User Instructions for CLENQT.FOR

These instructions are written to help users run the program CLENQT.FOR. This program requires an input file called EGM180.NOR which contains the WGS 84 n=m=180, normalized, geopotential coefficients. The source code for CLENQT.FOR is in FORTRAN 77 and it has been developed for use with MS-DOS commands.


This is an ASCII file containing the defree (n), order (m), and normalized geopotential coefficients (Cnm, Snm) in the following format:

n m Cnm Snm

These coefficients were developed using surface gravity, satellite altimetry, and elevation data.


The user can run CLENQT.FOR with EGM180.NOR to compute the following gravimetric quantities, here shown with the corresponding output term and unit:

  1. point free-air gravity anomaly (DELTA G) (mgal),
  2. point geoid height (N) (m),
  3. point north-south and east-west components of the deflection of the vertical (XI, ETA) (both in arcsec),
  4. point total deflection of the vertical (THETA) (arcsec),
  5. point radial component of the gravity disturbance vector (DIST R) (mgal), and
  6. point north-south and east-west components of the gravity disturbance vector (DIST NS, DIST EW) (both in mgal).

To load and execute the program, type the following sequence of commands:

  1. Copy both CLENQT.FOR and EGM180.NOR to the same directory.
  2. If the .FOR suffix is not compatible with your system's compiler, rename the file to CLENQT.F. then run the program through a FORTRAN compiler. If using a Lahey compiler, type the following commands to create an executable file (.EXE):
    • f77l3 clenqt.for (This creates CLENQT.OBJ)
    • 386link clenqt.obj (This creates CLENQT.EXE)
  3. Type this command to execute: clenqt.exe
    • The message "READING COEFFICIENT FILE" will appear on the screen indicating that the program is running.
    • The user is then prompted to enter the latitude, longitude, and the geodetic height (height above ellipsoid) for the point of interest. The latitude and longitude values must be in decimal degrees and the geodetic height must be in meters
    • After the point is entered, the computer will then calculate the gravimetric quantities and display them on the screen in the following format:
      PHI     LAMBDA     HT     N     DELTA G     DIST R     DIST NS
              DIST EW    XI     ETA   THETA
    • The program prompts the user to enter a "1" to continue or a "0" to stop.
    • The data will go to the screen only; there is no output file.

Point of Contact: Office of Geomatics
phone (314) 676-9127, DSN 846-9127

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