Help: Bathymetry, Gravity and Magnetic Profiles
Exploring Bathymetry, Gravity and Magnetic Profiles
Choose among Lamont, NGDC and ADGRAV datasets
Import and display your own MGD77-format data
Download data to your computer in MGD77 format
What is the MGD77 format?
Selecting Bathymetry, Gravity and Magnetic Profiles displays the ship tracks in the region of the ocean you are currently viewing.
Clicking on a specific track highlights the track in white. When the track is selected the track name is also highlighted in a list of all tracks that are visible in the Main Map Window. Using the datatype checkboxes (topo, mag, grav), one can choose to view only tracklines for which the selected types of data are available.
The all and none buttons toggle the view to show all the tracks or just the underlying bathymetry.
Choose among Lamont, NGDC and ADGRAV datasets
Choose the dataset you wish to view by selecting its radio button. Lamont data is from the archives at Lamont-Doherty Earth Observatory of Columbia University in Palisades, NY. NGDC data is from NOAA's National Geophysical Data Center in Boulder, CO. ADGRAV data is from the Antarctic Digital Gravity Synthesis, an international program to compile existing gravity data south of 60S.
Viewing Profiles
Pressing the View Profile button will bring the data for this track into your computer's memory from the database and display a profile of topography (topo), free-air gravity anomaly (grav) or magnetic field anomaly (mag) as selected with a radio button. The next button toggles from topo to grav to mag and then back to topo. Profiles are shown only when there is data. You can select tracks either by clicking on them in the Map Window or in the scrolled list.
When viewing profiles, the All and None buttons toggle the view to show all the tracks or just the single one selected. This is particularly useful to see how a track's data profile relates to the underlying bathymetry shown in the Main Map Window.
Enlarging the profile
The horizontal axis of the profile can be enlarged to show more detail by holding down the "control" key, which selects a magnifying glass cursor with a plus sign 
, and clicking on any part of the profile. Holding the "shift" and "control" keys while clicking selects a zoom out cursor 
that will reduce the size of the profile. The cursor may not change shape on all computers, but you can still use control-click to zoom in and control-shift-click to zoom out to expand or shrink the profile.
You will notice in the Main Map Window that the track selected is yellow with a highlighted red portion that is the section of the track visible in the Profile Window. The little circle 
on the track within the Map Window marks the current location of your cursor as it is moved left and right in the Profile Window. As you scroll through the profile, the red portion moves along the track to keep you referenced as to where the current profile view is located in the Map view.
When Lamont data is is loaded, the large information button 
adjacent to the profile panel brings up a scrollable window with metadata about the track selected. Press OK to close it.
When finished viewing track and profiles, press the close button to release computer memory and improve performance for other viewing options.
Download data in MGD77 format
Data from Lamont, NGDC and ADGRAV databases may be downloaded to your computer in the ascii MGD77 format. Select a leg from the scrollable list,
then click on Download Data. This window appears,
allowing you to choose a location on your computer for the track you wish to download. Do not change the name of the file. Press Save and the file will be downloaded.
Import and display your own MGD77-format data
If you have MGD77 datafiles (Y2K-compliant type 5 data records only, no headers) on your own computer, you may plot their tracks by clicking the Import Leg from MGD77 file button. This window appears.
Click Open. A control file and folder are created on your computer and the cruise name is added to the end of the scrollable list of tracks. Select it to see the location of the track.User's tracks will remain visible even when datasets (Lamont, NGDC, ADGRAV) are changed. At this time, you cannot view data profiles of files you have loaded.
