               Field-Aligned Dependant Propagation
A Program for the Assessment of E-layer Field-Aligned Propagation
                     Version 1.01 - May 1995
                       James M. Roop, K0BI

1.   INTRODUCTION

1.1  FLD-ALGN is a graphical field-aligned propagation analysis
     program that aides in the determination of possible auroral
     scatter and Field-Aligned Irregularity (FAI) propagation paths. 
     The program will "paint" the area bound by the aurora boundary
     ellipse for a specified station location for all possible auroral
     scattering locations.  Another option will show locations that
     can typically be worked by auroral scatter for a given K-index. 
     For FAI propagation, the program will display all possible
     scattering locations that will provide FAI propagation between
     two specified locations as well a plotting isoflection loci for a
     specified scattering location.

1.2  Station location is entered by "clicking" a location with a
     mouse.  Location information may also be entered by manually
     entering the locations Maidenhead grid square.

1.3  FLD-ALGN is based on the work of several articles that have
     appeared in QST.  These articles include Richard Miller,"Radio
     Aurora", QST, January 1985; Emil Pocock, "Practical Radio
     Aurora", QST, March 1990; and Thomas F Kneisel,
     "Ionospheric Scatter by Field-Aligned Irregularities at 144
     MHz", QST, January 1982.  These and other article are also
     found in "Beyond Line of Sight, A History of VHF Propagation
     from the Pages of QST', Emil Pocock, editor, ARRL (1992). 
     Another reference is Radio Auroras, Charlie Newton, G2FKZ
     (RSGB, 1991).

1.4  The program FLD-ALGN is copyrighted with all rights reserved
     by the author.  However, the unregistered version of
     FLD-ALGN, version 1.01 may be freely used.  The program
     may also freely distributed as long as no profits are realized. 
     Versions of FLD-ALGN that are registered to a specific person
     may not be distributed.
 
2.   SYSTEM REQUIREMENTS

2.1  CPU requirements:  A 286 or better system is required.  A math
     coprocessor is required for satisfactory performance.   Dismal
     performance will occur with anything less than a 486DX.

2.2  Monitor requirement:  Minimum requirements are an EGA
     monitor and display adaptor.

2.3  A Microsoft compatible mouse is required for full functionality.

3.   STARTING THE PROGRAM

3.1  The following files are required for FLD-ALGN version 1.01:

          FLD-ALGN.EXE   the program executable
          MAP.ESP        map image file
          MAGDIPV2.DAT   geomagnetic field (dip latitude) data

3.2  Generally, the program files should be in the same sub-
     directory.  To start the program, change directory to the
     appropriate sub-directory and enter: 

               FLD-ALGN <cr>

3.3  Map files, other than the default MAP.ESP, may be selected
     from the command line by entering, for example:

               FLD-ALGN CAN-USA.ESP <cr>

3.3.1          Map files for ES-PROP version 1.4 are usable with FLD-
               ALGN.  However, FLD-ALGN is only usable for
               CONUS and adjacent areas (southern Canada, northern
               Mexico and the Caribbean.

4.   PROGRAM OVERVIEW

4.1  Program options are selected by the function keys.  A menu is
     displayed listing the program options.  Location data is with the
     mouse by default when a mouse is detected.  Optional keyboard
     entry may be toggled by entering the letter "k" when the menu
     is displayed.  The message "kybd" appears below the lower
     right corner of the map to indicate keyboard entry.

4.2  [F1] Plot Isoflection Loci
     Plots isoflection loci (lines of equal reflection angle from the
     scatterer) for a given scattering location.  See T. Kneisel,
     "Ionospheric Scatter by Field-Aligned Irregularities at 144
     MHz".  FLD-ALGN plots contours similar to those shown in
     figure 3 of Kneisel's article.

4.2.1          An arc (in white) will be displayed representing the loci
               of possible FAI propagation path endpoints if the user
               location has been set and within range of the scattering
               location.  See 4.8 for details on setting the user location.

4.3  [F2] FAI Path Analysis
     Path endpoints are entered by using either the mouse or the
     keyboard.  If the two locations do not exceed the maximum
     distance for E-layer propagation, then all possible scattering
     location that are within range of either station are evaluated. 
     This exhaustive process is very computational intensive and
     requires a math coprocessor for satisfactory performance.  

4.3.1          At each point that is evaluated, the reflection angle to
               both of the path endpoint locations is evaluated.  For a
               scattering location to support propagation between the
               two path endpoints, the sum of the reflection angles to
               the two path endpoints must be equal to zero.  Since
               scattering locations are evaluated at discreet intervals of
               latitude and longitude, the likelihood of evaluating a
               location where the angles sum to exactly zero is low. 
               The program will plot a point if the sum of the angles is
               less than .75.  Points where the sum of the angles is less
               than .25 are plotted in red, whereas points where the sum of
               the angles is greater than .25 (but less than .75) are
               plotted in blue.

4.3.2          The time required to evaluate all points will be in excess of
               one-half hour when the program is run on a 486SX/25.

4.3.3          Scattering location evaluation can be ended by entering [F10]

4.3.4          After all the scattering locations have been evaluated (or
               the evaluation process interrupted as described in 4.3.3)
               specific scattering locations can be evaluated by pointing
               to the scattering location with the mouse.  If the left mouse
               button is clicked on valid scattering location, the program
               will display the azimuth and elevation angles to the
               scattering location from each of the path endpoints.  To exit
               this mode and return to the main menu, enter [F10] or click
               the right mouse button.

4.4  [F3] Aurora Boundary Ellipse
     FLD-ALGN plots isoflection loci for all possible scattering
     locations within range of an entered location.  The set of
     overlapping loci will define an area whose perimeter is known
     as the boundary ellipse (see E. Pocock, "Practical Radio
     Aurora").  The area that is displayed on the map by FLD-ALGN
     represents the area within which auroral scatter communications
     can be made.

4.4.1          If a user location has be set (see 4.8), FLD-ALGN will
               use that location , otherwise the user will be prompted to
               enter a location.

4.4.2          Aurora boundary ellipses can be inferred for any location
               entered on the map.  The areas that are displayed
               represent the best-case conditions where the auroral front
               will extend far enough south relative to the location of
               the entered station location.  From figure 4 in Miller,
               "Radio Aurora", it can be see that there are only 1.3
               auroras per year at a geomagnetic latitude of 52
               compared to 97 auroras per year for a geomagnetic
               latitude of 60.  Therefore, the auroral front will extend
               below 52 magnetic latitude less than 1% of the time for
               when aurora conditions will exist in the southern
               provinces of Canada. FLD-ALGN will display in blue
               those areas where to which auroral propagation is likely
               to exist less than 1% of the time.  Areas where auroral
               propagation is more likely to exist will be displayed in
               magenta.

4.4.3          [F10] will interrupt the aurora boundary ellipse evaluation
               process and re-display the menu.

4.4.4          FLD-ALGN attempts to evaluate the speed of the
               computer system and will evaluate fewer scattering
               locations for slower systems.  This is done in order to
               reduce the amount of time it takes to evaluate the auroral
               propagation area for a given location.

4.5  [F4] Auroral Paths for a Specified K-index
     FLD-ALGN determines all possible scattering locations at a
     specific magnetic latitude that is determined from the K-index. 
     The isoflection loci are plotted for scattering locations within
     range of an entered location. During magnetic storms, the
     auroral oval expands and moves southward.  The greater the
     intensity of the geomagnetic strom (an hence the K-index) the
     further south the auroral oval moves.  The magnetic latitude that
     FLD-ALGN uses for a given K-index was determined using 
     figure 8 of Richard Miller's article Radio Aurora in conjunction
     with a map displaying geomagnetic dip latitude (such as figure
     2 in Emil Pocock's Practical Radio Aurora.)

4.5.1          If a user location has be set (see 4.8), FLD-ALGN will
               use that location , otherwise the user will be prompted to
               enter a location.

4.6  [F5] Clear Map
     The map is erased and a new map is displayed.

4.7  [F6] Create PCX Graphic of Map 
     Registered copies of FLD-ALGN have the ability to create PCX
     format graphic files of the map.  The PCX format graphics files
     can be viewed by a number of graphics programs including
     Windows' Paintbrush.  Users of slower computers may find it
     useful to save the map image for future reference instead of
     having to regenerate the map.

4.8  [F7] Set User Location
     This option permits the user to set a location that will used in
     subsequent operations as described in sections 4.2, 4.4 and 4.5.
     If a user location was not set, then the user will be prompted to
     enter a location for those options.

4.8.1          The user location can be changed by entering a new
               location.

4.8.2          The user location can be cleared by clicking the right
               mouse button (or entering a null entry if entering by
               keyboard.)
 
4.9  [F8] Adjust Scattering Point Height
     The height at which auroral scattering is evaluated can be
     toggled the [F5] key.  Heights between 90 and 120 km can be
     selected.  The scattering height should be set before evaluation
     of FAI paths or auroral boundary ellipses.

     Maximum distances for auroral propagation appear to occur at
     lower scattering heights, i.e., 90 km.

4.8  [F10] End Program.
     [F10] terminate the program when the menu is displayed,
     otherwise, the evaluation in progress is interrupted and the menu
     is redisplayed.
