Constellation Observing System for Meteorology Ionosphere and Climate C

[Lawrence Naif]

Hi HamSci,

I am working with the Absolute total electron content from the COSMIC-2 Level 1b Data found here  Absolute total electron content (podTc2 format) (GLONASS from February 1, 2021 onwards).  

I am looking at the data range from 2024-04-07 To 2024-04-08 during last year's eclipse.   The data has the following features in the table below.   I cleansed that data because it has a lot of NA, particularly for the S4 scintillation index, and Radio Frequency Interference RFI and removed the coordinates for the GPs and LEO satellite and other things.

                lat        lon        TEC            S4                    elevation           RFI
        <num>         <num>       <num>       <num>               <num>         <num>
1: -22.63987 -168.82730  41.80902 0.0302452 -0.006522193 0.00002060531
2:  17.00366  -63.69627 551.88507 0.0584818 -9.500330000 0.00000000000
3:  17.02227  -63.63752 552.48350 0.0584818 -9.531371000 0.00000000000
4:  17.04085  -63.57877 553.04700 0.0584818 -9.562396000 0.00000000000
5:  17.05941  -63.52000 553.59173 0.0584818 -9.593407000 0.00000000000
6:  17.07796  -63.46122 554.13568 0.0571063 -9.624402000 0.00000000000

I got the following 

• Maximum TEC value: 1451.589
• Number of instances where TEC is at maximum: 1 
• Time range where TEC is at maximum: From: 2024-04-07 07:39:00 UTC  TO "2024-04-07 07:39:00 UTC" 

results make sense as expected?

Best Regards,

[Phil Erickson]

Hi Larry,

  That maximum value seems very high and I would not trust it.  This is a complicated measurement technique - and it really needs resources and discussion with people who deal with TEC on a regular basis.  What is the goal of your study?

73

Phil W1PJE

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[Kornyanat Hozumi]

Hello!

I’d like to offer a quick comment on the TEC value. Short answer is it sounds unrealistic for me.

From my experience working with vertical TEC (GNSS-to-ground path), values around 100 TECU can occur near the Equatorial Ionization Anomaly (EIA) crests in low-latitude regions like Thailand, particularly during geomagnetic storms. In contrast, mid-latitude locations such as Japan only see values that high on a rare occasion, typically **no more than once a year** during a strong event.

That said, since you're using absolute TEC from the podTc2 format, it’s important to note that these are slant TEC values (not vertical), measured along the full GNSS-to-LEO satellite path. So, a maximum TEC value of 1451.589 TECU is definitely high, but potentially reasonable if the signal path is very long and crosses a dense ionospheric region (like EIA, storm-enhanced density (SED), ...) at a very low elevation angle. Hmm…I am not quite sure.

I'd recommend taking a closer look at the arc geometry and elevation angles in your dataset. That can help determine whether this high TEC value reflects a real ionospheric feature or might instead be due to viewing geometry or edge effects or even an error. In case it is an error, it might be, for example, from the bias estimation process especially for the GNSS signals with low SNR.

Best regards,
Kornyanat Hozumi (Kukkai)

[Lawrence Naif]

Hi Phil, 

The goal is to detect and analyze TIDs. BTW, I break down the data into a 16x16 spatial grid. The spatial map is constructed using latitude and longitude bins and looks at averages of TEC, S4, RFI, and elevation in each cell.   I first construct the signal from the data and then do basic FFT stuff.  TID events are detected from FFT amplitude peaks (> 95th percentile).

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[Phil Erickson]

Hi Larry,

  Thanks.  Can you tell me what the spatial dimensions are of each of your grid points?  If you poke around the literature, you will find that TIDs come in many different spatial wavelengths and periods - Nathaniel W2NAF's work looks at medium scale TIDs with periods of 15-60 min and wavelengths of several hundred km (e.g. several degrees in lat/lon), but there are also large scale TIDs with much longer periods of >1 to 4+ hours and longer wavelengths of 1000+ km.  I am curious how your processing lines up with these spatio-temporal setpoints.

73

Phil W1PJE

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[Phil Erickson]

PS: of course, I forgot that Nathaniel's recent work (of which I'm a small part) also looks at LSTIDs!  Sorry for the momentary confusion.

[Lawrence Naif]

Hello Kukkai,

Correct, the TEC is measured along the LEO-GPS link. Any data that gives TEC vertically?

will check the elevation and arc in the data. 

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[Lawrence Naif]

Dimensions of the Spatial Map: 16*16 = 256 cells. Each cell covers a specific range of latitude and longitude. Latitude ranged from -21.2786 to 57.2707, and longitude from -118.2578 to 100.2022.    

F

or a 16x16 grid: Latitude bins: From -21.2786 to 57.2707, divided into 16 intervals, so each interval is approximately (57.2707 - (-21.2786)) / 16 approx 4.934 degrees, and Longitude bins: From -118.2578 to 100.2022, divided into 16 intervals, so each interval is approximately (100.2022 - (-118.2578)) / 16 approx 13.66 degrees So I represent each ecll as a rectangular region of about 4.934° latitude by 13.66° longitude.

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[Ethan Miller K8GU]

Yes, GNSS radio occultation data must be treated with special care.
If it has been processed with a spherical symmetry assumption, you
might be able to infer the presence of TIDs from an individual
retrieved profile that appears to violate physics.

There is a variant of this idea that has been done to determine
sporadic-E parameters:

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2009JA014399

Although the method in the paper is computationally burdensome, it may
not be necessary, depending on the goals of your study.

It will be very difficult to see anything meaningful regarding most
TIDs in grids that are 5 x 14 degrees.

73,

--Ethan, K8GU.

On Mon, May 19, 2025 at 1:47 PM 'Lawrence Naif' via HamSCI

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[Lawrence Naif]

Thanks Ethan,

I ''ll increase the grid size and make it closer to a typical TID scale, for example, 1° × 1° cell size for detecting TIDs with 100-500 km wavelengths

Best

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[David Themens]

The L1B dataset is the POD receiver TEC, not the occultation TEC. It's looking up from the satellite bus, so you can generally treat it similarly to ground-based TEC, but you'll want to apply a decently high elevation cutoff because of multipath and if you want to convert the slant TEC to vertical TEC, the projection function that you would use is slightly different than what you'd use for ground-based TEC measurements.

In the case here, all of the elevations are negative and the TEC values are unreasonably high, likely because of multipath from the low elevation.

Cheers,

David

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[Lawrence Naif]

Thanks David,

Is there a projection function to deal with the multipath from low elevation?

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[David Themens]

Hi,

With multipath, the easiest thing to do is just make sure that your elevation is high and positive. It depends a bit on the satellite that the receiver is on, since it can be caused by neighboring solar panels or other instruments, so the best practices without knowing what the multipath environment is like would be to use at least 30 degrees as the lower elevation cutoff, but to be safe, even 40 or 50 degrees may be warranted.

Cheers,

David

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[Lawrence Naif]

Thanks David,

Appreciate any leads to get data on loss rate assumptions in the electron continuity equation.  Is there any satellite data we can use to calibrate loss rate models?

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[Steve Cerwin]

One other thing you can do to limit variations from ground bounce multipath in your satellite data is to take control of your antenna elevation pattern.  If you put your own large ground plane under the antenna, your elevation pattern is set by your terms rather than by chance. A ground plane under your antenna with the assembly placed above the local terrain can reduce visibility to the low angles that contain multipath between the direct ray and ground-reflections. This will reduce amplitude variations as satellites ascend and descend from horizon to horizon. Any remaining pattern variations attributable to the ground plane can be quantified with antenna modeling software and accounted for. If your GPS antenna is a patch, just putting it on a large ground sheet should do it. 

73, Steve WA5FRF

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From: 'Lawrence Naif' via HamSCI <ham...@googlegroups.com>
Sent: Tuesday, May 20, 2025 9:24 PM
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Subject: Re: [HamSCI] Constellation Observing System for Meteorology Ionosphere and Climate C

 

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[Lawrence Naif]

looking for data that calibrates  the drivers of the Appleton–Hartree Equation.  I cant find this in the COSMIC-1 data are available at https://data.cosmic.ucar.edu/gnss-ro/cosmic1/. Appreciate any leads to satellite data sources to use in a model to model the below variables 

• electron collision frequency,
• electron plasma frequency, 
• electron gyro frequency, 
• ambient magnetic field strength

Thanks,

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