition of positions on a regular schedule. Time of a location is reported to +/- 1 second (including year, month, day). Up to 17 onboard archived positions and times may be reported over the Argos system. This allows a drifter to report half-hourly position information through Argos without loss of data during intervals when satellite orbital configuration lead to over flight gaps of six to eight hours.

2. OPERATION.

Buoy operation, Argos radio transmissions, and other optional functions, such as GPS functions are controlled by magnetic reed switches inside the hull. The magnets are provided with the buoy. In the figure to the right the magnets would be on the hull near the top end. 2.a. Starting and Stopping Buoy Transmissions. All ClearSat-1 buoys are shipped with a magnet attached on flat near the top end of the drifter hull. When it is in place the magnet prevents the buoy from operating and transmitting, which drains the batteries and can incur Argos charges if the transmissions are picked up by the satellite. After the magnet is removed from its flat on the hull, the transmitter will start transmitting in approximately 90 seconds. Replacing the magnet on flat "A" will stop transmissions in approximately 30 seconds.

Figure 1 ClearSat-1 (U.S. Coast Guard aluminum hull SLDMB version) set up and ready for deployment.

2.b. GPS (OPTION) Sampling Interval Adjustment.

A second magnet may be place on the hull to permit the user to alter the GPS location cycle. GPS Engine Initialization. If GPS has been off for a few days, or has been moved 50 miles, it should be allowed to initialize before the drifter is deployed to obtain rapid locations. Time to navigation mode under these conditions is usually three minutes. GPS will initialize if deployed, it just may take longer to obtain the first position. Follow these instructions to vary the GPS sampling rate. When the ClearSat-GPS is operating in the default mode the GPS update rate is one every 30 minutes.

1. Place magnet on reed switch position "A" and hold it there for 30 seconds before beginning Step 2. Tape magnet there for the rest of these steps. DO NOT TAKE OFF MAGNET FOR AT LEAST 2.5 MINUTES (SEE BELOW).
2. Begin this step exactly 30 seconds after placing magnet on "A". Place second magnet on reed switch position "B" for an interval corresponding to the GPS sampling rate that you desire. Two seconds correspond to one minute of GPS sampling rate. For examples, to sample once every 20 minutes, leave the magnet on "B" for 40 seconds, then remove. The longest sampling rate is once every 60 minutes (one hour). The shortest GPS sampling rate is 1 minute; however the practical limit is probably five minutes.
3. Remove magnet from "A" when 2.5 minutes, or more, have passed. Magnet "A" may be removed any time after 2.5 minutes, whenever it is necessary to start the drifter. In fact, the GPS cycle can be set up and magnet "A" left on for days, or weeks, until the drifter is operating.

3. Deploying the ClearSat-1.

The ClearSat-1 Drifter is shipped for manual deployment or deployment from and aircraft or moving vessel. Deployment systems for aircraft and ships underway are optional features and the user should refer to the special instruction accompanying those deployment systems.

3.a. Unpacking the ClearSat-1.

The ClearSat-1 is packed with its spars retracted and folded alongside the drifter hull , and with the spring-mounted antenna also folded along the hull. Notice that the antenna is folded toward the far side of the hull to allow its spring to bend in the largest possible radius. This is to prevent the spring being stretched, and if the drifter is repack, you should fold down the antenna in this way. Spars and antenna are held in place with water soluble packing tape. Remove all tape and deploy the arms before Placing the drifter in the water. NEVER HANDLE THE DRIFTER BY THE ANTENNA WHEN PLACING IN THE WATER OR REMOVING FROM THE WATER. HANDLING THE DRIFTER BY THE ANTENNA MAY CAUSE IRREPARABLE DAMAGE TO THE DRIFTER.

3.b. Deploying the ClearSat-1.

Before placing the ClearSat-1 into the water, inspect that it appears looks like the drifter in Figure 1. Please perform this final inspection:

1. Spars are securely set into their sockets.
2. Floats can move freely.
3. Antenna is extended.
4. Remove magnet from drifter hull.
5. If you have an Argos uplink receiver, check that you are receiving transmissions from the drifter.

The drifter is deployed by carefully lowering it into the water where the ship will not run over it.

1. Select a location on the vessel where the vessel will move away from the drifter.
2. Check that the vessel is at a dead stop, with only minimal leeway.
3. Holding the drifter by the spars or floats. gently lower it into the sea surface.
4. ClearSat-1 Argos Data Format.

4. ClearSat-1 Argos Data Format

Information on sea surface temperature and battery voltage are taken by the ClearSat-1 and sent via Argos transmission. These data are available to the user, along with location information from Service Argos. The message length is 32 bits. The information should be relayed to Service Argos to instruct them how to interpret sensor data.

5. GPS (OPTION) Operation.

When magnet is removed from "A" the GPS engine will begin attempting to navigate. If the magnet is removed while the instrument is inside, the engine most likely will not be able to navigate and battery power will be wasted. Time to first fix is a function of how long since the GPS engine last navigated and how far the instrument is from where it last navigate. If the almanac is too old (more than 7 days), or the displacements in time and location are too great (greater than 500 km), the Rockwell MicroTracker(tm) LP will default to its "cold start" mode which is an efficient algorithm for navigating. If the GPS engine is not able to navigate in an 20 minutes, the ClearSat controller shuts it down and a new attempt is made after 30 minutes have passed. For that period, the date and time are reported, but the position is set to the last valid position. Once the battery power drops below 8 volts, a level necessary for error-free operation of the MicroTracker(tm) LP, the ClearSat controller shuts the GPS down and reports the GPS repetition rate in byte 0, the battery voltage times 10 in byte 1 and an error flag, 15 (FH) in byte 2. All other bytes are set to 0

5.a. GPS Page 0 (Table 2 PAGE 0 BYTE NUMBER-DATUM. )

The Page 0 format is transmitted when the GPS engine is first started and is not navigating. Information from the acquisition mode is relayed so that satellite tracking and signal strength may be observed. If the GPS engine is not able to navigate within the GPS Repetition Rate interval, the ClearSat-1 controller allows the engine to continue attempting to navigate for another 20 minutes. If the GPS engine does not navigate after that period, the controller shuts down the GPS engine and does not restart for 30 minutes. The ClearSat controller switches from Page 0 after the MicroTracker(tm) LP has begun to navigate. Data is now transmitted in formats Page 1, 2, 3, and 4.

5.b. GPS Page 1 (Table 3 GPS Data Page 1).

This is the initial data page containing the most recent five location/position data. This data may be obtained by using PARSE, ver. 4.0. Once the GPS engine has started navigating, subsequent locations will occur typically in a few minutes after it is turned on. Universal date and time is reported to ± 1 second. Latitude and longitude are reported to ± 0.0001°.

5.c. GPS Page 2, 3, 4 (Table 4 GPS Data Page 2, 3, 4).

The most recent location/position is contained on these pages. Page 2 contains data from earlier positions 6, 7, 8, and 9; Page 3 contains data for earlier positions 10, 11, 12, and 13; Page 4 contains data for positions 14, 15, 16, and 17.

5.d. Argos GPS Data Optional Format.

This format allows for single pass parsing of the GPS data. Data resulting from this format will require additional treatment to provide complete information

5.e. PARSE GPS/Argos decoding software.

Refer to software documentation for use. Make a copy of the disk and store the disk in a safe place. Copy the contents of the disk onto an IBM-PC compatible computer (DOS version 5.0, or higher).

NOTES.

GPS Engine Initialization. If GPS has been off for a few days, or has been moved 50 miles, it should be allowed to initialize before the drifter is deployed. GPS will initialize if deployed, it just may take longer to obtain the first position.

Default GPS location Rate Set Up. The default setting is for GPS to update its position every 30 minutes, after being turned on.

Setting the GPS Sampling Interval (GPS (OPTION) Sampling Interval Adjustment.).

Checkout Procedure.

1. Turn on the drifter by removing the magnet. Verify that the drifter is operating by receiving an ARGOS transmission from the PTT transmitter.
2. This page (Page 0) will be displayed until GPS begins navigating and updates position. This should occur within 3 minutes if information is outdated, position has changed substantially, drifter has been off for a long time, or satellite positions are not favorable.

Satellite Signal Quality. Up to 12 satellite can be tracked by the GPS engine. "PRN" refers to the satellite number and "C/N₀ " refers to the signal to noise ratio. The range is 0-63, in units of dB Hz (>40 considered good).