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Data Analysis: Cracking
the Satellite Code
Grade: 9th - 12th
Goal: Students will be able to follow
a marine animal and identify where it travels, how deep
it dives, and various other behaviors. They will be able
to answer questions related to these animals and construct
a table based on this information.
Objective: Students will be able to:
· Learn how data is transmitted by satellite, and
how to decode the messages
· Read a nautical chart
· Create a table
Standards:
Geography: A-1, A-2, B-1, E-1, E-2
Mathematics: A-1, A-3, A-4, A-6, B-2, B-4, B-6, B-7, B-8,
C-1, D-1, D-2, D-3, E-3
Materials:
· Navigational chart of Gulf of Alaska and Bering
Sea
· Work sheet
Introduction:
Satellite telemetry tags provide a variety of data about
the animal's location and behavior. However, the data is
transmitted as a series of numbers that scientists must
decode. By accessing information found on the Project MASTER
web site, students can complete the attached worksheet.
The web site includes examples of the "raw data"
as well as data sets that have already been decoded.
Explanations and first two data sets adapted
from:
Greg Early
New England Aquarium
Central Wharf
Boston, Mass 02110
Example Data Reading:
|
21215
|
Date: 20.02.97
|
05:55:37
|
LC : 0
|
IQ : 45
|
|
Lat1: 51.254N
|
Lon1: 50.136W
|
(Animal location by latitude and longitude)
We will not decode the following three
lines for Project MASTER.
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
The following sets of numbers are the dive data. These
represent a "status message" if the first number
is even.
Number series:
|
146
|
144
|
93
|
188
|
|
09
|
172
|
15
|
18
|
|
05
|
56
|
57
|
121
|
What are the first two lines of the reading?
21215 = satellite tag identification number,
this is the animal's ID 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 and accuracy.
LC stands for Location Class. Location Classes
of 0 and up are 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 where on the map the
animal is.
What are the middle three lines of the
reading?
This information refers to the type and quality
of the transmission from the tag to the satellite. We will
not be decoding this data for Project MASTER.
What is 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.
This is a check for accuracy of the satellite transmission.
How to interpret the dive data:
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 this will give you depth
in meters (to convert it to feet divide by .3048).
2. The second number represents the animal's time at surface
for the past 6-hour period (multiply by 90 to get the surface
time in seconds).
3&4. The numbers of messages sent by the tag so far
(multiply by 256 and add to
#4). Remember that these tags will only transmit messages
when they are out of the water.
5. Pressure sensor status (electronic test to accurately
read dive depth) should be around 10.
6. Battery voltage (multiple by .064). The voltage should
be around 11-12 volts. If it falls below 7, the tag will
no longer work due to low power.
7. Seawater resistance at depth, checks the status of the
seawater switch (senses when the satellite tag is out of
the water and then turns on the transmission). This number
should 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 close to the satellite time
in the message header. The tag clock will drift abit (more
so when it is cold). If it is way off there is a problem.
12. Checksum - this number adjusts the total of the number
so they are evenly divisible by 256.
If the first number is not even then it
is a data histogram (bar graph).
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"(under water) or "dry".
This tag is programmed to think it is dry
when it sends five signals without wetting the salt switch
(this takes about 7 minutes out of the water). Numbers between
65 and 95 are "dry"; numbers between 97 and 127
are "wet".
Here are some examples, try and interpreting
them:
1.
|
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
|
2.
|
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
|
3.
|
19134
|
Date: 07.09.01
|
15:09:00
|
LC: 2
|
IQ: 68
|
|
Lat1: 72.343N
|
Lon1: 172.557W
|
Nb mes: 007 Nb mes>-120dB: 001 Best level:
-120 dB
Pass duration: 543s NOPC: 2
Calcul freq: 401 649034.0 Hz Altitude: 0 m
|
34
|
13
|
33
|
102
|
|
10
|
101
|
50
|
00
|
|
16
|
10
|
22
|
121
|
Satellite Tracking Data Worksheet
Satellite tag identification number: __________________
Date: _________________
Time at last location: ________________
1. Is this a complete / good message? How
do you know?
2. Is this a status or histogram message?
How do you know?
If this is a status message then:
1. What is the actual depth in feet the animal dove in the
last 24 hours? ___________feet
2. How much time has the animal spent at the surface in
the past six hours? ___________minutes
3. How many messages has the tag sent so far? ____________
If this is a histogram message then:
1. Is this a wet or dry tag, and how do you know?
More Questions:
1. What is the name of the animal we are tracking?
________________
2. Genus, species: _________________
3. Latitude: ____________ Longitude: ______________ (at
last known location)
4. If near or on shore, list the regional area, village,
town, or city the animal is closest to: ________________________
5. Where was the animal tagged and released? ______________________
6. How far has the animal traveled since it was released?
___________________
7. What is the depth of water at the current location? ____________(feet)
8. What percent of a 24-hour day did the animal spend at
the surface? ____________
Extension activities:
1. Create a table including date, latitude,
longitude, time and depth of dives for your animal.
a. Plot the location of the dives. At what location did
the animal make most of its deepest dives? What is the depth
of the water at that location? Was there any pattern to
the dive locations?
b. Calculate the percent of dives made at each specific
depth range. In what depth of water is it most of the time?
Why do you think the animal most frequently goes to that
depth?
c. What percentage of time is the animal spending at sea
versus a haul out location (time animal is out of the water)?
2. The scale of distance is one nautical mile equals one
minute of latitude. So if one degree equals 60 minutes of
latitude, how many nautical miles equal one degree of latitude?
Five degrees of latitude?
Note: statute mile = 5280 ft. in length / nautical mile
= 6076 ft. in length
Statute miles x .87 = nautical miles
Nautical miles x 1.15 = statute miles
3. The atmospheric pressure (atm) at sea level
is about 14.7lbs. /square inch. When a person dives the
pressure exerted by the water increases by 1 atm for every
10 meters (30-ft) the person goes down. Identify the deepest
dive made by the marine animal. What is the approximate
pressure exerted at that depth?
