[OpenMadrigal-developers] Re: Adding Tsyganenko model to Madrigal

[William Rideout]

John,

Here's my 3 suggested matlab methods I'll add to madmatlab.  These are general 
methods to map in either direction from geodetic into the GSM XY plane for a 
given time using the Tsyganenko model.

The general idea is to call the getGsmMap method once for every time of 
interest, which traces field lines from a grid around the globe (and so takes 
about 8 minutes to run).  You then call mapGeodeticToGsm or mapGsmToGeodetic 
using the returned matrix as an input parameter for each point of interest. 
These two methods are very fast.

Please let me know if they meet your needs.

I'll also create a script to make a jpeg image of TEC data in the GSM plane from 
either hemisphere using these methods, but that script is GPS specific and so I 
won't add it to the Madrigal Matlab API.

The three methods are:

1.

[gsmMap] = getGsmMap(madrigalUrl, alt, year, month, day, hour, min, sec)

     This method will create a mapping matrix from geodetic parameters at a 
given alt into the GSM XY plane.  The resultant gsmMap matrix is then used as an 
argument in the next two methods that go from geodetic to GSM, and GSM to 
geodetic.  (This method traces 5400 field lines and takes about 8 minutes to run).

     Inputs:

         madrigalUrl: home page of madrigal site to use.  Until installed on
         hyperion and released, this must be "http://grail/madrigal"

         alt: the reference altitude (for GPS data, use 450.0)

         year, month, day, hour, min, sec - specify time

2.

[xgsm, ygsm] = mapGeodeticToGsm(gsmMap, lat, long)

     Returns xgsm and ygsm given the gsmMap calculated above, and a lat and long

     If mapping fails, returns [NaN, NaN]

3.

[lat, long] = mapGsmToGeodetic(gsmMap, xgsm, ygsm, hemisphereFlag)

     Returns lat and long given the gsmMap calculated above, xgsm, ygsm,
and a hemisphereFlag (1=northern, 2=southern).  The hemisphere flag is required
since one GSM point can map into up to two geodetic points.  The hemisphere 
referred to is the magnetic one,so for example its still possible to get 
negitive latitudes when hemisphereFlag == 1.

     If mapping fails, returns [NaN, NaN]


Bill



John Foster wrote:
> Bill,
> 
> What you've done sounds very useful. I imagine that the TSYG_EQ_XGSM
> TSYG_EQ_YGSM points where the field line crosses the GSM XY plane will 
> be the most useful for our immediate needs.
> 
> A useful back-conversion wuld be to go from a EQ_XGSM, EQ_YGSM position
> (inside the Tsyganenko magnetopause) back to geographic lat and long (at
> a specified altitude, e.g. 400 km) for a given point in time. Then, we could
> take the IMAGE fetures and project them onto our ionospheric TEC
> viewing plane.
> 
> The last-mentioned features of the Tsyganenko model, don't sound too
> useful for our work.
> 
> Keep up the good work!
> 
> John F
> 
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> 
> 


-- 
Bill Rideout
MIT Haystack Observatory
Email: brideout at haystack.mit.edu
Phone: 781 981-5624