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COMPUTING TIME IN GEOGRAPHIC POSITIONS

Coordinates is a general term for numbers representing the degrees, minutes, and seconds of a geographic position. The correlation of time and geographic coordinates is a critical skill for members of the intelligence community. Once you have learned to convert time from local to ZULU and from ZULU to local, the conversion using positional coordinates is a simple matter.

Let's consider a typical position report. A position report is normally sent as two sets of numbers. The first set of numbers is the latitude (north or south). The second set of numbers is the longitude (east or west) and is the set that we use in time conversion. Normally, the longitude of a position report (the second set of numbers) is sent as a five-digit group. The first three digits of this group indicate the geographical degrees; the last two are the minutes. The group is followed immediately by an "E" (east) or a "W" (west) to indicate the hemisphere. For example, 115°30'W indicates the location is 115 degrees and 30 minutes west of the prime meridian.

There are 180° of longitude to the west of Greenwich and 180° longitude to the east (180°W longitude and 180°E longitude = International Date Line-the 180th meridian). Each degree can be broken into 60 minutes. As stated above, the five-digit longitude is normal; however, sometimes you will encounter a seven-digit longitude. This is simply a further breakdown of the minutes into seconds. One minute contains 60 seconds. When this occurs, the first three digits indicate degrees; the next two digits indicate minutes; and the last two digits indicate seconds. In any event, the longitude of a position will place the target into a specific time zone.

To determine this zone, we'll use a hypothetical position report sent in chatter: 12035'N 072042'W. We may disregard the first set of numbers (latitude) and concern ourselves only with the second set of numbers (longi­tude). The "0720" represents the number of degrees of longitude from the prime meridian (Greenwich) and the "42"' is the number of geographical minutes from the 072 degree line (72nd meridian). The "W" tells us that the target is located to the west of the prime meridian, in the western hemisphere.

NOTE: Remember, a time zone spans 150 of longitude, with the ZULU zone divided into 7'/20 of longitude east and 71/20 of longitude west of the prime meridian.

The first step in our computation is to draw a graphic chart showing the western half of the ZULU time zone. Now, label the western border of the ZULU time zone (71/20 west longitude, or 007030'W). We must now continue our chart, proceeding outward from ZULU, labeling the western borders of each of the time zones until we reach a point where the hypothetical longitude is equaled or exceeded. For example, the western border of zone

Once we reach the fast meridian to exceed the longitude (in this case, ROMEO zone's western border is the first of the western borders to exceed our longitude of 072042'W), we need go no further with our labeling. See figure 1-1. Longitude 072042'W falls to the west of zone QUEBEC, but not past zone ROMEO. Our longitude falls within the ROMEO zone, or zone +5.

After determining the time-zone designation for our target, we apply or reverse the sign, depending upon whether we want to determine the ZULU time from local time, or the local time from ZULU time. Longitudes in the eastern hemisphere are handled in the same way, except that the eastern borders are used instead of the western borders.

Let's look at another example. This time we will establish the target's time-zone designators (its longitudinal parameters). An unlocated ship sends its local time as 0945. Your local time is 1345B. The first step in solving this problem is to convert your local time to ZULU. Use the formula, FROM LOCAL TO ZULU-APPLY THE SIGN. All you have to do is subtract your time zone from your local time to arrive at ZULU. Zone BRAVO is -2. By subtracting the local time zone of -2 from your local time of 1345B, you arrive at ZULU time 1145Z. Since it has been established that it is 1145Z, and the target operator has given his local time as 0945, all you need to do is subtract the smaller figure from the larger. The difference will equate to the time zone of the target.

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