WhaleNet
Mathematics in Science and Research

Picture of a humpback whale breaching the surfaceSatellite Data Analysis
Analyze your own Satellite Data


Satellite Tag Data Analysis

How to interpret the satellite tagging data and use it to analyze the animal's behavior and position

Study Guide Questions and Skills Activities are at the bottom of this page.


Example Data Reading:

21215 Date : 20.02.97 05:55:37 LC : 0 IQ : 45

Lat1 : 51.254N Lon1 : 50.136W
Nb mes : 004 Nb mes>-120dB : 002 Best level : -116 dB
Pass duration : 282s NOPC : 3
Calcul freq : 401 649279.4 Hz Altitude : 0 m
146, 144, 93, 188
09, 172, 15, 18
05, 56, 57, 121

Key to the data header - the first two lines of the reading:

21215 =satellite tag identification number
Date: 20.02.97 = 20 Feb. 1997
05:55:37 = Time in Greenwich Mean Time, GMT (hour:minute:second)
LC & IQ reflect transmission quality

LC just stands for Location Class. Location Classes of 0 and up are the best (derived from 4 or more messages)- a Class 0 is good to within between 1,000 and 5,000 meters. Classes 1,2,3- get consistently more accurate. The letter classes are given no estimate of error, but the A's are better than the B's etc. It appears that some of the letter class locations are pretty good (i.e. several fixes over a short period are quite similar), but then others vary wildly- especially the longitude.

Lat1 and Long1 indicate position/fix

The data in the middle three lines of the reading:

This information refers to the type and quality of the transmission from the tag to the satellite and are beyond the scope of most educational programs.
Nb mes : 004 Nb mes>-120dB : 002 Best level : -116 dB
Pass duration : 282s NOPC : 3
Calcul freq : 401 649279.4 Hz Altitude : 0 m

Key to the series of numbers at the end of the reading:

This series of numbers is the dive data. There should be a series of 4, 8 or 12 numbers. All of the numbers in the series should add up to even multiples of 256. If they don't, then the message was incomplete or garbled somehow.

Therefore, the first thing to do is add up all of the numbers and divide the sum by 256. If you get a number with no remainder the message is good.

The first number in the series is an identifier, that tells you what type of message you are getting. If the number is even, the message is a status message. Status messages should be a series of twelve numbers, all of which tell something about the tag. (If the number is odd go to histograms, below.)

Status message numbers from left to right:

1. The first number is also the deepest depth recorded by the tag in the past 24 hours (midnight to midnight). To get the actual depth you multiply that number by 4 (the depth resolution for the tag) and ...viola ...depth in meters (to convert it to feet divide it by .3048)

2. Time at surface for the past 6 hour period (multiply by 90 to get the surface time in seconds).

3&4. The number of messages sent by the tag so far ( multiply by 256 and add to #4).

5. Pressure sensor status (should be around 10).

6. Battery voltage (multiply by .064). The voltage should be around 11-12 volts, below 7 it is bye bye tag.

7. Sea water resistance at depth, checks the status of the sea water switch and is supposed to be around 20.

8. Surface time for the 6 hours before #2 (multiply by 90 for time in seconds).

9, 10, 11 Time (hours, minutes and seconds) for the tag's clock. This should be pretty close to the satellite time in the message header. The tag clock will drift a bit (more so when it is cold). If it is way off there is big trouble.

12. Checksum - this number adjusts the total of the numbers so they are evenly divisable by 256

If the number is not even then it is a data histogram.

The first number is still an identifier that tells you whether it is a depth, duration or time at depth message. The tag stores data from four six hour time periods (while collecting the current data). The first number also tells you which time period the data was collected in, and if the tag was "wet" or "dry".

This tag is programmed to think it is dry when it sends five signals without wetting the salt water switch ( about 7 minutes out of the water). Numbers between 65 and 95 are "dry", numbers between 97 and 127 are "wet".

There are twenty four possible messages (4 time periods X 3 kinds of messages, depth, duration, time at depth, X 2 wet, or dry). (Actually it is even more complicated because, to save power, if a histogram has enough 0 values it will be sent as a 4 byte rather than an 8 byte message ....cripes......).


Another example - try interpreting it:

21215 Date : 20.02.97 05:55:37 LC : 0 IQ : 45

Lat1 : 51.254N Lon1 : 50.136W

Nb mes : 004 Nb mes>-120dB : 002 Best level : -116 dB
Pass duration : 282s NOPC : 3
Calcul freq : 401 649279.4 Hz Altitude : 0 m
146, 144, 93, 188
09, 172, 15, 18
05, 56, 57, 121


More Seal Satellite Data:

>
> 21215 Date : 20.02.97 10:20:18 LC : 0 IQ : 47
> Lat1 : 51.104N Lon1 : 50.277W
> Nb mes : 005 Nb mes>-120dB : 000 Best level : -124 dB
> Pass duration : 558s NOPC : 3
> Calcul freq : 401 649533.1 Hz Altitude : 0 m
> 146 158 94 112
> 10 177 15 144
> 10 27 05 126
>
> 21215 Date : 18.02.97 07:58:21 LC : 2 IQ : 60
> Lat1 : 50.994N Lon1 : 49.885W
> Nb mes : 005 Nb mes>-120dB : 000 Best level : -125 dB
> Pass duration : 215s NOPC : 2
> Calcul freq : 401 649351.6 Hz Altitude : 0 m
> 156 23 92 21
> 10 173 15 17
> 08 02 59 192
>
> 21215 Date : 15.02.97 16:46:52 LC : B IQ : 00
> Lat1 : 49.520N Lon1 : 46.074W
> Nb mes : 002 Nb mes>-120dB : 000 Best level : -128 dB
> Pass duration : 102s NOPC : 2
> Calcul freq : 401 649258.6 Hz Altitude : 0 m
> 105 02 00 00
> 01 03 06 139
>
> 21215 Date : 15.02.97 21:57:19 LC : A IQ : 00
> Lat1 : 49.347N Lon1 : 48.717W
> Nb mes : 003 Nb mes>-120dB : 000 Best level : -122 dB
> Pass duration : 102s NOPC : 3
> Calcul freq : 401 649308.9 Hz Altitude : 0 m
> 164 13 90 222
> 10 175 14 12
> 22 00 11 35
>
> 21215 Date : 12.11.96 08:58:10 LC : A IQ : 00
> Lat1 : 67.247N Lon1 : 60.383W
> Nb mes : 003 Nb mes>-120dB : 001 Best level : -120 dB
> Pass duration : 102s NOPC : 2
> Calcul freq : 401 649125.2 Hz Altitude : 0 m
> 206 137 41 110
> 10 171 14 100
> 09 01 38 187
>
> 21215 Date : 09.02.97 06:15:56 LC : A IQ : 60
> Lat1 : 48.020N Lon1 : 58.127W
> Nb mes : 003 Nb mes>-120dB : 000 Best level : -122 dB
> Pass duration : 102s NOPC : 0
> Calcul freq : 401 649390.6 Hz Altitude : 0 m
> 105 00 00 00
> 14 00 00 137

Many more data entries can be found in the WhaleNet Listservs.


Study Guide Questions and Skill Activities


Computer Skills and Activities:

1. Develop a spread sheet to calculate the dive depths for the data given the methods described on this page.
2. Make a database for the data showing: date, time, Latitude, Longitude, dive depths, the twelve number readouts, LC, and any other elements that you deem pertinent.
3. Analyze the data.
4. Email your studies, theories, and/or results of your data analysis to WhaleNet at pita@whale.wheelock.edu for exhibit and discussions.

Questions:

1. What was her deepest dive using this data?
2. How far did she travel per day (average)?
3. When was she dry? (What days?)
4. What trends do you observe in any of her behaviors?
5. What additional information would you need to pursue your theory(ies)?


Explanations and data supplied by:
Greg Early
New England Aquarium
Central Wharf
Boston, Mass 02110

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