Dear Alex,

you may try the website of CODE centre for orbit determenation 

ftp://ftp.unibe.ch/aiub/CODE

http://www.aiub.unibe.ch/content/research/satellite_geodesy/code___research/index_eng.html

Code will give you interpolated (spherical harmonic fitted) TEC maps on a 2.5x5.0 lat x lon grid in two-hour temproal resolution. Rather than just using the CODE maps, however, you can also look at the IONEX TEC maps generated by each of the global analysis centers (IGS, CODE, JPL, ESA, etc...). The CODE, IGS, and JPL maps are generally considered the more reliable. ftp://cddis.gsfc.nasa.gov/gnss/products/ionex/

Instructions on how to navigate their ftp and about the data format can be found here: http://cddis.gsfc.nasa.gov/Data_and_Derived_Products/GNSS/atmospheric_products.html#iono

You can also try Anthea Coster's Madrigal TEC maps, which don't use any interpolation (leaving you to choose how you want to interpolate the data). You can get that data here: http://madrigal.naic.edu/ No account is needed but they do ask for your email an institution information for their records.

Electron density is another beast all together. There doesn't really exist a reliable electron density model out there. The IRI has it's issues at high and low latitudes and the TIEGCM (http://www.hao.ucar.edu/modeling/tgcm/) isn't really at the stage where it can be considered for operational use. There are assimilation models out there, but none of them are openly available or run regularly.

For a formal evaluation, you may want to consider case-studies and seeing if you can get any of your data near one of the North American Incoherent Scatter Radars, which can get accurate, high-resolution electron density information. Poker Flat or Millstone Hill would probably be ideal. Poker Flat is a phased array scanning many beam directions at once and has a bunch of GPS receivers in its vicinity. Millstone Hill is in the central mid-latitudes with excellent range and is covered by an even larger array of GPS receivers. The ISR data can be retrieved from the same Madrigal site I posted a link to above. (They're also hosting an ISR Summer School in Europe this summer that you may be interested in attending -room, board, and flights are generally covered-). http://amisr.com/workshop

Alternatively, I'll be publishing my empirical electron density model for 60+ Magnetic Latitudes later this month. I'll send you the model as soon as I've finished optimizing it, if you want. Until then you can try the IRI and just see what kind of results you get. You can also scale IRI NmF2 to match map TEC, which may work OK at mid latitudes (big issues at high latitudes though).  

Thank you both for your suggestions. Both CODE and Madrigal seem promising.

I am hoping to find some individual or combined LOS TEC curves (from a case study), similar to those attached for TEC and L1 Delay. I need a map of the electron density (see attachment) rather than the VTEC for the time the TEC curves were measured. I will try to reconstruct the previously measured LOS TEC curves using ray-tracing.

David, this is exactly what I was hoping to do:

"For a formal evaluation, you may want to consider case-studies and seeing if you can get any of your data near one of the North American Incoherent Scatter Radars, which can get accurate, high-resolution electron density information. Poker Flat or Millstone Hill would probably be ideal. Poker Flat is a phased array scanning many beam directions at once and has a bunch of GPS receivers in its vicinity. Millstone Hill is in the central mid-latitudes with excellent range and is covered by an even larger array of GPS receivers. The ISR data can be retrieved from the same Madrigal site I posted a link to above."

I am not looking for TEC maps, but did check out Anthea Coster's Madrigal TEC maps and the videos by Juha Vierinen. Thank you for the great resources. The FTP server readme will definately be very helpful! Thank you!

In the first plot, you seem to show just a comparison between TEC maps (probably CODE, IGS, or JPL) and observations at a site by using the site-referenced ephemera to generate azimuth and elevation information and then simply using the thin shell ionospheric assumption (with likely shell height of ~450km). That is ultimately just an evaluation of the impact of the map interpolation scheme and of the effect of the thin shell assumption on modeled TEC.  

I'm a little confused as to what you're trying to asses here. I would think current electron density modelling errors would dominate your comparison... Even without those, I would think the only difference you would see between your raytracing TEC and that approximated from differential phase would be the result of our first order truncation of the refractive index Taylor series in our TEC calculations and the marginal difference resulting from path bending effects. I could be completely misunderstanding what you're trying to do here, so don't take the above too seriously.

That said, if you need processed line-of-sight GPS data, you can use the CHAIN GPS data. We provide RINEX files of the raw data, but if you have a particular location and time in mind, I can process it into TEC for you (remove biases, cycle-slips, etc...) and just send you an IDL save file. We also happen to have a GPS receiver within about a kilometer of the Resolute Incoherent Scatter Radar that might be useful to you; however, I doubt there's much in the way of ADS-B up there, if you need that. I can process and send you ISR data in an save file as well, if you want it (just choose an available time range). One of the advantages of going to such high latitudes is the lack of a plasmasphere contaminating your ionospheric reconstruction. At mid-latitudes you need to take the plasmasphere (above 1500km) into account in reconstruction.

I also have code lying around somewhere that can process the IGS and UNAVCO RINEX files into TEC. I'll take a look and send it to you once I find it (I've never been all that great keeping my codes in order and commented, hahaha). They have sites near the Millstone Hill and Poker Flat ISRs.

If you are just at mid-latitudes and need to do a GPS-based reconstruction, you may want to consider using Dr. Gulyaeva's IRI-Plas model, which tries to roughly account for plasmaspheric electron density by scaling densities above the IRI's 2000km boundary to IGS mapped TEC (http://www.ionolab.org/index.php?page=iriplasweb&language=en). It's still not a great model (has same issues as IRI and a few other nasty bits), but it's a step better than the IRI if you're doing GPS TEC work.

Simply by the nature of data availability, all of these models do not perform particularly well at high latitudes or over the oceans.

Thank you David. I will take a look at some data and get back to you when I have a date and time in mind ( I will need to look over the radar data) for the LOS TEC GPS data. The focus is for mid to high latitudes.

The first plot confused me a bit as well at first so I have contacted the author and am waiting for a reply.  I really just want to see if for a given ionosphere (from radar), my ray-tracing program can reproduce (from modeled ADS-B distributions)  the LOS TEC observations from GPS. Eventually I will use the modelled TEC to reconstruct the radar profile. At that point, if a reconstruction from GPS TEC is also avaiable for further comparison, that would be a bonus.

Hello, Alex.

Here are the TEC maps over South America. You just have to create an account and start downloading the data: http://www2.inpe.br/climaespacial/portal/en/

Cheers.