Think about the data you are going to collect, what will your stations spacings be? Why? Will you be collecting a grid of data or oblique profiles? What is the intensity of the magnetic field in your survey area? If you don't know, find out from the NGDC Geomag website and follow the directions to get the magnetic field value for your survey area. For the Missoula area use 56,000 nT.

Here's the real tip - set up all the field parameters (line number, etc.) for your survey, collect some bogus data in the lab (get a couple of lines worth so EOL increment is tested), and download those data to make sure they look like what you expect them to look like. This will take you about ten minutes and you will know if you have the set up procedure figured out.

IN THE FIELD: (if you get lost in the menu structure, 1C will always return you to the main menu)

Assemble the components as necessary for your survey. If you are collecting magnetic field data, screw one of the sensors onto the top of the four section staff. For gradiometer data the usual situation is to separate the two sensors with one section of staff (56 centimeters).

Turn the instrument on by pressing the power button (0F or CF turns it off).

Erase any existing data by pressing the 4 and 5 keys simultaneously then simultaneously press 9, 4, 7 & 3 (to spell "wipe") to complete the task. This step is not necessary unless you are going to collect a lot of data. However, the fewer files stored in the machine the easier it is to scroll through them.

LAB RULE: Once you put the instrument away it is fair for anybody else to erase any existing data.

Set the DATUM by pressing C for INFO in the main menu, then 0 (zero) for datum in the sub-menu. Pressing C again will let you change the datum to the appropriate value (from the USGS telnet site) for your area. Type in the correct value then E for ENTER, and F for ok and you should be back at the INFO sub-menu. Note that changing DATUM when there is data in memory will change the datum of raw data in memory. 1C returns you to the main menu.

Start the Survey by pressing A at the main menu. Usually the second line of the display will tell you what mode (base, mobile, or grad) it was last used in, occasionally you will have to tell it what mode to use. To change the mode press 63 (lower case nf) for new file to choose A for magnetic profiles or C for gradiometer data.

Set the Date and Time by selecting F for setup then C to change it or F if it's ok. C presents wyymmddhhmmss, the format line, for day of the week (w, monday is #1), month, day, hour, minute and second. Type in the correct digits, then F to start the clock, and F again for ok.

Assuming you followed the steps above the next display should look like:

01 .m (or .g)
file
F - ok C - change

Here .m is the file extension for mobile, if you chose Gradiometer the indicated file extension will be .g. In any case, this is the display you want next. There are a few ways to get there. First, you could follow the above instructions. Second, maybe you followed the above instructions earlier in the day and you know MOBILE, DATE and TIME were ok, so you skipped those steps. If so, from the main menu press A, F, F and it looks like the above.

To enter a file name press C; now the D & F keys move the flashing cursor. Enter letters, numbers and spaces with the key pad. Each key has four values, for example pressing 5 once yields j, another press gives you k, then l, then 5, then j... To spell out "steve": 8 F 88 F 33 F 9 F 33. Hit E to enter the file name, F for ok. Then you get to enter TEXT comments in the same manner, F for ok. Then ID is the next option which lets you enter up to a nine digit number, this seems to be of little use, F for ok.

You should now be in the Line and Station setup screen, the next several screens deal with the coordinate system for your survey. You will end up with a location label for each reading. You want to get your data such that it can be readily imported into Surfer. Surfer uses a lower-left origin with the x-coordinate increasing to the right and the y-coordinate increasing up. If you set the magnetometer's line increment to 0, the station increment positive, and the EOL increment positive and then collect data along lines going west-east, east-west, etc. then your line numbers will be Surfer-Y and station numbers Surfer-X. Of course if you are walking south-north, north-south, ... then stations will be on y-coordinates and the EOL increment and line spacing will be x-coordinates. Think about it and draw a sketch in your notes.

The magnetometer's assumption is that you will be doing several parallel lines and reversing your direction at the end of each line. Imagine several parallel lines(figure 1) striking NE with line numbers increasing to the NW; the EOL and station spacings would be positive with the line spacing about twice the station spacing. After downloading, you end up with a grid of data.

Set the line number and direction by using the keys for those tasks, they are labelled in blue. For example, B2 would change the direction to NW, C12E would change the line number to 12. If you are walking lines west-east, and you want a Surfer-like coordinate system, start at line (y coord) number zero (Figure 2). Keep track of your line numbers in your field book. Hit F for ok when line number and direction are correct.

Set the line increment and sign. The default is one for line increment and positive, change these depending on your collection scheme. If you want a Surfer-like coordinate system with west-east lines, start at line 0, with line increment equal to 0. Of course, if in the above step you set the starting line to #12 and intend to work back to line #1, B will toggle the increment to negative; F for ok.

Select the initial station number by pressing C for change number, entering the number, then E for Enter; you can enter a decimal point with A. B, followed by a direction key specifies a heading along the line (NE/SW if lines increase NW); F for ok.

Set the station increment the same way you set the line increment, here you can use two decimal places; A for the decimal point, B to toggle the sign. For the Surfer-like coordinate system on west-east lines (Figure 2), set the station increment to the station-spacing and collect data along lines; stations will then have x-coordinates in Surfer's system; F for ok.

Set the end-of-line (EOL) increment as above. For the Surfer-like coordinate system on west-east lines, set the EOL increment to the distance between lines (you are collecting along lines) and this will be your y-coordinate.

Set the cycle time using the A and B keys for + and - respectively. The choices are 3, 4, 5, 6, and 10. If you try to go below 3 you get a different screen. Selecting F on that screen tells the instrument to determine the cycle time based on an internally set maximum time and signal amplitude. Otherwise select one of the available cycle times based on your patience and necessary precision - experiment.

Select auto-tune by pressing F. Turn autotune off. According to GEM (3/2004), autotune is best used in base station mode only, so turn that off if it is on. Otherwise, if you hit a high gradient area, the instrument will autotune to a near-random number and never get back to where it should. The tuning of the instrument should agree with the nominal value of the magnetic field for the area (set under DATUM above). When tuning is complete, the display will tell you the 60Hz filter is set, this allows you to work a little closer to power lines. If you are in gradiometer mode you get the option to set the sensor spacing. The magnetometer is now ready to take readings.

START THE SURVEY by pressing any key other than A. When the measurement cycle is complete, the display will show something like this for magnetic profiles:

Magnetic mode:

The lower-left number is the noise level, if it exceeds 800 the display will show "high noise". If the signal is too low in amplitude "weak signal" will be shown. "High gradient" might also be indicated. If you do press the A key during reading mode you can correct your labels, tuning, END THE LINE, or delete a reading, etc.

At the END of LINE pressing A gives you several options:

A will let you change labels to reset line, station, EOL increment.

C to enable/disable autotuning.

E to adjust the line and station at the end of the line in case you walked too far or wish to start a new line at different coordinates. A F, F will return you to survey mode.

1C will always return you to the main menu where you can start a new file.

Back in the Lab

Download your data

Put the Instrument on the charger overnight before storing it.